Biological Rhythms: Implications for the

Worker

September 1991

OTA-BA-463

NTIS order #PB92-117589
Recommended Citation:

U.S. Congress, Office of Technology Assessment, Biological Rhythms: Implications for the

Worker, OTA-BA-463 (Washington, DC: U.S. Government Printing Office, September

1991).

For sale by the U.S. Government Printing office

Superintendent of Document\, M~il SIop: SSOP, Washington, DC 20402-9328”

ISBN 0–16-035497-8
Foreword

Approximately 20 million Americans work some form of nonstandard work schedule.

These schedules, which require that an individual work during nondaytime hours,

noncontinuous hours, or for extended periods, are referred to as “shift work. ” Recent

advances in the understanding of the biological rhythms of the body and their control by the

brain indicate that shift work can disrupt these rhythms, with possible adverse consequences

for the worker.

This report is the third in a series of OTA studies being conducted under an assessment

of “New Developments in Neuroscience. ” It was requested by the House Committees on

Appropriations; Energy and Commerce; Science, Space, and Technology; Veterans Affairs;

and the Senate Subcommittee on Science, Technology, and Space of the Committee on

Commerce, Science, and Transportation. The report discusses biological rhythms: what they

are, how they are controlled by the brain, and the role they play in regulating physiological

and cognitive functions. The major focus of the report is the examination of the effects of

nonstandard work hours on biological rhythms and how these effects can interact with other

factors to affect the health, performance, and safety of workers.

In addition, the report describes the Federal regulatory framework related to work hours

and the current status of biological rhythm and shift work research. The report presents a range

of options for congressional action related to the amount of research being conducted on these

topics, the collection of relevant workplace statistical data, and the congressional role in

ensuring the well-being of individuals engaged in nonstandard hours of work.

The first publication in OTA’s assessment of “New Developments in Neuroscience”

was Neurotoxicity: Identifying and Controlling Poisons of the Nervous System, published in

April 1990, and the second was Neural Grafting: Repairing the Brain and Spinal Cord, which

was published in September 1990. OTA was assisted in preparing this study by a panel of

advisers, a workshop group, and reviewers selected for their expertise and diverse points of

view on the issues covered by the assessment. OTA gratefully acknowledges the contribution

of each of these individuals. As with all OTA reports, responsibility for the content of this

report is OTA’s alone. The report does not necessarily constitute the consensus or

endorsement of the advisory panel, the workshop group, the reviewers, or the Technology

Assessment Board.

/J’/ AJ#d&- 2

JOHN H. GIBBONS

Director

.!, Ill
New Developments in Neuroscience Advisory Panel

Peter S. Spencer, Chair

Center for Research on Occupational and Environmental Toxicology

Robert H. Blank

Social Science Research Institute

Northern Illinois University

DeKalb, IL

James F. Childress

Department of Religious Studies

University of Virginia

Charlottesville, VA

Fred H. Gage

Department of Neuroscience

University of California, San Diego

La Jolla, CA

Bernice Grafstein

Department of Physiology

Cornell University, School

of Medicine

New York, NY

Oregon Health Sciences University

Portland, OR

Ronald Kartzinel

CIBA-GIEGY Pharmaceuticals

Summit, NJ

Alan Kraut

American Psychological Society

Washington, DC

Laurane G. Mendelssohn

Lilly Research Laboratories

Eli Lilly & Co.

Indianapolis, IN

Franklin E. Mirer

Health and Safety Department

United Auto Workers

Detroit, MI

Albert S. Moraczewski

Pope John XXIII Medical, Moral

Research, and Education Center

Houston, TX

Herbert Paroles

Department of Psychiatry

Columbia University

New York, NY

Richard M. Restak

Neurological Associates

Washington, DC

Biological Rhythms Study Panel

J. Robert Carr (ad hoc)

Howard University

Washington, DC

Mary A. Carskadon

Emma Pendelton Bradley Hospital

East Providence, RI

Charles A. Czeisler

Laboratory for Circadian and Sleep

Disorders Medicine

Brigham & Women’s Hospital

Boston, MA

Patricia J. DeCoursey

Department of Biology

University of South Carolina

Columbia, SC

David F. Dinges

Unit for Experimental Psychiatry

The Institute of Pennsylvania

Hospital

Philadelphia, PA

Alfred J. Lewy

Sleep and Mood Disorders

Laboratory

The Oregon Health Sciences

University

Portland, OR

Fred W. Turek

Department of Neurobiology

and Physiology

Northwestern University

Evanston, IL

Frank A. White (ad hoc)

Jones, Day, Reavis & Pogue

Washington, DC

NOTE: OTA appreciates and is grateful for the valuable assistance and thoughtful critiques provided by the advisory and study panel members. The

panels do not, however, necessarily approve, disapprove, or endorse this background paper. OTA assumes full responsibility for the report and

the accuracy of its contents.

iv
OTA Project Staff—Biological Rhythms: Implications for the Worker

Roger C. Herdman, Assistant Director, OTA

Health and Life Sciences Division

Michael Gough, Biological Applications Program Manager

Gretchen S. Kolsrud, Biological Applications Program Managerl

David R. Liskowsky, Project Director

Laura Lee Hall, Analyst

Joyce Ann Brentley, Legal Analyst

Andrew A. Monjan, NIH Detailee

Peter R. Andrews, Research Assistant

Timothy P. Condon, Project Director

Gary B. Ellis, Study Director

Wendy S. Pachter, Legal Analysts

Richard Chin, Legal Intern

Katherine Kelly, Legal Intern

Lawrence M. Sung, Legal Intern

Jill Swerdloff, Legal Intern

Support Staff

Cecile Parker, Office Administrator

Linda Rayford-Journiette, Administrative Secretary

Jene Lewis, Secretary

Contractors

Scott S. Campbell, New York Hospital-Cornell Medical Center

Kent S. Hull, Decision Science Consortium

Benjamin W. Mintz, Catholic University of America

Timothy H. Monk, University of Pittsburgh

Harriet B. Presser, University of Maryland

Carol S. Weisman, Johns Hopkins University

Blair Burns Potter (editor), Bethesda, MD

Julie Phillips (indexer), Oakton, VA

lhough Septaer 1989.

2~ou@ January 1991.

3hou@ August 1989.

q~ough May 1989.

Shou@ September 1990.
Contents

Chapter 1: Summary, Policy Issues, and Options for Congressional Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Chapter 2: Introduction and Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Chapter 3: Circadian Rhythms . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Chapter 4: The Prevalence and Use of Shift Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69

Chapter 5: Biological Rhythms and Work Schedules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Chapter 6: Legal and Regulatory Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 7: Case Study: Nuclear Powerplant Control Room Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 8: Case Study: Registered Nurses and Resident Physicians . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 9: Case Study: The Military . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Appendix A: International Regulation of Shift Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Appendix B: Federal Research Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Appendix C: Participants in Workshop on Shift Work and Extended Duty Hours . . . . . . . . . . . . . . . . . . . .

Appendix D: Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .

Appendix E: List of Contractor Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Appendix F: Decade of the Brain . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Appendix G: Acronymns and Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

123

143

155

185

199

217

222

223

227

228

230

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
Chapter 1

Summary, Policy Issues, and

Options for Congressional Action
... ... ... ... ... ... .. CC *. * C 4***

. ..*.........,.....*+*****,+***,,+***

;;

w . ..........*....*.*,.***.,,*** 13

*E

Tables

Table

Page 1-1. Shift Work in Various Employment Sectors

... ... ... .,. ... ,.. ... ... ,,, q., $**, ,* ,4**, 10 1-2. Demographic Profile of Shift Workers . . . . . . . . . . .

. . 1-

. . ., . . ..,..*
Chapter 1

Summary, Policy Issues, and Options for Congressional Action

Biological rhythms are changes in various physiological and behavioral functions of organisms that

repeat at regular intervals and provide a framework

of temporal organization for them. Biological

rhythms in humans have cycles ranging from

minutes to months; for example, stages of sleep and

the release of a number of hormones in the body

cycle with a rhythm measured in minutes, while the

female menstrual cycle is measured in days (box

l-A). Cycles in synchrony with the 24-hour

rotation of the Earth are probably the most

widely studied. External factors that disturb the

internal clock can produce deleterious effects. A

common example is jet lag, the malaise associated

with travel across time zones. In the case of jet lag,

the effect is short-lived and the body readjusts

relatively quickly to the local time at the new

location. Work schedules outside the standard

daytime hours can disrupt the biological rhythms

of the body. This disturbance can continue

unabated while other factors, such as sleep loss

and social disruption, compound the deleterious

effects. The results can be detrimental to some

workers’ health and ability to perform their jobs,

which in turn can adversely affect their safety

and that of society as a whole.

The term “shift work” is often applied to

schedules that include nondaytime hours of work,

but there is no consistent definition of the term. As

used in this report, shift work refers to any

nonstandard work schedule. It includes evening

or night work; a rotating shift, in which hours

change regularly (e.g., from day to evening to night);

a split shift, in which a period of work is followed

by a break and then a return to work; and extended

duty hours, consisting of long periods of work

(usually over 12 hours). This report focuses on the

impact these schedules can have on the body’s

biological rhythms.

Diverse occupations require or involve 24-hour

operations and use nonstandard work schedules.

They include manufacturing industries (e.g., chemical, steel, paper), utilities (e.g., powerplants), protecBox 1-A—Biorhythms Are Not Biological Rhythms

The scientific study of the biological rhythms of the body should not be confused with the theory of

biorhythms. No evidence exists to support the concept of biorhythms; in fact, scientific data refute their existence.

Based on a theory first proposed by the German scientist Wilhelm Fliess in 1897 and popularized in the 1970s,

biorhythm theory postulates that three cycles act in a concerted fashion to guide activity: a 23-day cycle that

influences physical strength, endurance, energy, and physical confidence; a 28-day cycle that influences feelings,

love, cooperation, and irritability; and a 33-day intellectual cycle that influences learning, memory, and creativity.

According to biorhythm theory, these three cycles are linked to an individual’s birth date and fluctuate in a constant

fashion throughout his or her life. Each cycle has a high and a low point. By mapping the high and low points of

the respective cycles and how they coincide or diverge, the theory states, performance can be charted, and critical

days when performance can be expected to be highest or lowest can be predicted.

Although a theory that provides a system for predicting human behavior and scheduling activities has appeal,

none of the contentions of biorhythm theory can be supported. No biological process with such a relationship to

the calendar date of birth has ever been identified, nor have any studies attempting to validate biorhythms been able

to do so. Thus, for example, attempts to validate the hypotheses using retrospective airplane crash reports and

athletic scores have consistently failed. While there clearly are human biological rhythms with cycles that can be

measured in days (the menstrual cycle being an example), there is no evidence for the existence of any of the three

biorhythms, let alone any predictive interaction. Given its nonfactual basis, biorhythm theory is relegated to the

realm of other popular pastimes, such as numerology, that can serve as a source of entertainment but have no

substantive or predictive value.

SOURCE D.C. Hoiley, C.M. Winge$C.M. DeRoshi% etaL, Effects of CircadianRhythm PhaseAlteration on PhysiologicalandPsycho\ogical

Variables: Imp!icatiow to Pilot Performance (Inchdng a Partially Annotated Bibliography.), NASA technical nmmorandum

TM-81277 (NM&t Field, CA: National Aeronautics and Space Administration March 1981).

–3–
4 ● Biological Rhythms: Implications for the Worker

tive and health services (e.g., police, fire and rescue,

hospitals), transportation (e.g., airlines, railroads,

trucking, shipping), major construction projects

(e.g., darns, tunnels), military operations, and, increasingly, services (e.g., retail stores, financial

institutions, entertainment and recreation, specialized services such as overnight deliveries).

At the Federal level, the Fair Labor Standards Act,

which was enacted in 1938, established a standard

40-hour workweek. Various hours of service acts

regulate maximum hours for a number of industries,

notably transportation. Some States regulate hours

of work, and collective bargaining agreements can

specify hours and shift schedules.

The Federal Government has authority to regulate

working conditions that endanger the safety and

health of workers through the Occupational Safety

and Health Administration (OSHA) of the Department of Labor or through individual Federal agencies that have the authority to regulate safety and

health within their own jurisdictions. OSHA can

impose standards and regulations on the workplace

when scientifically valid research and empirical data

indicate that conditions pose a significant risk of

harm to workers. Interactions between biological

rhythms and work schedules are examined through

basic research on underlying biological mechanisms; applied research studying human responses

to shift work in laboratory and field settings;

statistical information on the occurrence of injuries,

mishaps, deaths, and health problems in the workplace and the conditions under which they occur;

and demographic information about populations

working different schedules.

The effects of various work schedules on the

health and safety of workers and the impact they

could have on the public raise questions about

possible Federal actions to regulate some work

hours and schedules. These concerns are coupled,

however, with questions regarding the extent of

current knowledge about work schedules and their

effects, namely:

●

●

●

●

What types of schedules are being worked and

by whom?

What are the precise effects on the health,

performance, and general well-being of workers who work nondaytime hours?

What kinds of effects occur in what kinds of

schedules?

Who are the workers most likely to be affected?

What we envision as an internal clock is actually a group of

neurons in the brain that control daily rhythms.

SOURCE: R.M. Coleman, Awake at 3:cXl a.m. bv Choice or by Chance

●

●

●

●

(New York, NY: W.H. Freeman, 1986).”

What factors contribute to any observed effects

and to what degree?

What are the implications of these effects for

worker safety and the safety of the public?

What interventions can be taken to alleviate or

lessen deleterious effects?

Most important, is enough known at this time

to recommend specific ‘guidelines or regulations?

This report discusses current theories and ideas

pertaining to these questions and describes the latest

efforts to answer them.

CIRCADIAN RHYTHMS

Many biological activities rise and fall in rhythmic patterns in humans, other animals, plants, and

even single-celled organisms. This ability to keep

track of time, apparently a basic part of life, is under

genetic control. Geneticists have identified specific

genes in simple organisms that are responsible for

rhythmic cycles, and physiologists have identified a

certain part of the mammalian brain that controls

rhythms in more advanced organisms. Biological
Chapter 1--Summary, Policy Issues, and Options for Congressional Action ● 5

BOX 1-B--Cycles That Last From Minutes to Days

Circadian rhythms are a basic and well-recognized feature of human physiology and behavior. However,

biological rhythms that repeat more or less frequently than every 24 hours are also fundamental to the body’s

function. In general, ultradian rhythms (those with a length of less than 24 hours) and infradian rhythms (those with

a length greater than 24 hours) do not coincide with conspicuous environmental cues, and how they are generated

is not well understood.

Sleep cycles were one of the first ultradian rhythms characterized in humans. A complete cycle of dreaming

and nondreaming takes place about every 90 minutes. This finding prompted researchers to hypothesize that cycles

of enhanced arousal followed by diminished activity typify both waking and sleeping periods. This theory of a basic

rest-activity cycle has led to many studies of ultradian cycles in alertness-sleepiness, hunger, heart function, sexual

excitement, urine formation, and other functions.

Hormones are also released in ultradian cycles. Many are secreted in a more or less regular pattern every few

hours. More frequent cycles of release, every few minutes, have also been documented. Although the mechanisms

of hormone secretion have not been uncovered, patterned release has been shown to be extremely important for

proper functioning. For example, experiments have shown that, when replacing a deficient hormone, pulses of the

hormone, not a continuous supply, are required for effectiveness. Also, abnormalities in the production cycle of

hormones have been correlated with altered function. Although these cycles do not appear to be tightly coordinated,

it is clear that ultradian rhythms with a cycle of 90 minutes, as well as with cycles of a few minutes to several hours,

are a basic component of many human functions. How they are generated is unknown.

The most prominent infradian rhythm in humans is the menstrual cycle. Through a series of complex

interactions between the brain and reproductive organs, an egg is released by an ovary approximately every 28 days,

and the reproductive organs are prepared for possible fertilization. During each cycle, hormones are secreted in

varying amounts, and the reproductive tract and breast tissue are altered. Other systems, such as those involved in

immune function, may also be affected.

Although the menstrual cycle has long been recognized, how it is generated and how it interacts with other

factors have not been completely detailed. It is clearly affected by circadian rhythms. For example, a peak in the

secretion of luteinizing hormone, which triggers ovulation, usually occurs in the early morning hours. Also, phase

shifts, such as those produced by transmeridian flight, may interfere with the menstrual cycle. The menstrual cycle

may also have therapeutic implications. A recent study of the timing of breast cancer surgery in relationship to the

menstrual cycle has found fewer recurrences and longer survival in patients whose surgery occurred near the middle

of the menstrual cycle rather than during menstruation. That biological rhythms are often ignored is also indicated

in this study: less than half of the records evaluated in the study recorded the time of the last menstrual period.

SOURCE: Office of Technology Assessment 1991.

rhythms that repeat approximately every 24 When rhythms generated by the body are dishours are called circadian rhythms (box l-B)

(figure l-l).

In humans, body temperature, the secretion of

many hormones, the functioning of various organ

systems (e.g., cardiovascular, pulmonary, renal) and

the immune system, and sleep and wakefulness all

exhibit circadian rhythms. In addition to these

physiological activities, many psychological processes and mental functions that affect human performance exhibit circadian fluctuations. These include memory, reaction time, manual dexterity, and

feelings of alertness. The implications of human

circadian rhythms for shift workers form the

focus of this report (figure 1-2).

rupted by changes in environmental cues, as they are

in jet lag and in some work schedules, human

function can be compromised until realignment is

achieved. Patterns of sleep are disrupted, performance may be impaired, and a general feeling of

malaise may prevail.

Circadian rhythms are generated by an internal clock, or pacemaker, that is located in a

region of the brain called the suprachiasmatic

nucleus. Circadian rhythms persist even in the

absence of cues indicating the time or length of day,

such as light and dark. In humans, as inmost species,

light-dark cycles are very powerful entraining, or

synchronizing, agents, while sleep-wake schedules
6 ● Biological Rhythms: Implications for the Worker

Figure l-l—Circadian Rhythm

51 Maximum , Amplitud e

4

ifi- .&T

Cycle length

:

.—

Z3 Mean

~ 2; Minimum

I I

12 24

Time (hours)

Circadian rhythms have a single cycle length of approximately 24

hours. The amplitude, a measure of the degree of variation within

a cycle, is the difference between the maximum value and the

mean.

SOURCE: Office of Technology Assessment, 1991.

Figure 1-2—Circadian Timing of Various

Functions

Alertness

Temperature

(“F)

80

40

0

100.4

98.6

96.8

Growth hormone

(nanograms/ml)

Cortisol

(micrograms/100 ml)

Potassium

(milli equivalent/hr)

15

10

5

0

15

10

5

0

3

2

1

0

6 am Noon 6 pm Mid- 6 am Noon 6 pm Midnight night

Time of day

The timing of some functions that cycle with a circadian rhythm.

SOURCE: Adapted from R.M. Coleman, Awake at 3.00 a.m. by Choice or

by Chance (New York, NY: W.H. Freeman, 1986).

and social cues may also synchronize human circadian rhythms. An entraining agent can reset, or

phase shift, the internal clock; depending on when an

organism is exposed to such an agent, circadian

rhythms may be advanced, delayed, or not shifted at

all (figure 1-3). When circadian rhythms are reset,

the beginning and end of the cycle are shifted, but the

length and progression of changes within it remain

the same. The flexibility of a circadian rhythm in

adjusting to different environmental cues will determine the degree to which the timing of the function

controlled by that rhythm can be altered. In humans,

this has direct implications for the ability of the body

clock to readjust following changes in work schedules.

A standard schedule for most people is to awake

in the morning and go to bed at night, some 15 to 17

hours later. The person who arises at 5 a.m. and the

one who wakes 4 hours later both have 24-hour

rhythms and spend the major part of their waking

hours in the light and their sleeping hours in the dark,

but they can have different phases. Some members

of society have far different hours: a nurse or

chemical worker who goes to work at midnight

spends a major part of his or her waking hours in the

dark and must sleep through daylight hours. In some

situations, the work schedule changes in such a way

that individuals will constantly be changing waking

and sleeping times, and other functions that have a

circadian rhythm will continually be readjusting to

the new schedule.

While shift work may affect all circadian rhythms,

its effect on performance rhythms and sleep-wake

cycles are of particular concern. The timing of peaks

in performance varies with the nature of the task,

with peaks in many tasks (e.g., manual dexterity,

simple recognition, reaction time) paralleling the

peak in the circadian rhythm of body temperature.

Also, sleep deprivation and sleepiness disrupt most

types of performance. The timing and total amount

of sleep are related to a person’s environment and to

other circadian rhythms, notably body temperature,

with sleep occurring most readily when body

temperature is low. When individuals are required to

work at night, many types of performance can be

affected, which can reflect both the effect of

circadian rhythms and the lack of sleep. Thus, sleep

deprivation, combined with the influence of the

circadian pacemaker, can severely curtail performance at night.
Chapter 1--Summary, Policy Issues, and Options for Congressional Action ● 7

Day A

-2 Light

-1 pulse L

Om

1

2

3

4

5

o \

\

\

\

Figure 1-3--Phase Response Curve

B

1

\

t

\

\

\

\

\

\

\

\

-1 \

\

\

\ \

c D

\

\

\

5[

1

\

\

\

\

\

\

\

\

\ \

-3 \ +4 \

\

\

\

\

i

\

\

\

i

‘\ \

\

\ \

\

+4 \ \

Advance \

\

\

\ AD

E

‘w

Phase

o E

shift A

- 2 - B

Delay

-4 –

I Subjective day Subjective night I

1-1, , , , , I , I I I , , I 1 I , I , , -! ~—

0 6 12 18 24

Circadian time (hours)

Experiments demonstrate that exposure to light at different points in a single circadian cycle variably

shifts the internal pacemaker (A-E). The pulse of light given in mid-subjective day (A) has no effect,

whereas the light pulses in late subjective day and early subjective night (B and C) delay circadian

rhythms. Light pulses in late subjective night and early subjective day (D and E) advance circadian

rhythms. In the lower panel, the direction and amount of phase shifts are plotted against the time of light

pulses to obtain a phase response curve.

SOURCE: M.C. Mwre-Ede, F.M. Sulzman, and C.A. Fuller, The C/cJCks That Time Us (Cambridge, MA: Harvard

University Press, 1982).

Other factors also alter circadian rhythms. For

example, many physiological and behavioral functions, notably sleep, are altered with advancing age

in humans. As a result, adjustment to shift work

schedules and transmeridian flight is more difficult

among older people (age 45 and above) and a

considerable proportion of older people complain of

sleep problems. In addition, the timing of sleep is

very susceptible to circadian disruption; it is now

recognized that some types of insomnia most likely

result from circadian rhythm abnormalities.

There is great interest in the role the circadian

system may play in some mood disorders. It is

hypothesized that circadian rhythms are advanced,

delayed, or the amplitude dampened in seasonal

affective disorder (SAD), a mood disorder characterized by recurring autumn or winter depression which

is alleviated in the springtime; however, SAD has

not been proven to be a circadian rhythm disorder.

Also, it has been observed that people suffering from

nonseasonal depression may exhibit altered circadian patterns in physiological functions and that
8 ● Biological Rhythms: Implications for the Worker

their moods typically fluctuate daily, with improvement over the course of the day. These observations

suggest a link between altered circadian rhythms and

nonseasonal depression, although there is little

direct evidence to support this hypothesis. Finally,

some scientists are investigating the implications

circadian rhythms have for the timing of surgery and

the administration of drugs, in an effort to optimize

their therapeutic effects.

Interest in manipulating the internal clock has

grown with improved understanding of human

circadian rhythms. Several agents show promise for

manipulating circadian rhythms, and some are

currently in use. Recent research indicates that light,

especially bright light, is effective in shifting human

circadian rhythms, although the mechanism is not

well defined (figure 1-4). Researchers are investigating the capacity of melatonin, a hormone produced

in the brain, to act as a circadian synchronizing agent

in humans. Studies in animals suggest that administration of benzodiazepines, a class of hypnotic drug,

affects the circadian system. It is not clear, however,

whether the effect is due to direct action on the

circadian clock or to the drug’s ability to induce

motor activity. Finally, there is some evidence that

physical activity or arousal can synchronize the

biological clock, but further experimentation is

necessary to characterize this effect. The development or discovery of an agent that can manipulate

the internal clock would be helpful in situations such

as shift work, where a rapid realignment of the

circadian system is desirable.

PREVALENCE AND USE OF

SHIFT WORK

Shift work is required in any modern, industrially

developed country, and it is indisputably part of

work in the United States. Understanding shift work

and its impact on productivity, health, safety, and

quality of life depends on information about its

prevalence and use. The Office of Technology

Assessment (OTA) finds that the Federal Government’s collection of data pertaining to the

prevalence and use of shift work has been

inconsistent. This has precluded any accurate,

thorough measure of the scope and nature of shift

work in this country.

The most comprehensive data on the prevalence

of shift work in the United States are based on the

Current Population Survey (CPS), a household

Figure 1-4—Resetting the Human Pacemaker

With Light

A. 1

I

I

37.0

36.5

—

6 am Noon 6 pm Mid- 6 am Noon 6 pm

night I

B.

C. 1

;O Initial phase - 12 18 O+ 1 6

(hours) ,.4, I 1

I I

I 1 I 1 f

Final phase – 18 0 +

6 $ ‘2 ‘

8

I

I

l-= I

A@ = +8.0 hours

The first graph (A) illustrates the original circadian rhythm of body

temperature. Following exposure to bright light, as illustrated in B,

the rhythm of body temperature was significantly shifted (C).

SOURCE: C.A. Czeisler, R.E. Kronauer, J.S. AlIan, et al., “Bright Light

induction of Strong (Type O) Resetting of the Human Circadian

Pacemaker,” Science 244:1328-1332, 1989.

sample survey conducted monthly by the Bureau of

the Census (in the U.S. Department of Commerce)

for the Bureau of Labor Statistics (BLS) (in the U.S.

Department of Labor). In this survey a set number of

households are regularly asked a fixed list of

employment questions. In May of each year between

1973 and 1980, a supplement was added to the CPS

with questions on specific hours of employment, and

in May 1980 data were collected for the first time on

whether or not the principal job in the household was
Chapter 1--Summary, Policy Issues, and Options for Congressional Action ● 9

Figure 1-5-Percentage of Shift Workers Among

Full-Time Employees in the United States

Day shift 84.1

Other shifts 8.9

Rotating shifts 4.3

Night shift 2.7

SOURCE: E.F. Mellor, “Shift Work and Flexitime: How Prevalent Are

They?” Monthly Labor Review 109: 14-21, 1986.

worked on a rotating shift. From 1980 through 1984,

the CPS collected no information on work schedules. The next year, in May 1985, the supplement

again included questions related to hours of work

and work schedules. Since there have been no

supplements since 1985 that include shift work

questions, the 1985 data provide the most recent

estimates available. These data indicate that

approximately one in five Americans—20 million

people—is a shift worker. Approximately 2.0 million individuals are night workers, and another

3.1 million people work rotating shifts, which may

involve night work. The remaining individuals work

other types of nonstandard work schedules, such as

split shifts or evening hours. In 1991 another

supplement was added to the CPS.

A more recent and comprehensive national source

of data on shift work is the 1987-88 National Survey

of Families and Households, conducted by the

Center for Demography and Ecology at the University of Wisconsin. This survey asked the most

detailed questions on work schedules of any national

survey to date, including the hours work began and

ended each day of the week and shift rotation.

Although no analysis of the shift work data has been

completed yet, preliminary results on prevalence are

consistent with the May 1985 CPS findings.

Shift Work in Various Employment Sectors

Many occupations and industries use shift work;

in fact, 15.9 percent of all full-time workers are

engaged in shift work (figure 1-5). The factors that

lead to shift work vary considerably from sector to

sector.

Reasons for adopting shift work schedules include the following:

an extended period of time required to complete

a particular job or process;

a constant need or extended demand for services;

economic factors (e.g., expense of capital

investment, concerns about competitiveness);

and

technological advances.

From 1979 to 1984, capital-intensive industries

and continuous-process operations had as many as

50 percent of employees working evening or night

shifts. In contrast, less than 3 percent of workers in

labor-intensive industries are scheduled for an evening or night shift (table l-l).

Shift work is also prevalent in transportation

occupations and industries, including trucking, airlines, railroads, and shipping. Among those employed by public utilities and transportation industries, 20.6 percent are shift workers; 25.5 percent of

full-time motor vehicle operators are shift workers,

half of them on night or rotating shifts. While many

transportation sectors are governed by hours of

service regulations, those regulations do not preclude night work, shifts exceeding 8 hours in length,

or erratic scheduling.

Round-the-clock operations are also demanded by

various service industries, a significant and growing

sector of the U.S. economy. More than 38 percent of

persons employed full-time in service occupations

are shift workers, compared to the average of 15.9

percent of all full-time employed persons. Some

subgroups of the service sector exhibit an extremely

high prevalence of shift work. For example, 60.8

percent of full-time protective service workers (e.g.,

police and firefighters) are employed during nonstandard hours. Among workers in other service

industries, those employed in eating and drinking

establishments (47.6 percent) and in entertainment

and recreation (33.4 percent) are especially likely to

be shift workers.

Technological advances--office automation and

the increased importance of global communication

and interaction-provided powerful incentives for

the addition of a second and third shift. BLS reported

that between 1978 and 1985 the number of clerical

personnel working at night increased three times

faster than the number of all other night workers.
10 ● Biological Rhythms: Implications for the Worker

Table l-l—Shift Work in Various Employment Sectors

Total workers Standard

employed work schedule Shill work (percent)

Occupation or industry (thousands) (percent) Evening shift Night shift Rotating shift Total

Occupation

Managerial and professional

specialty. . . . . . . . . . . . . . . . . . .

Executive, administrative,

and managerial . . . . . . . . . . . . .

Professional specialty. . . . . . . . . .

Health-diagnosing

occupations . . . . . . . . . . . . .

Health assessment and

treating occupations. . . . . . .

Technical, sales, and administrative

support . . . . . . . . . . . . . . . . . . . .

Technicians and related support . . .

Health technologists and

technicians . . . . . . . . . . . . . . . .

Sales occupations . . . . . . . . . . . . . . .

Supervisors . . . . . . . . . . . . . . . . . .

Salesworkers, retail and

personal services . . . . . . . . . . .

Administrative support, including

clerical . . . . . . . . . . . . . . . . . . . .

Computer equipment

operators. . . . . . . . . . . . . . . . . . .

Mail and message distributing . . .

Service occupations . . . . . . . . . . . . .

Private household . . . . . . . . . . . . .

Protective service . . . . . . . . . . . . .

Service, except private

household and protective. . .

Food service . . . . . . . . . . . . . . .

Health service. . . . . . . . . . . . . .

Cleaning and building

service . . . . . . . . . . . . . . . . . .

Personal service . . . . . . . . . . . .

Precision production, craft,

and repair . . . . . . . . . . . . . . .

Mechanics and repairers . . . . . . .

Construction trades . . . . . . . . . . .

Other precision production,

craft, and repair . . . . . . . . . . .

Operators, fabricators,

and laborers . . . . . . . . . . . . .

Machine operators, assemblers,

and inspectors . . . . . . . . . . .

Transportation and materialmoving occupations . . . . . . .

Motor vehicle operators . . . . . .

Handlers, equipment cleaners,

helpers, and laborers . . . . . . . .

Farming, forestry, and fishing. . . . . .

Industry

Private sector. . . . . . . . . . . . . . . . . . .

Goods-producing industries . . . . .

Agriculture . . . . . . . . . . . . . . . . .

Mining . . . . . . . . . . . . . . . . . . . . .

Construction . . . . . . . . . . . . . . .

Manufacturing. . . . . . . . . . . . . .

Durable goods . . . . . . . . . . .

Nondurable goods . . . . . . . .

Service-producing industries . . . .

18,944

9,079

9,866

212

1,257

21,961

2,548

761

6,730

1,957

2,400

12,684

673

613

7,268

275

1,286

5,707

2,194

1,076

1,719

718

10,477

3,582

3,282

3,614

13,326

6,748

3,448

2,392

3,130

1,418

60,127

24,626

1,154

885

4,279

18,309

11,277

7,033

35,501

91.4

92.6

90.3

77.6

68.7

88.3

84.5

70.1

82.8

84.0

72.3

92.0

81.2

76.2

61.6

83.0

39.2

65.6

56.9

63.9

74.4

73.9

87.0

87.3

94.1

80.3

76.3

76.3

73.8

74.5

78.9

89.9

83.5

85.0

89.4

78.1

97.5

82.1

84.0

79.1

82.4

2.0

1.8

2.3

1.7

8.3

4.2

6.5

12.5

4.1

2.8

8.3

3.7

11,0

12.7

16.9

7.3

19.8

16.7

21.2

14.8

16.1

7.5

6.3

6.0

3.4

9.3

10.5

13.2

5.8

4.3

9.9

1.5

6.6

7.4

0.9

6.0

1.3

9.3

10.0

8.2

6.1

1.2

0.8

1.5

—

8.3

2.1

3.3

9.0

2.2

2.1

3.6

1.7

2.7

9.1

6.1

1.9

7.2

6.1

5.3

10.3

5.4

3.7

2.2

2.3

1.0

3.2

4.6

3.7

6.0

6.9

5.2

1.4

2.9

2.6

2.2

1.6

0.4

3.2

2.5

4.4

3.0

2.7

2.6

2.8

13.6

12.1

3.5

4.6

7.6

6.9

7.4

11.5

1.6

4.1

0.4

8.7

—

23.8

5.7

8.2

6.8

1.7

6.2

3.7

3.6

1.2

6.1

6.2

6.2

7.4

5.9

4.9

0.7

4.4

3.9

0.2

12.1

0.4

4.5

2.8

7.2

4.8

8.6

7.4

9.7

22.4

31.3

11.7

15.5

29.9

17.2

16.0

27.7

8.0

18.8

23.8

38.4

17.0

60.8

34.4

43.1

36.1

25.6

26.1

13.0

12.7

5.9

19.7

23.7

23.7

26.2

25.5

21.1

10.1

16.5

15.0

10.6

21.9

2.5

17.9

16.0

20.9

17.6
Chapter 1--Summary, Policy Issues, and Options for Congressional Action ● 11

Table l-l-Shift Work in Various Employment Sectors--Continued

Total workers Standard

employed work schedule Shift work (percent)

Occupation or industry (thousands) (percent) Evening shift Night shift Rotating shift Total

Transportation and public

utilities. . . . . . . . . . . . . . . . . . . .

Wholesale trade . . . . . . . . . . . . . .

Retail trade . . . . . . . . . . . . . . . . . .

Eating and drinking places . . . .

Finance, insurance, and

real estate . . . . . . . . . . . . . . . . .

Services . . . . . . . . . . . . . . . . . . . . .

Private household . . . . . . . . . . .

Business and repair . . . . . . . . .

Personal, except private

household . . . . . . . . . . . . . . .

Entertainment and recreation .

Professional services . . . . . . . .

Hospitals . . . . . . . . . . . . . . . . . .

Public sector . . . . . . . . . . . . . . . . . . .

Federal Government . . . . . . . . . .

State government . . . . . . . . . . . . .

Local government . . . . . . . . . . . . .

4,958

3,222

9,111

2,242

5,003

13,207

345

3,242

1,379

529

7,682

2,303

13,268

2,901

3,320

7,047

79.4

91.9

73.7

52.4

93.9

82.9

80.8

87.4

74.0

66.6

83.8

73.0

87.2

86.2

88.2

87.1

6.1

2.9

9.1

21.0

1.9

6.4

7.3

5.8

10.1

13.8

5.4

10.5

4.6

6.1

4.3

4.2

3.5

2.1

3.7

5.3

1.0

3.3

1.5

2.4

3.8

2.2

3.7

6.6

2.0

3.4

2.3

1.3

SOURCE: E.F. Mellor, “Shift Work and Flexitime: How Prevalent Are They?” Month/y Labor F?eview 109:14-21, 19S6.

6.4 20.6

0.9 8.1

8.6 26.3

12.5 47.6

1.1 6.1

3.9 17.1

0.7 19.2

3.1 12.6

6.6

7.3

3.6

8.5

3.7

2.8

3.0

4.5

26.0

33.4

16.2

27.0

12.8

13.8

11.8

12.9

Night work among technical and professional office

personnel has increased 36 percent during this time

period.

Who Are Shift Workers?

A higher percentage of young men, single men,

and black men are shift workers, Approximately

22.6 percent of black men employed full-time are

shift workers, versus 17.3 percent of white men

employed full-time. Among all men employed

full-time, 27.4 percent of those between the ages of

16 and 19 do not work a regular daytime schedule,

compared to 14.6 percent of men age 45 and older.

Among all men employed full-time, 21.1 percent of

single men and 16.5 percent of married men work

nonstandard hours. Although young, single, and

black men are more likely to be shift workers,

older, married, and white men, being the majority of full-time workers, form the majority of shift

workers (table 1-2).

Differences in shift work prevalence by sex

depend on whether Ml-time or part-time work is

considered. Considering only full-time wage and

salary earners age 16 and over, the BLS reports that

17.8 percent of men and 13.0 percent of women

are shift workers. Men are more likely than women

to be working night, miscellaneous, and rotating

shifts, whereas women are more likely than men to

work the evening shift. While men are more likely

than women to be shift workers, shift work is highly

prevalent among women in some employment

sectors, particularly nursing and other health services.

One-fourth of all dual-earner couples without

children and one-third of all dual-earner couples

with children include at least one spouse who

works a nonstandard shift. Moreover, shift work is

especially high among married couples with young

children. One study estimated that about 50 percent

of all young couples with children under the age of

5 in the United States include at least one spouse

who works nonstandard hours. Also, the prevalence

of shift work is considerably higher among unmarried parents. Both young dual-earner parents and

unmarried employed mothers are especially likely

to be working nonstandard hours.

The reasons individuals work nonstandard hours

vary and include both voluntary and involuntary

factors. Voluntary reasons include better child-care

arrangements, better pay, better arrangements for

care of other family members, and more opportunity

for education. Involuntary reasons include the inability to get any other job and the schedule being a

requirement of the job. A survey by the BLS

reported that only 28 percent of persons working

nonstandard hours did so voluntarily; 72 percent
12 . Biological Rhythms: Implications for the Worker

Table 1-2—Demographic Profile of Shift Workers

Total workers Standard

employed work schedule Shift work (percent)

Characteristic (thousands) (percent) Evening shift Night shift Rotating shift Total

Age

Men, 16 years and over. . . . . . . . . .

16 to 19 . . . . . . . . . . . . . . . . . . . . .

20 to 24 . . . . . . . . . . . . . . . . . . . . .

25 to 34 . . . . . . . . . . . . . . . . . . . . .

35 to 44 . . . . . . . . . . . . . . . . . . . . .

45 to 54 . . . . . . . . . . . . . . . . . . . . .

55 to 64 . . . . . . . . . . . . . . . . . . . . .

65 And over.... . . . . . . . . . . . . . .

43,779

1,139

5,567

14,281

10,630

7,094

4,594

474

29,616

777

4,346

9,510

7,080

4,753

2,838

311

73,395

82.2

72.6

80.0

80.0

83.6

85.4

85.5

85.4

87.0

71.1

84.0

87.5

88.9

88.4

87.3

85.8

84.1

6.8

11.8

8.5

7.8

5.7

5.3

5.6

2.8

5.5

12.8

6.7

5.3

4.8

4.6

5.3

7.3

6.3

3.0

4.7

3.5

3.3

2.7

2.7

2.1

2.5

2.3

4.0

2.0

2.2

2.3

2.2

2.6

3.8

2.7

4.9

7.0

5.0

5.6

5.0

3.9

3.8

4.0

3.3

9.4

5.1

3.3

2.2

2.8

3.2

—

4.3

17.8

27.4

20.0

20.0

16.4

14.6

14.5

14.6

13.0

28.9

16.0

12.5

11.1

11.6

12.7

14.2

15.9

Women,16y ears and over . . . . . . .

16 to 19 . . . . . . . . . . .. .....:...

20 to 24 . . . . . . . . . . . . . . . . . . . . .

25 to 34 . . . . . . . . . . . . . . . . . . . . .

35 to 44 . . . . . . . . . . . . . . . . . . . . .

45 to 54 . . . . . . . . . . . . . . . . . . . . .

55 to 64 . . . . . . . . . . . . . . . . . . . . .

65 And over.... . . . . . . . . . . . . . .

Total,16 years and over . . . . . . . . . .

Race and Hispanic origin

White . . . . . . . . . . . . . . . . . . . . . . .

Men . . . . . . . . . . . . . . . . . . . . . .

Women . . . . . . . . . . . . . . . . . . . .

Black . . . . . . . . . . . . . . . . . . . . . . . .

Men . . . . . . . . . . . . . . . . . . . . . .

Women . . . . . . . . . . . . . . . . . . . .

Hispanic origin.. . . . . . . . . . . . . . .

Men . . . . . . . . . . . . . . . . . . . . . .

Women . . . . . . . . . . . . . . . . . . . .

63,523

38,588

24,935

7,847

4,054

3,793

4,911

3,184

1,727

84.7

82.7

87.8

80.1

77.4

83.0

84.6

82.3

88.8

5.8

6.3

5.0

9.8

10.6

8.9

7.1

7.7

5.8

2.6

2.9

2.1

3.5

3.7

3.2

2.5

2.8

1.9

4.3

5.0

3.3

4.3

5.3

3.2

3.3

4.0

2.0

15.3

17.3

12.3

19.9

22.6

17.0

15.4

17.7

11.2

Marital status

Men

Single, never married . . . . . . . .

Married, spouse present . . . . .

Widowed, divorced,

or separated.. . . . . . . . . . . . .

9,703

29,666

78.9

83.5

9.3

5.7

3.6

2.7

5.0

5.1

21.1

16.5

4,410 80.4 8.5 3.6 4.0 19.6

Women

Single, never married . . . . . . . .

Married, spouse present. . . . .

Widowed,divorced,

or separated. . . . . . . . . . . . .

7,109

15,679

83.6

89.9

6.8

4.3

2.3

1.9

5.2

2.3

16.4

10.1

6,828 83.7 7.0 3.3 3.6 16.3

SOURCE: E.F. Meilo~ ’’ShiftWork and Flexitime: HowPrevalentAre They?’’ A4onth/yLdor/?etiewlO9fl4-2l ,19SS.

did so involuntarily, and 9 out of 10 of the latter

said the schedule was a requirement of the job.

formance,and social effects of shift work,as well

as changes in trends concerning the use of shift

work.

Shift Work Schedules The most common work schedule in the United

States, especially in the manufacturing sector, is

8 hours a day, 5 days a week on a single shift,

followed by 2 days off. Shift work schedules can be

used to cover 7 days a week of continuous operation,

with shift lengths ranging from 8 to 12 hours.Shifts

may be fixed, partially fixed, or rotating. Shift

rotation-that is, the time a worker spends on one

shift before moving to another-may be rapid (3

days) or gradual (4weeks),and it may move forward

Several hundred shift routines are in place in the

United States, but data characterizing specific

shift work schedules in various occupations and

industries in the United States have not been

collected by the Federal Government, labor

representatives, or industry. The absence of these

data, coupled with sparse demographic information about the populations of workers involved,

severely handicaps the study of the health, per-
Chapter I--Summary, Policy Issues, and Options for Congressional Action . 13

Box 1-C—The Compressed Workweek

The compressed workweek (CWW) refers to a schedule in which employees work approximately 40 hours in

fewer than 5 days. A variety of schedules, with a variety of rationales, can be said to constitute a CWW. Typically,

work is performed 10 or 12 hours per day, 3 or 4 days per week, and 3 or 4 days per week are free. Other possibilities

include a long break schedule; for example a schedule of 12-hour shifts may employ a sequence of 4 days on duty,

7 days off duty, 4 days on, 3 days off, 3 days on, 1 day off, 3 days on, and 3 days off. As with all types of shift work,

national data on the prevalence of specific CWW schedules are not available,

The CWW with 12-hour shifts appears to be common in the chemical industry (including petrochemical), the

petroleum industry, offshore oil rigs, and ministeel industries. Other types of employment that could adopt the

CWW include the paper industry, other manufacturing processes, utility industries (including nuclear powerplants),

nursing and other health fields, clerical work, administrative work, technical maintenance, and computer operations.

Information derived from management and employee comments, limited psychological testing, and

performance and safety records has highlighted some of the advantages and disadvantages of the CWW. In general,

the CWW appears to increase worker satisfaction because it allows more days and weekends off. For example, in

one plant, conversion to a CWW schedule with 12-hour shifts reduced the number of days on the job each year from

273 to 182. Also, when the CWW has 12-hour rotating shifts, fewer consecutive days are spent on the night shift

and there is more time to recuperate than with 8-hour shifts 5 days a week. This may lessen the fatigue associated

with rotating shifts and night work. While more days off may improve employee satisfaction, concerns about

increased moonlighting have been voiced and have been documented in one case. In general, however, studies have

failed to document an increase in moonlighting.

Data have suggested that not all employees endorse the CWW. Family responsibilities and previous work

experience appear to influence preference for the CWW. One study estimated that 28 percent of work sites adopting

a CWW will revert to the standard 8-hour day, 5-day week schedule, A few studies have indicated that women,

especially those with young children, and older employees may be less satisfied with a CWW.

The use of the CWW, especially with two 12-hour shifts replacing three 8-hour shifts, may be more

cost-effective for employers, since the number of shift changes is decreased (shift changes are the least productive

time in an operation), Absenteeism also appears to be diminished when the CWW is adopted. Replacement of absent

employees, however, may be more difficult with this schedule, since one common way of replacing an absent

employee is holding over another from a previous shift, which is ill-advised for shifts of 12 hours.

Concerns over performance and safety have been voiced in relation to the CWW, although few studies have

analyzed this issue. It has been suggested that fewer errors and accidents occur and productivity improves on CWW

schedules. Other studies suggest that a 12-hour day, 4-day week produces more fatigue and poorer sleep and

psychomotor performance than an 8-hour day, 5-day week.

Administrative problems may arise from the use of the 12-hour shift and the CWW. Since laws and regulations

regarding hours of work are generally based on the 8-hour day and 40-hour workweek, computation of hourly wage

and vacation time must be adjusted. Similarly, since exposure limits to noise, chemicals, and heat are generally

based on the 8-hour day, they may need to be recalculated.

SOURCE: OffIce of Technology Assessment 1991.

1

(day, evening, night) or backward (day, night, BIOLOGICAL RHYTHMS AND

evening). Other types of scheduling, such as the

compressed workweek (in which employees work

approximately 40 hours in fewer than 5 days) and

irregular scheduling (in which scheduled work shifts

are variable and erratic), also exist. Compressed

workweeks are used in the chemical and petroleum

industries and are becoming more common in other

employment sectors (box l-C); irregular schedules

are used in some employment sectors, including the

transportation and manufacturing industries.

WORK SCHEDULES

Any work schedule that requires people to work

when they would normally be sleeping (and sleeping

when they would normally be awake) will conflict

with the workers’ circadian cycles and can cause

disruption in circadian rhythms. These include

irregular or rotating shift schedules, which cause

workers to change constantly the hours that they

work, or extended duty hours, which require them to
14 . Biological Rhythms: Implications for the Worker

Figure 1-6-Relationship of Body Temperature, Work, and Sleep

in a Rapidly Rotating Schedule

38.0

37.5

37.0

36.5 1—

Work Sleep — —— ——

1st morning shift

1 I I r

6 am Noon 6 pm Mid- 6 pm

38.0

37.5

37.0

36.5 1

night

Work Sleep ——— — —

2nd morning shift

I I I I

6 am Noon 6 pm Mid- 6 am

night

Sleep Work Sleep

38.0-

37.5-

37.0-

36.5- 1st afternoon shift

I I I I I

6 am Noon 6 pm Mid- 6 am

night

Sleep — Work — ——— Sleep

38.0-

37.5-

37.0-

36.5- 2nd afternoon shift

I I I 1 I

6 am Noon 6 pm Mid- 6 am

night

1 Sleep Work

———-

38.0-

37.5-

37.0-

36.5- 1st night shift

I I I I I

6 am Noon 6 pm Mid- 6

night

I Sleep Work

38.0-

37.5-

37.0-

36.5- 2nd night shift

I

I I I I

6 am Noon 6 pm Mid- 6 am

night

I

Sleep Sleep

38.0-

37.5-

37.0 - U

k

36.5- 1st day off

I I I I I

6 am Noon 6 pm Mid- 6 am

night

Sleep

38.0-

37.5-

37.0-

[

36.5-

I I I I 1

6 am Noon 6 pm Mid- 6 am

night

Time of day

Graphs showing average body temperature of four workers on a 2-2-2 rotating shift system. On the night

shift, the low point of body temperature coincides with the work period.

SOURCE: S. Folkard, D.S. Minors, and J.M. Waterhouse, “Chronobiology and Shift Work: Current Issues and Trencs,”

Chronobiologia 12:31-54, 1985.
Chapter 1--Summary, Policy Issues, and Options for Congressional Action ● 15

work for extended periods of time. In these situations, the physiological changes caused by circadian rhythm disruption often interact with

other stressors associated with work schedules

(i.e., fatigue, sleep deprivation, and social or

domestic stress) to compound the effects on the

health, performance, and safety of the worker.

Effects of Work Schedules

Human beings are naturally diurnal creatures,

whose internal clocks are geared toward active

wakefulness during the day and sleep at night. Most

of society reflects this pattern. Normal work hours

end in the late afternoon, and social activities, as

well as the evening meal, usually a time for family

conversation, follow. The shift worker, who goes to

work or tries to sleep at that time, misses these

activities. Shift workers end up fighting the diurnal

trends and social attitudes that surround them. This

creates three sources of stress:

. disruption of circadian rhythms;

. sleep disruption and fatigue; and

. social and domestic disturbances.

How much stress is placed on the worker by each

of these sources varies, depending on the nature of

the work situation and the schedule employed. The

impact of these stressors and their resultant consequences may, in some individuals and some situations, lead to difficulties in coping with a work

schedule. Indeed, some experts assert that shift

workers never adjust to the stress associated with

this work. However, there is great variability

among people in their ability to adjust to shift

work, with some individuals suffering few, if any,

problems, and others finding certain work schedules intolerable. As a result, for some people shift

work is an inconvenience, while for others it can

have major adverse consequences. It should be

borne in mind, however, that even those individuals

who appear to adjust well to shift work may

experience negative effects on factors such as

performance or safety.

Work schedules can require an individual to be

awake and active at an inappropriate time during the

circadian cycle and can result in a state in which an

individual’s circadian rhythms are out of synchrony

(figure 1-6). An inappropriately phased circadian

system is in a state of disharmony akin to that of a

symphony orchestra without a conductor. That

disharmony can result in feelings of malaise and

Figure 1-7-

Hours

8 ~

6

4

2

n

-Length of Sleep of Permanent and

Rotating Shift Workers

u

A B c D

= Day = Afternoon, evening m Night

Average sleep lengths on different shifts for two samples of

permanent (A,B) and rotating (C,D) shift workers. Rotating shift

workers on the night shift had the shortest average sleep lengths.

SOURCE: M. Colligan and D. Tepas, “The Stress of Hours of Mkxk,”

Amerkan Industrial Hygiene Assoa”atkm Journal 47 S66%95,

1966.

fatigue, disrupted sleep, and attempts to perform

certain tasks at a less than optimal time in the

circadian cycle. The degree to which individuals are

affected by circadian disruption varies, with some

people being better able to tolerate circadian desynchronization than others.

Another prominent effect of work schedules,

especially those that require night work, is sleepiness and fatigue (figure 1-7). One of the most

common complaints among shift workers is the

inability to sleep as long as necessary during the day,

because of both internal factors, such as a desynchronized circadian system, and external factors,

such as daylight, a noisy environment, and family

and social demands. The net effect of these disruptions of sleep is often a state of chronic fatigue and

sleepiness referred to as sleep debt. There is some

variability among individuals in their ability to

sleep, and persons who find it easier to sleep at odd

times may adjust more readily to sleep disruptions

caused by work schedules.

Finally, work schedules may induce stress by

preventing workers from fulfilling family responsibilities and putting them out of synchrony with the

rest of society. Social companionship, parenting,

and sexual partner roles can all be compromised by

work schedules, and carrying their domestic work-
16 ● Biological Rhythms: Implications for the Worker

Figure 1-8-Prevalence of Disease in Shift Workers and Day Workers

Percent

60

40

20

0!

Percent

60

40

20

0 1

Work

experience

(years)

Shift workers

Day workers

Ch-ndal

0-3 4-12 13-2223-40 0-3 4-1213-2223-40

Circulatory system Digestive system

Diseases

Percent of shift workers and day workers at an oil refinery, subdivided into groups according to work

experience, suffering from circulatory and digestive diseases. Shaded bar indicates that there was a

statistically significant difference between the shift workers and day workers.

SOURCE: Adapted from M. Keller, “Health Risks Related to Shift Work: An Example of Time Contingent Effects of

lmng-Term Stress;’ International Archives of Ocx.wpationa/and Environmental Health 53:59-75, 1983.

load is a major source of difficulty for women lar disease and negative reproductive outcomes such

workers. Shift workers commonly feel alienated as babies with low birth weight and preterm births

from the community because they are unable to (figure 1-8). While there has not been extensive

attend evening or weekend educational, sports, research in the area, there is some evidence that

religious, or recreational events and are unable to decrements in performance occur as a result of

take advantage of community benefits. nonstandard hours and that a number of factors

besides circadian desynchronization contribute to

These stressors can have a variety of conse- them, notably sleep deprivation and fatigue. Inforquences, including decreased well-being, chronic mation about how shift-work-induced performance

malaise, and poor sleep; increased gastrointestinal decrements could affect productivity has not been

distress; and, perhaps, increased risk of cardiovascu- collected.
Chapter l-Summary, Policy Issues, and Options for Congressional Action . 17

The implications of shift work for safety have

not been examined thoroughly. Work schedules

may affect not only the worker’s safety, but the

public’s safety as well. Existing studies show that

time-of-day effects and sleep loss and fatigue can

contribute to transportation mishaps (figure 1-9), but

the amount of information regarding their effects on

rates of injury and mishap in other work settings is

too sparse for any conclusions to be drawn. Additional data on the frequency, nature, and magnitude

of such incidents are needed before measures to

prevent them can be designed.

Interventions

A number of interventions to counteract the

circadian desynchronization, sleep disturbances, and

social disruption associated with shift work are

being examined, but additional research is needed to

understand the mechanisms at work in specific

situations and to determine the effectiveness of these

interventions.

While the most direct intervention is to devise less

disruptive schedules, determiningg what is the best

schedule is difficult. For example, the least disruptive schedule from a circadian perspective may not

be optimal in terms of sleep and fatigue, or a

schedule that tries to avoid sleep loss effects may

create hardships for the worker in the social and

domestic arenas. The “best” schedule varies from

setting to setting, and the nature of a given job may

dictate what is optimal. From a strictly circadian

perspective, fixed shifts and shifts that rotate in a

clockwise direction (mornings, evenings, nights) are

probably the least disruptive; however, permanent

night workers often suffer from chronic sleep

disturbances, and the placement of shifts in a

clockwise rotating schedule may provide less opportunity to prepare for and recover from the night shift.

Expert opinion is divided as to whether a fast (1 to

3 days) or slow rotation (2 weeks or longer) is best,

and it may be that consideration of the type of task

to be performed (e.g., a simple repetitive task vs. one

requiring memory) would be helpful to determine

speed of rotation. One of the most popular rotation

frequencies is 1 week. It is also one of the most

problematic. One week is long enough to incur sleep

deprivation but not long enough to allow for

complete circadian readjustment, so the avoidance

of weekly rotating schedules maybe preferable from

a circadian perspective. Furthermore, extended duty

Figure 1-9-Fatigue-Related Vehicular Accidents

Number International data (n=6,052)

1,200 I

1,100

1,000 HII

900

800

700

600

500

400

300

200

4 nn I WV

Midnight 6 a.m. Noon 6 p.m. Midnight

Time of day

The distribution, by time of day, of 6,052 vehicular accidents that

were judged by investigators to be fatigue-related.

SOURCE: M.M. Mittler, M.A. Carskadon, C.A. Czeisler, et al., “Catastrophes, Sleep, and Public Policy: Consensus Report,” S/eep

11 :100-109, 1988.

schedules that result in sleep loss and fatigue should

be avoided.

Some interventions are designed to facilitate the

process of adjustment to shift work. There is some

evidence that bright light can help the circadian

system adjust to work schedules, and medications

that directly affect the circadian system or counteract

the effects of fatigue and sleep problems are also

being investigated. No drugs have yet been conclusively shown to have a direct effect on circadian

rhythms. While certain compounds are helpful in

inducing sleep (i.e., short-acting hypnotics, tryptophan, antihistamines) or maintaining alertness (i.e.,

amphetamines, caffeine), all have characteristics

that prohibit regular use. The use of sleep and

napping strategies to optimize a worker’s ability to

obtain adequate sleep is another area of investigation. Napping before a period of extended work is

helpful in improving performance during the work

period and can help workers on rotating shifts to

supplement their sleep periods.

Other possible interventions include monitoring

systems to detect when individuals may pose a risk

to themselves or others because their performance is

impaired. These can take the form of specific tests

administered to workers on the job to determine if

their performance on a task is suboptimal and

systems that provide real-time, on-the-job feedback
.—. ---

18 ● Biological Rhythms: Implications for the Worker

——-

to the worker. Finally, educational programs that

provide workers with information and strategies to

deal with the problems they may face and ease some

of the consequences of shift work are an important

area of intervention research.

Research Needs

All conclusions and inferences about the effects of

shift work are based on limited data. In the first

place, the effects of work schedules are complex and

often difficult to study. In the second place, OTA

finds that studies of shift work have received little

support in this country. Three basic types of

studies have been used to examine the effects of shift

work: field studies, in which subjects are studied in

their actual work environment; survey studies, in

which workers answer interview questions; and

laboratory studies, in which the work situation is

simulated in a controlled setting. There is a pressing

need for research into how to apply basic knowledge

about circadian rhythms and other factors in shift

work to studies of the workplace. Research is needed

to explain the various effects of work schedules, the

variables that contribute to difficulties in adjusting

to shift work, and interventions that could be used to

counteract them. In addition, there is a compelling

need for more studies of the interaction between

work schedules and safety in the workplace. Crucial

to this endeavor is more thorough collection of

workplace data regarding hours of work and the

occurrence of on-the-job accidents. The major mechanism for collection of data related to workplace

injuries and mishaps in the United States is the BLS.

Currently, the data being gathered by the BLS

provide no information that could help in assessing the impact of shift work on employee safety

and health.

LEGAL AND REGULATORY

ISSUES

Current Regulation

Some Federal regulations on work hours are

included in statutes and can be modified only by

legislative action. In other instances, legislation

delegates regulatory responsibility to an administrative agency which then promulgates requirements.

Many existing regulations came about as a result of

concern for public safety, notably within the transportation industry. In every case, existing regulations are concerned with total work hours in a freed

period of time, without specifically addressing shift

changes or regulation of proportion of day and night

work. There is also a substantial body of State

regulation in the area of employee hours and

conditions of work, some of which relates directly or

indirectly to work scheduling.

The Hours of Service Act, which regulates work

hours within the railroad industry, is an example of

a statute that imposed specific requirements. First

enacted in 1907, and enforced by the Federal

Railroad Administration, it limits work hours for

railroad employees and provides for penalties for

violators. The Fair Labor Standards Act of 1938,

which mandates a minimum wage for employees

and requires that employers pay an overtime premium for time worked in excess of 40 hours a week,

may influence work schedules indirectly. It also

limits the hours that may be worked by children

under 16.

The remainder of the current Federal regulation of

work hours takes the form of requirements imposed

by individual agencies, mostly within the Department of Transportation. Hours of service regulations

are imposed by the Federal Highway Administration

on truck and bus drivers, by the Federal Aviation

Administration on airline crews and dispatchers, and

by the Coast Guard on maritime crews. All of these

regulations specify maximum permissible hours of

service, and each contains details related to such

issues as minimum rest periods, methods for recording hours of service, and penalties for violations.

The Nuclear Regulatory Commission (NRC) has

issued a policy statement concerning maximum

work hours for licensed nuclear powerplant personnel. However, NRC policy statements are only

enforceable if a plant voluntarily incorporates them

into its technical specifications as part of the NRC

licensing procedure.

Areas of Potential Regulatory Action

Action related to work hours could take two

forms: the enactment of new (or amended) legislation covering work schedules or the promulgation of

new regulations under existing statutory authority.

With respect to the enactment of new Federal

legislation, there is no serious question regarding the

power and authority of Congress to take legislative

action to regulate work hours. State legislatures also

have authority to regulate economic matters, within
Chapter 1--Summary, Policy Issues, and Options for Congressional Action ● 19

the boundaries of both Federal and State constitutional limits.

The most likely source of authority to regulate

work schedules would be safety and health statutes.

Some of these deal specifically with occupational

safety and health, notably the Occupational Safety

and Health Act, which is implemented by OSHA.

With a few exceptions, the act covers all private

employees, and employers are obligated to comply

both with the occupational safety and health standards issued by OSHA and with the general duty

clause of the act. The general duty clause requires

that an employer provide employees with a

workplace “free from recognized hazards likely to

cause death or serious physical harm. ” If OSHA

were to determine that certain hours of work pose a

safety or health hazard to employees, it could issue

a specific standard, in accordance with the statutory

procedures, or regulate it under the general duty

clause. Standards and the general duty clause are

enforced through workplace inspections, citations,

and penalties. However, standards define employer

obligations, while under the general duty clause, the

employer’s obligation is established on a case-bycase basis. Thus, regulation under the general duty

clause would likely lead to less effective compliance

and would be more burdensome for the agency. The

Federal Mine Safety Act of 1977 empowers the

Mine Safety and Health Administration to issue

‘‘mandatory health and safety standards for the

protection of life and the prevention of injury in coal

and other mines. It could regulate hours of work in

mines in a reamer analogous to that of OSHA in

other industries.

Department of Transportation agencies have the

statutory authority to regulate work hours (existing

hours of service regulations), as do some other

Federal agencies. The Railroad Safety Act of 1970

is designed to protect railroad employees, passengers, and members of the public who may be affected

by railroad operations. Under the Energy Reorganization and Development Act the NRC has authority

to issue regulations governing nuclear materials in

order to protect health or to minimize danger to life

or property. This could provide sufficient authority

for the agency to regulate work schedules of covered

employees.

The Labor-Management Relations Act regulates

hours of work indirectly, by giving employees the

right to bargain collectively and to enter into

collective bargaining agreements. Under the act, the

employer and the union must bargain in good faith;

failure to do so is an unfair labor practice. The parties

are obligated to bargain only in certain areas,

including hours of employment.

CONCLUSIONS

There have been significant advances in the

description and understanding of biological rhythms

during the last decade. Basic research has delineated

many physiological and cognitive functions that

fluctuate in cycles, with circadian rhythms being the

most thoroughly characterized. Further research is

needed, however, into the mechanisms controlling

biological rhythms, the role they may play in

conditions such as aging and mental disorders, the

implications of biological rhythms for clinical pharmacology and medicine, and the testing of interventions to manipulate them.

There have not been equivalent advances in the

application of biological rhythm research to the

workplace. Available data indicate that the biological rhythm disruption associated with nonstandard

work schedules can, in conjunction with other

factors, adversely affect the health and safety of

workers. But there are significant gaps in the base of

knowledge related to the precise nature of the effects

that occur, the factors that influence individuals’

susceptibility to them, and the prevalence and

magnitude of such effects. Additional research and

collection of statistical data on the workplace are

needed in these areas.

Shift work is necessary in a modern, technological

society. An understanding of its effects on workers is essential in designing work schedules with

the least negative impact on the worker and

society, in developing interventions to alleviate

the problems workers encounter, and in directing

the guidance and regulation of work hours and

work schedules.

CASE STUDIES

To highlight the variety of settings in which shift

work can be found, OTA has selected three case

studies for closer examination. Each represents an

area of employment in which nonstandard work

hours may affect the public welfare as well as the

individual worker.
20 ● Biological Rhythms: Implications for the Worker

Nuclear Powerplant Control Room Operators

Control room operators continuously monitor all

indicators in the control room of a nuclear utility and

oversee the operations of all of its components.

These monitoring tasks require low-level sustained

vigilance, which could be degraded by the effects of

nonstandard work hours. Typically, powerplant

control room operators work either an 8- or 12-hour

per day rotating shift schedule.

The NRC licenses all nuclear powerplants and has

authority over them. It has issued policy statements

providing guidance on total working hours and

maximum consecutive hours of work for nuclear

powerplant operators. Although NRC policy statements are not enforceable per se, if a plant chooses

to incorporate them into its technical specifications

or administrative procedures, it must then follow

those policies. To date, 77 of the 111 nuclear

powerplants licensed by the NRC have incorporated

the policy statements regarding work hours into their

technical specifications. The NRC provides no

guidance or policy regarding the specific design of

work schedules. A panel convened under contract to

the NRC has made recommendations, but no action

has been taken on them to date, and they remain

under consideration by the NRC.

Although the primary responsibility for monitoring employees on the job rests with the management

of the utility that operates the powerplant, the NRC

maintains resident inspectors at all plants as a means

of monitoring compliance with regulations. If an

inspector observes that individuals are not performing their duties adequately, he or she notifies the

appropriate supervisor. Beyond the supervision

provided by the utility management and the observational oversight of the NRC resident inspectors, the

NRC has set forth no specific guidelines or regulations for monitoring control room operators for

performance deficiencies related to sleepiness, fatigue, or disrupted biological rhythms. The Commission has instituted regulations regarding fitness for

duty which are intended to ensure that all operators

and plant personnel are reliable, trustworthy, and not

under the influence of any substance (legal or

illegal), or mentally or physically impaired from any

cause, that would affect their ability to safely and

competently perform their duties. Currently, this

program is designed only to detect individuals using

legal or illegal substances. If deemed necessary or

desirable, it could be modified to include monitoring

for decrements in performance caused by sleepiness,

fatigue, or circadian desynchronization.

Registered Nurses and Resident Physicians

Registered Nurses

Registered nursing, the largest health care profession, is a predominantly woman’s profession. The

preponderance of women in nursing makes it

difficult to generalize from studies of shift work in

industries that employ primarily men. Shift work is

a common part of nurses’ lives, but there are no

national data about the prevalence of shift work in

nursing; few studies of the short- or long-term

consequences of shift work for nurses’ family and

social life, health, and work performance; and few

studies of the impact of different shift schedules on

the quality of patient care. The information that is

available indicates that a sizable proportion of

registered nurses work some nondaytime hours and

that shift work and the perceived lack of control over

scheduling are important factors in nurses’ job

dissatisfaction and job turnover. Nurses typically

work five 8-hour shifts per week on either a fixed or

rotating basis, although other schedules are sometimes used. Higher hourly wages for evening and

night shifts are common.

A study of nurses found that rotating shift work

was associated with more digestive problems, more

tension and stress, higher rates of injury, and

disruptions in family and social life. As with shift

workers in general, sleep disturbances are common

among nurses working nondaytime hours. Some

studies have found that nurses on rotating shifts take

more sick days and rate themselves lower on job

performance. Very little research has been conducted on the relationship between shift work and

quality of patient care by nurses. What research has

been conducted suggests two means by which shift

patterns might affect quality of nursing care. First,

patterns that are more compatible with circadian

rhythms could result in less fatigue and increased

alertness on the job. Second, shift work patterns that

are more satisfying to nurses could result in greater

nurse retention, unit cohesiveness, and continuity of

care across shifts.

More research is needed on various shift work

issues related to nursing, including the impact of

changes in the health care system on workload, shift

work, job stress, and related issues. Hospital nurses

today must cope with decreased length of patient
Chapter 1--Summary, Policy Issues, and Options for Congressional Action ● 21

stay and increased severity of disease as a result of

prospective reimbursement of hospitals. These factors may exacerbate work stress and health problems

in general, independent of shift work, or they may

interact with shift work to produce extremely high

stress levels among those nurses working undesirable shifts and confronting patients who require more

intensive nursing care.

Resident Physicians

Medical resident training has a long-standing

tradition of extended duty hours, often including

on-call periods of 24 hours or more. The major

rationale for these schedules has been to provide

continuity of care by observing and treating the

patient over an extended period. Traditionally, the

possible negative consequences of these schedules,

such as fatigue and sleepiness, which could have a

detrimental impact on resident performance and

quality of life, have received minimal attention.

Recently, however, consideration of these consequences has increased, partially as a result of an

incident in 1984 in which a young woman died while

being treated at a hospital in New York. An

investigation found that of the five factors contributing to her death, one was that the resident who

treated her had been on duty for an extended period

of time (the other four were related to the level of

supervision of the residents and other treatmentrelated issues). In response to this incident, the State

of New York enacted regulations that limit the hours

of work of hospital house staff. Implementation of

these regulations has had a high financial cost,

increasing New York State’s health department

budget by 3 percent.

Length of resident hours has traditionally been the

concern of the Accreditation Council for Graduate

Medical Education (ACGME). Within the past few

years, ACGME has moved to revise its requirements

for working hours and supervision of residents by

having its Residency Review Committees (RRCs),

which oversee the various medical-surgical specialties, introduce new standards. The responses of the

RRCs ranged from specific (emergency medicine:

no more than 60 hours per week with 12-hour shifts),

to general (thoracic surgery: responsibility of program director to ensure reasonable in-house duty

hours), to no response (general surgery and psychiatry). These revisions were made during 1988-89 and

took effect in the summer of 1989.

Information regarding the effects of extended

duty hours on residents and their patients is meager.

While anecdotal evidence supports the idea that

sleep deprivation associated with resident on-call

schedules can affect patient care, the studies that

have been conducted are equivocal. It is reported

that extended duty hours prolong the time it takes to

perform tasks but have no effect on the quality of

performance. There is even less information available on the contribution long hours can make to

health and family interactions.

The debate over the necessity for extended duty

hours for medical residents remains unresolved.

Until more information is gathered, a determination

of what will best serve the needs of the doctors and

the patients they care for cannot be made.

The Military

Many military situations demand that personnel

engage in duty schedules that can lead to circadian

rhythm disruption, sleep loss, and other stressors.

The operational situation surrounding an activity

determines the tempo at which tasks are to be

performed and the nature of the stressors associated

with job performance. A task performed during

routine operations or in training, for example, is very

different when performed under actual or simulated

combat conditions. Usually, activities that occur in

conjunction with combat or training for combat are

marked by an increased tempo and sustained hours

of duty. Since sustained operations requiring prolonged performance are integral to modern military

operations, some of the most salient problems

encountered are sleepiness and fatigue. Military

tasks that could be affected include vigilance tasks,

which require concentrated attention and alertness

(e.g., electronic tracking and surveillance, sentries);

operation and control of vehicles (e.g., aircraft,

mobile weapons systems, boats); maintenance, preparation, and operation of equipment (e.g., weapons

systems, communication systems); and command

and control activities.

Few specific military regulations or guidelines

relate to hours of service and scheduling, although

all services do regulate flight operations. These

regulations specify maximum allowable hours of

flight duty and may include stipulations regarding

transmeridian flight, minimum necessary rest periods, and the scheduling of flight operations. The

Navy has specific guidelines, which have been used
22 ● Biological Rhythms: Implications for the Worker

for centuries, for the scheduling of watches on board

ships. They require that personnel standing watch

constantly vary their hours of activity and sleep,

which results in a constant state of circadian

desynchronization. Beyond these regulations and

guidelines, decisions regarding hours of duty and

work schedules for military personnel are generally

left up to commanding officers, who base their

decisions on their knowledge of mission requirements and on the condition and limitations of their

personnel.

POLICY ISSUES AND OPTIONS

FOR CONGRESSIONAL ACTION

OTA has found that the significant progress made

in recent years in the understanding of biological

rhythms has not been matched by comparable

advances in the understanding of biological rhythm

disruption and its interaction with other factors in

shift work. The limited information from research

aimed at applying basic information about biological rhythms to work settings indicates that problems

can arise as a result of nonstandard work schedules

and that these problems affect the health, well-being,

and safety of workers, and in some instances the

public’s safety. However, further clarification and

definition are needed to determine the precise

nature, prevalence, and magnitude of such problems.

It is clear that for some workers nonstandard work

hours impose a hardship that needs to be recognized

and addressed. Three policy issues related to biological rhythms and work schedules were identified in

the course of this assessment:

the level of the Federal research effort in this

area;

the adequacy of Federal mechanisms for collecting workplace safety data related to hours of

work; and

the role of Congress in ensuring the well-being

of men and women who work nonstandard

hours.

Associated with each policy issue are several

options for congressional action. Some of the

options involve direct action. Others involve congressional oversight or direction of the executive

branch. The order in which the options are presented

does not imply any priority. Moreover, the options

are not, for the most part, mutually exclusive;

adopting one does not necessarily disqualify others

within the same category or in any other category.

Implementation of a combination of options might

produce the most desirable effects. It is also important to keep in mind that changes in one area may

have repercussions in other areas.

Issue 1: Is the current Federal research effort on

the effects of work schedules and the mechanisms for collecting information on work

schedules adequate?

Various Federal departments and agencies direct

and fund intramural and extramural research programs about biological rhythms and the effects of

work hours. Some programs are dedicated to basic

research related to biological rhythms, while others

are concerned with workplace issues. Many, especially those devoted to applied research in the

workplace, are limited in scope and are minimally

funded. Often, these programs focus on settings

directly related to the funding agency (e.g., the

Federal Railroad Administration conducts research

on railroad operations, the Department of Defense

studies military operations, etc.). Although the

information derived from such studies may be

applicable to other situations, few programs are

devoted to studying general issues related to work

schedules. The National Institute of Occupational

Safety and Health (NIOSH) in the Department of

Health and Human Services is an appropriate agency

to fund and conduct such research, but only a small

component of its research effort is devoted to this

area. Moreover, NIOSH itself is a relatively small

agency, and it may be unable to expand research in

any area without an overall increase in size.

The Bureau of Labor Statistics (BLS) is responsible for the collection of workplace data. Its collection of data on the demographics, prevalence, and

use of shift work is sporadic and inconsistent. The

last collection of any such data was in 1985, with

another scheduled for 1991.

Option I: Take no action.

If Congress takes no action, the Federal research

effort on the effects of work hours will continue at

its current pace and extent. Information from basic

research on biological rhythms and other pertinent

factors will continue to be gathered, while research

applying that knowledge to studies in the workplace

will remain limited. Statistical data that would

facilitate and augment this research will continue to

be gathered in a nonsystematic fashion. Taking no
Chapter 1--Summary, Policy Issues, and Options for Congressional Action .23

action will forestall the gathering of information

about the precise effects of various work schedules

on workers-information that is needed to better

understand what effects occur, to develop interventions that will help workers cope with these schedules and to steer guidance and regulation related to

the design of work schedules.

Option 2: Create a Federal interagency task force

to guide research efforts.

Congress could direct the establishment of an

interagency coordinating group to ensure maximum

use of U.S. research resources. Given the crossagency nature of issues related to hours of work, the

Committee for Health and Life Sciences of the

Federal Coordinating Council for Science, Engineering, and Technology under the auspices of the

Office of Science and Technology Policy is an

appropriate body to assume this role. The Committee could coordinate research efforts across Federal

agencies and set priorities for research. This would

expedite the transfer of information from basic

research to applied settings. The Committee could

also set priorities for the collection of statistical data

on the workplace by pertinent Federal agencies,

which would facilitate research.

Option 3: Convene a national commission of nongovernmental experts on biological rhythms,

work schedules, and their effects.

Congress could direct that a national commission

of nongovernmental experts be established to provide guidelines for research priorities and directions.

Since the guidance provided by such a commission

would affect several Federal agencies and departments, the commission could be directed to submit

its findings to the Federal Coordinating Council for

Science, Engineering, and Technology within the

Office of Science and Technology Policy to ensure

the widest possible dissemination of its recommendations. The findings and recommendations of this

commission could be used to coordinate and direct

research efforts in this area.

Option 4: Direct the Bureau of Labor Statistics to

expand the scope of its collection of data related

to work schedules and hours worked.

Congress could direct the BLS to increase the

consistency and scope of its collection of data

related to hours of work. This could include information regarding the types of schedules being used in

various industries and occupations and the demographics of the populations involved. Such data

could be collected at regular intervals to ensure an

up-to-date database. Before initiating this effort,

representatives from the BLS could meet with

representatives from the Occupational Safety and

Health Administration (OSHA) (in the Department

of Labor), NIOSH, and other pertinent agencies to

determine what information is needed and the best

format for its collection. These data would provide

a clearer picture of the nature and extent of work

schedules being used in the United States and the

people who work them. If Congress takes this action,

it will ensure the availability of pertinent information regarding the use of work schedules.

Option 5: Expand intramural and extramural research programs at the appropriate agencies and

departments.

Congress could increase Federal research on the

impact of work schedules on workers. This could

include directing the pertinent Federal agencies to

expand existing research programs and to develop

new programs, as well as increasing appropriations

of funds to support these efforts. Programs examining general issues related to hours of work could be

carried out by agencies within the Department of

Health and Human Services, notably NIOSH, and

the Department of Labor, while industry-specific

studies could be conducted by appropriate agencies,

such as the agencies of the Department of Transportation and the Department of Defense.

OTA concludes that available information fails to

answer questions about possible impacts of shift

work on health and safety and provides very little

information about possible interventions to alleviate

any effects. While those answers and that information can be obtained, to do so in a timely reamer will

require increases in research support.

Issue 2: Are current Federal mechanisms for the

collection of workplace safety statistics adequate?

BLS is the collector of workplace data related to

injuries and mishaps. Currently, BLS forms for

reportable injuries and illnesses include no questions

regarding time of day, hours of work, or work

schedules associated with an incident. OSHA may

record information on time of day and hours of work
24 . Biological Rhythms: Implications for the Worker

in its investigations of workplace fatalities and

catastrophic incidents in which five or more people

are injured or substantial damage to property occurs.

The National Transportation Safety Board routinely

collects information regarding the role that hours of

work might play in mishaps. Other Federal agencies

and departments may examine the role of work hours

when investigating incidents that occur within their

domains. This information is used to help determine

the cause of an event and is available to investigators

who want to examine possible contributing factors

in various types of work-related incidents.

Option 1: Take no action.

Workplace safety statistics will continue to be

collected in the current fashion if Congress chooses

to take no action. The data currently being collected

by the BLS provide no information that could

facilitate the assessment of the impact of work hours

on employee and public safety, and the data collected by other agencies mayor may not do so. Lack

of this information makes it difficult to determine

the frequency and severity of effects various work

schedules can have on employee---and public—

safety in different settings and occupations.

Option 2: Direct that the Bureau of Labor Statistics

increase its collection of workplace data.

Congress could direct the BLS to gather information on work schedules and hours of work in its

collection of data related to occupational injuries

and illnesses. Since including this information on

the BLS log sheets would increase the amount and

complexity of information an employer would have

to provide following a workplace incident, the BLS

could first assess the feasibility and best method of

obtainin g such data. This information could include

the time of day an incident occurred, the schedule

being worked by the individual involved, and how

many hours the person had worked previously. The

resulting database could be analyzed to clarify the

relationship between hours of work and workplace

accidents and illnesses. In addition, the BLS could

conduct targeted studies through its work injury

report activity to describe relationships between

work schedules and injuries.

Option 3: Direct the Occupational Safety and

Health Administration and other agencies that

collect workplace safety information to record

information on hours of work related to safety

incidents.

Congress could direct Federal agencies and departments that are involved in investigating safetyrelated incidents to routinely collect information

related to work schedules and hours of work. This

action would guarantee the availability of information that would make it possible to assess the

contribution of work hours to the occurrence of

accidents in various work settings and occupations.

Issue 3: Should Congress take steps to ensure the

well-being of workers engaged in nonstandard

hours of work?

Shift workers are exposed to a variety of circumstances and conditions not associated with standard

daytime schedules. While much information is still

needed, it is clear that nonstandard work hours can

have a variety of effects on some workers. Gastrointestinal complaints, difficulty sleeping, and disruptions in family and social life are common and may

affect the performance, well-being, and safety of the

worker—and, by extension, the public. While there

are some actions that can be taken to assist workers

in coping with some of these conditions and to lessen

their impact, there is currently little awareness of

them, either in government or in private institutions.

While concerns raised by nonstandard hours of work

do receive some Federal attention within specific

domains, the extent of activity in this area is narrow

and inconsistent.

Option 1: Take no action.

If no action is taken, the recognition and awareness by government and private institutions of the

impact of nonstandard work schedules will remain at

its current level. Most shift workers will have little,

if any, information to help them adjust to their work

schedules and few resources to assist them with

problems they may encounter. Furthermore, employers may not be aware of interventions to reduce

the impact of the problems posed by shift work.

Recognition by Federal agencies of the effects

nonstandard work hours can cause and the importance these agencies place on monitoring and

responding to them will continue to be low.
Chapter I-Summary, Policy Issues, and Options for Congressional Action ● 25

Option 2: Encourage the development of educational programs and support services for workers.

Congress could direct the Public Health Service,

in the Department of Health and Human Services,

and other Federal agencies to develop programs to

educate shift workers about the demands and stressors they may encounter as a result of their work

schedules. Congress could also provide incentives to

private industry to do likewise. These programs

could tell workers and their families about actions,

such as sleep and dietary strategies, they can take to

lessen some of the negative effects that may occur.

Congress could also encourage the development of

support services in the workplace, such as counseling and guidance programs, that would be available

for workers encountering difficulties associated with

their work schedules.

Option 3: Direct the Occupational Safety and

Health Administration to determine whether the

issuing of standards related to hours of work and

scheduling is warranted.

Under the Occupational Safety and Health Act,

OSHA may issue standards related to safety or

health risks that exist in the workplace. OSHA issues

standards once it determines there is sufficient

evidence that a hazard exists. Congress could direct

OSHA to evaluate the latest research on work hours

to determine if there is sufficient information

regarding health and safety impacts to guide the

development of standards related to shift work.

Available information regarding the effects work

schedules can have on the health and performance of

workers, their prevalence, and how they impinge on

safety would have to be considered. This evaluation

could involve Federal, State, and industry officials,

researchers, and representatives of labor organizations. In addition, Congress could direct OSHA to

keep up-to-date on progress in this field and to take

any action that might be warranted by new developments and findings.

Option 4: Direct Federal agencies with authority

over health and safety to review current regulations and determine whether they adequately address concerns raised by nonstandard work

hours.

A number of Federal agencies have the authority

to regulate health and safety requirements within

their jurisdiction. Many of these agencies currently

have hours of service requirements regulating certain aspects of work schedules. Congress could

direct these agencies to review their current regulations to ensure that they are consistent with, and

incorporate the results of, the latest research on shift

work and its effects on health and safety. This would

also require pertinent agencies to increase their

surveillance and collection of data regarding the

impact of shift work on worker health and safety in

their domains.

Option 5: Encourage labor and management to

include provisions regarding the safety and needs

of shift workers in collective bargaining agreements.

As part of the good-faith bargaining conducted

under the Labor-Management Relations Act, agreements regarding scheduling and hours of work are

often struck between labor and management. Congress could encourage labor and management representatives to include in their deliberations safety and

health concerns that some work schedules raise and

the special requirements and needs of workers

exposed to nonstandard hours. While neither labor

nor management is under any obligation to respond

to congressional interests, taking this action would

indicate Congress’ concern about the matter.

Option 6: Direct that measures be taken to further

ensure individual and public safety in settings

where nonstandard work hours are in effect.

Nonstandard work hours are often associated with

safety concerns. Congress could direct the Department of Labor and other agencies to increase efforts

to ensure that threats to worker and public safety are

being adequately addressed. This could include

increased surveillance of compliance with existing

regulations regarding hours of work and investigation into the development of devices and interventions that can lessen hazards.
Chapter 2

Introduction and Overview
Contents

Page

THE BODY CLOCK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Circadian Rhythms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

BIOLOGICAL RHYTHMS AND THE WORKPLACE . . . . . . . . . . . . . . . . . . ...*,... . . . . . . . .

FEDERAL GOVERNMENT OVERSIGHT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

THE OTA REPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CHAPTER PREFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .

Box

29

30

31

32

33

34

Box Page

2-A. Biorhythms Are Not Biological Rhythms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figures

Figure Page

2-1. Circadian Timing of Various Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

2-2. De Mairan’s Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Chapter 2

Introduction and Overview

A factory whistle blows and the workers leave

their stations, punch the clock, and file out into the

morning light. The graveyard shift is over. In a scene

that is repeated across the country every day, these

workers head home to face their nighttime, a

nighttime that is at odds with the rest of society and

the worker’s own internal clock. This is shift work,

and whether it involves a factory worker, a waitress

at an all-night diner, or an interstate truck driver, this

kind of scheduling can produce deleterious effects

on the worker and the public.

Shift work, including any permanent schedule of

extended duty hours, is an example of how the

body’s internal clock can be upset by external

factors. Another common example is jet lag, the

malaise associated with travel across time zones. In

the case of jet lag, the effect is short-lived and the

body readjusts relatively quickly. In the workplace,

however, disturbances of the body clock can continue unabated, and other factors, such as loss of

sleep and social disruption, can rapidly come into

What we envision as an internal dock is actually a group of neurons

in the brain that control daily rhythms.

SOURCE: R.M. Coleman, Awake at 3:00 a.m. by Choice or by Chance

(New York, NY: W.H. Freeman, 1986).

play to compound the effects. For some workers,

when this occurs the results can be deleterious

consequences for their health and ability to perform

their jobs, which in turn can have detrimental effects

on their safety and that of society as a whole.

This provokes several questions: What is the

body’s internal clock, what is its purpose, and how

does it work? For individuals and society as a whole,

how does shift work affect productivity, health, and

safety? Depending on the answer to the last question,

what should be done to lessen the detrimental effects

of shift work?

THE BODY CLOCK

One of the most predictable features of life on

Earth is exposure to the rhythmic environmental

changes caused by the planet’s movements. As

described by one scientist, “. . . the rotation of the

Earth on its polar axis gives rise to the dominant

cycle of the day and night; the revolutions of the

Earth around the Sun give rise to the unfailing

procession of the seasons; and the more complicated

movements of the Moon in relation to the Earth and

the Sun give rise to the lunar month and to the tidal

cycles” (7). Given the pervasiveness of these

rhythms, it is not surprising to find that most

organisms show alterations in their bodily processes

and their behavior in response to them. These cycles

are called biological rhythms, and the internal

biological mechanisms that control them are the

body clock (box 2-A).

Biological rhythms provide a temporal framework for an organism’s behavioral and physiological

functions (7). For example, many flowers open and

close at certain times of day or night, and honeybees

time their visits to plants to coincide with these

cycles. This increases pollination for the plants and

the collection of nectar for the bees. The activity of

organisms that live along the shoreline is often in

synchrony with the ebb and flow of the tide, ensuring

that feeding occurs at the optimal time. Certain

animals are active and search for food only at night

(nocturnal), while some do so only during the day

(diurnal). These are just a few examples of the

diverse activities and functions guided by the body

clock.

–29–
30 . Biological Rhythms: Implications for the Worker

Box 2-A—Biorhythms Are Not Biological Rhythms

The scientific study of the biological rhythms of the body should not be confused with the theory of

biorhythms. No evidence exists to support the concept of biorhythms; in fact, scientific data refute their existence.

Based on a theory first proposed by the German scientist Wilhelm Fliess in 1897 and popularized in the 1970s,

biorhythm theory postulates that three cycles act in a concerted fashion to guide activity: a 23-day cycle that

influences physical strength, endurance, energy, and physical confidence; a 28-day cycle that influences feelings,

love, cooperation, and irritability; and a 33-day intellectual cycle that influences learning, memory, and creativity.

According to biorhythm theory, these three cycles are linked to an individual’s birth date and fluctuate in a constant

fashion throughout his or her life. Each cycle has a high and a low point. By mapping the high and low points of

the respective cycles and how they coincide or diverge, the theory states, performance can be charted, and critical

days when performance can be expected to be highest or lowest can be predicted.

Although a theory that provides a system for predicting human behavior and scheduling activities has appeal,

none of the contentions of biorhythm theory can be supported. No biological process with such a relationship to

the calendar date of birth has ever been identified, nor have any studies attempting to validate biorhythms been able

to do so. Thus, for example, attempts to validate the hypotheses using retrospective airplane crash reports and ,

athletic scores have consistently failed. While there clearly are human biological rhythms with cycles that can be

measured in days (the menstrual cycle being an example), there is no evidence for the existence of any of the three

biorhythms, let alone any predictive interaction, Given its nonfactual basis, biorhythm theory is relegated to the

realm of other popular pastimes, such as numerology, that can serve as a source of entertainment but have no

substantive or predictive value.

S(XJRCE: DC. Honey, C.M. Winget, CM. DeRosti~ et al., Effkcts of Circadian Rhythm Phase Alteration on Physiological andPsychoiogical

Variables: Implications to Pilot Pe~ormance (Including a Partially Annotated Bibliography), NASA @eludcal nwrnorandum

TM-81277 (Moffet Piel~ CA: National Aeronautics and Space Administratio~ March 1981).

While biological rhythms are driven by an internal clock, external factors usually entrain, or synchronize, those rhythms with the physical environment.

The degree to which an internally generated rhythm

is affected by environmental factors varies with the

species and the function being controlled. The ease

with which a function adjusts its rhythm to environmental cues will determine the degree to which the

timing of that function can be altered. In humans,

this has direct implications for the ability of the body

clock to readjust following changes in schedules.

Circadian Rhythms

While biological rhythms have cycles ranging in

length from minutes to months, those in synchrony

with the 24-hour rotation of the Earth are probably

the most extensively studied. These circadian

rhythms are usually 20 to 28 hours long, and many

physiological and psychological functions follow

such a circadian cycle (figure 2-1).

Recognition that the activities of many plants and

animals exhibit rhythms which coincide with the

Phota credt: Dermis do Cr&co/Sky & Telescope A4agazir:e 24-hour cycle of day and night probably dates back

In each time zone, the daily rising of the Sun

synchronizes internal clocks throughout the

ecological community.

to humanity earliest contemplation of the temporal

order of nature. The realization that these cycles

were 1101 solely a consequence of environmental
Chapter 2--Introduction and Overview .31

Figure 2-l-Circadian Timing of

Various Functions

~@Q $-’ ~Q &@

# #

~@Q

~\ ~\@ ~ \

80

Alertness 40

0

100.4

Temperature 98.6

(“F)

96.8

15

Growth hormone ,(

(nanograms/ml)

;

(

1!

Cortisol

(micrograms/100 ml) ‘

Potassium

(mini equivalent/hr)

1 ,

, I

I 1 1 ,

I

I

P-”

i 1 1

6 am Noon 6 pm Mid- 6 am Noon 6 pm Midnight night

Time of day

The timing of some functions that cycle with a circadian rhythm.

SOURCE: Adapted from R.M. Coleman, Awake at 3.00 a.m. by Choice or

by Chance (New York, NY: W.H. Freeman, 1986).

influences did not occur until 1729, when French

astronomer Jacques d’Ortous de Mairan studied the

actions of a plant that normally opens its leaves

during the day and closes them at night (figure 2-2).

De Mairan observed that even when kept in the dark,

the plant opened and closed its leaves according to

the day-night cycle. This indicated that the force

driving the plant’s rhythms was internally generated

(5).

The first observations of circadian rhythms in

humans were made in 1866, when William Ogle

noted that fluctuations in body temperature varied in

synchrony with day and night (5). It was not until

more recent times that the endogenous nature of

circadian rhythms in humans was characterized (l).

To date, research has identified hundreds of biological variables in humans that exhibit a circadian

Figure 2-2—De Mairan’s Experiment

I

De Mairan observed a biological rhythm in plants.

SOURCE: R.M. Coleman, Awake at 3:00 a.m. by Choice or by Chance

(New York, NY: W.H. Freeman, 1986).

rhythm (5). These functions are both physiological

(e.g., body temperature, hormone production, sleepwake cycles) and psychological (e.g.,

performance, memory).

BIOLOGICAL RHYTHMS

THE WORKPLACE

cognitive

AND

Humans are diurnal, and for most of history they

obeyed the body clock’s mandate to be active during

the day and sleep at night. However, as civilization

evolved, the desire, ability, and need to contravene

this pattern of activity grew. The control of fire

enabled humans to penetrate the darkness and

explore the nighttime world. Since then, technological advances have led the way to societies whose

activities extend beyond the daylight hours. This

trend was accelerated with the Industrial Revolution

and the advent of readily available electric power. In

the last few decades, other technological and economic forces, such as the need to operate costly

equipment continuously, the requirement of some

manufacturing processes for uninterrupted operation, and the increasing demand for 24-hour serv-
32 ● Biological Rhythms: Implications for the Worker

Photo credit: Travis Amos

Flowering in the morning glory, as in many other plants, is timed by a circadian clock.

ices, have contributed to the ever-growing number

of occupations that operate around the clock.

As a result, many persons in these occupations

work nonstandard schedules that can put them out of

synchrony with their body clocks. The term “shift

work” is often applied to these schedules, but there

is no consistent definition of the term. In this report,

it includes evening and night work; split shifts, in

which a period of work is followed by a break and

then a return to work; rotating shifts, in which the

hours change regularly (e.g., from day to evening to

night); and extended duty hours, consisting of long

work periods (usually over 12 hours).

Many factors shape the experience of individuals

working these schedules, and the interactions among

them are complex (2-4,8). In addition to disrupting

biological rhythms, shift work can cause other

physiological factors, such as sleep deprivation and

fatigue, to come into play. It can also affect the

family and social life of workers, creating a situation

in which their schedules do not coincide with those

of the people around them. The cumulative effects of

these factors can adversely affect the health and

performance of workers and can jeopardize their

safety and that of the public; however, the degree to

which these effects occur, which workers are most

susceptible, and the work conditions under which

they occur have not been clearly delineated.

Many occupations require 24-hour operations.

They include industrial and manufacturing industries (e.g., chemical, steel, paper, powerplants),

protective and health services (e.g., police, fire and

rescue, hospitals), transportation (e.g., airlines, railroads, trucking, shipping), major construction projects (e.g., dams, tunnels), and, increasingly, services

(e.g., retail stores, financial institutions, entertainment

and recreation, specialized services such as overnight deliveries). It is estimated that one in five

workers in the United States does not regularly work

a standard daytime schedule (6). As a result, about

20 million workers are exposed to a wide range of

schedules that differ in the duration of the work

period, the hour of day, and the stability of the

schedule. Each of these schedules has different

effects on workers’ biological rhythms and related

factors as well.

FEDERAL GOVERNMENT

OVERSIGHT

In the United States, the laws that govern hours of

work consist of the Fair Labor Standards Act, which

was enacted in 1938 and established a standard

40-hour workweek, and various hours of service

acts, which regulate maximum hours of work for a

number of industries, notably transportation. In

addition, some States have regulations regarding

hours of work.

The Federal Government has broad authority to

regulate working conditions that endanger the safety

and health of workers through the Occupational

Safety and Health Administration (OSHA) of the

Department of Labor. In addition, some Federal

agencies have the authority to regulate safety and

health within their, own jurisdiction. Examples of

agencies that have exercised some authority over

safety and health issues include the Federal Highway Administration, the Nuclear Regulatory Commission, and the Federal Aviation Administration.

OSHA can address worker safety and health

issues by issuing standards that require employers to
Chapter 2--Introduction and Overview ● 33

put in place appropriate protective measures and by

inspecting for compliance. Where standards are not

available, OSHA can act to increase safety and

reduce health risks by enforcing the general duty

clause of the Occupational Safety and Health Act.

This requires employers in an industry that recognizes the existence of a serious hazard to take

feasible steps to reduce the risk of that hazard to

workers. OSHA can impose standards and regulations on the workplace when scientifically valid

research and empirical data indicate that conditions

impose a significant risk of harm to workers.

In the case of biological rhythms and their

interaction with work schedules, the collection of

data takes a number of forms, including basic

scientific information on underlying biological mechanisms; applied research examining the human

response in laboratory and field settings; and statistical information on the occurrence of injuries,

mishaps, deaths, and health problems in the

workplace and the conditions under which they

occur, as well as demographic statistics on schedules

being worked. The Federal Government’s role in the

collection of this information cuts across all of these.

Federally funded extramural and intramural basic

science research programs, through agencies such as

the National Institutes of Health and the Air Force

Office of Scientific Research, are a means of

providing information on basic biological mechanisms. Federal or federally sponsored applied research programs can be conducted under the auspices of agencies such as the Centers for Disease

Control (through the National Institute for Occupational Safety and Health) or other agencies, such as

the National Aeronautics and Space Administration,

the Department of Transportation, the Department

of Defense, and the Nuclear Regulatory Commission. Collection of workplace statistics is done by

OSHA and the Bureau of Labor Statistics within the

Department of Labor.

Concerns about the effects of various work

schedules on the health and safety of workers and the

impact they could have on the public raise questions

about the level of Federal involvement in the

regulation of work hours and the types of schedules

employed in various occupations. This concern is

coupled with questions regarding the extent of

knowledge about work schedules and their effects.

In 1984, the Subcommittee on Investigation and

Oversight of the Committee on Science and Technology of the U.S. House of Representatives held

hearings on biological rhythms and shift work

scheduling. It is interesting to note that many

questions posed at that time still await answers,

namely:

●

●

●

●

●

●

●

What types of schedules are being worked and

by whom?

What are the precise effects on the health,

performance, and general well-being of workers who work nondaytime hours?

What kinds of effects occur in what kinds of

schedules?

Who are the workers who may be most

affected?

What factors contribute to any effects that are

observed and to what degree?

What are the implications of these effects for

worker safety and the safety of the public?

Most important, is enough known at this time

to recommend specific ‘guidelines or regulations?

This report discusses the current theories and ideas

that pertain to these questions and describes the

latest developments in the effort to answer them.

THE OTA REPORT

The primary focus of this report is the human body

clock and what occurs when it is disrupted by

various types of work schedules. In the seven

chapters that follow, the Office of Technology

Assessment (OTA) examines possible interactions

of work schedules and biological rhythms and their

implications for the American worker and the

public. In addition, OTA examines the role of

Congress and the Federal Government in addressing

the public policy issues raised by this topic.

Chapter 3 reviews the most recent developments

in understanding the body clock. It presents basic

scientific information about biological rhythms,

how they are regulated by the body, and how

extrinsic factors can affect their functioning. In

chapter 4, the forces driving the use of nonstandard

work schedules are presented, as is a description of

the population of U.S. workers who work them.

Chapter 5 examines what can occur when work

schedules impinge on the normal activity of the body

clock. How disruption of biological rhythms interacts with other factors to affect the health, performance, and well-being of workers is described. The

implications of these effects for the public’s safety

and possible interventions to counteract them are
34 ● Biological Rhythms: Implications for the Worker

also addressed. Chapter 6 discusses the Federal role

in regulating work hours and overseeing worker

health and safety. Finally, in order to highlight the

variety of settings in which nonstandard work hours

can be encountered, OTA has selected three case

studies to examine in closer detail. These case

studies also represent occupations in which any

adverse effects of nonstandard work hours that occur

may affect the public welfare:

● nuclear powerplant control room operators

(ch. 7),

● registered nurses and resident physicians (ch. 8),

and

. the military (ch. 9).

CHAPTER 2 REFERENCES

1.

2.

Aschoff, J., and Wever, R. A., “Spontanperiodik des

Menschenbei Ausschluss Aller Zeitgeber,” Naturwissenschaften 49:337-342, 1962.

Colligan, M.J., and Tepas, D.I., “The Stress of Work

Hours,” American Industrial Hygiene Association

3.

4.

5.

6.

7.

8.

Journal 47:686-695, 1986.

Folkard, S., Minors, D. S., and Waterhouse, J.M.,

“Chronobiology and Shift Work: Current Issues and

Trends,” Chronobiologia 12:31-54, 1985.

Monk, T.H., “Coping With the Stress of Shift Work,”

Work and Stress 2:169-172, 1988.

Moore-Ede, M. C., Sulzman, F.M., and Fuller, C.A.,

The Clocks That Time Us, Physiology of the Circadian

Timing System (Cambridge, MA: Harvard University

Press, 1982).

Presser, H. B., “The Growing Service Economy:

Implications for the Employment of Women at

Night,” Studies in Industrial and Organizational

Psychology. Shift Work: Health, Sleep and Performance, vol. 10, G.C. Cesana, K. Kogi, and A.

Wedderburn (eds.) (Frankfurt am Main: Verlag Peter

Lang, 1990).

Saunders, D. S., An Introduction to Biological Rhythms

(New York, NY: Halsted Press, 1977).

Scott, A.J. (cd.), Shift Work, Occupational Medicine

State-of-the-Art Reviews (Philadelphia, PA: Hanley &

Belfus, 1990).
Chapter 3

Circadian Rhythms
Contents

Page

GENERAL PROPERTIES OF CIRCADIAN RHYTHMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

THE CELLULAR CLOCK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

THE PACEMAKER IN THE BRAIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...........40

HUMAN CIRCADIAN RHYTHMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

The Body Circadian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

The Timing of Sleep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Human Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

DISRUPTION OF CIRCADIAN RHYTHMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,...49

Aging and the Body Clock . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Sleep Disorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Chronobiology and Mood Disorders . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 51

CONTROLLING CIRCADIAN RHYTHMS IN HUMANS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Melatonin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Benzodiazepines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Other Chemical Substances and Diet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,. 57

SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+....*. 58

CHAPTER PREFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Boxes

Box Page

3-A. Circadian Rhythms and Drugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ● . . . . . . . . . . . . . 43

3-B. Cycles That Last From Minutes To Days . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

3-C. Napping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

3-D. Jet Lag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Figures

Figure

3-1. Circadian Rhythm

3-2. Synchronized and

Page

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Free-Running Circadian Rhythms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3-3. Phase Response Curve -

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3-4. Gene Expression in the Pacemaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3-5. The Transplanted Pacemaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....*.,. . . . . . . . . 41

3-6. Human Circadian Rhythms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42

3-7. Human Circadian Rhythms in the Absence of Time Cues . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

3-8. Sleepiness During the Day . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47

3-9. Circadian Rhythms of Alertness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

3-10. Aging and the Pacemaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*.....* . . . 50

3-11. Levels of Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

3-12. Resetting the Human Pacemaker With Light. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....*.., . . .54

3-13. Bright Light and Air Travel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....,.*, . . . . . . . . 55

3-14. Melatonin Rhythms and Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . 56

Table

Table

3-1. Differences Between Rapid Eye Movement

Slow Wave Sleep (SWS) . . . . . . . . . . . . . . . .

Page

(REM) Sleep and

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Chapter 3

Circadian Rhythms

Many biological functions wax and wane in

cycles that repeat each day, month, or year. Such

patterns do not reflect simply an organism’s passive

response to environmental changes, such as daily

cycles of light and darkness. Rather, they reflect the

organism’s biological rhythms, that is, its ability to

keep track of time and to direct changes in function

accordingly. Biological rhythms that repeat approximately every 24 hours are called circadian

rhythms (from the Latin circa, for around, and dies,

for day) (61) (figure 3-l).

Human functions, ranging from the production of

certain hormones to sleep and wakefulness, demonstrate circadian rhythms. This chapter summarizes

the basic properties of circadian rhythms and addresses the following questions:

How are circadian rhythms generated?

How are they influenced by the environment?

What specific human functions display circadian rhythms?

What implications do these rhythms have for

health and performance?

How can circadian rhythms be manipulated?

GENERAL PROPERTIES OF

CIRCADIAN RHYTHMS

Circadian rhythms display several important characteristics. First, circadian rhythms are generated

by an internal clock, or pacemaker (9,124).

Therefore, even in the absence of cues indicating the

time or length of day, circadian rhythms persist. The

precise length of a cycle varies somewhat among

individuals and species. Although organisms generate circadian rhythms internally, they are ordinarily

exposed to daily cycles in the environment, such as

light and darkness. The internal clock that drives

circadian rhythms is synchronized, or entrained,

to daily time cues in the environment (figure 3-2).

Animal research has shown that only a few such

cues, such as light-dark cycles, are effective entraining agents (12). In fact, the light-dark cycle is the

principal entraining agent in most species, and

recent research suggests that it is very powerful in

synchronizing human circadian rhythms. The sleepwake schedule and social cues may also be important entraining agents in humans.

.-

An entraining agent can actually reset, or

phase shift, the internal clock (12). Depending on

when an organism is exposed to such an agent,

circadian rhythms may be advanced, delayed, or not

shifted at all. This variable shifting of the internal

clock is illustrated in a phase response curve (PRC)

(figure 3-3). PRCs were first derived by exposing

organisms housed in constant darkness to short

pulses of light (40,65,125). The organisms were

isolated from all external time cues. When light

pulses were delivered during the portion of the

organism’s internal cycle that normally occurs

during the day (therefore called subjective day), they

had little effect on circadian rhythms. In contrast,

when light pulses were delivered late during the

organism’s nighttime, circadian rhythms were advanced. Light pulses delivered early during subjective night delayed circadian rhythms.

Several factors make it difficult to identify time

cues that can reset the internal clock. First, there is

no way to examine the function of the circadian

pacemaker directly. The pacemaker’s activity can

only be evaluated through the circadian rhythms it

drives, but unfortunately such functions are subject

to other influences. Environmental stimuli may alter

a particular circadian rhythm without disturbing the

Figure 3-l—Circadian Rhythm

5 Maximum Amplitude

4

i’flGr -

Cycle length K

.-o Mean

G3

c—

li2

i

Minimum

12 24

Time (hours)

Circadian rhythms have a single cycle length of approximately 24

hours. The amplitude, a measure of the degree of variation within

a cycle, is the difference between the maximum value and the

mean.

SOURCE: Office of Technology Assessment, 1991.
38 . Biological Rhythms: Implications for the Worker

pacemaker at all. For example, going to sleep causes

a temporary lowering of body temperature, without

shifting the circadian cycle. Second, a function that

exhibits a circadian rhythm may be controlled by

both the circadian pacemaker and other systems in

the body. For example, the timing and quality of

sleep are controlled by circadian rhythms and other

factors. Finally, classical techniques used to evaluate the pacemaker in animals and to generate a PRC

involve complete isolation from all time cues (e.g.,

constant darkness) for several days, a difficult

approach in human studies. Alternative methods for

evaluating potential entraining agents in humans

have been devised (see later discussion).

THE CELLULAR CLOCK

Circadian rhythms exist even in single cells. In

fact, studies have shown that a wide range of cell

functions exhibit circadian rhythms (159). Precisely how cells generate circadian rhythms is not

known, but protein synthesis is critical to the process

(50,168).

Figure 3-2-Synchronized and Free-Running Circadian Rhythms

Midnight 6 am Noon 6 pm Midnight

1

Day 1

1

Imposed light-dark

schedule; rhythm

entrained.

1

1

1

5

I I

r I

I I

1 I

10

I I

I 1

Self-selected

light-dark cycle; I 1

rhythm free-runs.

I I

I 1

I

15

I 1

~ Timing of peak cortisol secretion

Plot of human sleep and maximum cortisol secretion when synchronized to the environment and when free of environmental input.

SOURCE: Adapted from G.S. Richardson and J.B. Martin, “Circadian Rhythms in Neuroendocrinology and Immunology: Influence of Aging,” Progress in

NeuroEndocrinlmmunology 1:18-20, 1988.
Chapter 3-Circadian Rhythms ● 39

Specific genes code for circadian rhythms.

Genetic control of circadian rhythms has been

examined most extensively in the fruit fly (Drosophila melanogaster), an organism that has played a

key role in the study of genes and inheritance

(63,76,142). Initially, painstaking studies were conducted, using chemicals that cause genetic mutations to alter circadian rhythms (77). It was found

that mutations on the X chromosome disrupted the

fruit fly’s circadian rhythms by accelerating, slowing, or eliminating them. A specific gene on the X

chromosome, called the per gene, has been identified, cloned, and characterized (15,25,64,202).

Other genetic mutations influencing circadian

rhythms have been identified in the fruit fly (71), and

genes other than the per gene have been found to

control circadian rhythms in other species. The frq

gene, for example, controls circadian rhythms in

bread mold (Neurospora crassa) (52,63). A genetic

mutation altering circadian rhythms in hamsters has

been identified (13 1). In these experiments, a mutant

Figure 3-3-Phase Response Curve

Day

-4

-3

-2

-1

0

1

2

3

4

5

/4 B c D E

Light

pulse

■

\ i~ [

■ ,

E

\

\ 1 \

\

\

\

\

\ \

\ \

\ \

\

\ \

\

\

\ \

\

\

I \ \

o \

- l \ -3\ +4 \ +2 ;

\

\ \

\

\

\

/

\

\ \

\ \

\

I

\

i

\

\ \

\

A

I

\

\

\

\ I

+4 \

\

Advance \

\

\

\

D 1’

+2 \ \

\

Phase 0 – E

shift A

- 2 - B

Delay

- 4 – c

Subjective day Subjective night

Circadian time (hours)

I

Experiments demonstrate that exposure to light at different points in a single circadian cycle variably

shifts the internal pacemaker (A-E). The pulse of light given in mid-subjective day (A) has no effect,

whereas the light pulses in late subjective day and early subjective night (B and C) delay circadian

rhythms. Light pulses in late subjective night and early subjective day (D and E) advance circadian

rhythms. In the lower panel, the direction and amount of phase shifts are plotted against the time of light

pulses to obtain a phase response curve.

SOURCE: M.C. Moore-Ede, F.M. Sulzman, and C.A. Fuller, The Chxks That Time Us (Cambridge, MA: Harvard

University Press, 1982).
40 . Biological Rhythms: Implications for the Worker

Figure 3-4-Gene Expression in the Pacemaker

Dark

Light m

200 phl 50 pM

Photographs from the pacemaker (the suprachiasmatic nucleus) of hamsters housed in darkness (A and B) or following a pulse of light (C

and D). The silver grains indicate the activation of the c-fos gene. Data show that exposure to light that would reset circadian rhythms

stimulates the c-fos gene.

SOURCE: J.M. Kornhauser, D.E. Nelson, K.E. Mayo, et al., “Photic and Circadian Regulation of c-fos Gene Expression in the Hamster Suprachiasmatic

Nucleus,” Neuron 5: 127-134, 1990.

gene was linked to a shortened circadian cycle.

Finally, recent research has implicated the c-fos

gene in resetting the internal clock (figure 3-4) (see

next section).

THE PACEMAKER IN THE BRAIN

The circadian rhythms of various functions in

humans, such as hormone production, body temperature, and sleepiness, are normally coordinated—

i.e., they bear a specific relationship to each other.

This temporal organization suggests that some

biological timekeeping device must drive, regulate,

or at least integrate various circadian rhythms. In

mammals, considerable experimental evidence indicates that a region of the brain called the suprachiasmatic nucleus (SCN) is the circadian pacemaker (98). The SCN, composed of a cluster of

thousands of small nerve cells, is located within a

region of the brain, the hypothalamus, that controls
Chapter 3--Circadian Rhythms ● 41

such basic functions as food intake and body

temperature.

Various lines of evidence pinpoint the SCN as the

primary mammalian pacemaker. Nerve cells in the

SCN can generate circadian rhythms when isolated

from other areas of the brain (59,60,70,98,136,

147,158,161,180). The integrity of the SCN is

necessary for the generation of circadian rhythms

and for synchronization of rhythms with light-dark

cycles (70,185). Compelling evidence that the SCN

functions as the primary circadian pacemaker comes

from animal studies of SCN transplantation

(41,48,83,129,155). In these experiments, the SCN

is destroyed, abolishing circadian rhythms. When

fetal brain tissue containing SCN nerve cells is

transplanted into the brains of these animals, circadian rhythms are restored (129) (figure 3-5).

Light in the environment influences mammalian

circadian rhythms by synchronizing the SCN. Light

activates cells in the eye, which in turn activate the

SCN (122,149,154). Recent animal experiments

have shown that light activates the c-fos gene within

Figure 3-5-The Transplanted Pacemaker

Photograph of transplant of fetal hamster suprachiasmatic nucleus (arrow) into the brain of an adult hamster.

SOURCE: P.J. DeCoursey and J. Buggy, “Circadian Rhythmicity After

Neural Transplant to Hamster Third Ventricle: Specificity of

Suprachiasmatic Nuclei,” Brain Research 500:263-275, 1989.

cells in the SCN (figure 3-4) (79,132,150). The c-fos

gene is a proto-oncogene, which is associated with

growth, stimulation of nerve cells, and, in pathological conditions, tumor formation.

It is clear that the SCN serves as the primary

circadian pacemaker in mammals, but there are still

many unknowns concerning its activity. How does

the SCN, with its tens of thousands of nerve cells and

a wide variety of brain chemicals, generate circadian

rhythms? How does the SCN coordinate or drive

overt circadian rhythms in the animal? Little is

known about how the SCN interacts with other parts

of the brain to generate and synchronize overt

rhythms. Is the SCN the only circadian pacemaker in

mammals? There is evidence that other areas of the

nervous system produce circadian rhythms. For

example, data suggest that cells in the mammalian

eye are capable of generating circadian rhythms

(135,169). Also, circadian rhythms of meal anticipation and temperature have been reported to persist

despite destruction of the SCN (147).

HUMAN CIRCADIAN RHYTHMS

Consider the following reported data: the frequency of heart attacks peaks between 6 a.m. and

noon (117, 140); asthma attacks are most prevalent at

night (96); human babies are born predominantly in

the early morning hours (57,73). While these patterns do not necessarily indicate that the events are

driven by the circadian pacemaker, they do suggest

temporal order in the functioning of the human body.

This temporal organization appears to be beneficial;

the human body is prepared for routine changes in

state, such as awakening each morning, rather than

simply reacting after shifts in demand (113) (figure

3-6). In addition, these regular cycles in the body

present considerations for diagnosis of health problems and for the timing of medical treatment

(62,102) (box 3-A).

Although daily fluctuations in various human

functions have been documented for more than a

century, that does not prove that they are controlled

by the circadian pacemaker. Not until individuals

were examined in temporal isolation could human

circadian rhythms be verified. The first studies

sequestering humans from all time cues were

reported in the early 1960s (10). During the course

of these and other studies, which lasted days, weeks,

and even months, individuals inhabited specially

designed soundproof and lightproof rooms that
42 ● Biological Rhythms: Implications for the Worker

Figure 3-6-Human Circadian Rhythms

I ●

/

●

●

I

.- -. --- - ~

t

● K + Excretion ●

6

I/ Q.’ ,\

Growth hormone

nun-mm

4

\

\

6 am Noon 6 pm

Circadian rhythms of sleep, body temperature, growth hormone, cortisol, and urinary potassium in a human subject.

SOURCE: Adapted from G.S. Richardson and J.B. Martin, “Circadian Rhythms in Neuroendocrinology and Immunology: Influence of Aging,” Progress in

. . — NeuroEndocrinlmmuno/ogy 1 :16-20, 1988.

excluded any indication of the time of day, such as

clocks, ambient light, or social interactions. In this

temporal vacuum, individuals were instructed to

sleep and eat according to their bodies’ clocks.

These studies indicated that daily fluctuations in

some human functions are generated by an

internal clock (35,192). While these studies of

humans isolated from time cues provide insight into

the operation of the human circadian pacemaker, the

approach presents difficulties; it is time-consuming

and expensive, and it is difficult to recruit subjects

for extended study. Alternative methods have been

developed for evaluating human circadian rhythms,

and these are discussed in subsequent sections.

In the following sections, an overview of various

human circadian rhythms is presented, as are some

medical implications (boxes 3-A and 3-B). Data on

human sleep and performance rhythms, which are

intimately related to shift work concerns, are discussed in detail.

The Body Circadian

Several hormones are secreted in a cyclic

fashion (181). The daily surge of prolactin and

growth hormone, for example, appears to be triggered by sleep (182,183). Sex hormones are secreted

at varying levels throughout the day, the pattern of

secretion reflecting the fertility, reproductive state,

and sexual maturity of the individual. Secretions of

glucose and insulin, a hormone important for regulating the metabolism of glucose, also exhibit

circadian rhythms. Glucose concentrations in the
Chapter 3-Circadian Rhythms ● 43

Box 3-A-Circadian Rhythms and Drugs

Since the human body is not static Or constant in its function over time, its responses to drugs are likely to vary

over time. Thus, not only the dosage, but also the timing of administration influences a drug’s effects, both

therapeutic and toxic. Chronopharmacoloy, the study of circadian rhythms and the timing of drug treatment, has

important clinical implications.

From the time a drug is administered until it is eliminated from the body, it is acted on by many organs,

including the intestines, the cardiovascular system, the liver, and the kidneys. Absorption, distribution, and

elimination of drugs--i. e., pharmacokinetics—are subject to circadian variation. A tissue’s responsiveness to a

drug, which may reflect the number of receptors, or binding sites, on target cells or their metabolic activity, also

exhibits circadian rhythms. Changes in the effects of a drug when administered at different times over the course

of a 24-hour period stem from the circadian variation in pharmacokinetics and tissue responsiveness. Proper timing

of drug administration can enhance its therapeutic actions and diminish unwanted side effects.

The most advantageous schedule of administration must be determined for each drug. Even drugs with only

slight differences in structure maybe handled differently by the body. For example, injection of the anticancer drug

adriamycin into the abdomen of rats leads to toxic effects on bone marrow; intravenous injection has toxic effects

on the heart. Different scheduling of these two modes of adriamycin injection significantly reduced these side

effects. Ideally, the administration of drugs in clinical situations should be adapted to each patient’s circadian

rhythms.

The main reason to consider circadian rhythms when timing drug administration is the balance between the

toxicity of a compound and its therapeutic. effects. Anticancer drugs are the most prominent example. Many

anticancer drugs currently in use kill replicating cells—all replicating cells, malignant or not. The side effects

associated with these drugs generally limit the amounts that are administer@ seriously restricting their

effectiveness. Attempts to minimize the toxic side effects of anticancer drugs, thus permitting increased doses,

presumably with improved effectiveness against the disease, lie at the root of the search for an optimal drug delivery

schedule.

Optimal drug delivery schedules for more than 29 anticancer agents have been determined in animal studies.

Furthermore, the action of newer agents, including tumor necrosis factor and interleukin-2, has demonstrated a

sensitivity to circadian rhythms. Studies have also been implemented to determine the optimum timing of anticancer

drugs used in combination, a common medical practice for the treatment of cancer.

The chronopharmacology of several anticancer agents has been studied in humans. Specific therapies evaluated

include the agents 5-fluoro-2-deoxyuridine (FUDR) for the treatment of metastatic adenocarcinoma and the

combination of doxorubicin and cisplatin for ovarian and bladder cancer. The regimens chosen were found to

diminish side effects significantly and in some cases to extend survival time. FUDR was delivered by an automatic

pump, which can be programmed to release drugs at a variable rate over time. This device is surgically implanted

in the patient and can be noninvasively programmed by an external computer.’ Drug supplies in the pump are

replenished via simple injection, In general, clinical studies to date, while preliminary, suggest that by carefully

timing the administration of anticancer drugs, their therapeutic effects maybe improved, toxic effects diminished,

or both.

SOURCE: Off!ce of Technology Assessment, 1991. -1

blood peak late at night or early in the morning has important clinical implications. For example,

(181), and insulin secretion peaks in the afternoon

(118).

The secretion of cortisol, a steroid hormone

important for metabolism and responses to stress,

fluctuates daily, peaking in the very early morning

hours and falling to a negligible amount by the end

of the day (181). Besides its use as a marker for the

internal pacemaker, the circadian rhythm of cortisol

secretion may drive other rhythms in the body and

blood tests used to diagnose suspected excess

cortisol production will be most sensitive during the

evening. Also, cortisol-like steroid hormones used

therapeutically to treat asthma and allergies and to

suppress the immune system, are best administered

in the morning, when they interfere least with the

body's own cortisol production.

Circadian rhythms in cardiovascular function

have long been recognized. Indicators of heart and
44 ● Biological Rhythms: Implications for the Worker

Box 3-B-Cycles That Last From Minutes To Days

Circadian rhythms are a basic and well-recognized feature of human physiology and behavior. However,

biological rhythms that repeat more or less frequently than every 24 hours are also fundamental to the body’s

function. In general, ultradian rhythms (those with a length of less than 24 hours) and infradian rhythms (those with

a length greater than 24 hours) do not coincide with conspicuous environmental cues, and how they are generated

is not well understood.

Sleep cycles were one of the first ultradian rhythms characterized in humans. A complete cycle of dreaming

and nondreaming takes place about every 90 minutes. This finding prompted researchers to hypothesize that cycles

of enhanced arousal followed by diminished activity typify both waking and sleeping periods, This theory of a basic

rest-activity cycle has led to many studies of ultradian cycles in alertness-sleepiness, hunger, heart function, sexual

excitement, urine formation, and other functions.

Hormones are also released in ultradian cycles. Many are secreted in a more or less regular pattern every few

hours. More frequent cycles of release, every few minutes, have also been documented. Although the mechanisms

of hormone secretion have not been uncovered, patterned release has been shown to be extremely important for

proper functioning. For example, experiments have shown that, when replacing a deficient hormone, pulses of the

hormone, not a continuous supply, are required for effectiveness. Also, abnormalities in the production cycle of

hormones have been correlated with altered function. Although these cycles do not appear to be tightly coordinated,

it is clear that ultradian rhythms with a cycle of 90 minutes, as well as with cycles of a few minutes to several hours,

are a basic component of many human functions. How they are generated is unknown.

The most prominent infradian rhythm in humans is the menstrual cycle. Through a series of complex

interactions between the brain and reproductive organs, an egg is released by an ovary approximately every 28 days,

and the reproductive organs are prepared for possible fertilization. During each cycle, hormones are secreted in

varying amounts, and the reproductive tract and breast tissue are altered. Other systems, such as those involved in

immune function, may also be affected.

Although the menstrual cycle has long been recognized, how it is generated and how it interacts with other

factors have not been completely detailed. It is clearly affected by circadian rhythms. For example, a peak in the

secretion of luteinizing hormone, which triggers ovulation, usually occurs in the early morning hours. Also, phase

shifts, such as those produced by transmeridian flight, may interfere with the menstrual cycle. The menstrual cycle

may also have therapeutic implications. A recent study of the timing of breast cancer surgery in relationship to the

menstrual cycle has found fewer recurrences and longer survival inpatients whose surgery occurred near the middle

of the menstrual cycle rather than during menstruation. That biological rhythms are often ignored is also indicated

in this study: less than half of the records evaluated in the study recorded the time of the last menstrual period.

SOURCE: Office of Technology Assessment 1991.

blood vessel function that demonstrate daily rhythms of the respiratory system. Which respirarhythms include blood pressure, heart rate,

blood volume and flow, heart muscle function,

and responsiveness to hormones (84). The daily

fluctuations in cardiovascular function are further

illustrated by symptoms of disease. Data have shown

that abnormal electrical activity in the heart and

chest pains peak at approximately 4 a.m. in patients

suffering from coronary heart disease (189,190). As

stated earlier, the number of heart attacks has been

shown to peak between 6 a.m. and noon (1 17,140).

These temporal characteristics of cardiovascular

disease indicate the importance of careful timing in

their assessment, monitoring, and treatment (120).

The widely recognized pattern of nighttime increases in asthma symptoms highlights the circadian

tory functions are responsible for nocturnal asthma

symptoms? Exposure to allergy-producing substances, the respiratory system’s responsiveness to

compounds that can initiate an asthma attack, daily

changes in the secretion of certain hormones, cells in

the lung and blood that may be important mediators

of asthma, and the recumbent position have all been

suggested as possible mechanisms (16,163). The

prevalence of asthma attacks at night has led to drug

treatment approaches that take circadian rhythms

into account.

Other organ systems also reveal circadian fluctuations. Kidney function and urine formation vary over

the course of a 24-hour period; there are daytime

peaks in the concentrations of some substances in
Chapter 3--Circadian Rhythms ● 45

the urine (sodium, potassium, and chloride) and

nighttime peaks in others (phosphates and some

acids) (78). Urine volume and pH also peak during

the day. Immune system and blood cell functions

cycle daily, as do cell functions in the stomach and

intestinal tract (85,1 12).

The Timing of Sleep

Daily cycles of sleep and wakefulness form the

most conspicuous circadian rhythm among humans.

Traditionally, about 8 hours each night are devoted

to sleep. While neither the function of sleep nor how

it is regulated is completely understood, it is clear

that sleep is a basic requirement that cannot be

denied very long. Even a modest reduction in

sleep leads to decrements in performance, especially at night. Furthermore, when deprived of a

night or more of sleep, individuals can find sleep

impossible to resist, especially in monotonous

situations, and they experience brief episodes of

sleep, called microsleeps (45,104).

Classic studies indicate that sleep is not a homogeneous state (42,75). Polysomnography, the measurement of electrical activity in the brain, eye

movement, and muscle tone, has revealed distinct

stages of sleep (table 3-l). During stages 1 through

4, sleep becomes progressively deeper. In stages 3

and 4, which constitute slow wave sleep (SWS), the

eyes do not move, heart rate and respiration are slow

and steady, and muscles retain their tone but show

little movement. Dreams are infrequent. As sleep

continues, dramatic changes occur: brain activity

appears similar to that seen during wakefulness,

heart rate and respiration increase and become

erratic, dreams are vivid and frequently reported,

and the eyes move rapidly. This stage of sleep is

rapid eye movement (REM) sleep. Typically, cycles

of non-REM sleep (stages 1 through 4) and REM

sleep repeat every 90 to 100 minutes throughout the

course of a night’s sleep.

When synchronized to the 24-hour day, the

timing of sleep usually bears a characteristic

relationship to the environment and to other

circadian rhythms in the body. In general, humans

retire for sleep after dark, when body temperature is

falling. Morning awakening coincides with an upswing in body temperature. With the exception of an

occasional afternoon lull (box 3-C), wakefulness

continues throughout the day, and body temperature

reaches its zenith during the late afternoon.

Studies of humans isolated from all time cues

have unveiled several characteristics about the

timing of the sleep-wake cycle and the circadian

pacemaker. In isolation, circadian rhythms are

approximately 25 hours long (figure 3-7). While the

sleep-wake and body temperature cycles are a

similar length at first, their relationship gradually

changes, until body temperature decreases during

wakefulness and increases during sleep (34,35).

Prolonged temporal isolation, for many days or

weeks, sometimes leads to a dramatic dissociation of

Table 3-l—Differences Between Rapid Eye Movement (REM) Sleep

and Slow Wave Sleep (SWS)

Factors concerning sleep REM sleep SWS (stages 3 and 4)

Brain

Measured activity High Low

Cerebral blood flow High Low

Oxygen consumption High Low

Temperature High Low

Body

Eyes Rapid movements No movements

Pupils Dilated Normal

Heart rate Increased and variable Slow and steady

Respiration Increased and variable Slow and steady

Behavior

Movements Occasional twitches None

Dream reports Frequent and vivid Infrequent and vague

Deprivation Agitated and impulsive Withdrawn and physical

complaints

SOURCE: Office of Technology Assessment, adapted from D.F. Dinges, “The Nature and Timing of Sleep,”

Transactions & Studies of the College of Physicians of Philadelphia 6:177-206, 1964.
46 ● Biological Rhythms: Implications for the Worker —.—— —

Box 3-C—Napping

Are human beings biologically programmed to

nap? Divergent lines of evidence, both direct and

indirect, suggest that midafternoon napping is an

inherent aspect of human behavior. No other

species exhibits exclusively once-a-day, or monophasic, sleep patterns. Indeed, as children develop,

the midafternoon nap is generally relinquished only

when school interferes. Adult napping is more

prevalent than most Americans realize, especially

in other cultures and among persons who may be

sleep-deprived, More than 50 percent of all college

students, for example, nap at least once a week.

Napping also appears to increase among retired

Americans.

There are other indications that a midafternoon

nap is natural in humans. When human circadian

rhythms are analyzed in a time-free environment,

napping is common. The postlunch dip, or the

midafternoon decrease in human performance regardless of food intake, may reflect a proclivity for

sleep at that time. Decreased human performance

presumably accounts for the midafternoon peak in

traffic accidents. Moreover, the decline in human

performance corresponds to peaks in sleepiness.

Measures of sleepiness using the multiple sleep

latency test demonstrate a more rapid onset of sleep

in the afternoon. Pathological conditions, such as

narcolepsy, or frequent, uncontrolled sleeping, also

exhibit a midafternoon peak in sleep episodes.

Insight into human napping behavior may have

some practical implications. While mood and

subjective feelings of sleepiness may not be affected by napping, performance during extended

periods of work can be improved. In addition, the

scheduling of brief episodes of sleep during sustained periods of work maybe optimized: research

suggests that napping before, rather than after,

extended periods of work is best for reducing the

effects of sleep loss.

SOURCE: Office of Teclmolo~ Assessment 1991.

body temperature and sleep-wake cycles, a state

called internal desynchronization (10) (figure 3-7).

In some individuals, while the body temperature

cycle maintains a 25-hour length, the sleep-wake

cycle may become 30 to 50 hours long, with sleep

occupying 6 to 20 hours per cycle. Despite the

apparent lack of synchrony between sleep-wake and

body temperature cycles, further studies show that a

relationship is maintained between the two (34,204).

REM sleep is more prevalent as body temperature

Figure 3-7—Human Circadian Rhythms in

the Absence of Time Cues

I

~ ,.. . --- - ,

I

,,1

,(1

Free-run desynchronization

:<

/qcdg L.m ● ,,tu, e : “

I 1 ),9 (1,,1! r )

An idealized example of human sleep-wakefulness and temperature rhythms in a time-free environment.

SOURCE: D. F. Dinges, “The Nature and Timing of Sleep,” Transactions

& Studies of the College of Physicians of Philadelphia 6:

177-206.1984.

rises. Similarly, wake times correlate to rising body

temperature, regardless of when the sleep period

began. Sleep is of short duration if it begins at the

body temperature’s low point; sleep is long if it

begins near the peak of the body temperature

rhythm, with wake time occurring at the next body

temperature peak. These studies indicate that

circadian rhythms influence total sleep time

(165).

Other characteristics of the timing of sleep and

wakefulness have been discerned. How long it takes

to fall asleep in a sleep-promoting environment at

different times throughout the day can be measured

using the multiple sleep latency test. Studies using

this technique have shown that individuals fall

asleep most rapidly at two times, during the

middle of the night and during the middle of the

afternoon (figure 3-8) (19, 138). Conversely, experiments have demonstrated that there are times

during the course of the day when falling asleep

is very difficult (81).

In summary, sleep is a necessary component of

life. When synchronized to the 24-hour day, sleep

typically occurs during the night hours and bears a

constant, if complex, relationship to other circadian
Chapter 3-Circadian Rhythms ● 47

Figure 3-8-Sleepiness During the Day

Number “

‘“~

“ Midnight 6 am Noon 6 pm Midnight

Time of day

Episodes of unintentional sleep over the course of a day.

SOURCE: M.M. Mitler, M.A. Carskadon, C.A. Czeisler, et al., “Catastrophes, Sleep, and Public Policy: Consensus Report,” S/eep

11:100-109, 1988.

rhythms. Particular components of sleep, including

total amount of sleep and sleepiness, are governed

by the circadian clock. Therefore, periods of sleep

are not readily rescheduled, deferred, or resisted.

The requirement for sleep and the control of its

timing have important implications for work schedules and shift work (see ch. 5).

Human Performance

Physiological variables such as body temperature,

hormone levels, and sleep are not the only human

functions that exhibit circadian rhythms. Human

performance, including psychological processes and

mental functions, also exhibits circadian fluctuations (26). Diverse components of human performance, including memory, reaction time, manual

dexterity, and subjective feelings of alertness, have

been dissected experimentally to ascertain when

they peak during the course of a day and how they

are affected by circadian rhythm disruption.

Research conducted during the first half of this

century indicated that some aspects of human

performance improve over the course of the day,

climaxing when peak body temperature is achieved.

Subsequent experiments determined that the timing

of peak performance varied with the nature of the

task being assessed. Several factors, including

perceptual involvement, the use of memory, and

the amount of logical reasoning required, appear

to be important in determining when particular

types of performance peak during the circadian

cycle. Performance of tasks involving manual dexterity, simple recognition, and reaction time appears

to parallel the circadian rhythm of body temperature,

peaking when body temperature is highest, in the

late afternoon (54,107,110,111). Verbal reasoning

seems to peak earlier in the circadian cycle and may

adjust more quickly than other types of performance

to such disruptions as jet lag (box 3-D) (69,107,

110,11 1). An individual’s assessment of mood and

alertness also exhibits circadian rhythms. For example, when subjects are asked to indicate their level of

alertness, weariness, happiness, or other moods on a

visual scale at regular times throughout the course of

the day, consistent circadian patterns emerge (figure

3-9) (54,106,108,109,173).

Variation in performance may also reflect subtle

differences between tasks and the way in which a

task is approached (53). For example, when subjects

were asked to identify the larger of two spheres, it

was found that, if speed of identification was

assessed, the usual relationship with temperature

held—that is, subjects became faster over the course

of the day. However, if accuracy of response became

the benchmark, peak performance occurred in the

morning (27,107). Short-term and long-term memory also appear to peak at different times during the

24-hour cycle (53). Motivation can influence performance, too. It has been shown that when an

incentive is offered, such as a significant sum of

money, circadian decrements in performance maybe

overcome to some extent (26,68). The latter study

(68) indicated, however, that sleep deprivation and

circadian rhythms can overcome even the strongest

incentive influencing performance. Further complicating the picture is the observation that individuals

are not always accurate judges of their own mood,

alertness, or ability. For example, a short nap maybe

able to counteract decrements in performance

caused by lack of sleep without alleviating subjective feelings of sleepiness (56).

Many aspects of human performance decline

to minimal levels at night, reflecting not only the

influence of the circadian pacemaker, but also the

lack of sleep (14). Sleep deprivation, even for one

night, is one of the most important disrupting factors

of human mental and physical function (46). Sleep

loss influences several aspects of performance,

leading to slowed reaction time, delayed responses,

failure to respond when appropriate, false responses,

slowed cognition, diminished memory, and others.
48 ● Biological Rhythms: Implications for the Worker

Box 3-D—Jet Lag

Transmeridian air travel, especially across several time zones, can severely disrupt circadian rhythms. It may

produce an unpleasant and somewhat disabling constellation of symptoms collectively labeled jet lag. Jet lag varies

among individuals and may include trouble sleeping, daytime sleepiness, gastrointestinal disruption, and reduced

attention span. Physical and mental performance may also be seriously diminished following transmeridian flight.

What precipitates jet lag? Stress and loss of sleep associated with air travel certainly contribute to postflight

fatigue; however, these factors alone do not interrupt circadian rhythms. Rather, conflict between the traveler’s own

circadian clock and external rhythms in a new time zone is the primary agent of jet lag. The timing of meals, activity,

and sleep no longer coincides with that customary in the new time zone. Furthermore, environmental cues,

especially light, promote synchronization between circadian rhythms and the new time zone. Since different

circadian rhythms may adjust to the new time zone at different rates, the air traveler experiences a period when

internally generated rhythms are no longer in synchrony with each other. The lack of synchrony between internal

and external rhythms, as well as among different internal rhythms, probably results in the malaise and diminished

performance associated with jet lag.

How long it takes to adjust to a new time zone and recover from jet lag depends on several factors, including

the number of time zones crossed, the direction of travel, differences among individuals, age, and the particular

circadian rhythm involved. The number of time zones crossed, or hours phase shifted, significantly influences the

occurrence and duration of jet lag; resetting the circadian system can take as many as 12 days following a 9-hour

flight across several time zones. Even a l-hour time shift can require at least a day for complete adjustment.

The direction of air travel may also influence the severity of jet lag. Most, but not all, studies indicate a more

rapid adjustment to westward than to eastward travel. Also, the severity and duration of jet lag vary markedly among

individuals. One rule of thumb is that persons with less variable body temperature rhythms become synchronized

to a new time zone more rapidly. (Older persons, who may exhibit a reduction in circadian variation, generally have

more difficulty adjusting to a new time zone.) What mechanisms determine how quickly phase shifts occur is not

known. As mentioned, various circadian rhythms adjust to external cues at various rates. For example, it may take

2 days for the sleep-wake cycle to adjust to a 6-hour time zone shift but 5 or more days for body temperature rhythm

to be entrained. Furthermore, recovery from jet lag may not proceed linearly: some data indicate that sleep and

performance may improve the first day following a phase shift and languish the next.

Measures to hasten adjustment to a new time zone, including the use of certain drugs, bright light, exercise,

and diet, are under investigation. Improved understanding of human circadian rhythms has prompted

recommendations from scientists about how best to confront jet lag. Short trips of only a few days across time zones

probably do not warrant an attempt to adjust to the local time zone. In these situations, it is best to try to schedule

activities and sleep as close to one’s internal clock as possible in order to avoid jet lag. For longer trips, suggestions

for resetting one’s interred clock include adopting the new schedule immediately and maximizing exposure to

environmental cues, especially light at specific times (figure 3-12). The problems are very complex for international

air crews, who fly rapid sequences of transmeridian flights (see ch. 4) combined with irregular hours of work and

rest. The kinds of jet lag countermeasures that may suffice for occasional transmeridian travelers (use of hypnotics,

scheduled bright light exposure, and so on) are generally not practical-and may even be hazardous-for

individuals exposed to repeated time zone changes. These issues are being addressed in a broad program of field

and laboratory research being conducted by the Aviation Human Factors Branch at the National Aeronautics and

Space Administration’s Ames Research Center (see app. B).

SQUR~: Ol%ce of Teckology Assessment 1991.

The circadian clock also leads to a nighttime or mood assayed. Other factors, such as fatigue and

minimum in many types of performance (26,104). motivation, also profoundly influence human perThus, sleep deprivation combined with the influence formance. Furthermore, a discrepancy may exist

of the circadian pacemaker can severely curtail between an individual’s own assessment of his or

performance at night. These factors have important her ability to perform and the performance that is

implications for shift work (see ch. 5). actually demonstrated. When individuals are synIn summary, circadian rhythms can cause per- chronized to the natural day-night cycle, many types

formance to vary according to the nature of the task of performance reach minimum levels during the
Chapter 3-Circadian Rhythms ● 49

Figure 3-9-Circadian Rhythms of Alertness

80

Alertness

7 0 -

60 -

50 -

40 -

1

1 I I I I I I I I I I I I I I I I

8 am Noon 4 pm 8 pm Midnight

The circadian rhythms of subjective alertness and body temperature from persons synchronized to a 24-hour day.

SOURCE: T.H. Monk, M.L. Moline, J.E. Fookson, et al., “Circadian

Determinants of Subjective Alertness,” Journa/ of Bio/ogica/

Rhyfhms 4:393-404, 1989.

night, reflecting the combined influence of the

circadian pacemaker and the lack of sleep.

DISRUPTION OF CIRCADIAN

RHYTHMS

When rhythms generated by the body conflict

with those in the environment, function is compromised until the rhythms are realigned. Patterns of

sleep are disrupted, performance may be impaired,

and a general feeling of malaise may prevail. Data

linking disrupted circadian rhythms with some

mental and sleep disorders also point to the importance of an intact circadian system for health. The

following section discusses specific situations, other

than shift work, that may be associated with altered

or disrupted circadian rhythms. Shift work is discussed in chapter 5.

Aging and the Body Clock

Are circadian rhythms altered by the aging

process? The stereotypes of diminished daytime

alertness and early morning rising among the

elderlyl hint at possible circadian alterations. Studies confirm that many physiological and behavioral functions that typically display circadian

rhythms are altered with advancing age in

humans. For example, there are usually conspicuous

changes in sleep habits, such as earlier onset of

sleepiness, early morning awakening, and increased

daytime napping (93,101). During sleep, there is an

increase in the number and duration of waking

episodes, there is a reduction in the nondreaming

phases of sleep, the first REM phase occurs earlier

in the night, and the tendency to fall asleep is

increased during the day (18,20,29). Other circadian

rhythms, such as body temperature, activity, and the

secretion of hormones, including cortisol, are also

altered with age (29,93,138,193).

While factors such as changing social habits,

medication, and disease processes can impinge on

functions that exhibit circadian rhythms, such as

sleep, activity, alertness, and hormone secretion,

research suggests that aging affects the circadian

system itself. A decrease in the amplitude and length

of various cycles with age has been observed in

animal studies, including longitudinal studies (114,

126,196). 2 Studies of various circadian rhythms in

humans have suggested that the length of the

circadian cycle shortens with age and that the

amplitude of circadian rhythms is blunted

(28,105,160,186,193). Furthermore, coordination of

various circadian rhythms, such as body temperature, hormone levels, and the sleep-wake cycle, may

be lost with age (105,186).

What is the basis for these changes in circadian

rhythms with age? It has been suggested that a

decreased number of nerve cells in the SCN correl~nge~ ~ c~=&m rh~s ass~~ted with aging, as discussed in this sectiom may refer to different POptitions of older PeOPle. Most res~ch

on sleep parameters focused on subjects age 65 or older. Anatomical changes in the brain have been observed in subjects over 80. Di.filculties associated

with shift work or jet lag have generally been studied in subjects age 45 or older.

?Lmgitudinal studies involve analysis of aparticularfimctionin individual subjects over a period of time. They areespeciallyuseful for detmnining

effeets that exhibit a great deal of variation among individuals, as circadian rhythms do. While longitudinal data emcerningcircadian rhythms in animals

have been collected (114, 126), no similar data are available on humans.
50 ● Biological Rhythms: Implications for the Worker

Figure 3-10-Aging and the Pacemaker

‘x) h

‘fl

u

Normal period

Normal amplitude

Shorter period

Lower amplitude

Phase shift to

earlier hours

Morning insomnia

Daytime sleepiness

The influence of the pacemaker (SCN) on the length and amplitude of circadian rhythms, linking the

decreased amplitude in rhythms with disturbed sleep among the elderly.

SOURCE: Adapted from G.S. Richardson and J.B. Martin, “Circadian Rhythms in Neuroendocrinology and

Immunology: Influence of Aging,” Progress in NeuroEnd~rin/mmunology 1 :16-20, 1988.

lates with a decrease in cycle length and perhaps

dampened amplitude (figure 3-10) (29,139). Support

for this idea is derived from several studies: when

some SCN neurons are destroyed in young animals,

the length and amplitude of circadian rhythms are

diminished, much as they diminish with advancing

age (37,123). A decrease in the number or function

of SCN neurons has been associated with aging in

rats (24,141). Similarly, a decrease in the number

of SCN neurons and the overall size of the SCN was

documented in humans over the age of 80 (66,

166,167).

Other biological changes with age may impinge

on circadian rhythms. For example, relay of synchronizing cues, such as light, may be hampered.

There is evidence that some eye problems that occur

with age may impede the transmission of light

information to the SCN (162). It is possible that

changes in the eye may precede and even induce

changes in the SCN. Several studies of humans and

animals have reported diminished responsiveness to

synchronizing cues with age, despite a decrease in

the amplitude of circadian rhythms, which normally

eases synchronization (29).

While many elderly people fail to report any

circadian rhythm-based problems, some studies

have illuminated difficulties. For example, adjusting

to rotating shift work schedules and transmeridian

flight is more difficult among older people (134). In

addition, advanced sleep phase syndrome, a disorder

in which sleep occurs earlier than usual, appears to

be common among the elderly (174). A considerable

proportion of older people complain of sleep problems: one study found that 33 percent of older people

visiting a general practitioner complain of frequent

early morning awakening (97). Lessened performance and alertness during the day may result from

fatigue or the lack of synchrony among circadian

rhythms. Thus, changes in circadian rhythms with

age may cause a broad spectrum of effects,

ranging from no complaints whatsoever, to disturbances of everyday life, to severe health

problems.
Chapter 3-Circadian Rhythms ● 51

Sleep Disorders

Just as the timing of sleep is the most prominent

indicator of circadian rhythms in humans, it may

also be the cycle most susceptible to disruption (32).

It is now recognized that some types of insomnia

most likely result from abnormalities in circadian rhythms. In the recently revised International

Classification of Sleep Disorders (2), several sleep

disorders are ascribed to problems with circadian

rhythms, including:

. advanced sleep phase syndrome,

. delayed sleep phase syndrome, and

● non-24-hour sleep-wake disorder.

Advanced sleep phase syndrome is a common

sleep disorder among the elderly, affecting up to

one-third of that population (97). It involves early

onset and offset of sleep. Research indicates that

diminished circadian cycle length and amplitude

underlie the disorder (28,193). Advanced sleep

phase syndrome may have several consequences,

including decreased daytime alertness, overuse of

hypnotics and other drugs, and social disruption.

Delayed sleep phase syndrome, or insomnia, is

characterized by abnormal delay of sleep onset and

waking (2). Persons with this form of insomnia are

generally teenagers and young adults. They complain that, on retiring at a bedtime common for most

individuals, they are unable to fall asleep. Waking in

time for early morning classes or work is also

difficult, and they may suffer from fatigue caused by

inadequate sleep at night. If individuals with this

disorder are permitted to retire and arise at a later

hour, although out of step with the environment and

society, they can achieve an adequate amount of

sleep. It is postulated that the cause of this disorder

may be either an abnormally long circadian cycle or

a diminished responsiveness to cues in the environment that reset the circadian pacemaker each day

(33,119).

Non-24-hour sleep-wake disorder is also likely to

reflect disruption of the circadian system. Individuals suffering from this disorder find themselves

retiring for and waking from sleep at progressively

later times (2). When the timing of sleep onset and

awakening coincides with that of the world around

them, individuals with this disorder are asymptomatic. When their circadian rhythms are not in

synchrony with the environment, individuals with

this disorder complain of insomnia, difficulty awakPhoto credit: Neal Owens, Sun Box Co., Rockville, MD

A light box used for the treatment of SAD.

ening, and fatigue. One survey showed that 40

percent of blind persons may suffer from non-24-

hour sleep-wake disorder (100). These data indicate

that the inability to perceive light-dark cycles

probably causes the disorder.

Chronobiology and Mood Disorders

While seasonal tendencies in mood disorders

have been noted for hundreds of years, the recent

surge in research into circadian rhythms has triggered a systematic examination of this phenomenon.

Several current hypotheses suggest that an alteration

of circadian rhythms leads to various mood disorders. Furthermore, exposure to bright light appears

to be an effective therapeutic intervention in some

cases. Continued research is necessary, however, to

verify the link between circadian rhythm disruption

and mood disorders. In the 1980s, researchers first

documented a mood disorder involving a recurring autumn or winter depression (144). Currently, this form of seasonal affective disorder

(SAD) is the subject of extensive study; although the

symptoms and diagnostic criteria are somewhat

disputed, SAD and its treatment with bright light are

generally recognized by the psychiatric community

(1,17,58). Each fall or winter, individuals suffering

from SAD may tire easily, crave carbohydrates, gain

weight, experience increased anxiety or sadness, and

exhibit a marked decrease in energy (144,146). With

protracted daylight in the spring, patients emerge

from their depression and sometimes even display
52 ● Biological Rhythms: Implications for the Worker

Figure 3-1 l—Levels of Light

Intensity (Iux) 5)1,1.X$’

100,000

10,000

2,000

200

0

Sunny

day

Cloudy

day

Bright

artificial

light

1I

Ordinary

room

light

The comparative intensity of light. Bright artificial light is effective

for shifting human circadian rhythms.

SOURCE: A. Lewy, Oregon Health Sciences University, 1991.

modest manic symptoms. Epidemiological studies

indicate that SAD is related to latitude, with the

number of cases increasing with distance from the

equator (127,143).

Although there is no agreement about how light

therapy works, data from several studies suggest that

it is a useful treatment for SAD (144,170). The

recommended protocol for treatment involves exposure to light with an intensity of 2,500 lux (which is

equivalent in intensity to outdoor light at dawn) for

2 to 5 hours per day (figure 3-1 1). Some researchers

have asserted that shorter periods of exposure to very

bright light (e.g., 10,000 lUX for 30 minutes) may

also relieve symptoms (170,172). Data from several

studies suggest that morning exposure to light is

most effective in relieving symptoms of SAD,

although this issue is unresolved (17,89,170,172).

The cause of SAD and the way in which light

therapy alleviates it are not known. It has been

hypothesized that circadian rhythms are delayed or

possibly that the amplitude is dampened (17,86,89).

To date, however, SAD has not been proven to be

a circadian rhythm disorder. Problems that plague

this area of research include heterogeneous populations of study subjects, small sample sizes, lack of

adequate controls, lack of longitudinal studies, and

the absence of controls for the effects of sleep,

activity, and light on circadian rhythms (17,1.72).

Further studies are necessary to delineate the basis of

SAD.

Nonseasonal depression is a significant cause of

mental illness in the United States, affecting nearly

1 in 12 Americans. Although not proven, several

observations suggest a link between altered circadian rhythms and nonseasonal depression (17,32).

Among persons suffering from depression, mood

typically fluctuates daily, with improvement over

the course of the day. Persons also demonstrate

seasonal patterns, with an apparent increase in the

incidence of depression, as indicated by hospital

admissions, electroconvulsive therapy, and suicide

records, in the spring and autumn. Various physiological functions may exhibit an altered circadian

pattern in depression, notably the timing of REM

sleep. In people suffering from depression, the frost

REM episode occurs earlier after sleep begins, and

REM sleep is abnormally frequent during the early

hours of sleep (80). Rhythms of body temperature,

hormone and brain chemical secretion, and sleepwake cycles deviate during episodes of depression,

peaking earlier than is the norm or, more commonly,

exhibiting dampened amplitude.

The action of various antidepressant drugs and

therapies provides further evidence for a link between circadian rhythm disruption and depression

(49,58). Some animal studies have shown that

several classes of antidepressant drugs either lengthen

the circadian cycle, delay distinct circadian rhythms,

or influence synchronization with environmental

cues. Studies showing that late-night sleep deprivation temporarily alleviates depression also suggest,
Chapter 3-Circadian Rhythms .53

but do not prove, a link between circadian rhythms

and nonseasonal depression. Assessment of 61

studies, with more than 1,700 patients, indicated that

missing one night’s sleep halted depression immediately in 59 percent of the patients (the next sleep

episode usually resulted in the return of depression,

and in more than a quarter of the patients a manic

episode was triggered) (198).

While this information suggests a potential causative relationship between circadian rhythm disruption and depression, little direct evidence supports

the hypothesis that nonseasonal depression is a

circadian disorder. For example, only a few studies

have indicated a phase advance or blunted circadian

amplitude. Most studies share similar problems as

those described above for SAD, including heterogeneous samples, small sample sizes, and failure to

evaluate circadian rhythms isolated from the influence of the environment.

CONTROLLING CIRCADIAN

RHYTHMS IN HUMANS

Interest in manipulating the internal clock has

grown with improved understanding of human

circadian rhythms and increasing awareness of

circadian rhythm disruption, whether precipitated by

intrinsic factors (e.g., sleep disorders, blindness,

mental disorders, or aging) or extrinsic factors (e.g.,

air travel across time zones and shift work) (box

3-D). Several agents are under investigation or have

been proposed for use in manipulating circadian

rhythms. In order to assert that an agent’s primary

action is on the circadian system, several questions

must be addressed, including: How are circadian

rhythms modified? Are all circadian rhythms altered

or only certain rhythms, such as the sleep-wake

cycle? How is the circadian pacemaker influenced?

Does the effect vary at different times during the

circadian cycle (i.e., has PRC been evaluated)? Does

the agent have any side effects or drawbacks?

Several agents show promise for manipulating

human circadian rhythms, including:

●

●

●

●

●

light,

melatonin,

benzodiazepines,

other chemical substances and diet, and

activity.

Light

Light-dark cycles are the single most important environmental cue for synchronizing the

internal clock to the Earth% 24-hour cycle. As

mentioned, light’s ability to reset the internal clock

was first discovered by exposing organisms to

pulses of light at “different times throughout the

circadian period (40,65,125). In these experiments,

exposure to light at night produced the largest shifts

in rhythms, with late-night pulses advancing

rhythms and pulses during the early part of the night

delaying them. Other studies have shown that the

phase-shifting effects of cycles of light and dark are

similar to those of light pulses.

The synchronizing effect of light on human

circadian rhythms has only been recognized in the

last 10 years (33). Previously, social contacts were

thought to synchronize human circadian rhythms,

since light-dark cycles apparently failed. This conclusion was questionable, for several reasons. First,

subjects were permitted to use lamps at will in the

original study and therefore were never completely

limited to an imposed light-dark cycle. Also, the

design of the studies prevented discrimination between the effects of social contact and those of rest,

activity, or eating. A subsequent study reported

synchronization of human circadian rhythms when

an absolute light-dark cycle was imposed, but the

experiment did not differentiate between the effects

of the light-dark cycle and the timing of sleep on

circadian rhythms, since subjects always retired to

bed at the time lights were turned out.

The discovery that bright light (2,500 lux) suppresses the production of the human hormone

melatonin (92) triggered a reassessment of light’s

effects on human circadian rhythms. In one study,

light-dark cycles were shown to significantly synchronize human circadian rhythms (195). Subsequent studies illustrated the phase-shifting effects of

light on humans. For example, in one study,

exposure to 4 hours of very bright light (7,000 to

12,000 lux) was shown to delay circadian rhythms in

a single subject whose rhythms were unusually

advanced (figure 3-12) (28). These and other studies

support the hypothesis that bright light shifts human

circadian rhythms, the size and direction of the shift

depending on when in the cycle exposure takes place

(38,39,43,44,47,67,9O,91,1O3, 195).
54 ● Biological Rhythms: Implications for the Worker

Figure 3-12—Resetting the Human Pacemaker

With Light

I

I

I

intensity light (150 lux) modifies the phase-shifting

effects of very bright light, a pattern that resembles

the effect of light on circadian rhythms in other

b

“.

.- . “.. “ 4-””

I~J organisms. Recent experiments have provided fur- 1 /..

I

ther evidence of the similarity of light’s effects on

I

I .“ human and other species’ circadian rhythms (72).

1

..”

1. The methods used in these human studies to

=-c

.- 1

I 1 1 1 t

Final phase – 18 0

c.

6 ~ 12 18

i f

I

I

I

37.0 -

36.5-

1

I

I

f+

36.0 ‘~’’/lY~1<~’’/<’’Y~~’~’’’Y4’’~(=’1/4

6 am Noon 6 pm Mid- 6 am Noon 6 pm

night

Time of day t2 t,

k 1

A@ = +8.0 hours

The first graph (A) illustrates the original circadian rhythm of body

temperature. Following exposure to bright light, as illustrated in B,

the rhythm of body temperature was significantly shifted (C).

SOURCE: C.A. Czeisler, R.E. Kronauer, J.S. AlIan, et al., “Bright Light

Induction of Strong (Type O) Resetting of the Human Circadian

Pacemaker,” W“ence 244:1328-1332, 1989.

More recent studies report a human PRC to light

(31,194). For example, one study exposed human

subjects to varying cycles of very bright light (7,000

to 12,000 lux), ordinary room light, and darkness

(31). The greatest shift in circadian rhythms (several

different rhythms were measured) was produced

when the exposure to very bright light occurred

approximately 3 hours before the usual waking time;

exposure immediately preceding or following this

time maximally delayed or advanced rhythms,

respectively. This study also suggested that lowevaluate and manipulate circadian rhythms differ

from the methods used in animal studies, leaving

room for speculation concerning the mechanism by

which light produces its effects. The influence of

sleep, fatigue, or darkness in these studies is not

known, nor is the mechanism by which light

influences human circadian rhythms well defined.

However, accumulating evidence shows that, as in

other animal species, light, especially bright light,

is effective in shifting human circadian rhythms.

The phase-shifting properties of bright light have

been applied in several situations:

●

●

●

●

Exposure to bright light is now used in certain

clinical centers and research settings to treat

some sleep disorders and elderly persons suffering from circadian rhythm disruption.

A published research plan for exposure to

sunlight has been proposed to speed recovery

from jet lag (figure 3-13) (36).

Recent studies have evaluated the influence of

bright light and darkness cycles on the circadian rhythms, sleep, and performance of

workers at night (see ch. 5) (30).

Although the basis for SAD has not been

definitely linked to circadian rhythm disruption, bright light therapy appears to be beneficial for patients (145,170).

The potential adverse effects of using light to reset

circadian rhythms (as well as in the treatment of

SAD) have not been systematically studied. Since it

is a nonpharmacological intervention, it probably

presents fewer detrimental effects. It has been

argued that since the intensity of light used to

modulate human rhythms is far less than the

intensity of outdoor daylight, there is little risk

involved. However, experience with SAD has led to

some concern that artificial bright light may present

a risk of damage to the eye (171). To date, studies

evaluating the health of the eye following bright

light therapy for SAD have failed to document any

damage, although the risk of long-term effects has

not been ruled out. Also, it is not clear what harmful

consequences, if any, would result from repeated
Chapter 3-Circadian Rhythms ● 55

Figure 3-13-Bright Light and Air Travel

Hypothetical phase response curve

+

o

—

within established safety guidelines following several hours of exposure to wide-spectrum fluorescent

light of 7,000 to 12,000 lux (30). Evidence shows

that W radiation is not necessary for adjusting

rhythms, although it may have some effect on them.

Bright light may also produce unpleasant but transient side effects of irritability, eyestrain, headaches,

or insomnia.

12 ! I

Sunrise

.

/

1

/ &

/ / / o -

/

/

/

/

/

P

/

4 “

/

8- .~”

,=

1 2 -

/

/ /

I I I I I I I I 1 1 I 6 12 18 0 6

Circadian time (hours)

I I

Photoperiod at destination (day 1)

I

I ~ Portion of photoperiod that will

L

accelerate reentrainment

Portion of photoperiod that will

retard reentrainment

Exposure to bright light following travel across time zones may

influence circadian rhythms. For example, after flying 2 hours from

the west to the east, it is suggested that bright light exposure begin

at dawn for 2 hours.

SOURCE: S. Daan, and A.J. Lewy, “Scheduled Exposure to Daylight: A

Potential Strategy To Reduce Jet Lag Following Transmeridian

Flight,” Psychopharmacology Bulletin 20:566-5687 1984.

resetting of the circadian pacemaker, such as when

using bright light to help shift workers adjust to their

changing work schedules.

Exposure to ultraviolet (W) radiation is another

potential concern raised by the use of bright lights.

In research and clinical settings (for the treatment of

SAD), fluorescent lighting, both that emitting W

radiation and that designed to limit it, has been used.

One study reported that exposure to W light was

Melatonin

The hormone melatonin is produced by the pineal

gland, a small, pealike structure that in humans sits

deep within the brain. In lower vertebrates, the

pineal gland is positioned near the top of the skull

and detects light directly, thus its designation as the

third eye (3). In m ammals, including humans,

information about light in the environment is

transmitted from the eye through multiple nerve

cells to the pineal gland (74,200). Melatonin secretion is normally limited to nighttime hours, a pattern

of secretion that is. regulated in two ways: 1) light

suppresses the pineal gland’s production of melatonin, and 2) melatonin secretion is regulated by the

circadian pacemaker, exhibiting a circadian rhythm

even in the absence of environmental cues (figure

3-14) (94,95). For this reason, melatonin can be used

as a marker for circadian rhythms (90,91); however,

its usefulness may be limited because it is so readily

inhibited by light.

In many species, melatonin is a gauge of day

length, or photoperiod. Seasonal changes in day

length alter the amount and duration of melatonin

secretion, thereby regulating the timing of fertility,

birth of offspring, and other functions. Although

responsiveness to day length generally has not been

considered a prominent human feature, several

human functions, including the onset of puberty,

semen production, and some forms of depression

(see earlier discussion), display seasonal patterns.

The pineal gland’s nighttime secretion of melatonin is postulated to be important for circadian

rhythms in many species (178). In some species,

including some birds, the pineal gland serves as the

circadian pacemaker (99,203). In other species, the

pineal gland does not serve as the primary pacemaker, but its removal disrupts circadian rhythms

(8,156). Studies have shown that daily melatonin

injection can synchronize circadian rhythms in rats,

apparently by a direct effect on the pacemaker in the

brain (7,21-23,133,137). These and other data sug-
56 . Biological Rhythms: Implications for the Worker

80

60

40

20

Figure 3-14—Melatonin Rhythms and Light

1 am 2 am 3 am 4 am 5 am

Time of day (hours)

Exposure to bright light shown to inhibit human melatonin

production (indicated by solid line) when compared to controls

(dashed line).

SOURCE: A. Lewy, T.A. Wehr, F.K. Goodwin, et al., “Light Suppresses

Melatonin Secretion in Humans,” Soience 210:1267-1269,

1960.

gest that the pineal gland and melatonin production

may synchronize various circadian rhythms in at

least some mammals.

The effect of melatonin on circadian rhythms has

also been examined in humans. In some early

studies, melatonin both succeeded and failed to act

as a synchronizing agent. Other studies reported that

melatonin counteracted subjective feelings of jet lag

(4,8,121) (see box 3-D), although how it did so was

not clear. Some data indicated that melatonin

directly influenced circadian rhythms (4,8); however, others failed to confirm this effect (6). Furthermore, the effects of melatonin on jet lag varied

considerably among individuals (4). It was suggested that melatonin counters jet lag by facilitating

sleep, since it has sedative properties.

A few studies have used blind persons, who are

often not synchronized with the environment, to

assess melatonin’s effect on the circadian pacemaker. In one such study, it was reported that

administration of melatonin synchronized the disturbed sleep-wake cycle of a blind individual (5). In

another study, a phase advance was produced by

daily administration of melatonin in four of five

blind subjects with free-running rhythms (151,152).

More recently, orally administered melatonin synchronized circadian rhythms in a blind subject (153).

Also, melatonin has been reported to cause circadian

phase shifts, the direction and magnitude of which

appear to vary with the timing of its administration,

in sighted individuals (87,88). While another study

failed to demonstrate administered melatonin’s ability to synchronize or shift circadian rhythms (55),

this failure may be due to the timing of melatonin

administration. Further study is necessary to

delineate melatonin’s action on human circadian

rhythms.

Benzodiazepines

Several studies in rodents have shown that treatment with benzodiazepines, a class of hypnotic

drugs which includes Valium, can alter circadian

rhythms (130,179). The phase-shifting effects of the

short-acting benzodiazepine triazolam (trade name

Halcion) have been most extensively studied in the

golden hamster. In most of these studies, the timing

of locomotor activity (i.e., wheel-running) has been

used as a measure of circadian rhythms, although

hormonal secretions have also been used. Injection

of triazolam produced pronounced phase shifts in

wheel-running, the particular effect depending on

the dose and timing of administration (177). Triazolam’s ability to shift wheel-running was attenuated after a few days of repeated administration,

indicating a growing tolerance to the drug.
Chapter 3--Circadian Rhythms ● 57

Besides its ability to cause phase shifts in

circadian rhythms, triazolam was also shown to

synchronize circadian rhythms when regularly administered. Furthermore, when hamsters experienced a shift in the timing of the light-dark cycle,

administration of triazolam at the appropriate time

expedited their readjustment (187).

Some data suggest that triazolam’s influence on

circadian rhythms in hamsters is predicated on its

ability to induce locomotor activity (1 16). Triazolam

treatment of hamsters increases activity (176). When

locomotor activity is suppressed in hamsters, triazolam no longer produces phase shifts (188). However, stimulation of activity may not be necessary for

triazolam’s circadian effects in all species.

Is triazolam, or other benzodiazepines, likely to

emerge as a jet lag pill, capable of shifting human

circadian rhythms? Preliminary studies in humans

have suggested that it may facilitate shifts in

circadian rhythms, or at least promote sleep when

circadian rhythms are in conflict with the environment (184). In addition, the activity and safety of this

class of drugs have been well characterized in

humans, since benzodiazepines are commonly used

to manage insomnia and anxiety. However, while

benzodiazepines are useful pharmaceutical agents,

they do carry the risk of serious side effects,

including memory problems and agitation. They can

also exacerbate depression. Long-term use of this

type of drug can lead to dependency; therefore,

repeated use of benzodiazepines for circadian

rhythm adjustment is not tenable. Furthermore, any

effects of benzodiazepines on circadian rhythms

in humans have yet to be thoroughly evaluated.

As is the case for their effect on activity, the effects

of benzodiazepines on circadian rhythms in humans

may be very different from their effects on hamsters.

Other Chemical Substances and Diet

Researchers have speculated that several other

chemicals may manipulate circadian rhythms in

mammals, including carbachol, phenobarbital, theophylline, and lithium (11,148,175,191,197). Many

of these agents affect specific chemical systems in

the brain that are important for nerve cell communication and impinge on the circadian pacemaker.

Other agents are characterized by generalized stimulatory or sedative properties (157,164). There are

no data, however, indicating that these substances influence human circadian rhythms. Furthermore, powerful unwanted side effects cast doubt

on the usefulness of many of these substances in

counteracting jet lag or shift work.

A popularized diet has been said to manipulate

circadian rhythms and has been promoted as an

antidote for jet lag (51,199). These claims are based

on hypothetical effects of the diet on chemical

systems in the brain. Specifically, it has been

asserted that morning meals rich in proteins boost

concentrations of catecholamines in the brain and

consequently stimulate activity. Evening meals rich

in carbohydrates purportedly increase concentrations of serotonin, a sleep-inducing chemical in the

brain. While a few animal studies suggest that diet

can modulate these brain chemicals (82), the protocol used in these experiments does not relate directly

to the recommendations for humans. This dietary

protocol has not been shown to influence circadian rhythms in humans.

Activity

That the timing of arousal and physical activity is

intimately linked to the time of day and circadian

rhythms appears self-evident; a few studies suggest

that physical activity or arousal can synchronize the

internal clock (176). The apparent link between

triazolam’s stimulation of activity and its circadian

effects on hamsters has renewed interest in this

30-year-old proposal (9,176). In fact, many agents

purported to alter circadian rhythms also alter the

amount of activity in animals.

Experiments in rodents demonstrated that simply

having access to a running wheel changes the length

of the circadian cycle (13,201). A few other studies

indicated that when specific periods of physical

activity or other forms of arousal are provided, a

phase shift in the circadian cycle can be produced

(116,128,176). One study reported phase response to

“doses” of activity: variable phase shifts resulted

from periods of arousal or social activity at different

times during the 24-hour period (115).

Although these studies suggest that activity

modulates circadian rhythms in animals, further

experimentation is necessary to characterize this

effect. Since the state of being active or aroused is so

general, there is some question as to what specific

features of this state affect circadian rhythms.

Finally, the impact of activity and arousal on

circadian rhythms has yet to be carefully evaluated

in humans.
58 ● Biological Rhythms: Implications for the Worker

SUMMARY AND CONCLUSIONS

Research has indisputably demonstrated that living organisms, ranging from single cells to humans,

are able to keep track of time and to direct changes

in function accordingly. Such functional cycles that

repeat approximately every 24 hours are called

circadian rhythms. Circadian rhythms are generated

by living organisms and are genetically determined.

Environmental cues synchronize circadian rhythms

in organisms, the most important cue being lightdark cycles. In mammals, including humans, a

region of the brain called the suprachiasmatic

nucleus serves as the circadian pacemaker.

Most organs in the human body display circadian

rhythms. Especially significant for shift work are

sleep-wakefulness and performance rhythms. Daily

cycles of sleep and wakefulness are a conspicuous

circadian rhythm in humans. Studies have shown

that the circadian pacemaker significantly influences the timing and quality of sleep. Therefore,

periods of sleep are not easily rescheduled, deferred,

or resisted. Human performance, assessed by measures of reaction time, cognitive processes, and

mood, also displays circadian rhythms, which vary

according to the nature of the task or mood assayed.

Factors such as fatigue and motivation also profoundly influence human performance. When individuals are synchronized to the natural day-night

cycle, many performance rhythms diminish to minimal levels at night. This nighttime attenuation of

performance reflects the combined effects of circadian rhythms and the lack of sleep.

Research during the last few decades has demonstrated that humans have an internal clock and

suggests that violation of its temporal order may

exact a price in health and performance. When

internally generated circadian rhythms conflict with

environmental cycles, which happens following

transmeridian flight and in some schedules of shift

work, performance may be impaired, sleep disordered, and a general malaise experienced. Data

indicate that the generation of circadian rhythms is

altered with aging and in certain sleep disorders.

Circadian rhythms may also be altered in certain

mental disorders.

Several agents, including light, melatonin, benzodiazepines, other chemical substances, diet, and

activity, are under investigation for their ability to

adjust or shift circadian rhythms. Data indicate that

bright light, the most extensively studied agent, can

shift human circadian rhythms. How it does so,

however, is not completely understood. Further

research is necessary to substantiate the circadian

effects of the other agents in humans.

CHAPTER 3 REFERENCES

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

American Psychiatric Association, Diagnostic and

Statistical Manual of Mental Disorders (III-R)

(Washington, DC: 1987).

American Sleep Disorders Association, The International Classification of Sleep Disorders. Diagnostic and Coding Manual (Lawrence, KS: Allen

Press, 1990).

Arendt, J., “Melatonin and the Pineal Gland,”

Biological Rhythms in Clinical Practice, J. Arendt,

D.S. Minors, and J.M. Waterhouse (eds.) (London:

Wright, 1989).

Arendt, J., Aldhous, M., English, J., et al., “Some

Effects of Jet-lag and Their Alleviation by Melatonin,” Ergonomics 30:1379-1393, 1987.

Arendt, J., Aldhous, M., and Wright, J., “Synchronization of a Disturbed Sleep-Wake Cycle in a Blind

Man by Melatonin Treatment,” Lancet 1:772-773,

1988.

Arendt, J., and Broadway, J., ‘Light and Melatonin

as Zeitgebers in Man,” Chronobiology International 4:273-282, 1987.

Armstrong, S. M., “Melatonin: The Internal Zeitgeber in Mammals?” Pineal Research 7:157-202,

1989.

Armstrong, S.M., Cassone, V.M., Chesworth, M.J.,

et al., “Synchronization of Mammalian Circadian

Rhythms by Melatonin," Journal of Neural Transmission 21(supp.):375-394, 1986.

Aschoff, J., “Exogenous and Endogenous Components in Circadian Rhythms,” Cold Spring Harbor

Symposium on Quantitative Biology 25:11-

26, 1960.

Aschoff, J., “Circadian Rhythms in Man: A SelfSustained Oscillator With an Inherent Frequency

Underlies Human 24-Hour Periodicity,” Science

148:1427-1432, 1965.

Aschoff, J., “Circadian Activity Rhythms in Hamsters and Rats Treated With Imipramine in the

. . Drinking Water,” Chronobiologia 16:9-20, 1989.

Aschoff, J. (cd.), Handbook of Behavioral Neurobiology, vol. 4, Biological Rhythms (New York NY:

Plenum Press, 1981).

Aschoff, J., Figala, J., and Poppel, E., “Circadian

Rhythms of Locomotor Activity in the Golden

Hamster (Mesocricetus auratus) Measured With

Two Different Techniques,” Journal of Comparative Physiology and Psychology 85:20-28, 1973.
Chapter 3--Circadian Rhythms ● 59

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

Aschoff, J., Giedke, H., Poppel, E., et al., “The

Influence of Sleep-Interruption and of Sleep Deprivation on Circadian Rhythms in Human Performance,’ Aspects of Human Efficiency: Diurnal

Rhythm and Loss of Sleep, W.P. Colquhoun (cd.)

(London: English University Press, 1972).

Bargiello, T.A., Jackson, F.R., and Young, M.W.,

“Restoration of Circadian Behavioral Rhythms by

Gene Transfer in Drosophila,” Nature 312:752-

754, 1984.

Barnes, P.J., “Circadian Rhythms in the Respiratory System,” Biological Rhythms in Clinical

Practice, J. Arendt, D.S. Minors, and J.M. Waterhouse (eds.) (London: Wright, 1989).

Blehar, M. C., and Lewy, A.J., “Seasonal Mood

Disorders: Consensus and Controversy,” Psychopharmacology Bulletin 26:465-494, 1990.

Carskadon, M.A., “Daytime Sleepiness: Clinical

Consequences and Treatment,” The NIH Consensus Development Conference on the Treatment of

Sleep Disorders of Older People (Bethesda, MD:

National Institutes of Health, 1990).

Carskadon, M.A., and Dement, W. C., “Daytime

Sleepiness: Quantification of a Behavioral State,”

Neuroscience & Biobehavioral Reviews 11:307-

317, 1987.

Carskadon, M. A., Van den Hoed, J., and Dement,

W.c., “Insomnia and Sleep Disturbances in the

Aged: Sleep and Daytime Sleepiness in the Elderly,” Journal of Geriatric Psychiatry 13:135-151,

1980.

Cassone, V. M., Chesworth, M.J., and Armstrong,

S.M., “Dose Dependent Entrainment of Rat Circadian Rhythms by Daily Injection of Melatonin,”

Journal of Biological Rhythms 1:219-229, 1986.

Cassone, V.M., Chesworth, M.J., and Armstrong,

S.M., “Entrainment of Rat Circadian Rhythms by

Daily Injection of Melatonin Depends on the

Hypothalamic Suprachiasmatic Nuclei,” Physiology and Behavior 36:1111-1121, 1986.

Cassone, V.M., Roberts, M.H., and Moore, R.Y.,

“Effects of Melatonin on 2-deoxyglucose Uptake

Within the Rat Suprachiasmatic Nucleus,’ American Journal of Physiology 255:332-337, 1988.

Chee, C.A., Roozendaal, B., Swaab, D.F., et al.,

‘ ‘Vasoactive Intestinal Polypeptide Neuron Changes

in the Senile Rat Suprachiasmatic Nucleus,” Neurobiology of Aging 9;307-312, 1988.

Citri, Y., Colot, H.V., Jacquier, A. C., et al., “A

Family of Unusually Spliced and Biologically

Active Transcripts Encoded by a Drosophila Clock

Gene,” Nature 326:42-47, 1987.

Colquhoun, P., “Rhythms in Performance,’ Handbook of Behavioral Neurobiology, VOL 4, Biological

Rhythms, J. Aschoff (cd.) (New York, NY: Plenum

Press, 1981).

297-935 - 91 - 3 QL 3

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

Craig, A., and Condon, R., “Speed-Accuracy TradeOff and Time of Day,’ Acta Psychological 58:115-

122, 1985.

Czeisler, C.A., Allan, J. S., Strogatz, S.H., et al.,

“Bright Light Resets the Human Circadian Pacemaker Independent of the Timing of the SleepWake Cycle, “Science 233;667-671, 1986.

Czeisler, C.A., Dumont, M., Richardson, G. S., et

al., “Disorders of Circadian Function: Clinical

Consequences and Treatment,” The NIH Consensus Development Conference on the Treatment of

Sleep Disorders of Older People (Bethesda, MD:

National Institutes of Health, 1990).

Czeisler, C.A., Johnson, M.P., Duffy, J.F., et al.,

“Exposure to Bright Light and Darkness To Treat

Physiologic Maladaptation to Night Work” New

England Journal of Medicine 322:1253-

1259, 1990.

Czeisler, C.A., Kronauer, R.E., Allan, J. S., et al.,

“Bright Light Induction of Strong (Type O) Resetting of the Human Circadian Pacemaker,” Science

244:1328-1332, 1989.

Czeisler, C.A., Kronauer, R.E., Mooney, J.J., et al.,

“Biologic Rhythm Disorders, Depression, and Phototherapy: A New Hypothesis,’ Psychiatric Clinics

of North America 10:687-709, 1987.

Czeisler, C.A., Richardson, G. S., Zimmerman, J.C.,

et al., “Entrainment of Human Circadian Rhythms

by Light-Dark Cycles: A Reassessment,” Photochemistry and Photobiology 34:239-247, 1981.

Czeisler, C.A., Weitzman, E.D., Moore-Ede, M. C.,

et al., ‘Human Sleep: Its Duration and Organization

Depend on Its Circadian Phase,’ Science 210:1264-

1267, 1980.

Czeisler, C.A., Zimmerman, J. C., Ronda, J.M., et

al., “Timing of REM Sleep Is Coupled to the

Circadian Rhythm of Body Temperature in Man,”

Sleep 2:329-346, 1980.

Daan, S., and Lewy, A.J., “Scheduled Exposure to

Daylight: A Potential Strategy To Reduce Jet Lag

Following Transmeridian Flight,” Psychopharmacology Bulletin 20:566-568, 1984.

Davis, F. C., and Gorski, R.A., “Unilateral Lesions

of the Hamster Suprachiasmatic Nuclei: Evidence

for Redundant Control of Circadian Rhythms,”

Journal of Comparative Physiology, A 154:221-

232, 1984.

Dawson, D., Morris, M., and Lack, J., “Average

Phase Response Curves in Humans for a 4 Hour

Exposure to Evening Light,” Sleep Research 18:413,

1989.

Dawson, D., Morris, M., and Lack, J., “The

Phase-Shifting Effects of a Single 4 Hour Exposure

to Bright Morning Light in Normals and DSPS

Subjects,” Sleep Research 18:415, 1989.
60 . Biological Rhythms: Implications for the Worker

40.

41.

42.

43.

44.

45.

46.

47.

48.

49.

50.

51.

52.

53.

DeCoursey, P.J., “Daily Light Sensitivity Rhythm

in a Rodent,” Science 131:33-35, 1960.

DeCoursey, P. J., and Buggy, J., “Restoration of

Locomotor Rhythmicity in SCN-lesioned Golden

Hamsters by Transplantation of Fetal SCN,” Neuroscience Abstracts 12:210, 1989.

Demerit, W., and Kleitman, N., “Cyclic Variations

in EEG During Sleep and Their Relation to Eye

Movements, Body Motility and Dreaming,” Electroencephalography and Clinical Neurophysiology

9:673-690, 1957.

Dijk, D.J., Beersma, D. G. M., Daan, S., et al.,

“Bright Morning Light Advances the Human

Circadian System Without Affecting NREM Sleep

Homeostasis,” American Journal of Physiology

256:R106-R111, 1989.

Dijk, D.J., Visscher, C.A., Bloem, G. M., et al.,

‘‘Reduction of Human Sleep Duration After Bright

Light Exposure in the Morning,” Neuroscience

Letters 73:181-186, 1987.

Dinges, D.F., “The Nature of Sleepiness: Causes,

Contexts and Consequences,” Perspectives in Behavioral Medicine: Eating, Sleeping, and Sex, A.J.

Stunkard and A. Baum (eds.) (Hillsdale, NJ: Lawrence Erlbaum, 1989).

Dinges, D.F., “Probing the Limits of Functional

Capability: The Effects of Sleep LoSS on ShortDuration Tasks,” Sleep, Arousal and Performance:

Problems and Promises, R.J. Broughton and R.

Ogilivie (MIs.), in press.

Drennan, M., Kripke, D.F., and Gillin, J. C., “Bright

Light Can Delay Human Temperature Rhythm

Independent of Sleep,” American Journal of Physiology 257:R136-R141, 1989.

Drucker-Colin, R., Aguilar-Roblero, R., GarciaHernandez, F., et al., “Fetal Suprachiasmatic Nucleus Transplants: Diurnal Rhythms Recovery of

Lesioned Rats,” Brain Research 311;353-357,

1984.

Duncan, W. C., and Wehr, T.A., “Pharmacological

and Non-Pharmacological chronotherapies of Depression,” Annual Review of Chronopharmacology, A. Reinberg, M. Smolensky, and G. Labrecque

(eds.) (New York NY: Pergamon Press, 1988).

Dunlap, J. C., and Feldman, J.F., “On the Role of

Protein Synthesis in the Circadian Clock of Neurospora crassa,” Proceedings of the National Academy of Sciences, USA 85:1096-1100, 1988.

Ehret, C.F., and Scanlon, L. W., Overcoming Jet Lug

(New York NY: Berkley, 1983).

Feldman, J.F., and Dunlap, J. C., “Neurospora

crassa: A Unique System for Studying Circadian

Rhythms,” Photochemistry and Photobiology Review 7:319-368, 1983.

Folkard, S., and Monk, T.H., “Circadian Rhythms

in Human Memory, ’ British Journal of Psychology

54.

55.

56.

57.

58.

59.

60.

61.

62.

63.

64.

65.

66.

71:295-307, 1980.

Folkard, S., Wever, R.A., and Wildgrubert, C.M.,

“Multi-Oscillatory Control of Circadian Rhythms

in Human Performance, ’ Nature 305:223-225,

1983.

Folkard, S., Arendt, J., Aldhous, M., et al., “Melatonin Stabilizes Sleep Onset Time in a Blind Man

Without Entrainment of Cortisol or Temperature

Rhythms, Neuroscience Letters 113:193-

198, 1990.

Gillberg, M., “The Effects of Two Alternative

Timings of a One-Hour Nap on Early Morning

Performance,’ Biological Psychology 19:45-54,

1984.

Glattre, E., and Bjerkedal, T., “The 24-Hour

Rhythmicity of Birth,” Acta Obstetrics and Gynecology Scandinavia 62:31-36, 1983.

Goodwin, F. K., and Jamison, K. R., ManicDepressive Illness (New York, NY: Oxford University Press, 1990).

Green, D. J., and Gillett, R., “Circadian Rhythm of

Firing Rate Recorded From Single Cells in the Rat

Suprachiasmatic Brain Slice,” Brain Research

245:198-200, 1982.

Groos, G.A., and Hendriks, J., “Circadian Rhythm

in Electrical Discharge of Rat Suprachiasmatic

Neurones Recorded in Vitro,” Neuroscience Letters 34:283-388, 1982.

Halberg, F., “Physiologic 24-hour Periodicity in

Human Beings and Mice, the Lighting Regimen and

Daily Routine,’ Photoperiodism and Related Phenomena in Plants and Animals, R.B. Withrow (cd.)

(Washington, DC: American Association for the

Advancement of Science, 1959).

Halberg, F., “Implications of Biological Rhythms

for Clinical Practice,” Hospital Practice 12:139-

149, 1977.

Hall, J. C., and Rosbash, M., “Mutations and

Molecules Influencing Biological Rhythms,” Annual Review of Neuroscience 11;373-393, 1988.

Hamblen, M., Zehring, W.A., Kyriacou, C.P., et al.,

‘‘Germ-Line Transformation Involving DNA From

the Period Locus in Drosophila Melanogaster:

Overlapping Genomic Fragments That Restore

Circadian and Ultradian Rhythmicity to Pep and

Per– Mutants,” Journal of Neurogenetics 3:249-

291, 1986.

Hastings, J. W., and Sweeney, B.M., “A Persistent

Diurnal Rhythm of Luminescence in Gonyaulax

polyedra,” Biological Bulletin 115:440-458, 1958.

Hofman, M.A,, Fliers, E., Goudsmit, E.L., et al.,

“Morphometric Analysis of the Suprachiasmatic

and Paraventricular Nuclei in the Human Brain: Sex

Differences and Age-Dependent Changes,” Journal of Anatomy 160:127-143, 1988.
Chapter 3-Circadian Rhythms ● 61

67.

68.

69.

70.

71.

72.

73.

74.

75.

76.

77.

78.

79.

800

Honma, K., and Honma, S., “A Human Phase

Response Curve for Bright Light Pulses,” Japanese

Journal of Psychiatric Neurology 42:167-

168, 1988.

Home, J.A., and Pettitt, A.N., “High Incentive

Effects on Vigilance Performance During 72 Hours

of Total Sleep Deprivation,” Acta Psychologica

58:123-139, 1985.

Hughes, D.G., and Folkard, S., “Adaptation to an

8-Hour Shift in Living Routine by Members of a

Socially Isolated Community,” Nature 264:432-

434, 1976.

Inouye, S.T, and Kawamura, H., “Persistence of

Circadian Rhythmicity in a Mammalian Hypothalamic ‘Island’ Containing the Suprachiasmatic Nucleus,” Proceedings of the National Academy of

Sciences, USA 76:5962-5966, 1979.

Jackson, F.R., ‘The Isolation of Biological Rhythm

Mutations on the Autosomes of Drosophila melanogaster,” Journal of Neurogenetics 1:3-15, 1983.

Jewett, M.E., Kronauer, R.E., and Czeisler, C.A.,

“Light-Induced Suppression of Endogenous Circadian Amplitude in Humans,” Nature 350:59-62,

1991.

Kaiser, H., and Halberg, F., “Circadian Periodic

Aspects of Birth,” Annals of the New York Academy

of Sciences 98:1056-1068, 1962.

Klein, D. C., ‘‘Photoneural Regulation of the Mammalian Pineal Gland,” CIBA Foundation Symposium 17, Photoperiodism, Melatonin and the Pineal, D. Evered and S. Clark (eds.) (London: Pitman,

1985).

Kleitman, N., Sleep and Wakefulness (Chicago, IL:

University of Chicago Press, 1963).

Konopka, R. J., “Genetics of Biological Rhythms in

Drosophila,” Annual Review of Genetics 21:227-

236, 1987.

Konopka, R.J., and Benzer, S., “Clock Mutants of

Drosophila melanogaster,” Proceedings of the

National Academy of Sciences, USA 68:2112-2116,

1971.

Koopman, M. G., Minors, D. S., and Waterhouse,

J.M., “Urinary and Renal Circadian Rhythms,”

Biological Rhythms in Clinical Practice, J. Arendt,

D.S. Minors, and J.M. Waterhouse (eds.) (London:

Wright, 1989).

Kornhauser, J. M., Nelson, D.E., Mayo, K.E., et al.,

“Photic and Circadian Regulation of c-fos Gene

Expression in the Hamster Suprachiasmatic Nucleus,” Neuron 5:127-134, 1990.

Kupfer, D.J., Frank E., Jarrett, D. B., et al., “Interrelationship of Electroencephalographic Sleep

Chronobiology and Depression,” Biological

Rhythms and Mental Disorders, D.J. Kupfer, T.H.

Monk, and J.D. Barchas (eds.) (New York, NY:

Guilford Press, 1988).

81.

82.

83.

84.

85.

86.

87.

88.

89.

90.

91.

92.

Lavie, P., “Ultrashort Sleep-Waking Schedule, III.

‘Gates’ and ‘Forbidden Zones’ for Sleep,” Electroencephalography and Clinical Neurophysiology

63:414-425, 1986.

Leathwood, P., “Circadian Rhythms of Plasma

Amino Acids, Brain Neurotransmitters and Behavior,” Biological Rhythms in Clinical Practice, J.

Arendt, D.S. Minors, and J.M. Waterhouse (eds.)

(London: Wright, 1989).

Lehman, M.N., Silver, R., Gladstone, W.R., et al.,

‘‘Circadian Rhythmicity Restored by Neural Transplant: Immunocytochemical Characterization With

the Host Brain,” Journal of Neuroscience 7: 1626-

1638, 1987.

Lemmer, B., “Circadian Rhythms in the Cardiovascular System,” Circadian Rhythms in Clinical

Practice, J. Arendt, D.S. Minors, and J.M. Waterhouse (eds.) (London: Wright, 1989).

Levi, F., Reinberg, A., and Canon, C., “Clinical

Immunology and Allergy,” Biological Rhythms in

Clinical Practice, J. Arendt, D.S. Minors, and J.M.

Waterhouse (eds.) (London: Wright, 1989).

Lewy, A., and Sack, R., ‘‘Phase Typing and Bright

Light Therapy of Chronobiologic Sleep and Mood

Disorders,’ Chronobiology and Psychiatric Disorders, A. Halaris (cd.) (New York NY: Elsevier,

1987).

Lewy, A., Sack, R.L., and Latham, J., “Circadian

Phase Shifting of Blind and Sighted People With

Exogenous Melatonin Administration: Evidence

for a Phase Response Curve,” paper presented at the

Second Annual Conference of the Society for Light

Treatment and Biological Rhythms, New York

NY, May 1990.

Lewy, A., Sack, R.L., and Latham, J., “Melatonin

and the Acute Suppressant Effect of Light May Help

Regulate Circadian Rhythms in Humans,” Advances in Pineal Research 5:285-293, in press.

Lewy, A., Sack R.L., Miller, S., et al., “Antidepressant and Circadian Phase-Shifting Effects of Light,’

Science 235:352-354, 1987.

Lewy, A., Sack R.L., and Singer, C.M., “Assessment and Treatment of Chronobiologic Disorders

Using Plasma Melatonin Levels and Bright Light

Exposure: The Clock-Gate Model and the Phase

Response Curve,” Psychopharmacology Bulletin

20: 561-565, 1984.

Lewy, A., Sack, R. L., and Singer, C.M., “Immediate and Delayed Effects of Bright Light on Human

Melatonin production: Shifting “Dawn” and “Dusk”

Shifts the Dim Light Melatonin Onset (DLMO),”

Annals of the New York Academy of Sciences

453:253-259, 1985.

Lewy, A., Wehr, T. A., Goodwin, F.K., et al., “Light

Suppresses Melatonin Secretion in Humans,” Science 210:1267-1269, 1980.
62 ● Biological Rhythms: Implications for the Worker

93.

94.

95.

96.

97.

98.

99.

100.

101.

102.

103.

104.

105.

106.

Lieberman, H.R., Wurtman, J.J., and Teicher, M.H.,

“Circadian Rhythms of Activity in Healthy Young

and Elderly Humans,” Neurobiology of Aging

10:259-265, 1989.

Lynch, H.J., Jimerson, D. C., Ozaki, Y., et al.,

“Entrainment of Rhythmic Melatonin Secretion

From the Human Pineal to a 12-Hour Phase Shift in

the Light-Dark Cycle, “Life Science 23:1557-1564,

1978.

Lynch, H.J., Wurtman, R. J., Moskowitz, M.A., et

al., “Daily Rhythm in Human Urinary Melatonin,”

Science 187:169-171, 1975.

McFadden, E. R., “Asthma: A Nocturnal Disease,”

American Journal of Medicine 85:1-70, 1988.

Mant, A., and Eyland, E.A., “Sleep Patterns and

Problems in Elderly General Practice Attenders: An

Australian Survey,” Community Health Studies

12:192-199, 1988.

Meijer, J.H., and Rietveld, W.J., “Neurophysiology

of the Suprachiasmatic Circadian Pacemaker in

Rodents,” Physiological Review 69:671-707, 1989.

Menaker, M., “Aspects of the Physiology of

Circadian Rhythmicity in the Vertebrate Nervous

System,” The Neuroscience: Third Study Program, F.O. Schmitt and F.G. Worden (eds.) (Cambridge, MA: MIT Press, 1974).

Miles, L.E.M., and Wilson, M.A., “High Incidence

of Cyclic Sleep/Wake Disorders in the Blind,”

Sleep Research 6:192, 1977.

Minors, D. S., Rabbitt, P. M. A., Worthington, H., et

al., “Variation in Meals and Sleep-Activity Patterns

in Aged Subjects; Its Relevance to Circadian

Rhythm Studies,” Chronobiologia International

6:139-146, 1989.

Minors, D. S., and Waterhouse, J.M., “Chronobiochemistry: An Overview of Circadian Rhythms and

Some Applications to Clinical Medicine and Biochemistry,’’Annals of Clinical Biochemistry 24(supp.):

16-27, 1987.

Minors, D. S., and Waterhouse, J.M., “The Influence of Light on the Entrainment of the Circadian

System: An Introduction,” Studies in Industrial

and Organizational Psychology, Shift Work:

Health, Sleep and Performance, vol. 9, G. Costa, G.

Cesana, K. Kogi, et al. (eds.) (Frankfurt am Main:

Verlag Peter Lang, 1989).

Mitler, M.M., Carskadon, M.A., Czeisler, C.A., et

al., “Catastrophes, Sleep and Public Policy: Consensus Report,” Sleep 11:100-109, 1988.

Monk, T.H., “Shift Work and the Older Worker,”

The NIH Consensus Development Conference on

the Treatment of Sleep Disorders of Older People

(Bethesda, MD: National Institutes of Health, 1990).

Monk, T.H.., Fookson, J.E,, Moline, M.L., et al.,

“Diurnal Variation in Mood and Performance in a

107.

108.

109.

110.

111.

112.

113.

114.

115.

116.

117.

118.

119.

120.

Time-Isolated Environment,” Chronobiology International 2:185-193, 1985.

Monk, T.H., and Leng, V. C., “Interactions Between

Inter-Individual and Inter-Task Differences in the

Diurnal Variations of Human Performance,’ Chronobiology International 3:171-177, 1986.

Monk, T.H., Leng, V. C., Folkard, S., et al., “Circadian Rhythms in Subjective Alertness and Core

Body Temperature,” Chronobiologia 10:49-55,

1983.

Monk, T.H., Moline, M.L., Fookson, J.E., et al.,

‘‘Circadian Determinants of Subjective Alertness,”

Journal of Biological Rhythms 4:393-404, 1989.

Monk, T.H., Weitzman, E.D., and Fookson, J.E.,

“Circadian Rhythms in Human Performance Efficiency Under Free-Running Conditions,” Chronobiologia 11:343, 1984.

Monk, T.H., Weitzman, E.D., Fookson, J.E., et al.,

‘‘TaskVariables Determine Which Biological Clock

Controls Circadian Rhythms in Human Performance,” Nature 304:543-545, 1983.

Moore, J.G., “Circadian Rhythmicity in Gastric

Emptying, Acid Secretion and Mucosal Damage by

Drugs: Implications for Drug Therapy,” Chronopharmacology: Cellular and Biochemical Interactions, B. Lemmer (cd.) (New York, NY: Marcel

Dekker, 1989).

Moore-Ede, M.C., “Physiology of the Circadian

Timing System: Predictive vs. Reactive Homeostasis,” American Journal of Physiology, 250:R737-

R752, 1986.

MOM, L.P., “Age-Related Changes in Hamster

Circadian Period, Entrainment and Rhythm Splitting,” Journal of Biological Rhythms 3:237-248,

1988.

Mrosovsky, N., ‘‘Phase Response Curves for Social

Entrainment,” Journal of Comparative Physiology

162:35-46, 1988.

Mrosovsky, N., and Salmon, R.A., “A Behavioral

Method for Accelerating Reentrainment of

Rhythms to New Light-Dark Cycles,” Nature

330:372-373, 1987.

Muller, J.E., Stone, P.H., Turin, Z.G., et al., “The

Milis Study Group: Circadian Variation in the

Frequency of Onset of Acute Myocardial Infarction,” New England Journal of Medicine 313:1315-

1322, 1985.

Nejean, L., et al., “Circadian and Ultradian

Rhythms in Serum Glucose and Insulin,” Chronobiology International 5:227-236, 1988.

Ozaki, N., Iwata, T., Itoh, A., et al., “Body

Temperature Monitoring in Subjects With Delayed

Sleep Phase Syndrome, ’’Neuropsychobiology 2O: 174-

177, 1988.

Pepine, C. J., “Circadian Variations in Myocardial

Ischemia,” Journal of the American Medical Asso-
Chapter 3--Circadian Rhythms ● 63

121.

122.

123.

124.

125.

126.

127.

128.

129.

130.

131.

132.

133.

134.

135.

ciation 265:386-390, 1991.

Petrie, K., Conaglen, J.V., Thompson, L., et al.,

“Effect of Melatonin on Jet Lag After Long Haul

Flights,” British Medical Journal 298:705-707,

1989.

Pickard, G.E., “The Afferent Connections of the

Suprachiasmatic Nucleus of the Golden Hamster

With Emphasis on the Retinohypothalamic Projection,” Journal of Comparative Neurology 211:65-

83, 1982.

Pickard, G.E., and Turek, F.W., “The Suprachiasmatic Nuclei: Two Circadian Clocks?” Brain

Research 268:201-210, 1985.

Pittendrigh, C. S., “Circadian Rhythms and the

Circadian Organization of Living Systems,” Cold

Spring Harbor Symposium on Quantitative Biology

25:159-182, 1960.

Pittendrigh, C. S., and Bruce, V. G., “An Oscillator

Model for Biological Clocks,’ Rhythmic and Synthetic Processes in Growth, D. Rudnick (cd.)

(Princeton, NJ: Princeton University Press, 1957).

Pittendrigh, C. S., and Daan, S., “Circadian Oscillations in Rodents: A Systematic Increase of Their

Frequency With Age,” Science 186:548-550, 1974.

Potkin, S., Zetin, M., Stamenkovic, V., et al.,

“Seasonal Affective Disorder: Prevalence Varies

With Latitude and Climate,” Clinical Neuropharmacology 9(supp. 4):181-183, 1986.

Pratt, B.L., and Goldman, B.D., “Environmental

Influences on Circadian Periodicity of Syrian Hamsters,” Physiology and Behavior 36:91-95, 1986.

Ralph, M.R., Foster, R. G., Davis, F. C., et al.,

“Transplanted Suprachiasmatic Nucleus Determines

Circadian Period,” Science 247:975-978, 1990.

Ralph, M.R., and Menaker, M., ‘‘Effects of Diazepam on Circadian Phase Advances and Delay s,”

Brain Research 372:405-408, 1986.

Ralph, M.R., and Menaker, M., “A Mutation of the

Circadian System in Golden Hamsters,” Science

241:1225-1227, 1988.

Rea, M.A., “Light Increases Fos-Related Protein

Immunoreactivity in the Rat Suprachiasmatic Nuclei,” Brain Research Bulletin 23: 577-581, 1989.

Redman, J., Armstrong, S., and Ng, K.T., “FreeRunning Activity Rhythms in the Rat: Entrainment

by Melatonin,” Science 219:1089-1091, 1983.

Reinberg, A., Andlauer, P., Guillet, P., et al., “Oral

Temperature, Circadian Rhythm Amplitude, Aging

and Tolerance to Shift Work,” Ergonomics 23:55-

64, 1980.

Reme, C.E., Wirz-Justice, A., and Terman, M.,

“The Visual Input Stage of the Mammalian Circadian Pacemaking System. I. Is There a Clock in

the Mammalian Eye?” Journal of Biological

Rhythms, in press.

136.

137.

138.

139.

140.

141.

142.

143.

144.

145.

146.

147.

148.

149.

150.

Reppert, S.M., and Uhl, G.R., “Vasopressin Messenger Ribonucleic Acid in Supraoptic and Suprachiasmatic Nuclei: Appearance and Circadian Regulation During Development,’’Endom”nolo# 1202483-

2487, 1987.

Reppert, S.M., Weaver, D.R., Rivkees, S.A.,et al.,

“Putative Melatonin Receptors in a Human Biological Clock” Science 242:78-81, 1988.

Richardson, G. S., Carskadon, M.A., Orav, E.J., et

al., “Circadian Variation of Sleep Tendency in

Elderly and Young Adult Subjects,” Sleep 5:s82-

s92, 1982.

Richardson, G.S., and Martin, J.B., “Circadian

Rhythms in Neuroendocrinology and Immunology:

Influence of Aging,” Progress in NeuroEndocrinImmunology 1:16-20, 1988.

Rocco, M.B., Barry, J., Campbell, S., et al.,

“Circadian Rhythms and Coronary Artery Disease,” American Journal of Cardiology 59(supp.

1):13C-17C, 1987.

Roozendaal, B., Van Gool, W.A., Swaab, D.F., et

al., “Changes in Vasopressin Cells of the Rat

Suprachiasmatic Nucleus With Aging,” Brain Research 409:259-264, 1987.

Rosbash, M., and Hall, J. C., “The Molecular

Biology of Circadian Rhythms,” Neuron 3:387-

398, 1989.

Rosen, L.N., Targum, S.D., Terman, M., et al.,

‘‘Prevalence of Seasonal Affective Disorder at Four

Latitudes,” PsychiatryResearch 31:131-144, 1990.

Rosenthal, N.E., Sack, D.A., Gillin, J. C., et al.,

‘‘Seasonal Affective Disorder: A Description of the

Syndrome and Preliminary Findings With Light

Therapy,” Archives of General Psychiatry 41:72-

80, 1984.

Rosenthal, N.E., Sack, D.A., Skwerer, R.G., et al.,

“Phototherapy for Seasonal Affective Disorder,”

Seasonal Affective Disorders and Phototherapy,

N.E. Rosenthal and N.C. Blehar (eds.) (New York

NY: Guilford Press, 1989).

Rosenthal, N.E., and Wehr, T.A., “Seasonal Affective Disorders,” Psychiatric Annals 17:670-674,

1987.

Rusak B., “The Mammalian System: Models and

Physiology,’ Biological Clocks and Environmental

Time, S. Daan and E. Gwinner (eds.) (New York

NY: Guilford Press, 1989).

Rusak B., and Bina, K. G., “Neurotransmitters in

the Mammalian Circadian System,’ Annual Review

of Neuroscience 13:387-401, 1990.

Rusak, B., and Boulos, Z., “Pathways for Photic

Entrainment of Mammalian Circadian Rhythms,”

Photochemistry and Photobiology 34:267-

273, 1981.

Rusak B., Robertson, H. A., Eisden, W., et al.,

“Light Pulses That Shift Rhythms Induce Gene
64 . Biological Rhythms: Implications for the Worker

151.

152.

153.

154.

155.

156.

157.

158.

159.

160.

161.

162.

163.

Expression in the Suprachiasmatic Nucleus,” Science 248:1237-1240, 1990.

Sack, R.L., and Lewy, A.J., “Melatonin Administration Phase Advances Endogenous Rhythms in

Man,” Sleep Research 17:396, 1988.

Sack, R.L., Lewy, A.J., and Hoban, TM., “Free

Running Melatonin Rhythm in Blind People: Phase

Shifts With Melatonin and Triazolam Administration,’ Temporal Disorder in Human Oscillatory

Systems, L. Rensing, U. an der Heiden, and M.C.

Mackey (eds.) (New York, NY: Springer-Verlag,

1987).

Sack, R.L., Stevenson, J., and Lewy, A.J., “Entrainment of a Previously Free-Running Blind

Human With Melatonin Administration,” Sleep

Research 19:404, 1990.

Sadun, A.A., Schaechter, J.D., and Smith, L.E.H.,

“A Retinohypothalamic Pathway in Man: Light

Mediation of Circadian Rhythms,” Brain Research

302:371-377, 1984.

Sawaki, Y., Nihonmatsu, I., and Kawamura, H.,

‘‘Transplantation of the Neonatal Suprachiasmatic

Nuclei Into Rats With Complete Bilateral Suprachiasmatic Lesions, ’ Neuroscience Research 1:67-

72, 1984.

Scalabrino, G., Ferioli, M.E., Nebuloni, R., et al.,

“Effects of Pinealectomy on the Circadian

Rhythms of the Activities of Polyamine Biosynthetic Decarboxylases and Tyrosine Aminotransferase in Different Organs of the Rat,” Endocrinology 104:377-384, 1979.

Schneider-Helmert, D., and Spinweber, C.L,, “Evaluation of L-Tryptophan for Treatment of Insomnia:

A Review,” Psychopharmacology 89:1-7, 1986.

Schwartz, W., and Gainer, H., “Suprachiasmatic

Nucleus: Use of (14C)-labeled Deoxyglucose Uptake as a Functional Marker,” Science 197:1089-

1091, 1977.

Schweiger, H. G., Hartwig, R., and Schweiger, M.,

‘‘Cellular Aspects of Circadian Rhythms,” Journal

of Cell Science 4(supp.):181-200, 1986.

Sharma, M., Palacios-Bois, J., Schwartz, G., et al.,

“Circadian Rhythms of Melatonin and Cortisol in

Aging,” Biological Psychiatry 25:305-319, 1989.

Shibata, S., and Moore, R. Y., “Electrical and

Metabolic Activity of Suprachiasmatic Nucleus

Neurons in Hamster Hypothalamic Slices,” Brain

Research 438:374-378, 1988.

Shinowara, N.L., London, E.D., and Rapoport, S.I.,

“Changes in Retinal Morphology and Glucose

Utilization in Aging Albino Rats,” Experimental

Eye Research 34:517-530, 1982.

Smolensky, M.H., Barnes, P.J., Reinberg, A., et al.,

“Chronobiology and Asthma, I. Day-Night Differences in Bronchial Patency and Dyspnea and

164.

165.

166.

167.

168.

169.

170.

171.

172.

173.

174.

175.

176.

Circadian Rhythm Dependencies,’ ‘Journal of Asthma

23:320-342, 1986.

Spinweber, C.L., “L-Tryptophan Administered to

Chronic Sleep-Onset Insomniacs: Late-Appearing

Reduction of Sleep Latency,” Psychopharmacology 90:151-155, 1986.

Strogatz, S.H., Kronauer, R.E., and Czeisler, C.A.,

“Circadian Regulation Dominates Homeostatic Control of Sleep Length and Prior Wake Length in

Humans,” Sleep 9:353-364, 1986.

Swaab, D.F., Fisser, B., Kamphorst, W., et al., “The

Human Suprachiasmatic Nucleus; Neuropeptide

Changes in Senium and Alzheimer’s Disease,”

Basic and Applied Histochemistry 32:33-54, 1988.

Swaab, D.F., Fliers, E., and Partiman, T.S., “The

Suprachiasmatic Nucleus of the Human Brain in

Relation to Sex, Age and Senile Dementia,’ Brain

Research 342:37-44, 1985.

Takahashi, J. S., Murakami, N., Nikaido, S. S., et al.,

“The Avian Pineal, a Vertebrate Model System of

the Circadian Oscillator: Cellular Regulation of

Circadian Rhythms by Light, Second Messengers,

and Macromolecular Synthesis,” Recent Progress

in Hormone Research 45:279-352, 1989.

Terman, J. S., Reme, C.E., and Wirz-Justice, A.,

“The Visual Input Stage of the Mammalian Circadian Pacemaker System. II. The Effect of Light

and Drugs on Retinal Function, ’ Journal of Biological Rhythms, in press.

Terman, J. S., Terman, M., Quitkin, F.M., et al.,

“Light Therapy for Seasonal Affective Disorder: A

Review of Efficacy,” Neuropsychopharmacology

2:1-22, 1989.

Terman, M., Reme, C.E., Rafferty, B., et al.,

“Bright Light Therapy for Winter Depression:

Potential Ocular Effects and Theoretical Implications,” Photochemistry and Photobiology 51:781-

792, 1990.

Terman, M., Terman, J. S., and Rafferty, B., “Experimental Design and Measures of Success in the

Treatment of Winter Depression by Bright Light,”

Psychopharmacology Bulletin 26:505-510, 1990.

Thayer, R.E., “Towards a Psychological Theory of

Multidimensional Activation (Arousal)” Motivation and Emotion 2:1-35, 1978.

Thorpy, M.J., “Classification and Definition of

Sleep Disorders,” The NIH Consensus Development Conference on the Treatment of Sleep Disorders of Older People (Bethesda, MD: National

Institutes of Health, 1990).

Turek, F. W., “Pharmacological Probes of the Mammalian Circadian Clock: Use of the Phase Response

Curve Approach,” Trends in Pharmacological

Sciences 8:212-217, 1987.

Turek, F. W., “Effects of Stimulated Physical Activity on the Circadian Pacemaker of Vertebrates,”
Chapter 3-Circadian Rhythms ● 65

Biological Clocks and Environmental Time, S.

Daan and E. Gwinner (eds.) (New York, NY:

Guilford Press, 1989).

177. Turek, F. W., and Losee-Olson, S., “A Benzodiazepine Used in the Treatment of Insomnia PhaseShifts the Mammalian Circadian Clock” Nature

321:167-168, 1986.

178. Turek, F.W., McMillan, J.P., and Menaker, M.,

“Melatonin: Effects on the Circadian Locomotor

Rhythm of Sparrows,” Science 194:1441-1443,

1976.

179. Turek, F.W., and Van Cauter, E., “Altering the

Mammalian Circadian Clock With the Short-Acting

Benzodiazepine, Triazolam,’ Trends in Neurological Science 12:535-541, 1988.

180. Uhl, G.R., and Reppert, S.M., “Suprachiasmatic

Nucleus Vasopressin Messenger RNA: Circadian

Variation in Normal and Brattleboro Rats,’ Science

232:390-392, 1986.

181. Van Cauter, E., “Endocrine Rhythms,” Biological

Rhythms in Clinical Practice, J. Arendt, D.S.

Minors, and J.M. Waterhouse (eds.) (London:

Wright, 1989).

182. Van Cauter, E., L’Hermite, M., Copinschi, G., et al.,

“Quantitative Analysis of Spontaneous Variations

of Plasma Prolactin in Normal Men,’ American

Journal of Physiology 241:E355-E363, 1981.

183. Van Cauter, E., and Refettoff, S., “Multifactorial

Control of the 24-Hour Secretory Profiles of Pituitary Hormones,” Journal of Clinical Endocrinology and Metabolism 8:381-389, 1985.

184. Van Cauter, E., Van Onderbergen, A., Boosson, D.,

et al., ‘‘Triazolam Accelerates the Adaptation of the

Circadian Rhythm of Cortisol to an 8-Hour Delay of

the Sleep-Wake Cycle in Man,” Society for Neuroscience Abstracts 13:1040, 1987.

185. Van Den Pol, A.N., and Powley, T., “A FineGrained Anatomical Analysis of the Role of the Rat

Suprachiasmatic Nucleus in Circadian Rhythms of

Feeding and Drinkin“ g,” Brain Research 160:307-

326, 1979.

186. Van Gool, W.A., and Mirmiran, M., “Aging and

Circadian Rhythms,” Progress in Brain Research,

vol. 70, W.A. Van Gool and F. Van Haaren (eds.)

(Amsterdam: Elsevier, 1986).

187. Van Reeth, O., and Turek, F.W., “Adaptation of

Circadian Rhythmicity to Shift in Light-Dark Cycle

Accelerated by a Benzodiazepine,’ American Journal of Physiology 253 R204-R207, 1987.

188. Van Reeth, O., and Turek, F.W., “Stimulated

Activity Mediates Phase Shifts in the Hamster

Circadian Clock Induced by Dark Pulses or Benzodiazepines,” Nature 339:49-51, 1989.

189. von Arnim, T, Hofling, B., and Schreiber, M.,

‘‘Characteristics of Episodes of ST Elevation or ST

Depression During Ambulatory Monitoring in

Patients Subsequently Undergoing Coronary

Angiography, “ British Heart Journal 54:484-488,

1985.

190. Waters, D.D., Miller, D.D., Bouchard, A., et al.,

“Circadian Variation in Variant Angina,” American Journal of Cardiology 54:61-64, 1984.

191. Wee, B.E.F., and Turek, F.W., “Carbachol Phase

Shifts the Circadian Rhythm of Locomotor Activity

in the Djungarian Hamster,” Brain Research 505:209-

214, 1989.

192. Weitzman, E.D., Czeisler, C. A., and Moore-Ede,

M. C., “Sleep-Wake, Neuroendocrine and Body

Temperature Circadian Rhythms Under Entrained

and Non-entrained (Free-Running) Conditions in

Man,” Biological Rhythms and their Central Mechanism, M. Suda, O. Hayaishi, and H. Nakagawa

(eds.) (Amsterdam: Elsevier, 1979).

193. Weitzman, E.D., Moline, M.L., Czeisler, C.A., et

al., ‘Chronobiology of Aging: Temperature, SleepWake Rhythms and Entrainment,” Neurobiology

3:299-309, 1982.

194. Wever, R.A., “Light Effects on Human Circadian

Rhythms: A Review of Recent Andechs Experiments,” Journal of Biological Rhythms 4:161-185,

1989.

195. Wever, R.A., Polasek, J., and Wildgruber, C.M.,

‘ ‘Bright Light Affects Human Circadian

Rhythms,” Pflugers Archives 396;85-87, 1983.

196. Wise, P.M., Cohen, I.R., Weiland, N.G., et al.,

“Aging Alters the Circadian Rhythm of Glucose

Utilization in the Suprachiasmatic Nucleus,” Proceedings of the National Academy of Sciences, USA

85:5305-5309, 1988.

197. Wollnik, F., Turek, F.W., Majewski, P., et al.,

“Phase Shifting the Circadian Clock With Cycloheximide: Response of Hamsters With an Intact or

a Split Rhythm of Locomotor Activity,” Brain

Research 496:82-88, 1989.

198. Wu, J. U., and Bunney, W.E., “TheBiologicalB asis

of an Antidepressant Response to Sleep Deprivation

and Relapse: A Review and Hypothesis,’ American

Journal of Psychiatry 147:14-21, 1990.

199. Wurtman, J.J., Managing Your Mind and Mood

Through Food (New York NY: Rawson, 1986).

200. Wurtman, R.J., Axelrod, J., and Fischer, J.E.,

‘‘Melatonin Synthesis in the Pineal Gland: Effect of

Light Mediated by the Sympathetic Nervous System,” Science 143:1328-1330, 1964.

201. Yamada, N., Shimoda, K., Ohi, K., et al., “FreeAccess to a Running Wheel Shortens the Period of

Free-Running Rhythms in Blinded Rats,” Physiology and Behavior 42:87-91, 1988.

202. Zehring, W.A., Wheeler, D.A., Reddy, P., et al.,

“P-element Transformation With Period Locus

DNA Restores Rhythmicity to Mutant, Arrhythmic

Drosophila melanogaster,” Cell 39:369-376, 1984.
66 . Biological Rhythms: Implications for the Worker

203. Zimmerman, N.H., and Menaker, M., “The Pineal 204. Zulley, J., Wever, R., and Aschoff, J., “The

Gland: The Pacemaker Within the Circadian Sys- Dependence of Onset and Duration of Sleep on the

tern of the House Sparrow,” Proceedings of the Circadian Rhythm of Rectal Temperature, ”

National Academy of Sciences, USA 76:999-1003, Pflugers Archives 391:314-318, 1981.

1979.
Chapter 4

The Prevalence and

Use of Shift Work
Contents

Page

THE DEMOGRAPHICS OF SHIFT WORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Defining a Shift Worker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69

Sources of National Data on Shift Work . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . ., ● . . . . . 69

Estimates of Shift Work Prevalence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Shift Workers in Various Employment Sectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Who Are Shift Workers? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

WHY DO EMPLOYEES PERFORM SHIFT WORK? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

SHIFT WORK SCHEDULES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

CHAPTER 4 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Boxes

Box Page

4-A. The Compressed Workweek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

4-B. 40 Hours Plus: Overtime and Moonlighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Figures

Figure Page

4-1. Percentage of Shift Workers Among Full-Time Employees in the United States . . . . . . . . 72

4-2. A Month in the Life of a Locomotive Engineer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

4-3. Four Days With an International Flight Crew . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -75

4-4. Shift Work History and Preference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8l

Tables

Table Page

4-1. Sources of National Data on Shift Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

4-2. Shift Work in Various Employment Sectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

4-3. Demographic Profile of Shift Workers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77

4-4. Three Mills and Their Schedules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

4-5. Potential Advantages and Disadvantages of 12-Hour Schedules . . . . . . . . . . . . . . . . . . . . . . . 82
Chapter 4

The Prevalence and Use of Shift Work

Some 20 million Americans—approximately one

in five employed persons-can be broadly defined

as shift workers, that is, they do not work a standard

daytime schedule (15). Instead, they work evenings,

nights, a split or extended shift, or rotating shifts.

These shift schedules, some of which conflict with

biological rhythms and social time order, are used in

many occupations and industries, ranging from the

health care professions to the manufacturing and

transportation industries to clerical positions. Various factors, including demand for services, the

amount of time required to perform a procedure or

task, technological advances, and expense, have led

to the spread of shift work. Clearly, shift work is

required in any modern, industrially developed

country.

This chapter discusses and evaluates the prevalence of shift work in the United States. It describes

national sources of data on shift work, the prevalence of shift work and its use in different employment sectors, and the demographic characteristics of

shift workers. A final section outlines available data

on specific work schedules. Although economic and

technological factors significantly influence the use

of shift work and specific schedules, they are beyond

the scope of this chapter.

THE DEMOGRAPHICS OF

SHIFT WORK

A basic demographic issue in any consideration of

shift work is its overall prevalence. Since estimates

of shift work vary with the definition used, it is

important to consider how shift work is measured in

national surveys. Who is a shift worker? In general,

a shift worker is defined as someone who does not

regularly work a standard daytime schedule. But

what is standard? Not only is this an arbitrary

determination, so is the definition of an evening,

night, or split shift and of what constitutes shift

rotation. There is considerable variation in the work

hours of nonstandard schedules, depending on the

nature and place of employment.

Defining a Shift Worker

National demographic surveys generally ask about

shift work in one of two ways:

●

●

by having respondents classify their shift, with

minimal, if any, instruction provided; and

by asking respondents about the specific hours

they work (each day or most days of the week)

and then determiningg their shift status according to precise guidelines.

Each approach has limitations.

Self-classification provides responses that are

difficult to interpret. For example, some respondents

may call themselves ‘‘day workers’ when they

work between 1 p.m. and 9 p.m.; others with the

same hours of employment may regard themselves

as “evening workers. ’ The advantage of selfclassification is that it requires only one question on

the questionnaire, minimizing respondent time and

cost.

In contrast, a series of questions is required to

obtain people’s actual work hours. This series might

include some or all of the following: the time work

begins, the time work ends, and whether the shift

rotates. These questions may be asked with regard to

most days during a reference week prior to the

survey or for all days of the week. Although more

time-consuming and costly, this procedure allows

for precise definition of shifts. These definitions,

although explicit, vary by researcher, depending in

part on whether the investigator is considering

starting time only or both starting and ending time,

and whether shift rotation is taken into account. For

example, a person who works during the day within

the reference period of the survey may actually work

a rotating shift, but this will not be clear unless a

question about shift rotation is asked.

Sources of National Data on Shift Work

The most comprehensive data on the prevalence of shift work in the United States are based

on supplements to the Current Population Survey (CPS) (table 4-l). The CPS is a household

sample survey conducted monthly by the Bureau of

the Census (within the U.S. Department of Commerce) for the Bureau of Labor Statistics (BLS)

-69–
70 . Biological Rhythms: Implications for the Worker

Table 4-l—Sources of National Data on Shift Work

Survey Conducted by Years administered Size

Current Population Survey (CPS)

May supplement . . . . . . . . . . . . . . Bureau of Labor Statistics 1972 to 1980; 55,000 to 60,000 households

1985,1991

June supplement . . . . . . . . . . . . . Bureau of Labor Statisticsa

1982 55,000 to 60,000 households

Quality of Employment Survey . . . . . Institute for Social Research, 1977 1,515 persons

University of Michigan

National Survey of Families

and Households . . . . . . . . . . . . . . Center for Demography and 1987 to 1988 13,017 persons and spouses

Ecology, University of Wisconsin or cohabitants

National Longitudinal Survey,

Youth Cohort . . . . . . . . . . . . . . . . . Center for Human Resource 1979 to present 12,686 persons and spouses

Research, Ohio State University

a sponsored by the National Institute of Child Health and Human Development.

SOURCE: Office of Technology Assessment, 1991.

(within the U.S. Department of Labor). A portion of

the labor force in the United States is regularly asked

a freed list of questions regarding employment. The

number of households surveyed each month generally ranges from about 55,000 to 60,000. Data are

collected for all members of the household age 16

and over, and beginning in 1980 some basic

demographic questions on children in the household

were also asked. In May of each year between 1973

and 1980, a supplement was added to the CPS with

questions on the specific hours of employment

(beginning and ending time) for the principal job

held the previous week and questions on whether

more than one job was held (but none on the hours

employed in nonprincipal jobs). In May 1980, data

were collected for the first time on whether or not the

principal job was a rotating shift. All questions on

specific work hours were asked only of wage and

salary earners (self-employed persons were excluded).

Between 1980 and 1985 there were no supplements to the May CPS on work schedules. However,

in May 1985 there was a supplement which went

beyond the earlier ones to include questions on

which days and hours people worked and, for

persons with more than one job, the hours work

began and ended on the second job. Whereas the

work hours continued to be asked with regard to the

reference week, shift rotation was defined differently in 1985, affecting the precision with which one

can compare the 1985 results with those from earlier

years. In May 1985, employed persons were also

asked to categorize their usual work shift; interviewers were given rough guidelines to help if there was

difficulty.1 Unlike the previous May CPS supplements, in 1985 the shift work questions were asked

of all employed persons. A supplement with shift

work questions was added to the May 1991 CPS,

which will provide the most recent estimates of

national shift work prevalence since 1985.2

In addition to the May CPS supplements, the

June 1982 CPS supplement contained some data

on shift work. This supplement (sponsored by the

National Institute of Child Health and Human

Development) focused on fertility and child care and

included questions on the time work began and

ended (but not shift rotation) for employed women

with children under the age of 5. The supplement

provided the first opportunity to consider at a

national level shift work in relation to child care use,

although it is limited to women with pre-school age

children.

Until recently, the only other national data on shift

work were from the 1977 Quality of Employment

Survey (QES). This survey was a national probability sample3 of 1,515 persons age 16 and over who

were working for pay for 20 or more hours per week.

Although the survey was conducted in earlier years,

only in 1977 were questions asked on the specific

lm~ cps ~b~ ~Omation on ~ household rnern~rs fiorn One ad~t rn~b~. &COrd~gly, me Work sched~es of W employed perSOIIS We

reported by one person and thus are more subject to error than if truly self-reported.

2Appropriations for me BLS ~ve been reduced by nearly $14.5 million over the last 3 years, undoubtedly limitkg data collection (9).

3A ~tio~ probabili~ .samp~e is selected on he basis of statisti~ proced~es mat, wi~ appropriate weighting, yield a sample that represents the

total U.S. population and can be generalized accordingly.
Chapter 4--The Prevalence and Use of Shift Work ● 71

working hours of respondents and their employed

spouses, if married. Moreover, because of the

sample design and the definition of shift work, the

data are problematic in assessing the prevalence of

shift work in the United States in 1977.4

A recent and comprehensive source of data on

shift work at the national level is the 1987-88

National Survey of Families and Households, conducted by the Center for Demography and Ecology

at the University of Wisconsin. This survey is a

national probability sample of 13,017 respondents

and, for those married or cohabiting, their spouses

and partners. It asks the most detailed questions

about work schedules of any national survey to date,

including the hours work began and ended for each

day of the week and shift rotation. It also includes

detailed data on family attitudes and behavior.

Although no analyses of the effects of shift work

have been completed using these data, preliminary

results on prevalence are consistent with the 1985

May CPS findings (17).

Although specific to a particular age group,

another key source of data for the study of shift work

in the United States is the National Longitudinal

Survey, Youth Cohort, conducted for the BLS by the

Center for Human Resource Research at Ohio State

University. This survey is a national probability

sample of 12,686 persons age 14 to 21 as of January

1, 1979, the year of the first interview, with annual

interviews thereafter. A self-defined shift status was

asked of employed persons almost every year of the

study. Beginning in 1983, employed persons with

children were also asked the specific hours their

work began and ended, as well as the work hours of

employed spouses, if married. Questions about shift

rotation were asked in some years but not others. In

1988 through 1990, specific hours worked and shift

rotation questions were asked of all employed

persons, not just those with children, and all

employed spouses, if married. These data, however,

have not yet been analyzed.

The above sources are all based on household

surveys, and information is collected from one or

more household members. The BLS has collected

data on shift work and scheduled weekly hours from

employers, in the Area and Industry Wage Surveys,

for various years since the end of World War II.

Although the findings of these surveys are reported

only for specific industries and selected metropolitan areas, they are important because they provide

data on pay differentials by shift status.

Estimates of Shift Work Prevalence

The most widely used estimates of the prevalence

of shift work in the United States are from the May

CPS supplements, starting with 1973. Between 1973

and 1980, BLS published tabulations of full-time

nonfarm workers (employed 35 or more hours per

week), and the determination of the work schedule

was based on beginning and ending times of shifts.

A day shift was defined as half or more hours of

employment between 8 a.m. and 4 p.m., an evening

shift as most hours between 4 p.m. and midnight, a

night shift as most hours between midnight and 8

a.m., and a miscellaneous shift as fewer than 6 or

more than 12 hours a day (including split shifts).

Based on these criteria, the prevalence of shift

work changed little between 1973 and 1980, at least

for full-time nonagricultural workers (data on parttime workers are not available): about one out of six

full-time workers was employed in shift work (24).

This proportion, however, is an underestimate, since

persons on rotating shifts were not identified prior to

1980. Accordingly, everyone on a rotating shift who

worked a day schedule in the reference week of the

survey was classified as a day rather than a nonday

worker. Adjusting for this misclassification in the

1980 data, it has been estimated(11) that one out of

five full-time nonagricultural wage and salary

workers in the United States was a shift worker.

Again, these figures relate to the principal job only

(6.2 percent of the employed population in 1989 held

multiple jobs) (19).

The 1985 CPS data on work shifts are not strictly

comparable to those for 1973 to 1980 because of

definitional differences, as noted above. Crude

comparisons suggest little change in the overall

prevalence of shift work between 1980 and 1985.

From tabulations of the May 1985 CPS, it can be

estimated that one in five nonagricultural workers

(both wage and salary workers and the selfemployed, part-time and full-time combined) was

@oth part-time and full-time workers were grouped together, with no minimum hours required for the employment of spouses of respondents but

a 20-hour minimum for respondents themselves. Shift workers were defined as persons who did not begin work between 3:30 a.m. and 11:59 a.m. and

thus include spouses who work a few hours in the afternoon.
72 . Biological Rhythms: Implications for the Worker

Figure 4-l—Percentage of Shift Workers Among

Full-Time Employees in the United States

Day shift 84.1

Other shifts 8.9

Rotating shifts 4.3

Night shift 2.7

SOURCE: E.F. Mellor, “Shift Work and Flexitime: How Prevalent Are

They?” Month/y Labor /?eview109: 14-21, 1986.

employed in shift work (figure 4-1).5 This estimate

is based on specific work hours (as in earlier years),

but it closely approximates figures based on the

respondent’s categorization of his or her shift status

and is limited to wage and salary workers only,

part-time and full-time combined (8).6 According to

the BLS figures, persons working part-time (fewer

than 35 hours per week) were much more likely to

be working a shift (47.5 percent) than those working

hill-time (15.9 percent) (8).

In the 1985 CPS supplement, 2.7 percent of

full-time workers and 5.0 percent of part-time

workers were classified as night workers. Therefore,

approximately 2.0 million individuals work at night.

Another 4.3 percent of full-time workers, approximately 3.1 million people in the population, reported

working rotating shifts. While some, if not most, of

these individuals occasionally work at night, the

survey does not differentiate rotation schedules that

include night work from those that do not.

Shift Workers in Various Employment Sectors

Many occupations and industries involve shift

work. The factors that lead to shift work, however,

vary considerably. Specific reasons for adopting

shift work schedules include:

●

●

●

●

an extended period of time required to complete

a particular job or process,

a constant need or extended demand for services,

economic factors (e.g., the expense of capital

investment, the need for maximum competitiveness), and

technological advances.

In the following section, the prevalence of shift work

in various employment sectors is discussed (table

4-2).

In manufacturing, the use of shift work and night

operations may reflect several considerations. A

high ratio of capital investment to labor costs is an

important incentive for maximizing the use of plants

and equipment and therefore operating at night (5).

Continuous-process industries, like basic steel, may

operate around the clock to avoid high startup and

shutdown costs. Some industries are characterized

by processes that require extended periods of time

(more than 12 hours) for completion. This is the case

for many chemical manufacturing processes. Other

factors, such as increased demand for a product and

favorable utility rates at night, also favor the

establishment of 24-hour operations.

The importance of capital investment for the

prevalence of shift work and night operations is

borne out by data collected by the BLS from

industries in large metropolitan areas (5). For the

period 1979 to 1984, capital-intensive industries and

continuous-process operations had as many as 50

percent of employees working evening or night

shifts.7 In contrast, less than 3 percent of workers in

labor-intensive industries are scheduled for an evening or night shift.

Shift work is prevalent in transportation occupations and industries, including trucking, airlines,

railroads, and shipping (table 4-2).8 Among those

employed by public utilities and transportation

industries, 20.6 percent are shift workers. Of fulltime motor vehicle operators, 25.5 percent are shift

workers, approximately half of them working night

or rotating shifts (8). While many transportation

sectors are governed by hours of service regulations,

these regulations do not preclude night work, shifts

%ble 4-2 lists a lower estimate than one in five, based on self-deftition rather than actual hours, and is limited to full-time workers only.

6~1 ~ublish~ ~b~atiom on ~ work by the B~ for 1985 me b~~ on ~~+at~go~ofl ~d are lmted to wage and XWOlkerS.

7~Me ~eys have been repeated since 1984.

8shift .s~hed~es and how of ~mice re@atiom for tie ~~ortation industry ~ discussed in detail in ch. 6.
Chapter 4--The Prevalence and Use of Shift Work ● 73

Figure 4-2—A Month in the Life of a Locomotive Engineer

~oQ

+

~Q& ~Q& ~Q&

Date 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30 I

31

I

r! On-duty time (200.08 hours)

~~ Off-duty time at away. from-home terminal

~] Off-duty time at home

Actual work history of a locomotive engineer on a pool freight run of 182 miles, from October 1 to 31,

1990.

SOURCE: C.E. Anderson, Brotherhood of Locomotive Engineers, 1991.

exceeding 8 hours, or erratic scheduling (figures 4-2 For example, continuous service is required from

and 4-3). police and firefighters, hospital staff, nightguards,

Around-the-clock operations are also demanded and military personnel. Persons employed in the

by various service industries, which area significant retail and entert ainment industries are also involved

and growing sector of the U.S. economy. Certain in shift work.

services may be in demand during nonstandard

hours because of the nature of the service itself or the The 1985 CPS data illustrate the disproportionneeds of customers employed during standard hours. ately high percentage of shift workers in service
74 . Biological Rhythms: Implications for the Worker

Table 4-2-Shift Work in Various Employment Sectors

Total workers Standard

employed work schedule Shift work (percent)

Occupation or industry (thousands) (percent) Evening shift Night shift Rotating shift Total

Occupation

Managerial and professional

specialty . . . . . . . . . . . . . . . . . . .

Executive, administrative,

and managerial . . . . . . . . . . . . .

Professional specialty. . . . . . . . . .

Health-diagnosing

occupations . . . . . . . . . . . . .

Health assessment and

treating occupations. . . . . . .

Technical, sales, and administrative

support . . . . . . . . . . . . . . . . . . . .

Technicians and related support . . .

Health technologists and

technicians . . . . . . . . . . . . . . . .

Sales occupations . . . . . . . . . . . . . . .

Supervisors . . . . . . . . . . . . . . . . . .

Salesworkers, retail and

personal services . . . . . . . . . . .

Administrative support, including

clerical . . . . . . . . . . . . . . . . . . . .

Computer equipment

operators. . . . . . . . . . . . . . . . . . .

Mail and message distributing . . .

Service occupations . . . . . . . . . . . . .

Private household . . . . . . . . . . . . .

Protective service . . . . . . . . . . . . .

Service, except private

household and protective. . .

Food service . . . . . . . . . . . . . . .

Health service . . . . . . . . . . . . . .

Cleaning and building

service . . . . . . . . . . . . . . . . . .

Personal service . . . . . . . . . . . .

Precision production, craft,

and repair . . . . . . . . . . . . . . .

Mechanics and repairers . . . . . . .

Construction trades . . . . . . . . . . .

Other precision production,

craft, and repair . . . . . . . . . . .

Operators, fabricators,

and laborers . . . . . . . . . . . . .

Machine operators, assemblers,

and inspectors . . . . . . . . . . .

Transportation and materialmoving occupations . . . . . . .

Motor vehicle operators . . . . . .

Handlers, equipment cleaners,

helpers, and laborers . . . . . . . .

Farming, forestry, and fishing. . . . . .

Industry

Private sector. . . . . . . . . . . . . . . . . . .

Goods-producing industries . . . . .

Agriculture . . . . . . . . . . . . . . . . .

Mining . . . . . . . . . . . . . . . . . . . . .

Construction . . . . . . . . . . . . . . .

Manufacturing. . . . . . . . . . . . . .

Durable goods . . . . . . . . . . .

Nondurable goods . . . . . . . .

Service-producing industries . . . .

18,944

9,079

9,866

212

1,257

21,961

2,548

761

6,730

1,957

2,400

12,684

673

613

7,268

275

1,286

5,707

2,194

1,076

1,719

718

10,477

3,582

3,282

3,614

13,326

6,748

3,448

2,392

3,130

1,418

60,127

24,626

1,154

885

4,279

18,309

11,277

7,033

35,501

91.4

92.6

90.3

77.6

68.7

88.3

84.5

70.1

82.8

84.0

72.3

92.0

81.2

76.2

61.6

83.0

39.2

65.6

56.9

63.9

74.4

73.9

87.0

87.3

94.1

80.3

76.3

76.3

73.8

74.5

78.9

89.9

83.5

85.0

89.4

78.1

97.5

82.1

84.0

79.1

82.4

2.0

1.8

2.3

1.7

8.3

4.2

6.5

12.5

4.1

2.8

8.3

3.7

11.0

12.7

16.9

7.3

19.8

16.7

21.2

14.8

16.1

7.5

6.3

6.0

3.4

9.3

10.5

13.2

5.8

4.3

9.9

1.5

6.6

7.4

0.9

6.0

1.3

9.3

10.0

8.2

6.1

1.2

0.8

1.5

—

8.3

2.1

3.3

9.0

2.2

2.1

3.6

1.7

2.7

9.1

6.1

1.9

7.2

6.1

5.3

10.3

5.4

3.7

2.2

2.3

1.0

3.2

4.6

3.7

6.0

6.9

5.2

1.4

2.9

2.6

2,2

1.6

0.4

3.2

2.5

4.4

3.0

2.7

2.6

2.8

13.6

12.1

3.5

4.6

7.6

6.9

7.4

11.5

1.6

4.1

0.4

8.7

—

23.8

5.7

8.2

6.8

1.7

6.2

3.7

3.6

1.2

6.1

6.2

6.2

7.4

5.9

4.9

0.7

4.4

3.9

0.2

12.1

0.4

4.5

2.8

7.2

4.8

8.6

7.4

9.7

22.4

31.3

11.7

15.5

29.9

17.2

16.0

27.7

8.0

18.8

23.8

38.4

17.0

60.8

34.4

43.1

36.1

25.6

26.1

13.0

12.7

5.9

19.7

23.7

23.7

26.2

25.5

21.1

10.1

16.5

15.0

10.6

21.9

2.5

17.9

16.0

20.9

17.6
Chapter 4--The Prevalence and Use of Shift Work ● 75

Total workers Standard

employed work schedule Shift work (percent)

Occupation or industry (thousands) (percent) Evening shift Night shift Rotating shift Total

Transportation and public

utilities. . . . . . . . . . . . . . . . . . . .

Wholesale trade . . . . . . . . . . . . . .

Retail trade . . . . . . . . . . . . . . . . . .

Eating and drinking places . . . .

Finance, insurance, and

real estate . . . . . . . . . . . . . . . . .

Services . . . . . . . . . . . . . . . . . . . . .

Private household . . . . . . . . . . .

Business and repair . . . . . . . . .

Personal, except private

household . . . . . . . . . . . . . . .

Entertainment and recreation .

Professional services . . . . . . . .

Hospitals . . . . . . . . . . . . . . . . . .

Public sector . . . . . . . . . . . . . . . . . . .

Federal Government . . . . . . . . . .

State government . . . . . . . . . . . . .

Local government . . . . . . . . . . . . .

4,958

3,222

9,111

2,242

79.4

91.9

73.7

52.4

6.1

2.9

9.1

21.0

3.5

2.1

3.7

5.3

6.4

0.9

8.6

12.5

20.6

8.1

26.3

47.6

5,003

13,207

345

3,242

93.9

82.9

80.8

87.4

1.9

6.4

7.3

5.8

1.0

3.3

1.5

2.4

1.1

3.9

0.7

3.1

6.1

17.1

19.2

12.6

1,379

529

7,682

2,303

13,268

2,901

3,320

7,047

74.0

66.6

83.8

73.0

87.2

86.2

88.2

87.1

10.1

13.8

5.4

10.5

4.6

6.1

4.3

4.2

3.8

2.2

3.7

6.6

2.0

3.4

2.3

1.3

6.6

7.3

3.6

8.5

3.7

2.8

3.0

4.5

26.0

33.4

16.2

27.0

12.8

13.8

11.8

12.9

SOURCE: E.F. Mellor, “Shift Work and Flexitime: How Prevalent Are They?” Month/y Labor Review 109:14-21, 1986.

Figure 4-3-Four Days With an International Flight Crew

Crews t i m e 1 2: 55 a m

2 am

4 am

6 am

8 am

10 am

Noon

2 p m

4 p m

6 pm

8 p m

10 pm

Midnight

Local time 4:10 p m

Local t i me 8:45 am I

Crew’s time 12:15 p m 7 hrs. 50 reins.

between flight s 15 hrs. 20 reins.

between flight s

Crew’s time 4:00 p m

Crew’s time 9:10 pm

I

3 hrs. bet. flights

Day 1 Day 2 Day 3

\

In flight I—— 1 Between fligh t

International trip schedule for a single flight crew.

SOURCE: Courtesy B. Edmunds, Airline Pilots Association, 1991.
76 . Biological Rhythms: Implications for the Worker

occupations (8).9 More than 38 percent of those

employed full-time in service occupations are

shift workers, compared to the average of 15.9

percent for all full-time employed persons. This

prevalence of shift work in service occupations

holds true among some professional groups; while

only 9.7 percent of full-time professionals overall

are shift workers, 22.4 percent of full-time professionals in health-diagnosing occupations (e.g., doctors and dentists) are shift workers, as are 31.3

percent of professionals in the health assessment and

treatment occupations (e.g., registered nurses and

therapists) (table 4-2).10 Some subgroups among the

service sector exhibit an extremely high prevalence

of shift work. For example, 60.8 percent of full-time

protective service workers (e.g., police and firefighters) are employed during nonstandard hours. Among

persons employed in service-producing industries,

those employed in eating and drinking places (47.6

percent) and in entertainment and recreation (33.4

percent) are especially likely to be shift workers.

Technological advances and the increased importance of global communication and interaction

have become powerful incentives for the addition of

a second and third shift. BLS reported that between

1978 and 1985, the number of clerical personnel

working at night increased three times faster

than the number of all other night workers (4).

Night work among technical and professional office

personnel increased 36 percent during this period.

Competitive pressures, either to accelerate information processing and the services provided by these

industries or to conduct business in different time

zones, are important factors in the increased hours of

work in the office environment. The high cost of

office automation equipment and large computer

centers may lead to an increase in the hours of

operation in order to make the best use of the

investment. Night hours may also be established to

take advantage of less expensive and more readily

available computer time from computer programming and data analysis services (10).

Who Are Shift Workers?

Shift work may have different health and social

effects on men as compared to women, single as

compared to married persons, and parents as compared to nonparents. In fact, some of the advantages

and problems associated with shift work have been

attributed to marital and child-care responsibilities.

This section presents demographic data on the

prevalence of shift work among men, women,

married persons, and persons with child-rearing

responsibilities.

Analysis of data from the CPS supplements and

other sources noted above yields an assessment of

the personal characteristics of shift workers in

relation to regular daytime workers (comparisons

based on self-reporting of full-time wage and salary

earners in 1985) (8) (table 4-3). Among full-time

employed men, 27.4 percent between the ages of 16

and 19, compared to 14.6 percent age 45 and over,

do not work a regular daytime schedule (8). Thus,

younger men are more likely to work nonstandard

schedules than older men. Also, single men are more

likely to be shift workers than married men. Among

fill-time employed single and married men, 21.1

and 16.5 percent, respectively, work nonstandard

hours. Black men are more likely to work nonstandard hours: approximately 22.6 percent of full-time

employed black men are shift workers, compared to

17.3 percent of white men. There is little difference

in frequency of shift work between whites and

persons of Hispanic origin. Although young, single,

and black men are more likely to be shift

workers, older, married, and white men, being

the majority of full-time workers, form the

majority of shift workers.

Gender differences in shift work prevalence

depend on whether full-time or part-time work is

considered. Considering only full-time wage and

salary earners age 16 and over (based on selfreporting), the BLS reports that 17.8 percent of

men and 13.0 percent of women are shift workers

(8) (table 4-3). Since women are more likely than

men to work part-time, gender differences are not

substantial when all employed persons, part-time

and full-time, are considered. As of May 1985

(based on actual work hours), 20.3 percent of men

and 17.1 percent of women age 18 and over in

nonagricultural occupations were shift workers (15).

Men are more likely than women to work night,

miscellaneous, and rotating shifts, whereas women

are more likely than men to work the evening

shift (14).

%Jote that the BLS reports this only for fnll-tirne wage and salary earners, and it is based on the respondent’s designation of the shift worked.

IoShift work prev~ence and patterns in the health professions are considered in detail inch. 8.
Chapter 4--The Prevalence and Use of Shift Work ● 77

Table 4-3--Demographic Profile of Shift Workers

Total workers Standard

employed work schedule Shift work (percent)

Characteristic (thousands) (percent) Evening shift Night shift Rotating shift Total

Age

Men, 16 years and over . . . . . , . . . . 43,779 82.2 6.8 3.0

16 to 19 . . . . . . . . . . . . . . . . . . . . . 1,139 72.6 11.8 4.7

20 to 24 . . . . . . . . . . . . . . . . . . . . . 5,567 80.0 8.5 3.5

25 to 34 . . . . . . . . . . . . . . . . . . . . . 14,281 80.0 7.8 3.3

35 to 44 . . . . . . . . . . . . . . . . . . . . . 10,630 83.6 5.7 2.7

45 to 54 . . . . . . . . . . . . . . . . . . . . . 7,094 85.4 5.3 2.7

55 to 64 . . . . . . . . . . . . . . . . . . . . . 4,594 85.5 5.6 2.1

65 And over.... . . . . . . . . . . . . . . 474 85.4 2.8 2.5

Women,16 years And over . . . . . . . 29,616 87.0 5.5 2.3

16 to 19 . . . . . . . . . . . . . . . . . . . . . 777 71.1 12.8 4.0

2o to 24 . . . . . . . . . . . . . . . . . . . . . 4,346 84.0 6.7 2.0

25 to 34 . . . . . . . . . . . . . . . . . . . . . 9,510 87.5 5.3 2.2

35 to 44 . . . . . . . . . . . . . . . . . . . . . 7,080 88.9 4.8 2.3

45 to 54 . . . . . . . . . . . . . . . . . . . . . 4,753 88.4 4.6 2.2

55 to 64 . . . . . . . . . . . . . . . . . . . . . 2,838 87.3 5.3 2.6

65 And over.... . . . . . . . . . . . . . . 311 85.8 7.3 3.8

Total,16 years and over . . . . . . . . . . 73,395 84.1 6.3 2.7

Race and Hispanic origin

White . . . . . . . . . . . . . . . . . . . . . . . 63,523 84.7 5.8 2.6

Men . . . . . . . . . . . . . . . . . . . . . . 38,588 82.7 6.3 2.9

Women . . . . . . . . . . . . . . . . . . . . 24,935 87.8 5.0 2.1

Black . . . . . . . . . . . . . . . . . . . . . . . . 7,847 80.1 9.8 3.5

Men . . . . . . . . . . . . . . . . . . . . . . 4,054 77.4 10.6 3.7

Women . . . . . . . . . . . . . . . . . . . . 3,793 83.0 8.9 3.2

Hispanic origin. . . . . . . . . . . . . . . . 4,911 84.6 7.1 2.5

Men . . . . . . . . . . . . . . . . . . . . . . 3,184 82.3 7.7 2.8

Women . . . . . . . . . . . . . . . . . . . . 1,727 88.8 5.8 1.9

Marital status

Men

Single, never married . . . . . . . . 9,703 78.9 9.3 3.6

Married, spouse present . . . . . 29,666 83.5 5.7 2.7

Widowed,divorced,

or separated . . . . . . . . . . . . . . 4,410 80.4 8.5 3.6

Women

Single, never married . . . . . . . . 7,109 83.6 6.8 2.3

Married, spouse present . . . . . 15,679 89.9 4.3 1.9

Widowed,divorced,

or separated . . . . . . . . . . . . . 6,828 83.7 7.0 3.3

SOURCE: E.F. MelloL ’’ShiftWork and flexitime: How PrevalentAre They?’’ hfonth/yLaborRetiewlO9fl4-2l ,1986.

4.9

7.0

5.0

5.6

5.0

3.9

3.8

4.0

3.3

9.4

5.1

3.3

2.2

2.8

3.2—

4.3

4.3

5.0

3.3

4.3

5.3

3.2

3.3

4.0

2.0

5.0

5.1

4.0

5.2

2.3

3.6

17.8

27.4

20.0

20.0

16.4

14.6

14.5

14.6

13.0

28.9

16.0

12.5

11.1

11.6

12.7

14.2

15.9

15.3

17.3

12.3

19.9

22.6

17.0

15.4

17.7

11.2

21.1

16.5

19.6

16.4

10.1

16.3

A detailed analysis of the job characteristics of

female shift workers, based on the May 1985 CPS,

included women age 18 and over employed in

various occupations and industries, both fill- and

part-time (15). It therefore focused on the seven

occupations with the highest percentage of women

working freed nights, namely (in rank order),

registered nurses, nurses’ aides, practical nurses,

food preparation and service workers, textile operators, janitors, and cashiers. Over half (58.9 percent)

the women who worked fixed nights were employed

in these seven occupations, and close to half of them

worked evenings (49.1 percent) or a rotating shift

(42.lpercent). In contrast,only 14.8 percent of those

who worked freed days and 19.4 percent of those

who worked a miscellaneous shift (more than 12

hours a day, including split shifts) were in these

occupations. As for industry, 48.3 percent of all

women who worked freed nights in 1985 were in

medical services, compared to 18.0 percent who

worked freed evenings, 20.5 percent who worked

rotating shifts, 9.0 percent who worked miscellaneous shifts, and 11.2 percent who worked freed days.

Among all employed women, 12.9 percent were in

medical services, compared to 3.2 percent of all

employed men.

Since the CPS collects similar data on all household members, it is possible to consider the work
78 ● Biological Rhythms: Implications for the Worker

schedules of husbands and wives jointly when both

are employed (dual-earner couples). From the perspective of a couple, the prevalence of shift work is

high. Based on the May 1980 CPS data, one-fourth

of all dual-earner couples without children and

one-third of all dual-earner couples with children

included at least one spouse who did shift work

(12). An analysis of the May 1985 data for dualearner couples with children showed a similar

proportion (one-third) (16).

A study of full-time dual-earner couples, based on

the May 1980 CPS, showed that although employed

wives are more likely than employed husbands to be

service workers, service work produces a higher

likelihood of shift work among husbands (50.7

percent) than wives (30.3 percent) (12). Within

service occupations, the highest prevalence of shift

work for husbands was among protective service

workers (66.0 percent); the highest prevalence for

wives was in health service (36.7 percent).

Given that couples who are young and couples

who have children are more likely to work nonstandard hours, it is not surprising to find a remarkably

high prevalence of shift work among young dualearner parents with children under age 5. It is

estimated that about 50 percent of all young

couples with children under the age of 5 in the

United States include at least one spouse who

works nonstandard hours (13). This estimate is

based on an analysis of the parents in the National

Longitudinal Study, Youth Cohort, as of 1984, when

they were age 19 to 26. Among those employed

full-time, mothers were about as likely as fathers to

work nonstandard shifts (29.0 and 30.2 percent,

respectively), but there were differences in the type

of shift: fathers were more likely than mothers to

work freed nondays (19.1 percent and 14.8 percent,

respectively), and mothers were more likely than

fathers to work a rotating schedule (14.2 percent and

11.1 percent, respectively). Over one-fourth of all

part-time employed mothers in this sample (26.9

percent) were on rotating schedules, and an additional 14.7 percent were freed nonday workers;

accordingly, about two-fifths of part-time employed

mothers were nonday workers.

An analysis of shift work among women age 18 to

44 with pre-school age children, based on the June

1982 CPS, showed that the prevalence of shift work

was considerably higher among unmarried than

married mothers (11). Thus, among persons with

children, it is both young dual-earner parents

and unmarried employed mothers who are especially likely to be working nonday hours. Whether

these particular subgroups are increasing is unknown.

WHY DO EMPLOYEES PERFORM

SHIFT WORK?

The previous discussion provides evidence that

shift work has a broad demographic sweep, including people of differing age, gender, marital status,

and type of employment. The diversity of individuals working nonstandard schedules suggests that the

motivation, concerns, and needs of these workers are

not uniform. In the following section, the reasons

individuals give for working nonstandard schedules

are discussed.

Why do employees perform shift work? Some

workers prefer nonday work. A survey of workers

from four plants found that most of the permanent

night shift workers prefer to work that shift (22).

Data from the May 1985 CPS, however, suggest that

many individuals do not prefer shift work. Respondents were asked their main reason for working a

nonday shift. Answers were coded into subsets of

voluntary and involuntary reasons. Voluntary reasons included better child-care arrangements, better

pay, better arrangements for care of other family

members, and more time to attend school. Involuntary reasons included inability to get any other job

and requirement of the job. The BLS reported that

only 28 percent of persons not working a regular

daytime schedule gave a voluntary reason (e.g., to

accommodate child care); 72 percent gave involuntary reasons, and 90 percent of these said the

schedule was a job requirement (8).

An analysis of fill-time, dual-earner couples in

the May 1980 CPS also indicates that the type of

employment is exceedingly important in determining an individual’s schedule (12). In this study,

occupational and industrial differences in shift work

were more pronounced than personal characteristics

such as age, race, union membership, or multiple

jobs.

A separate analysis of dual-earner couples with

children considered the reasons why parents were

working nonday schedules (16). It was found that

fathers and mothers differ considerably in their main

reasons for doing so. For only a small minority of
Chapter 4--The Prevalence and Use of Shift Work . 79

fathers the primary reason for working nondays

is child care (5.6 percent) or other family caregiving (2.5 percent), compared to close to a majority

of mothers (34.3 percent for child care and 12.3

percent for other family caregiving). Better pay is

not a common reason for either gender, although it

is more relevant for fathers than mothers.

Among these dual-earner couples, the main reason for working nonstandard hours varies by type of

shift as well as gender. Clearly, it is difficult to

provide care to family members on a regular basis

when one works a rotating shift. Thus, persons who

work fixed nondays are more likely than persons

on a rotating shift to do so primarily in order to

care for children or other family members,

including the elderly. As might be expected, the

age of the youngest child is important: child care is

most likely to be the reason for working nonday

hours when employed wives have children under the

age of 6 (41.9 percent) (16).

SHIFT WORK SCHEDULES

While the traditional work schedule is typified by

40 hours of work during the daylight hours, an

increasing variety of work schedules is in place in

the United States (3,6,18). Shift work schedules

involve working hours outside the standard workday

(8 a.m. to 4 p.m.) (21). The Federal Government

does not collect data characterizing specific shift

work schedules employed by occupations and

industries in the United States. Although the

samples used in the national studies that ask

scheduling questions are large, the actual number of

shift workers in the samples is not sufficiently large

to analyze the different types of schedules. Furthermore, private industry and labor representatives do

not formally collect data concerning shift work and

schedules (20). The dearth of information concerning shift work schedules has led researchers to

conclude that:

. . . neither trade organizations nor labor unions

maintain quantitative data on the type and distribution of shift work practices in their industries. Even

where information on shift schedules was available,

it was cumbersome and complex. . . . More comprehensive data were maintained by the Bureau of Labor

Statistics (BLS) . . . although this information . . . is

woefully inadequate for characterizing industries by

types and distribution of shift systems (l).

Available information suggests that several

hundred shift routines are in place in the United

States (3,18). Several factors contribute to this

variation. Schedules vary significantly among industries and occupations and according to the type

of work performed. Since shift schedules are generally determined at individual work sites, diverse

schedules are found even within a single industry,

reflecting geographic and regional differences (table

4-4). Work schedules are also influenced by certain

laws and regulations (see ch. 6). The Fair Labor

Standards Act of 1938 established the standard

40-hour workweek that now covers nearly 60

percent of all wage and salary workers and is part of

the social norm (18). Another standard has been

derived from many Federal and State statutes, as

well as union contracts: the 8-hour day. These legal

standards bear particularly on schedules involving a

compressed workweek (box 4-A), extended duty

hours, and overtime (box 4-B). Tradition in a

particular occupation or industry, labor costs, and

availability of skilled labor also influence the type of

shift system in place at a work site.

Research suggests that the most common shift

schedule in the United States, especially in the

manufacturing sector, involves working 5 days on a

single shift, followed by 2 days off (2,7). Such a

schedule can involve 8-or 12-hour shifts and 3 (day,

evening, and night) or 2 (day and evening or day and

night) shifts per day, which may be fixed, rotating,

or a combination of the two (partially fixed). Shift

work systems are also employed to cover 7 days a

week of continuous operation, such as in the service

sector or in continuous-process manufacturing. Again,

the length of the scheduled workday may range from

8 to 12 hours. Shifts maybe fixed, partially fixed, or

rotating. Shift rotation may be rapid (3 days) or long

(4 weeks); it may proceed forward (day, evening,

night) or backward (day, night, evening). Other

types of shift scheduling exist, and these may be

increasing in popularity. For example, the compressed workweek, in which employees work approximately 40 hours in fewer than 5 days, is

common in certain employment sectors, and its use

may be expanding (see box 4-A). Irregular scheduling, in which shifts are variable and erratic, is used

in some employment sectors, including the transportation and manufacturing industries (figures 4-2 and

4-3). While data have not been collected to document this work practice, labor representatives have
80 ● Biological Rhythms: Implications for the Worker

Table 4-4-Three Mills and Their Schedules

5-week rotational 8-hour shift schedule: Cosmopolis, WA--pulp/paper mill

(week 5 is a repeat of week 1)

Shift Time

Day 7:30 a.m. to 3:30 p.m. Letters A through D represent groups of workers.

Evening 3:30 p.m. to11 :30 p.m.

Night 11 :30 p.m. to 7:30 a.m.

Fixed-shift 8-hour schedule: operate 7days/week: Adel, GA—panel mill

(employees do not rotate-week 5 Is a repeat of week 1)

5-week rotational 12-hour shift schedule: Valliant, OK—pulp/paper mill

(week 5 is a repeat of week 1)

SOURCE: M. Waters, Weyerhaeuser Co., Tacoma, WA, 1990.

indicated to the Office of Technology Assessment

(OTA) their concern about its increasing use (23).

How specific shift work schedules are selected

at individual work sites in the United States has

not been carefully documented. Schedules may be

dictated by management or, more commonly, derived from discussion between management and

unionized or nonunionized employees. Clearly, the

absence of information concerning specific shift

work systems and how they are derived handicaps

the study of the health, performance, and social

effects of shift work, as well as the derivation of

sound shift work policies.

SUMMARY AND CONCLUSIONS

Shift work, a required dimension of work in any

industrially developed country, encompasses a wide

range of nonstandard work schedules, including

evening work, night work, split or extended shifts,

and rotating shifts. While national data indicate that

shift work is prevalent, there are large gaps in these

data. OTA finds that the Federal Government’s

collection of data pertaining to the prevalence and

use of shift work has not been consistent.

The most recent and comprehensive data, collected by the BLS in 1985, indicate that one out of
Chapter 4--The Prevalence and Use of Shift Work ● 81

.—

Box 4-A—The Compressed Workweek

The compressed workweek (CWW) refers to a schedule in which employees work approximately 40 hours in

fewer than 5 days. A variety of schedules, with a variety of rationales, can be said to constitute a CWW. Typically,

work is performed 10 or 12 hours per day, 3 or 4 days per week, and 3 or 4 days per week are free. Other possibilities

include along break schedule; for example, a schedule of 12-hour shifts may employ a sequence of 4 days on duty,

7 days off duty, 4 days on, 3 days off, 3 days on, 1 day off, 3 days on, and 3 days off. As with all types of shift work,

national data on the prevalence of specific CWW schedules are not available.

The CWW with 12-hour shifts appears to be common in the chemical industry (including petrochemical), the

petroleum industry, offshore oil rigs, and ministeel industries. Other types of employment that could adopt the

CWW include the paper industry, other manufacturing processes, utility industries (including nuclear powerplants),

nursing and other health fields, clerical work, administrative work, technical maintenance, and computer operations.

Information derived from management and employee comments, limited psychological testing, and

performance and safety records has highlighted some of the advantages and disadvantages of the CWW (table 4-5).

In general, the CWW appears to increase worker satisfaction because it allows more days and weekends off. For

example, in one plant, conversion to a CWW schedule with 12-hour shifts reduced the number of days on the job

each year from 273 to 182. Also, when the CWW has 12-hour rotating shifts, fewer consecutive days are spent on

the night shift and there is more time to recuperate than with 8-how shifts 5 days a week. This may lessen the fatigue

associated with rotating shifts and night work (see ch. 5). While more days off may improve employee satisfaction,

concerns about increased moonlighting have been voiced and have been documented in one case. In general,

however, studies have failed to document an increase in moonlighting.

Data have suggested that not all employees endorse the CWW. Family responsibilities and previous work

experience appear to influence preference for the CWW (see figure 4-4). One study estimated that 28 percent of work

sites adopting a CWW will revert to the standard 8-hour day, 5-day week schedule. A few studies have indicated

that women, especially those with young children, and older employees maybe less satisfied with a CWW,

The use of the CWW; especially with two 12-hour

shifts replacing three 8-hour shifts, may be more

cost-effective for employers, since the number of shift

changes is decreased (shift changes are the least

productive time in an operation). Absenteeism also

appears to be diminished when the CWW is adopted.

Replacement of absent employees, however, may be

more difficult with this schedule, since one common

way of replacing an absent employee is holding over

another from a previous shift, which is ill-advised for

shifts of 12 hours.

Concerns over performance and safety have been

voiced in relation to the CWW, although few studies

have analyzed this issue (see ch. 5). It has been

suggested that fewer errors and accidents occur and

productivity improves on CWW schedules. Other

studies suggest that a 12-hour day, 4-day week

produces more fatigue and poorer sleep and psychomotor performance than an 8-hour day, 5-day week.

Administrative problems may arise from the use

of the 12-hour shift and the CWW. Since laws and

regulations regarding hours of work are generally

based on the 8-hour day and 40-hour workweek,

computation of hourly wage and vacation time must be

adjusted, Similarly, since exposure limits to noise,

chemicals, and heat are generally based on the 8-hour

day, they may need to be recalculated.

SOURCE: CMfke of Technology Assessment 1991.

Figure 4-4--Shift Work History and Preference

Percent responding

100

80

60

40

20

0

8-hour 8- and 12- 12-hour

shifts only hour shifts shifts only

Experience with 8- and 12- hour shifts

= Prefer 6 hours ~ Prefer 8 hours

~~ Prefer 10 hours m Prefer 12 hours

Data drawn from a study of 2,115 hourly and salary workers

employed at four industrial sites.

SOURCE: D. Tepas, “Condensed Working Hours: Questions and Issues,”

Stud/es in lndustdalandOrganizatiwd Psychology. Shilhvodc

Healthf S/eepandPerformanca, vol. 9, G. Costa, G. Cesana, K.

Kogi,et al. (eds.) (Frankfurt am Main: Verlag, Peter Lang, 1989).
82 Biological Rhythms: Implications for the Worker

Table 4-5-Potential Advantages and Disadvantages of 12-Hour Schedules

Factor Advantage Disadvantage

Most workers like it, which could result in:

. Increased job satisfaction; less difficulty in recruiting new personnel x

. Improved employee morale x

. Decreased absenteeism due to proportionate loss of pay x

● Sleep time more easily adjusted to two shifts instead of three shifts x

● Decreased attrition (decreased training cost, more experienced operators) x

More days off and more consecutive days off

● Workers like days off and weekends off (75 to 85 more days off) x

. There is more time with family, leisure time, time to conduct personal business x

. Workers take less personal time off x

. Workers lose touch with operations

● Workers might be tempted to moonlight, travel great distances, or engage in

exhausting recreation on consecutive days off and return to work fatigued

x

x

Shift turnovers reduced from 3 per day to 2 per day

● Reduced number of communication errors during shift turnover x

● Improved continuity of operations x

● More chance that the crew that begins a maintenance job or begins an evolution will

be the same crew that ends it. This contributes to quality work and job satisfaction. x

● Reduction in commute time and commute cost by about one-third. x

Within any 1 day, 12 hours of work is more fatiguing than 8 hours of work

● Alertness and safety might decline x

● Because the day is longer, workers might work at a slower pace x

● Workers need more breaks x

. 8-hour night shifts are difficult; 12-hour night shifts are more difficult x

● 12-hour shifts might be more difficult for older workers x

Over several consecutive days, 12 hours of work per day is more fatiguing than

8 hours of work per day

. Less time for rest exists between consecutive workdays; fatigue might accumulate x

● Fewer consecutive workdays and more rest days will dissipate fatigue x

SOURCE: Adapted from U.S. Nuclear Regulatory Commission, IWJREG/Ci?-4248 Recommendations for NRC Po/icy on Shift Schecfu/ing and Overtime at

Nuc/ear Power Plants (Richland, WA: Pacific Northwest Laboratory, 1985).

five full-time workers—approximately 20 million

Americans-is a shift worker. Approximately 2.0

million individuals are night workers, and 3.1

million people work rotating shifts, which may

involve night work. These individuals are most

likely to be employed in capital-intensive manufacturing industries, transportation, and service industries.

Shift work is done by 17.8 percent of men and

13.0 percent of women employed full-time. Data

indicate that young, single, and black men are more

likely to be shift workers; however, older, married,

and white men, being the majority of full-time

workers form the majority of shift workers. While

men are more likely than women to be shift workers,

shift work is highly prevalent among women in

some employment sectors, including nursing and

health services. Data suggest that shift work affects

many families, especially those with young children.

It is estimated that 50 percent of all young,

dual-earner couples with children under the age of 5

include at least one spouse who works nonstandard

hours.

There are hundreds of different shift work schedules in place. However, data concerning the specific

properties of shift work schedules, such as the

involvement of night work, shift length, the number

of consecutive days worked, and the use of rotating

shifts, have not been collected by the Federal

Government, labor representatives, or industry. The

absence of such data severely handicaps the study of

the health, performance, and social effects of shift

work, as well as changes in trends concerning the use

of shift work.

CHAPTER 4 REFERENCES

1.

2.

Colligan, M.J., “Methodological and Practical Issues

Related to Shift Work Research,” Journal of Occupational Medicine 22:163-166, 1980.

Ergonomics Group, Eastman Kodak Co., Ergonomic

Design for People at Work, vol. 2 (New York, NY:

Van Nostrand Reinhold, 1986).
Chapter 4--The Prevalence and Use of Shift Work ● 83

Box 4-1340 Hours Plus: Overtime and Moonlighting

Overtime and moonlighting have always played a significant role in American industry. As is the case with

shift work, working extended hours at one or more jobs may raise performance and safety questions (see ch. 5).

The supplement to the May 1985 Current Population Survey (CPS) provides information on the prevalence

and demography of overtime work. From these data, the BLS estimated that 21.4 million persons work more than

40 hours per week at one job. It was further estimated that 10.5 million Americans receive premium pay for overtime

work usually at the rate of one-and-a-half times their normal pay. With few exceptions, individuals receiving

premium pay for overtime worked more than 40 hours a week: further, they averaged 9.6 hours of overtime. Nearly

two-thirds of these employees reported working 1 to 8 hours beyond 40 hours; 16 percent reported 16 hours or more

beyond 40 hours.

Overtime compensation was more common in certain occupations, including precision production, craft and

repair, and operators, fabricators, and laborers. These groups account for more than half of all workers receiving

premium pay for overtime. Within industry groups, mining, manufacturing, transportation, public utilities, and

construction most commonly receive premium overtime pay. Of the approximately 60 percent of employees not

being compensated for work beyond 40 hours per week most were in managerial, professional, technical, sales, and

administrative support jobs, which are outside the provisions of the Fair Labor Standards Act (see ch. 6).

Overtime may be used by employers to meet unexpected or excessive short-term demand, to fill in for absent

workers, or, when used regularly, as a cost-saving device (i.e., it costs less to pay overtime premiums than to hire

new workers, with their pensions, sick leave, and health insurance benefits). Data indicating the extent to which

overtime work is voluntary or mandatory for employees are lacking.

A supplement to the May 1989 CPS survey addressed the issue of holding more than one job, or moonlighting.

In this survey the CPS defined a moonlighter as an employed person who 1) had a wage- or salary-paying job with

two employers or more, 2) was self-employed and also held a job paying a wage or salary, or 3) worked as an unpaid

family worker on the primary job (the one at which the greatest number of hours are worked) and had a secondary

job paying a wage or salary.

It was estimated that 7.2 million persons hold two or more jobs, which is a 52 percent increase from 1980.

Among men, 4.1 million, most of them married, moonlight. Of men with more than one job, 82+8 percent hold one

full-time job and one part-time job; 11.3 percent hold two part-time jobs; and 5.8 percent work two full-time jobs.

On average, men holding two jobs work a total of 55.8 hours per week.

This survey indicated a sharp increase in the number of women working multiple jobs. Some 3,1 million

women hold more than one job, averaging 47.1 hours of work per week. Women makeup 43 percent of all persons

holding multiple jobs, in contrast to an estimated 15 percent in 1970. Among women who moonlight, 64 percent

hold one full-time job and one part-time job; 33 percent hold two part-time jobs; and 2.9 percent hold two full-time

jobs. Most women with more than one job were widowed, divorced, or separated.

Individuals work more than one job for various reasons. Among the reasons were the following: to meet regular

expenses (35.5 percent); to pay off debts (8.9 percent); to save for the future (16.2 percent); and to gain experience

in a different occupation (14.7 percent). The highest rates of moonlighting were found in public administration (8.8

percent), service industries (7.8 percent), educational services (11.1 percent), and male protective service workers

(11.8 percent).

SOURCES: D.E. Carr, “Overtime Work: An Expaded View,” Monthly Labor Review 109:36-39, 1986; J.F. Stinsoq Jr., “Multiple Job

1301ding Up Sharply in the 1980s,” A40nthly Lubor Review 113:3-10, 1990.

3. Flaim, P. O., “Work Schedules of Americans: An Scheduling, S. Folkard and T.H.. Monk (eds.) (New

Overview of New Findings,’ Monthly Labor Review

109:3-6, 1986.

4. Hagen, R. P., “Why Not Add a Night Shift,”

Administration Management, 47:32-33, 1986.

5. King, S. L., and Williams, H. B., “Shift Work Pay

Differentials and practices in Manufacturing,’ Monthly

Labor Review 108:26-33, 1985.

6. Kogi, K., “Introduction to the Problems of Shift

Work,” Hours of Work: Temporal Factors in Work

York, NY: John Wiley & Sons, 1985).

7. Kroemer, K. H. E., Kroemer, H. J., and KroemerElbert, K. E., “Engineering Physiology: Basis of

Human Factors/Ergonomics, ” Work Schedules and

Body Rhythms, 2d ed. (New “fork, NY: Van Nostrand

Reinhold, 1990).

8. Mellor, E. F., “Shift Work and Flexitime: How

Prevalent Are They?’ Monthly Labor Review 109:14-

21, 1986.
84 ● Biological Rhythms: Implications for the Worker

9.

10.

11.

12.

13.

14.

15.

16.

Norwood, J.L., “Distinguished Lecture on Economics in Government: Data Quality and Public Policy,’

Journal of Economic Perspectives 4:3-12, 1990.

Polston, M.V., “Staffing Your 24-Hour Computer

Center,” Datamation 33:75-76, 1987.

Presser, H.B., “Shift Work Among American Couples: The Relevance of Job and Family Factors,”

Night and Shift Work: Long-Term Effects and Their

Prevention, M. Haider, M. Keller, and R. Cervinka

(eds.) (Frankfurt am Main: Verlag Peter Lang, 1986).

Presser, H. B., “Work Shifts of Full-Time DualEarner Couples: Patterns and Contrasts by Sex of

Spouse,” Demography 24:99-112, 1987.

Presser, H. B., “Shift Work and Child Care Among

Young Dual-Earner American Couples,’ Journal of

Marriage and the Family 50:133-148, 1988.

Presser, H. B., “Can We Make Time for Children?

The Economy, Work Schedules, and Child Care,”

Demography 26:523-543, 1989.

Presser, H. B., “The Growing Service Economy:

Implications for the Employment of Women at

Night,” Studies in Industrial and Organizational

Psychology. Shiftwork: Health, Sleep and Performance, vol. 10, G.C. Cesana, K. Kogi, and A.

Wedderburn (eds.) (Frankfurt am .Main: Verlag Peter

Lang, 1990).

Presser, H.B., “The Complex Work Schedules of

Dual- Earner Couples in the United States: Choice or

Necessity?” paper presented at the Annual Meeting

17.

18.

19.

20.

21.

22.

23.

24.

of the American Sociological Association, Washington, DC, Aug. 11-15, 1990.

Presser, H. B., “Work Schedules and the Gender

Division of Household Labor,” paper presented at

the Annual Meeting of the National Council on

Family Relations, Seattle, WA, Nov. 9-11, 1990.

Smith, S.J., “The Growing Diversity of Work

Schedules,” Monthly Labor Review 109:7-13, 1986.

Stinson, J.F., Jr., “Moonlighting by Women Jumped

to Record Highs,” Monthly Labor Review 109:22-

25, 1986.

Taste, D. L., and Colligan, M.J., Shift Work Practices

in the United States, DHEW Pub. No. 77-148

(Washington, DC: U.S. Government Printing Office,

1977).

Tepas, D.I., “Flexitime, Compressed Work Weeks

and Other Alternative Work Schedules,” Hours of

Work: Temporal Factors in Work Scheduling, S.

Folkard and T.H. Monk (eds.) (New York, NY: John

Wiley & Sons, 1985).

Tepas, D. I., and Mahan, R.P., “The Many Meanings

of sleep, “ Work and Stress 3:93-102, 1989.

U.S. Congress, Office of Technology Assessment,

proceedings of the workshop “Shift Work and

Extended Duty Hours,” Washington, DC, May 23,

19900

U.S. Department of Labor, Bureau of LaborStatistics

Summary 81-13 (Washington, DC: September 1981).
Chapter 5

Biological Rhythms and

Work Schedules
Contents

WORK SCHEDULES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

METHODOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

STRESSORS CAUSED BY WORK SCHEDULES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Disruption of Circadian Rhythms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Sleep Disruption and Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Social and Domestic Disturbances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

CONSEQUENCES OF WORK-RELATED STRESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

INTERVENTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

Work Schedules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

Sleeping and Napping Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Medication and Drug Therapies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Employee Education and Clinical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Fitness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

RESEARCH NEEDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

CHAPTER 5 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Boxes

Box Page

5-A. Night Shift Paralysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

5-B. The Grounding of the Exxon Valdez . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

5-C. The Philadelphia Police Story . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

5-D. Astronauts and Bright Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Figures

Figure Page

5-1.

5-2.

5-3.

5-4.

5-5.

5-6.

5-7.

5-8.

5-9.

5-1o.

5-11.

Table

Relationship of Body Temperature, Work, and Sleep on a Permanent Night Shift . . . . . . 90

Relationship of Body Temperature, Work, and Sleep in a Rapily Rotating Schedule . . . 91

Length of Sleep of Permanent and Rotating Shift Workers . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Sleep Duration and Fatigue in Aircrews During a 4-Day Trip . . . . . . . . . . . . . . . . . . . . . . . . . 94

Length of Sleep of Permanent Night Shift Workers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Shifts Interfering With Eating Habits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97

prevalence of Disease in Shift Workers and Day Workers . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Work Performance in Various Job Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Fatigue-Related Vehicular Accidents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

Measures of Performance on 8-Hour and 12-Hour Shifts . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

Effects of Bright Light on the Adjustment of One Worker to Shift Work . . . . . . . . . . . . 109

5-C-1. Original and Newly Instituted

Table

Page

Schedules for the Philadelphia Police Study . . . . . . . . . 104
Chapter 5

Biological Rhythms and Work Schedules

As discussed in chapter 3, disruption of biological

rhythms can result in physiological changes that

adversely affect both health and performance. In the

workplace, certain types of work schedules can

require persons to work at inappropriate points in the

circadian cycle and cause disruptions of biological

rhythms, notably circadian rhythms. However, in

these situations, the physiological changes caused

by disruption of circadian rhythms often interact

with other stressors associated with work schedules

(fatigue, sleep deprivation, and social or domestic

stress) to compound the effects. This chapter discusses these interactions, their consequences, and

possible interventions to prevent them.

WORK SCHEDULES

The characteristics of work schedules that can be

varied include the length of the work period, the

placement of the work period in the 24-hour day, the

regularity of that placement, the speed at which the

placement changes, and the ratio of work time to rest

time. Any schedule that requires workers to work

when they would normally be sleeping (and

sleeping when they would normally be awake)

can disrupt circadian rhythms (31). This includes

schedules that require workers to constantly change

the hours that they work or to work for extended

periods of time.

Shift work is not new (103,144). Historically,

bakers have worked through the night to ensure fresh

bread in the morning, and in ancient Rome deliveries

were restricted to the night hours in order to relieve

traffic congestion. With the initiation of the Industrial Revolution, more and more work processes

required fill-time operation. Since then, there has

been an increase in the prevalence of shift work as

industrial needs for 24-hour operations combined

with more and more service industries providing

evening or around-the-clock coverage.

Thus, the person will frequently be changing the

scheduled hours he or she works. In a fixed shift

schedule, the worker always has the same work

hours.

Work that continues for long periods of time

(i.e., usually beyond 12 hours) and causes workers to decrease or miss their normal sleep is

considered extended duty hours. Often there is not

a clear distinction, or there is overlap, between shift

work and extended duty hours. For example, workers on a rotating shift schedule may work overtime,

exposing them to both extended duty hours as well

as the rotating shift. Extended duty hours can lead to

disruptions in circadian rhythms that interact with

other factors, especially loss of sleep and fatigue, to

affect health and performance. (Sleepiness is the

inclination to sleep, whereas fatigue is weariness due

to physical and mental exertion.) It is possible to

experience one without the other, but both, either

alone or in concert, can have deleterious effects. This

is especially true if such work schedules are consistently marked by extended work periods interspersed with relatively short rest periods and are

irregularly scheduled. Examples of occupations that

involve extended duty hours are medical and surgical residencies at hospitals, military operations,

long-haul trucking runs, and any setting in which

there is frequent overtime work.

As described in chapter 4, a variety of shift

schedules are used in work settings, including

schedules of fixed or rotating shifts. In a rotating

shift schedule, the individual works one shift for

a period of time before rotating to the next shift.

–87–
88 . Biological Rhythms: Implications for the Worker

METHODOLOGY

Because the effects of work schedules are

sometimes subtle and involve a number of factors, they can be difficult to study. Frequently, the

most important variables are those that occur outside

the workplace (e.g., quality of sleeping during the

day, social effects), thus research relies to a large

extent on self-report and anecdotal information.

Three basic classes of studies have been used to

examine effects of work schedules: 1) field studies,

2) survey studies, and 3) laboratory studies.

Field studies, in which the researcher studies

subjects in their actual work environment, are

comparatively rare in the world literature and

largely absent from the U.S. literature because of

the high cost and difficulty of getting substantive

physiological, production, or subjective measures

from a group of workers for a reasonable period of

time (e.g., one complete cycle of a rotating shift

schedule). Field studies often have a small sample

size and require a dedicated group of volunteer

subjects if circadian rhythm or sleep variables are to

be measured properly. Such studies can provide an

invaluable picture of what is happening to the sleep,

circadian rhythms, and performance of shift workers

under various conditions. An example of field

studies that have been carried out in the United

States are those conducted by the National Aeronautics and Space Administration (NASA) on fatigue,

sleep, and circadian rhythms in flight crews. Field

studies in other occupations have been carried out in

Sweden (5), West Germany (84), the United Kingdom (158), and France (129).

Physiological measures taken in field studies are

typically in the domains of circadian rhythms and

sleep. Body temperature is the preferred variable in

measures of circadian rhythms because it is easily

measured and reliable in indicating the status of the

circadian system. Ideally, sleep is measured by

directly monitoring physiological functions (e.g.,

brain activity, eye movements, muscle activity)

during sleep, but this is often impractical, so

subjective measures, such as sleep diaries or sleep

questionnaires, are used. Another method, which has

been used more recently, is wrist activity monitors

worn by workers to collect information on activity

levels, from which amounts of sleep are inferred

(128). Mood, social and family factors, and performance can be measured by self-report tests, sometimes

augmented by measures of on-the-job performance.

Survey studies are considerably easier to conduct and usually involve questioning the worker

in one or two interviews or classroom-type

sessions. These data are augmented by data from

personnel, health service, and absenteeism files and

a review of production figures. Neither circadian

rhythm nor sleep diary measures can be obtained

directly in survey studies. Data on these variables are

gleaned from questions about perceived levels of

alertness while on duty and average timing and

quality of sleep after various shifts. Survey studies

are often carried out before and after an intervention

in order to assess its impact (36). Contamination b y

placebo effects,l which can endanger the validity of

outcomes, is a problem that needs to be carefully

controlled for in survey studies (116).

Laboratory studies attempt to simulate the

workplace in a controlled situation. In some cases,

workers are used as subjects, but since that is often

impractical, studies usually use other individuals as

subjects (86,175). The major advantage of laboratory studies is that they are the best way to get

accurate, clear, and complete recordings of sleep and

circadian rhythms (and mood and performance

measures) without all of the interference and missing

of readings that are so characteristic of field studies.

The disadvantage is that some factors that play a role

in the real work situation (e.g., social and domestic

strains, the length of exposure to the schedule being

studied) and the types of stress experienced may not

be replicated exactly. Another important consideration in laboratory studies is the nature of the task the

subject is to perform. In some cases, when general

information about the effects of a work schedule on

variables such as performance, alertness, and vigilance is desired, standardized tasks and tests can be

used. However, in studies of the effects of a schedule

on a specific type of job, simulators are used to

recreate the work environment. For example, simulators that replicate an aircraft cockpit, a nuclear

powerplant control room, or an air traffic control

tower are effective aids in the study of the effects of

work schedules on worker performance during

specific job-related tasks.

l~e place~ effect is when an htervention that has no real, direct action results in an effecti e.g., when a subj=t reports fee~g better after ~v~g

been given a sugar pill. The effect is due not to the intervention but to the subject’s anticipating an effect from the intervention.
Chapter 5--Biological Rhythms and Work Schedules ● 89

STRESSORS CAUSED BY WORK

SCHEDULES

Human beings are essentially diurnal creatures,

whose internal clocks are naturally geared toward

sleep and inactivity at night and activity and

wakefulness during the day. Because of this, the vast

majority of human society is structured with the

expectation that work will be done during the day,

recreation in the evening, and sleep during the night.

Morning and evening rush hours are catered to by

mass transit; prime-time television, sports events,

and social gatherings occur in the evening; and a

quiet environment is enforced at night. Social

taboos, for example, protect a day worker’s sleep

from nonemergency telephone calls at 2 a.m., but

none protects a night worker’s sleep from 2 p.m.

calls. Thus, the shift worker is very often fighting

both the natural diurnal trend and sociocultural

attitudes.

Consequently, there are three sources of stress, or

stressors, for the shift worker:

~ disruption of circadian rhythms,

. disruption of sleep and fatigue, and

● social and domestic disturbances.

These stressors act alone and in combination to

produce adverse effects on the worker. The first two

are physiological effects associated with the hours of

work and the length of the work period. The third can

result from the worker’s interactions at home and

with the rest of society as a result of the work

schedule. How much stress these three sources

place on the worker varies with the nature of the

work situation and the work schedule. For the

person working extended duty hours, sleep loss and

fatigue may be the most salient factor, while for the

rotating shift worker, circadian disruptions may be

as important.

The impact of these stressors and their resultant

consequences may, in some individuals and some

situations, lead to difficulties in coping with the

work schedule. There is great variability among

people in their ability to adjust to shift work, with

some individuals suffering few, if any, problems

and others finding certain work schedules intolerable. It should be kept in mind, however, that even

those individuals who appear to adjust well to shift

work may experience negative effects on factors

such as performance or safety. Also, for some individuals, some of the nonphysiological characteristics of shift work (e.g., improved access to daytime

services, more time with young children, a sometimes lighter workload, higher pay) may be positive

attributes. For others, the negative factors associated

with shift work make adaptation difficult. In a study

of 9,000 shift workers, it was found that 20 percent

had difficulty adapting to shift work (140). This

percentage rises as one moves to older age groups.

In a study of an Austrian oil refinery, it was found

that more than 80 percent of the sample expected to

be unable to continue shift work until retirement

(88).

Disruption of Circadian Rhythms

As previously mentioned, work schedules can

have two consequences related to circadian rhythms.

First, a schedule may require that an individual be

awake and active at an inappropriate time during the

circadian cycle. Second, work schedules can result

in a state in which the individual’s circadian rhythms

are out of synchrony. As described in chapter 3, the

circadian system is kept on track by an entrainment

mechanism that uses time cues in the environment

(light-dark) and the behavior of the individual

(social interaction, meal times, sleep-wake schedule,

and so on). This entrainment mechanism keeps an

individual’s circadian cycles aligned and in tune

with the 24-hour rotation of the Earth. The process

of adjustment to the abrupt, large changes in routine

caused by shift work is slow, typically taking a week

or more (82,108,175) (figure 5-1). Not only does the

inherent inertia of the circadian system slow adaptation to a work schedule, the presence of competing

time cues (e.g., light-dark. social cues) further slows

the adjustment process.

Irregular work schedules (e.g., those routinely

experienced by locomotive engineers) and schedules

that involve frequent crossing of time zones (transmeridian airline crews) result in chronic circadian

desynchronization. In rotating shift work, although

the rotation schedule is freed and regular, the length

of time spent on a given shift may not be sufficient

to allow for complete resynchronization of the

circadian system. In weekly rotations, complete

re-entrainment may never occur, and the worker may

be in a perpetual state of circadian desynchronization (150). In a rapidly rotating schedule (1 to 3 days)

shift changes occur so quickly that the circadian

system does not have enough time to begin resynchronizing before the next rotation change; as a
90 ● Biological Rhythms: Implications for the Worker

result, the worker’s cycles remain diurnal (figure circadian cycles never actually takes place in shift

5-2). However, the individual will be out of syn- work due to the competing influences of cues in the

chrony when he or she is working on the night shift. society telling workers that they are on an abnormal

Some researchers (56,82) maintain that, regard- schedule. Even in permanent night shift work, if the

less of rotation length, complete realignment of worker does not maintain the same schedule on days

Figure 5-l—Relationship of Body Temperature, Work, and Sleep

on a Permanent Night Shift

1 Sleep Work Sleep

37.5

37.0

36.5

Reference day

36.0 I I 1 I I 36.0 /

3rd night shift

1 I I I

37.5

37.0

36.5

6 am Noon 6 pm Mid- 6 am

night

I Sleep Work

\

— — ———

36.0 1st night shift

I 1 I r 1

6

37.5

I

37.0

36.5

1

am Noo n 6 pm Mid- 6 am

night

Sleep Work

36.0 2nd night shift

I I 1 I 1 6 am Noon 6 pm Mid- 6 am

night

37.5

37.0

36.5

36.0

6 am Noon 6 pm Mid- 6 am

night

Sleep Work

-~

7th night shift

6 am Noon Mid- 6 pm 6 am

night

I Sleep Work

37.5

37.0

36.5

I

36.0 21st night shift

I I I I I

6 am Noon 6 pm Mid- 6 am

night

Time of day

Graphs showing average body temperature of workers on the day preceding the start of night work and

on days on the night shift. By the seventh night, body temperature has synchronized to the night

schedule.

SOURCE: Adapted from S. Folkard, D.S. Minors, and J.M. Waterhouse, “Chronobiology and Shift Work: Current

Issues and Trends,” Chronobio/ogia 12:31-54, 1985.
‘(

Chapter 5--Biological Rhythms and Work Schedules ● 91

38.0

37.5

37.0

36.5 1

Figure 5-2—Relationship of Body Temperature, Work, and Sleep

in a Rapidly Rotating Schedule

Work Sleep — -— — .

1st morning shift

6 am Noon 6 pm Mid- 6 pm

night

Work Sleep —— — — -

38.0 -

37.5 -

37.0 -

36.5- 2nd morning shift

1 I I I

6 am Noon 6 pm Mid- 6 am

night

Sleep Work

— —————

38.0-

37.5-

\

37.0-

36.5 1st afternoon shift

I I I

Sleep

\

1 ---

6 am Noon 6 pm Mid- 6 am

night

Sleep Work Sleep — — ——— +

38.0-

37.5-

\

37.0-

36.5- 2nd afternoon shift

1 I I I

6 am Noon 6 pm Mid- 6 am

night

38.0

37.5

37.0

36.5

Sleep

1st night shift

I I I

6 am Noon 6 pm

I Sleep

Work

-—— —.

\

T

Mid- 6 am

night

Work

I n

~-– – – -1

1 zna nlgnl snl 36.5 + ,

I I A : . , . , .ft’

I 1

I I I I I

6 am Noon 6 pm Mid- 6 am

night

Sleep Sleep

38.0-

37.5-

37.0- UL

36.5- 1st day off

I I 1 I

6 am Noon 6 pm Mid- 6 am

night

38.0

37.5

37.0

36.5

6 am Noon 6 pm Mid- 6 am

night

Time of day

Graphs showing average body temperature of four workers on a 2-2-2 rotating shift system. On the night

shift, the low point of body temperature coincides with the work period.

SOURCE: S. Folkard, D.S. Minors, and J.M. Waterhouse, “Chronobiology and Shift Work: Current Issues and Trends,”

Chronobiologia 12:31-54, 1985.

297-935 - 91 - 4 QL 3
92 . Biological Rhythms: Implications for the Worker

off as on workdays, he or she will rapidly revert to

the natural diurnal orientation (105,165). In such

circumstances, the circadian system never fully

synchronizes to the night schedule.

A desynchronized circadian system produces a

number of effects on the individual. First, since the

circadian system sets the time for sleep and wakefulness, a disrupted circadian system will interfere with

both sleep and daytime functioning. Daytime sleep

will be disrupted by daytime mechanisms, and the

ability to stay awake at night will be impaired by

circadian functions that are normally associated with

sleeping (5,7,56). In some tasks, particularly monotonous ones such as driving, vigilance, monitoring,

and quality control, this may lead to decrements in

performance that compromise productivity and safety

(42,57,108). Second, as discussed in chapter 3, the

ability to perform certain types of tasks is also on a

circadian cycle. A desynchronized circadian system

results in the person’s attempting to perform certain

tasks at a time in the circadian cycle when his or her

ability to perform those tasks is not optimal (56).

Finally, an inappropriately synchronized circadian

system is in a state of disharmony akin to that of a

symphony orchestra without a conductor. The disharmony itself may result in feelings of malaise and

fatigue, as well as certain gastrointestinal symptoms

(37,140).

The degree to which individuals are affected by

circadian disruption varies (132). There is often an

interaction between aging and circadian rhythms,

which would indicate a greater susceptibility to

rhythm disturbances with age (see ch. 3) (80). These

factors suggest that some people may be better

able to tolerate the circadian desynchronization

associated with shift work than others.

Sleep Disruption and Fatigue

Schedules that require work during nighttime

hours are associated with sleepiness and fatigue.

About 60 to 70 percent of workers on rotating shifts

complain of sleep disruption (141), and general

fatigue is reported more frequently by shift workers

than by day workers (5). In a study of diverse

occupational settings that included steel workers,

meteorologists, and police, 80 to 90 percent of the

subjects reported that they experienced fatigue

during night work (6). Sleepiness is generally

associated more with the night shift than the

morning and afternoon shifts. The most common

complaint is the inability to sleep as long as

necessary during the day (2). Permanent night

workers also have shortened sleep, although to a

lesser extent than rotating shift workers (38,172)

(figure 5-3). Sleep disturbances and fatigue can

occur as a result of the irregular hours typically

worked by railroad engineers (154,159), the work

schedules and jet lag experienced by commercial

airline pilots (64,67), the watch schedules aboard

merchant ships (142), and the extended on-call

schedules of resident physicians in hospitals. Any

job involving long work periods, whether as a result

of overtime or as part of the regular schedule, can

result in sleep loss and fatigue (box 5-A).

A worker’s sleep can be disrupted by both

endogenous and exogenous factors. As mentioned

earlier, the endogenous factors stem from the

desynchronized circadian system, which has failed

to prepare the body and mind for sleep and wakes the

system up before 7 or 8 hours of restful sleep have

been obtained (5,56). Often, workers will complain

of being wakened by exogenous factors (e.g., traffic

noise, children playing), whereas in reality it is their

desynchronized circadian system that is the culprit

(4,59). Workers will also experience fatigue and

sleep loss from any work schedule that requires them

to stay up for long hours.

Exogenous factors can be just as big a problem.

The daytime environment is much less conducive to

sleep than the nighttime. Daylight can intrude on

Figure 5-3-Length of Sleep of Permanent and

Rotating Shift Workers

Hours

8 1

6 -

4 -

2-

0’

A B c D

= Day = Afternoon, evening m Night

Average sleep lengths on different shifts for two samples of

permanent (A,B) and rotating (C,D) shift workers. Rotating shift

workers on the night shift had the shortest average sleep lengths.

SOURCE: M. Colligan and D. Tepas, “The Stress of Hours of VWk,”

Ameiican Indstrial Hygiene Assoa’athn Journal 47;S86-695,

19s6.
Chapter 5--Biological Rhythms and Work Schedules . 93

Box 5-A—Nigbt Shift Paralysis

One consequence of sleep deprivation is the occurrence of a ram phenomenon known as night shift paralysis.

This condition is marked by a momentary paralysis, usually lasting about 2 minutes, during which individuals are

aware of their surroundings but are unable to make voluntary movements. Night shift paralysis has been observed

in studies of nurses, naval officers, printers, and air traffic controllers and is associated with high levels of sleepiness.

In a study that looked at night shift paralysis in 435 air traffic controllers from 17 countries, 26 claimed tohave

experienced night shift paralysis at some time during their careers. A total of 75 incidents was reported by these

26 controllers. The researchers conducting the study calculated that the potential for an accident resulting from an

occurrence of this paralysis is 0.5 time in each individual’s working life. No accidents or near misses were associated

with any of the episodes of night shift paralysis reported in this study.

Factors identified as contributing to the occurrence of night shift paralysis include time of night, the number

of consecutive night shifts the person had worked, and having worked both a morning and a night shift on the same

day. Of the 75 reported incidents, 56 took place during the night shift, 12 during the day shift, and 7 during the

morning shift. Interestingly, it was observed that individuals who were more rigid in their sleeping habits were more

likely to experience night shift paralysis than persons who were able to fall asleep at unusual times. This seemingly

paradoxical finding maybe due to the fact that flexible sleepers may suffer less sleep deprivation when working

shifts (see text),

The researchers concluded that the incidence of night shift paralysis maybe a useful reflection of the extent

of sleep deprivation. They also suggested that its occurrence maybe reduced by limiting the number of successive

night shifts to one and by not allowing an individual to work both a morning and a night shift on the same day, Thus,

while night shift paralysis is an extremely uncommon event, it does illustrate how work schedules can cause sleep

deprivation, with potentially far-reaching effects.

SOWRCl% S. Follrard and R. Condoni “Night SMt Paralysis in Air Traffk Control Clf33cers,” Ergonomics 30:1353-1363, 1987.

sleep if the sleeping quarters are not sufficiently morning or afternoon shifts, but depending on the

darkened. Households are noisier, and there is a

much greater chance of interruption from telephones

ringing, televisions playing, and general activity

both inside and outside the home. In addition, the

worker may feel compelled to interrupt sleep voluntarily in order to meet family and social demands

that occur during the day (101,153). Consequently,

day sleep is much more susceptible to disruption by

domestic commitments (shopping, child care, and so

on) than is night sleep. Very often, social and

domestic disharmonies (see later discussion) tend to

develop because family members get blamed for

sleep disruptions that may not be entirely their fault.

In addition, if a shift worker takes on another job, the

likelihood that he or she will set aside adequate time

for sleep diminishes further.

The net effect of these sleep disruptions is lack

of sufficient sleep, which often results in a state of

chronic fatigue and sleepiness referred to as sleep

debt (5). This is especially true for rotating shift

workers while they are on the night shift, permanent

night workers, and individuals who are routinely

subjected to long and irregular hours of work that

extend into the night. For rotating shift workers,

there may be some respite while they are on the

design of the schedule, the degree to which they

recoup the sleep lost during the night shift will vary.

Sleep debt has important implications for worker

performance, safety, and health (figure 5-4).

Individuals vary in their ability to sleep. Some

people are more rigid in their sleep habits and have

trouble sleeping at unusual times, while others seem

to be more flexible in their ability to sleep at odd

times. Some evidence suggests that people who find

it easier to sleep at odd times may have an easier

adjustment to the disruptions in sleep that can occur

from work schedules (33,57).

Social and Domestic Disturbances

Work schedules may induce stress by preventing the worker from fulfilling important family

roles (167). Social companionship, parenting, and

sexual partner roles can all be compromised by work

schedules. These effects may be major and can

severely affect mood, motivation, and sleep, therefore having indirect effects on performance and

safety. Marital problems, excessive domestic load,

and community alienation have all been documented

as a result of the strain placed on workers by work
94 ● Biological Rhythms: Implications for the Worker

Figure 5-4-Sleep Duration and Fatigue in Aircrews

During a 4-Day Trip

A.

Sleep duration (hours)

87

7.5-

7 -

6.5-

6 -

5.5-

5

Pretrip Trip

B

T

Posttrip

T

schedules. A survey of 1,028 married couples in the

United States found that shift work is associated

with lower-quality family time and more frequent

family conflicts (148). Another study found that

shift work increased the probability of divorce from

7 to 11 percent over the 3-year period of the study

(178). A more dramatic effect was reported in a

study of 1,490 workers (152) in which an almost 50

percent increase in divorce and separations was

found among those on freed night shifts compared to

morning and evening shifts. When asked whether

they were satisfied with the amount of time they had

available to spend with family and friends, workers

on night or evening shifts were about half as likely

to respond “yes” as their morning shift colleagues.

Similar findings come from Europe and Scandinavia. In a 15-year study of 504 Swedish paper mill

workers (87), the divorce rate among shift workers

was double that of day workers.

Excessive domestic workload represents a major

source of stress from shift work for women workers.

Married women are often expected by their husbands to continue to run the household, raise the

children, and do domestic chores; shift work can

/

compound this burden (63). For these women there

is usually insufficient free time available for household duties, and time is therefore borrowed from

sleep. It has been observed that female night workers

I I I I

1 2 3 4

Day of trip

A) Self-reported sleep duration of aircrews on a 4-day trip and the

? days preceding and following the trip. B) Subjective ratings of

fatigue during the trip.

SOURCE: Adapted from R.C. Graeber, “Aircrew Fatigue and Circadian

Rhythms,” Human Factors in Aviation, El. Weiner and D.C.

Nagel (eds.) (San Diego, CA: Academic Press, 1988).

with- two children slept about 9 hours less per week

than their unmarried female colleagues (63).

With the increase in dual-income families, a more

common mode of arranging child care is for spouses

to work different shifts (113,125). This splitting of

child-care responsibilities between two working

individuals also extends to nonspouse care givers. A

study showed that one-third of grandmothers who

provide child care for their grandchildren, and who

are employed, work a different shift than the

children’s mothers (126).

Finally, social problems are encountered by

shift workers. Society is geared toward a Monday

to Friday, daytime work schedule. Several researchers (167) have found that shift workers may feel

alienated from the community because they are

unable to attend evening educational, sports, or

religious meetings or weekend recreational events.

Team or club membership becomes difficult because

of irregular attendance, and few shift workers hold

office in clubs and. societies. The shift worker can

feel left out of community benefits and opportuni-
Chapter 5--Biological Rhythms and Work Schedules ● 95

Photo credit: David Liskowsky

Obtaining adequate sleep during the day is often difficult

for the shift worker.

ties. Such effects are much less frequent in company

towns, where shift work is the rule rather than the

exception, and as a consequence nonstandard work

schedules are considerably better tolerated (174).

CONSEQUENCES OF WORKRELATED STRESSORS

The three stressors previously described (circadian rhythm disruption, sleep disruption, social

and domestic disturbances) can combine to cause a

variety of problems for the worker. The degree to

which a person suffers from the consequences of

work-related stressors varies greatly among individuals. At the present time, not enough is known to

make a definite statement about who will or will not

be able to cope with shift work. As was mentioned

earlier, the ability of a person to adjust to circadian

disruption and sleep disturbances may affect his or

her ability to tolerate the demands caused by work

schedules. For example, circadian rhythm patterns

are not the same in all people. Some people have

consistently longer free-running periods and a wider

amplitude between their maximum and minimum

daily body temperatures. Evidence suggests that

these individuals are better able to tolerate shift work

than persons with naturally shorter free-ruming

periods and a narrower body temperature range

(20,129,130,131). However, it is not clear if these

characteristics are a benefit in all shift work schedules.

Other characteristics related to sleep habits and

personality have been combined to divide people

into two categories. It has been hypothesized that

these categories may have some validity in predicting success in coping with work schedules. A

morning person is someone who gets up easily and

is active in the morning, has a hard time sleeping

late, and falls asleep quickly in the evening. In

contrast, an evening person is more alert at night,

able to sleep late in the morning, and takes a long

time to fall asleep at night. It is thought that the

evening person is more adaptable to varying work

schedules (106,1 10,120). Additional information is

needed to test the validity of this hypothesis and to

identify more clearly variables that might make

some individuals better able to cope with changing

work schedules than others.

Another important factor in determiningg who will

cope best with shift work is age. As one ages, the

internal clock and sleep patterns change (figure 5-5).

The internal clock may become harder to reset with

age, and sleep becomes more fragile and easily

disrupted. These effects usually begin to occur after

the age of 45. For example, a survey of rotating shift

workers found that older workers (45 to 60 years old)

had more difficulty adjusting to night and afternoon

shifts than did younger workers (79). It is not

uncommon for a person who has been working shifts

all of his or her career without undue strain to start

having trouble coping as he or she gets older. A

variety of health problems can appear with age and

can add to the difficulty of coping with shift work

(109).

While these factors suggest who might be best

suited for shift work, the combined effects of

these and other factors (e.g., physical ailments,

family and social status) increase the variability

of individuals’ ability to cope with shift work (90).

As a result, for some people, shift work is only an
96 ● Biological Rhythms: Implications for the Worker

Figure 5-5-Length of Sleep of Permanent

Night Shift Workers

420-

4oo -

380-

360-

*

340

1 I

3204 1 I 1 1

18-29 30-39 40-49 50-59

Age group

Graphs showing the average sleep length for male and female

permanent night shift workers, according to age.

SOURCE: D. Tepas, Department of Psychology, University of Connecticut,

1990.

inconvenience, while for others it can have major

consequences. It has been estimated that about 20 to

30 percent of shift workers actively dislike their

schedule (56). Often, workers who find they cannot

adjust to the demands of shift work change to day

jobs. Thus, there is a strong self-selection process in

operation that has important implications for studies

of the effects of work schedules. The populations

being studied may represent individuals who are

indifferent to or who can tolerate the negative

consequences of shift work, and thus the studies may

underestimate the true effects of nonstandard schedules (11 1).

Health

The stressors described in the previous section

may interact to have negative effects on the health of

a worker. In general, these effects result from

chronic, repeated exposure to stressors, for example,

the continuing circadian desynchronization that

rotating shift workers experience or the constant

stress placed on night workers to meet family and

social obligations during the day. Surveys have

shown that shift workers, particularly those on

rotating shifts, have a higher incidence of sick leave,

a higher rate of visits to clinics at the work site, and

poorer scores on a variety of indexes of health

(11 1,112). Thus it appears that a greater proportion of shift workers than day workers suffer

general health complaints. For example, a study of

policemen found that those working rotating shifts

reported a higher incidence of complaints of muscle

aches, respiratory infections, and gastric complaints

than did officers working days (123). In addition to

general health complaints, there is some relationship

between shift work schedules and the occurrence of

specific disorders, primarily gastrointestinal problems.

Shift workers, particularly those on night shifts,

commonly complain of gastrointestinal disorders

(94,111), including general gastric discomfort and

peptic ulcer disease (15,37,111,140). One study

comparing the incidence of peptic disease in night

workers and in day workers showed that the two

groups begin to differ only after 5 years of exposure

to their respective work schedules (10). There are

probably several reasons for the higher incidence of

gastrointestinal complaints among night workers.

Intestinal enzymes are secreted in a circadian cycle

that is disrupted by night or shift work schedules,

contributing to digestive distress. Also, the link

between meal patterns and the circadian system,

which has to suspend appetite and voiding in order

to allow 7 or 8 hours of uninterrupted sleep, may

play a role. For example, the eating habits of shift

workers tend to be irregular, with workers not

adjusting their meal schedules to match their work

schedules (47,56,72,120). It is also often difficult to

obtain high-quality meals at odd hours (56) (figure

5-6). The link between eating habits and gastrointestinal complaints in shift workers indicates an area in

which employee education might play a useful role.

Risk factors associated with gastrointestinal disorders, such as increased alcohol and tobacco consumption, have also been shown to be higher in shift

workers than in day workers (10,149). Finally, the

psychological stress associated with family disharmony or social disruption could contribute to

gastrointestinal problems.

Another major medical concern is cardiovascular

disease; however, the link between it and shift work

is not as strong as that for gastrointestinal problems.

While some earlier reviews of the field did not find

compelling evidence of a link (72,140), more recent

research from Sweden (87) has demonstrated that

shift work is associated both with increased risk of

cardiovascular disease and with its associated risk

factors (122). A study of Akron police officers

showed that rotating shift work may be associated

with high levels of norepinephrine (a body chemical

that causes an increase in heart rate and blood
Chapter 5--Biological Rhythms and Work Schedules .97

Figure 5-6-Shifts Interfering With Eating Habits

80

70

60 1

50{

40]

30

20

10 \

nL

Day Afternoon Night

Shift

The percentage of coal miners reporting that a given shift

interfered with their eating habits.

SOURCE: J.C. Duchon and C.M. Keran, “Relationship Among Shiftworker

Eating Habits, Eating Satisfaction, and Self-Reported Health in

a Population of Miners,” Journa/of Work ard Sfress 4:1 11-120,

1990.

pressure), which could place workers at higher risk

of cardiovascular problems (54). A recent review of

the literature related to cardiovascular disease and

the work environment concluded that ”... the better

studies in the field consistently find a modestly

higher incidence of cardiovascular disease among

shift workers” (89).

Finally, a few studies present data suggesting a

slightly increased risk of miscarriage, preterm birth,

and lower birth weight among women who work

rotating shifts or irregular hours (12,14). A study of

complications during pregnancy and adverse outcomes of pregnancy found no link to shift work, but

it did note an association between shift work and a

tendency for babies to be smaller for their gestational age (1 19).

Beyond these specific disorders, the adverse

effects of shift work on workers’ health seem to be

diffuse, affecting some workers’ general sense of

well-being. These workers frequently report sleep

disturbances and fatigue, menstrual problems, increased feelings of irritation and strain, increased

use of alcohol and other drugs (tranquilizers, caffeine), and a general feeling of malaise that maybe

exacerbated by psychological stress related to being

less satisfied in the domestic and social areas of their

lives (65,112). It has also been proposed that the

stresses associated with shift work might exacerbate

preexisting health conditions, increasing their severity without increasing their incidence (29).

A related health problem maybe the inability of

the shift worker to comply with health and medication regimens. As discussed in chapter 3, the body’s

metabolism and response to drugs are generally

circadian. Also, symptoms of some disorders, such

as diabetes, depression, and asthma, evidence significant circadian fluctuations. A shift worker could be

in the position of taking medication at inappropriate

or constantly changing times. Also, variable work

schedules could make it difficult to coordinate

taking medication with the work-rest cycle and

mealtimes, thus interfering with the worker’s ability

to take medication at all (29).

In summary) shift work schedules are associated

with increased gastrointestinal complaints among

workers and may be a risk factor in cardiovascular

disease and such pregnancy outcomes as low birth

weight and preterm births (figure 5-7). Beyond these

specific ailments, the health effects of such work

schedules generally manifest themselves as complaints of decreased well-being, chronic malaise,

and poor sleep. Shift maladaptation syndrome is the

term used to describe the effects of long-term shift

work on the health of workers who have never been

able to adjust to it.

Performance

The effects of work schedules on performance are

part of a complex set of factors that shape a person’s

performance in a given situation. These factors

include the circadian, sleep and fatigue, and social

and domestic stressors already described. They also

include the type of task to be performed (e.g.,

vigilance, physical, cognitive), motivational effects

(which are significantly influenced by social and

family concerns), the work schedule being employed, and individual differences among workers

(e.g., personality, age, health, sleep needs, behavior

patterns) and how they adjust to changes in routine.

Unlike health effects, performance decrements may

occur soon after exposure to a work schedule.

As discussed in chapter 3, performance on a

number of different types of tasks displays a

circadian rhythm, and different types of performance

differ in their normal phase and the degree to which

they are affected by outside influences. For example,

tasks involving signal detection, reaction time, and

handling of simple arithmetic correlate with cir-
98 ● Biological Rhythms: Implications for the Worker

Figure 5-7—Prevalence of Disease in Shift Workers and Day Workers

Percent

60

40

20

0

Percent

6 0 –

40-

20-

0-

Work

experience

(years)

Shift workers

[

Day workers

dl

0-3 4-12 13-2223-40

Circulatory system

0-3 4-1213-2223-40

Digestive system

Diseases

Percent of shift workers and day workers at an oil refinery, subdivided into groups according to work

experience, suffering from circulatory and digestive diseases. Shaded bar indicates that there was a

statistically significant difference between the shift workers and day workers.

SOURCE: Adapted from M. Keller, “Health Risks Related to Shift Work: An Example of Time Contingent Effects of

lxmg-Term Stress;’ International Archives of Ocwpationaland Environmenfai Health 53:59-75, 1983.

cadian changes in body temperature, peaking during

the afternoon, while performance of cognitive tasks

involving memory may peak in the morning (28,56).

Performance can be directly affected by circadian

desynchronization and inappropriately timed activity, as well as by the loss of sleep they can cause.

There is a large body of literature regarding the

effects of fatigue and sleep deprivation on performance; these factors clearly have a negative effect on

the performance of most tasks (28,91).

In contrast to the fairly extensive research on

the circadian component of performance and the

effects of sleep deprivation on performance,

much less research has been done on the complex

interaction of variables that occurs in a work

setting that can also affect worker performance.

To determine the effects of work schedules on

performance, studies can examine the performance

of a worker either on a standardized test battery after

being exposed to a certain work schedule or on the
Chapter 5--Biological Rhythms and Work Schedules ● 99

actual task the job involves. A factor that can

complicate the study of intershift differences in task

performance and perhaps mask the effects of shift

work is the difference in working environments. Not

only environmental conditions, such as lighting

levels, but also supervision levels, group morale, and

distractions can all vary between night shifts and day

shifts. Also, poorer performance can occur on the

night shift simply because no one is available to

repair broken machines (102). The work itself may

be quite different on the night shift. Very often,

certain parts of the job are saved for the night shift,

either because the process demands it (preparing

things for shipment in the morning) or because it

places less demand on the night workers. In continuous-process operations, complicated development

work may intrude during the day but not at night

(40).

The relatively few studies that have recorded

24-hour real-task data in the field demonstrate

decreased performance at night. They have shown

that the speed at which a task can be performed

decreases at night (21,182) and the probability of

making an error, missing a warning signal, or

nodding off while driving is highest at night

(17,58,75,127) (figure 5-8). In addition, some evidence shows a pronounced postlunch dip in these

measures. More recent studies have found the risk of

accidents involving truck drivers between midnight

and 2 a.m. to be more than double the average during

the day (69). Job performance of nurses, as measured

by a questionnaire filled out by supervisors, was

found to be lower in those on a rotating shift than in

those on freed day, afternoon, or night shifts (27).

Studies using other measures of performance have

also found effects related to work schedules. For

example, results of a study that measured manual

dexterity and search performance of 10 factory

workers on a rotating shift showed the workers

performed worst on the tests when working the night

shift (181). The tests were administered just before

the start of a shift and after 4 and 8 hours of work.

Another study brought shift workers into the laboratory during nonwork hours for performance testing

and measures of brain activity during sleep. These

workers continued to work at their normal

workplace, but they commuted to and from the

laboratory rather than home (155,156). Their performance on a vigilance task was examined just

before bedtime, at bedtime, and on awakening. The

study involved 10 night workers, 10 day workers,

Figure 5-8-Work Performance in Various

Job Settings

Time of day

Mid8 am Noon 4 pm 8 pm night 4 am 8 am

I I 1 I

r I I , I I

I 1 1 I I I 1 I , I I

3 am Noon 4 pm 8 pm Mid- 4 am 8 am

Fast

Speed of

answering

switchboard

slow

Low

Error frequency

in reading meters

High

Low

Frequency of

“nodding off”

while driving

High

Fast

Speed of joining

threads (spinners)

slow

Low

Frequency of

train drivers

missing warning

signal

High

Low

Frequency of

minor accidents

in hospital

High

night

Time of day

Variations in measures of on-the-job performance, by time of day,

from a variety of studies.

SOURCE: Adapted from T.H. Monk, “Shiftworker Performan-,” Shiftwork, Occupational Medb’ne State-of-the-Art Revfews, A.J.

Scott (ed.)(Philadelphia, PA: Hanley & Belfus, 1990).
100 . Biological Rhythms: Implications for the Worker

and 10 (slowly) rotating shift workers who were

working day or evening shifts at the time they were

tested. Night shift workers performed worst on all

three performance tests, but there were no reliable

differences between the other two groups. The

differences in performance were not accompanied

by equivalent differences in body temperature, but

they were correlated with brain activity during sleep

in a way that is typical of subjects undergoing

chronic partial sleep deprivation.

Similar results were obtained when 12 shift

workers were studied for one complete cycle of their

weekly rotating shift in the field rather than in the

laboratory (158). Reaction speeds on both a simple

and a complex reaction-time test were slower among

workers on the night shift. There was also strong

evidence of an increasing deterioration in performance, which the authors interpreted as a buildup of

partial sleep deprivation. The effects on a number of

different measures of performance of the 4-hourson, 8-hours-off schedule typically used on merchant

ships for standing watch has also been examined

(32). There was only a partial adaptation of circadian

rhythms to this schedule, and most performance

measures showed lower values during the night

hours. The decrements in performance were exacerbated by disturbances in sleep that occurred as a

result of the split hours of sleep time necessitated by

this schedule. These studies demonstrate some of the

effects that disrupted circadian rhythms can have on

performance and their interaction with other factors

involved in shift work, notably sleep deprivation.

The studies described above examine the effects

on performance of work schedules involving rotating shifts or night shifts. Jobs that require sustained or extended duty hours can also affect

performance. For example, jobs such as crosscountry truck driving require long hours of constant

attention, often in a boring or repetitive environment, while jobs such as those of residents in

hospitals involve continuous work, interrupted by

periods of reduced activity or rest breaks. While

circadian disruption plays a role in the performance

decrements observed under these conditions, sleep

loss is probably an equally salient factor (91).

A laboratory study that required subjects to

perform 54 hours of continuous work found that

reaction time, logical reasoning, vigilance, and

encoding and decoding messages all declined in a

stepwise fashion; that is, declines in performance

were interspersed with plateaus in performance (11).

The declines in performance were paralleled by

subjective ratings of fatigue and sleepiness; the

greatest declines occurred in conjunction with the

lowest point in the circadian cycle of body temperature. Similar results have been described when a

computerized test battery was used to measure

performance (115). While these studies show that

decrements in performance can occur as a result of

extended duty hours, a number of other studies

found that certain kinds of performance are more

sensitive to sustained operations than others (91). In

general, these studies found that psychological

tasks, such as cognitive, vigilance, long-term memory, decisionmaking, and perceptual-motor tasks,

were more likely to be adversely affected by

sustained operations than were physical tasks involving gross motor activity and strength.

Thus it is reasonable to assert that, in general,

shift work decreases performance and that a

number of factors besides circadian desynchronization contribute to this decrease, notably sleep

deprivation and fatigue. A great deal more information still needs to be derived, however. As with

health effects, there is a complex interaction of

factors that under actual working conditions could

contribute to or counteract decrements in performance (namely, nature of the task, speed at which the

task is performed, work schedule employed, worker

age, family and social factors, motivation). More

information is needed to delineate the effects of

these interacting factors in a given work situation. A

better understanding of how performance on different types of tasks can be affected will make it

possible to devise interventions and countermeasures.

Safety

The factors described earlier also have an impact

on worker safety. Performance decrements resulting

from sleepiness, circadian disruption, or distraction

by family problems can cause situations that might

compromise the safety of the individual and, depending on the nature of the job, public safety as

well.

In the United States, the major mechanism for

collecting data related to workplace injuries and

mishaps is the Bureau of Labor Statistics (BLS) in

the Department of Labor. Currently, BLS forms for

reportable injuries and illnesses include no questions
Chapter 5--Biological Rhythms and Work Schedules ● 101

regarding the time of day an incident occurred, the

type of schedule an employee involved in an

incident was working, the number of hours since the

employee began work, or the total number of hours

or shifts the employee had worked over the preceding days. Thus, data currently being gathered by

the BLS provide no information that could

facilitate an assessment of the impact of shift

work on employee safety and health. The Occupational Safety and Health Administration, within the

Department of Labor, may record information on

time of day and hours of work when investigating

workplace fatalities and catastrophic incidents in

which five or more persons are injured or substantial

property damage is caused.

Data on injuries can be put to three possible uses.

First, they can be used to investigate whether the

work environment or supervisory practices were

different on a particular shift and to see if schedule

changes had any effect on injury rate. Second, they

can be used for research examining features of the

work environment and schedules that are related to

injury rates. Finally, the data can be used in

providing surveillance of the workplace.

Another source of data is the National Transportation Safety Board (NTSB), which investigates transportation-related mishaps. In its investigations the

NTSB routinely collects information regarding the

role work hours might play in such incidents. Other

Federal agencies and departments (e.g., the Nuclear

Regulatory Commission or the Department of Transportation) may examine the role of work hours when

investigating incidents that occur within their domain. For example, the U.S. Army, as part of its

Army Safety Management Information System,

maintains a database regarding Army aircraft accidents involving a death or loss of an aircraft (55).

This database includes information related to sleep

and work periods. To date, no analysis of these data

has been performed to determine the role of duty

hours in these incidents.

Other sources of information related to work

schedules and their implications for worker safety

include surveys of specific industries or work sites

and data from other countries. As described earlier,

studies of the effects of work hours are often

confounded by the fact that in some settings the

conditions surrounding night work are quite different from those surrounding day work. This is

particularly true of industrial or manufacturing

settings.

While it is possible that the performance

decrements that occur in shift work will translate

into an increased rate of mishaps and injuries in

the workplace, the published data in this area are

meager. Some studies in industrial settings have not

found an increase in injuries related to night shifts or

shift work [injuries at a chemical plant (118), U.S.

coal miners (173), survey of industrial accidents in

New Zealand (49)], while others found that, although injury rates were higher during the day, the

severity of the injuries suffered at night was greater

[iron and steel mill workers in Singapore (121), U.S.

iron miners (166)]. On the other hand, a survey of

occupational mishaps in a glass factory and a steel

factory and data on occupational mishaps occurring

in Ontario over a 5-year period found that the

number of occurrences peaked just before and after

lunch, as well as between 2 a.m. and 4 a.m. (180). A

survey of a paint factory in the United States found

that the injury rate was 25 percent higher for night

shift workers than for day shift workers (95). It was

also noted that this effect was most pronounced in

the last 3 hours of the night shift. Thus, there is some

indication that shift work can result in decreased

safety in an industrial setting; however, there is no

complete characterization of the types of settings

most likely to be affected. Until there are more

data on the relationship between work hours and

workplace mishaps, the extent to which mishaps

are caused by shift work will remain uncertain

and the development of interventions to counteract them will be hindered.

In contrast, examination of factors contributing to

transportation mishaps shows the role of circadian

disruption, sleep loss, and fatigue (figure 5-9). These

three factors have been noted in specific incidents

involving every mode of transportation, including

airline, railroad, maritime, and highway driving

(93). Studies have shown that the risk of a truck

driver’s being involved in a traffic collision is higher

for trips occurring at night. One study identified the

period between midnight and 4 a.m. as the most

dangerous, with the peak being between midnight

and 2 a.m. (69), while another identified the period

between 4 a.m. and 6 a.m. as the most crucial (100).

The chances of an accident were increased further if

the driver had been on the road or working for an

extended period of time (69), and the effects of

sleepiness and fatigue were compounded if the
102 ● Biological Rhythms: Implications for the Worker

Figure 5-9--Fatigue-Related Vehicular Accidents

Number International data (n=6,052) 1,200 I

1,100; ~ I

Midnight 6 a.m. Noon 6 p.m. Midnight

Time of day

The distribution, by time of day, of 6,052 vehicular accidents that

were judged by investigators to be fatigue-related.

SOURCE: M.M. Mittler, M.A. Carskadon, C.A. Czeisler, et al., “Catastr&

phes, Sleep, and Public Policy: Consensus Report,” Sleep

11:100109, 1988.

driver was on an irregular schedule (100). A recent

study by the NTSB highlighted the role of combined

sleep loss and fatigue and its interaction with drug

use in a study of fatal-to-the-driver heavy truck

crashes in the United States (117). The report found

that sleep loss and fatigue was the most frequently

cited single cause or factor in the fatal crashes

examined and that many of the drivers involved in

these incidents were also impaired by alcohol or

other drugs. Another study of crashes involving

large trucks in the United States found that the

“relative risk of crash involvement for drivers

whose reported driving time exceeded 8 hours was

almost twice that for drivers who had driven fewer

hours’ (76). Similar results were found in a study of

naval pilots who were involved in serious mishaps

(destroyed aircraft, fatalities) during a 5-year period

(19). Pilots who had worked at least 10 hours before

a mishap were more likely to have been at fault than

pilots who had worked less than 10 hours. Also, the

mishap rate was significantly related to time of day,

with pilots having a lower rate of incidents during

daytime hours.

Safety consequences of shift work can affect not

only the worker, but also the public. They have been

listed as contributing to such highly publicized

incidents as the Three Mile Island nuclear powerplant accident and the grounding of the Exxon

Valdez (box 5-B). In these incidents, the strain of

extended duty hours and the time of day may have

led to errors in attention, decisionmaking, and

response to pertinent information. Events such as

these can threaten thousands of lives and seriously

affect the well-being of surrounding communities.

At the other end of the spectrum are less publicized

but more common examples of threats to public

safety, such as accidents involving interstate truckers. Any occupation involved with public safety and

welfare can be influenced by the effects of work

schedules and their attendant problems. Decrements

in performance among police, free, and health care

personnel could result in negative outcomes for the

public. Additional data on the occurrence of

incidents threatening the public safety are needed

to derive a clearer understanding of their frequency, nature, and magnitude. Such information can serve as the basis for preventive measures.

INTERVENTIONS

The previous sections have described the consequences and impact shift work can have in a variety

of realms. This section describes some interventions

that may be used to lessen those effects. While a

number of different interventions are being examined as possible means to counteract circadian

desynchronization, sleep disturbances, and social

disruption associated with work schedules, definitive statements regarding their effectiveness cannot

be made yet. Additional research is needed on the

mechanisms at work in specific situations and on the

effectiveness of these interventions.

Work Schedules

Since a number of possible negative consequences are associated with shift work, an obvious

approach to prevention is to avoid the use of such

schedules. However, around-the-clock operations

are a fact of life in many occupations, so the best

intervention regarding scheduling is to identify

those schedules that will have the least unfavorable

impact on the individual. Making such a determination is difficult, because a schedule that may be the

most beneficial from a circadian perspective may not

be optimal in terms of sleep and fatigue, or a

schedule that tries to avoid sleep loss may create

hardships for the worker in the social or domestic

arena. Also, the nature of the job and the type of

performance it requires may make a schedule

suitable for one type of task but not suitable for

another. As stated by one researcher,” . . . the effects
Chapter 5--Biological Rhythms and Work Schedules ● 103

Box 5-B—The Grounding of the Exxon Valdez

At about midnight on the morning of March 24,1989, the tanker Exxon Valdez, loaded with almost 1.3 million

barrels of crude oil, ran aground on Bligh Reef in Prince William Sound, Alaska, Approximately 258,000 barrels

of oil spilled, resulting in severe damage to the environment. Damage to the vessel was put at $25 million, and the

cost of the cleanup during 1989 was $1.85 billion. In the opinion of the National Transportation Safety Board

(NTSB), which investigated this incident, the probable causes for the grounding of the tanker were:

s the failure of the third mate to properly maneuver the vessel because of fatigue and excessive workload;

o the failure of the master to provide a proper navigation watch because of impairment from alcohol;

* the failure of the Exxon Shipping Co. to provide a fit master and a sufficiently rested crew for the Exxon

Valdez;

● the lack of an effective vessel traffic service because of inadequate equipment and manning levels,

inadequate personnel training, and deficient management overnight; and

* the lack of effective piloting services.

This incident is an example of a situation in which negative work schedule effects combined with other factors

to bring about an event that had broad implications for the public well-being. Prominent among the NTSB findings

were a number that concerned the policies of Exxon

Shipping related to the manning of its tankers. The

NTSB found that these policies created conditions that

were conducive to fatigue among tanker crews. In the

case of the Exxon Valdez, the result was that there were

no rested deck officers available to stand watch while

the ship sailed through Prince William Sound, and the

ability of the third mate to corm the vessel was

impaired by fatigue.

Among the NTSB’s recommendations related to

work hours were that Exxon Shipping and other oil

shipping companies eliminate personnel policies that

encourage employees to work long hours and implement manning policies that prevent long working

hours. Also, the NTSB recommended that shipping

companies forbid deck officers to combine both

navigation and cargo watch duties using a schedule of .

// .“ , :

6 hours on, 6 hours off, The NTSB recommended that

,.

.,

,.,. ,/

the U.S. Coast Guard develop means to enforce the rule ,, ,

,, ,/.

that officers on watch during departures from port must

/

be sufficiently rested; that it expedite study programs

Photo crdii: W?. Woody, /Vatior?a/ Transportation Safety Board

to establish manning levels and safeguards to use in the The Exxon Valdez.

manning review process; and that it establish manning

standards that will ensure crews are large enough to handle heavy workloads. Finally, the NTSB reiterated previous

safety recommendations to the Department of Transportation that it expedite research programs to study the effects

of fatigue, sleep loss, and circadian factors on transportation system safety; that it disseminate information and

educational material to transportation industry personnel regarding these effects; and that it review and upgrade

hours of service regulations in all transportation modes to ensure that they reflect the latest research on these factors.

SOUR~: National Transportation Safety Board, Marine Accident Repor4 Grounding of the Zlxxon VukZez on Bligh l?eef, Prince WiZZium

sound, AK, Mar. 24,1989, NTSB/MAR-90/04 (Springfield, VA: National Teehnical Information Sewice, 1990).

of any particular work schedule are likely to be regime represents a compromise rather than an

myriad and complex, potentially exerting a differen- ideal’ (28) (box 5-C).

tial influence on the various parameters of worker

physical, psychological, and social adjustment. As a The variable parameters of a schedule include

consequence, the implementation of a specific work fixed or rotating shifts, direction and speed of
104 ● Biological Rhythms: Implications for the Worker

Box 5-C—The Philadelphia Police Story

In 1983, a shift rescheduling program was conducted for the City of Philadelphia in an effort to enhance the

work schedules employed by the city’s police department. The two-phase project was carried out in one of the city’s

police districts. It consisted of an evaluation of the existing schedule and the design of an improved schedule (phase

1), as well as the implementation of the new schedule and an education program for the officers (phase 2). (Table

5-C-1 compares the old and new schedules.)

In phase 1 of the study it was found that the existing four-platoon work schedule had a number of deleterious

effects on the officers. This included 50 percent of the officers reporting poor quality sleep; 80 percent reporting

that they fell asleep at least once a week while on the night shift; 25 percent reporting that they had been involved

in an actual or near-miss automobile accident due to sleepiness during the past year; over 75 percent of officers’

families being dissatisfied with their work schedules; and 35 percent taking either an entire week to adjust or never

adjusting to the weekly shift rotation.

In phase 2 of the study, a three-platoon system was initiated for 177 officers, and educational sessions were

conducted during the implementation process. The new schedule incorporated proportional staffing (so the number

of officers on duty was proportional to the number of calls for service), reversal of shift rotation from

counterclockwise to clockwise, reduction in the rate of shift rotation from 1 to 3 weeks, and the elimination of

regularly scheduled 6-day weeks (see table 5-C-1). Following implementation of the new schedule there was a

fourfold decrease in the number of officers reporting poor sleep, twice as many reporting no daytime fatigue, a

decrease in the number of sleep episodes on the job, a decline in the on-the-job motor vehicle accidents per mile

driven, an increase in the level of alertness on the night shill, and a reduction in the use of sleeping pills and alcohol.

Families of officers reported a nearly fivefold increase in satisfaction with the new schedule.

This study shows that considering biological rhythms when designing a shift schedule for a specific work

setting can lessen the negative effects that can occur. It also points out the importance of coupling schedule redesign

with educational programs for the workers to assist them in adjusting.

Table 5-C-l—Original and Newly Instituted Schedules for the

Philadelphia Police Study

Schedule

Characteristic Old New

rotation, length of a shift, and the starting time of a (56). Also, as discussed earlier, permanent night

shift. Fixed shifts should result in the least circadian workers often suffer from chronic sleep disturbances

disruption, assuming workers maintain the same and at-e permanently out of synchrony with the rest

schedule on days off as on workdays. They often do of society. This latter factor, depending on an

not, however, and under such conditions permanent individual’s personality and family situation, may

shift schedules take on the nature of a rotating shift cause significant social and domestic strain.
Chapter 5--Biological Rhythms and Work Schedules ● 105

Direction of Rotation

Based on the fact that under free-running conditions the human body clock has a natural tendency

to run slow, with a preferred period slightly longer

than the 24 hours of nature and society (176) (see ch.

3), the human circadian system appears to adjust

more slowly to phase advances than to phase delays

(13,81). From a circadian perspective, then, clockwise shift rotation (mornings, then evenings, then

nights) should be easier to cope with than counterclockwise rotation (nights, then evenings, then

mornings). Although this hypothesis still needs to be

properly tested, there is some evidence to support it

(36). However, a study that used survey data from a

group of workers indicated that, in terms of the

amount of time available for sleep, a counterclockwise schedule afforded more opportunity to prepare

for and recover from the night shift (48). Furthermore, it is possible that the timing of a worker’s

actual sleep, which can be influenced by social

demands, does not necessarily coincide with an ideal

circadian schedule (160).

Speed of Rotation

The speed of rotation in a shift system is the

number of days an individual spends on a particular

shift before switching to a new schedule or to days

off. There are a multitude of different shift schedules

currently in use (85,150). Many of them approximate a weekly rotation, with an employee working

from 4 to 7 days on a shift before changing.

However, faster (1 to 3 days) or slower (more than

7 days) rotating systems may also be used.

A rapidly rotating system, as noted earlier, will

result in the individual’s circadian system remaining

diurnal, since not enough time elapses for circadian

rhythms to adjust to a new routine (56,105). This

avoids the problems associated with a circadian

system that is going through a phase adjustment to

a new schedule. Also, the shorter rotation does not

allow a sleep debt to accumulate, since the number

of consecutive days when the worker has to engage

in day sleep remains small. The tradeoff is that,

while they are on night shifts, workers will be out of

synchrony with their circadian systems and performance could be affected (56,105). Also, rapid rotation

may have a greater impact on family and social

interactions because of the continual schedule changes

(56).

A slowly rotating schedule has the advantage of

allowing greater time for circadian readjustment. A

study of 42 shift workers at a surface mine showed

that some measures of adjustment (mood, episodes

of awakening during sleep) improved during the

second week of a 2-week shift rotation (46).

However, a slowly rotating schedule can result in

sleep debt and fatigue due to more consecutive

periods of day sleep. This problem can be exacerbated if the worker reverts to a diurnal schedule on

days off.

Since a weekly shift rotation results in both

insufficient time for the body clock to readjust

completely and enough time to build up a sizable

sleep debt (158), it is this schedule of rotation that is

most likely to produce physiological problems

(8,36,140,146). However, a weekly system may

have the advantage of allowing a worker to engage

more easily in social and family activities (56).

What is the best rotation system to use? Expert

opinion is divided. Many favor rapid rotation with

very short (1- or 2-day) rounds of duty on one shift

before changing to a different one (3,140). Others

favor much slower rotation speeds, with 3 weeks or

more at one shift before moving to a different

schedule (36,11 1). One factor that may help determine the most desirable speed of rotation is the task

to be performed. As previously discussed, there is

some evidence that different tasks not only have

different best times during the circadian cycle, but

also adjust at different rates to a change in routine

(56,57). It may be that simple, repetitive tasks,

which are performed relatively poorly at night and

adjust rather slowly, would be best performed using

a slow shift rotation, which allows circadian synchronization to be maintained for longer periods.

Tasks involving immediate retention and high memory loads might be performed relatively well during

the night shift, even in diurnally oriented individuals

(107). In these cases, rapidly rotating shifts might be

more suitable: the circadian system retains its

diurnal orientation, and there is no gradual buildup

of sleep loss (158). Further information is needed to

determine whether the speed of shift rotation can

have differential effects on various types of tasks. If

the main goal is to” minimize physiological disruption, a weekly rotating shift seems to be the least

desirable; either a more slowly (36) or more rapidly

(83,179) rotating system may be preferred.
106 . Biological Rhythms: Implications for the Worker

Shift Duration

In rotating shift systems, the length of a shift is

typically 8 hours, although longer shifts, often 12

hours, are sometimes used. The advantage of 12-

hour shifts is that the workweek is compressed into

3 or 4 days, giving the worker more days off for

leisure and recuperation. The disadvantage is that

the extra 4 hours of work per day could lead to

increased fatigue and decreased alertness on the job.

Such effects have been demonstrated in both laboratory (139) and field studies (134,138). In one field

study, conducted at a nuclear powerplant, it was

shown that workers on a 3- to 4-day, 12-hour shift

system reported increased fatigue and performed

more poorly on tests designed to measure alertness

than did workers on a 5- to 7-day, 8-hour system

(138). These effects were most pronounced in the

12-hour night shift, where there was an interactive

effect between fatigue and the low point of the

circadian cycle. Interestingly, despite these decrements, examination of performance on job tasks

(e.g., filling out log books, occurrence of unusual

events) conducted at the same time as the other

testing indicated no difference between the 8- and

12-hour shift systems (96) (figure 5-10).

A comparison of the number of health complaints

reported by workers in the chemical industry in

Germany showed no difference between a rapidly

rotating 12-hour and a weekly rotating 8-hour shift

schedule (62). The use of a compressed workweek

with 12-hour days is also becoming more common

in nonrotating shift schedules (see ch. 4). While

compressed workweeks are generally well received

by workers, they raise concerns about fatigue

effects, longer exposure to workplace hazards (e.g.,

noise, chemicals, repetitive motion tasks), and

complications associated with workers holding a

second job (29). Also, workers who have long

commutes may be at greater risk driving on the

highways. Additional studies are needed to fully

evaluate these factors and to determine how the

extended workday can affect performance and safety,

especially in regard to night shifts, where circadian

effects would also be present. As with speed of

rotation, the type of job to be performed might affect

whether 12-hour shifts are appropriate. Long shifts

may be more suitable in jobs that do not require

intense concentration, are not monotonous or dangerous, and do not involve heavy physical activity

(102).

Figure 5-10-Measures of Performance on 8-Hour

and 12-Hour Shifts

2.6 iI

1.6

1.0

i

o— — x— x— x 0-0-0 ~,% —o-u —0—0 —-0

0.6

1

0

[ \ I I \ 1 I 1 1 1 1 I 1 I

8 am 10 am Noon 2 pm 4 pm 6 pm 8 pm 10 pm Mid- 2 am 4 am 8 am 8 am

Time of day

+ 12-hour day O 8-hour swing

● 12-hour night ❑ 8-hour night

X 8-hour day

Standard

B. Shift Mean error

8-hour, day 0.174 0.028

8-hour, swing 0.188 0.028

8-hour, night 0.164 0.022

12-hour, day 0.194 0.025

12-hour, night 0.112 0.014

A) Number of errors, by time of day, on a laboratory measure of

performance (grammatical reasoning task) for workers on 8-hour

and 12-hourshiftschedules. Significant performance decrements

occurred on the 12-hour shift. B) The average number of errors of

entering data into log books per hour on 8-hour and 12-hour shifts.

There were no differences between shifts.

SOURCE: P.M. Lewis, D.J. Swaim, and R.R. Rosa, Ewdusttion of the

12-Hour Shift Schedule at the Fast F/ux Test Fad/ity(Riohland,

WA: Pacific Northwest Laboratory, 1986).

Extended duty hours almost invariably result in

loss of sleep and fatigue. As previously described,

extended periods of sustained work can lead to

impaired performance in most psychological tasks.

As a result, periods of extended duty hours without

adequate time to recuperate from fatigue and lost

sleep can have detrimental effects on worker performance and safety.

Because of their disruptive nature, schedules that

divide the day into multiple work shifts interspersed

with rest periods-namely, split shifts-are rare.

The most common use of split shifts is for standing

watch aboard merchant and military ships, where a

4-hours-on, 8-hours-off schedule is often employed.

These schedules have been shown to result in
Chapter 5--Biological Rhythms and Work Schedules ● 107

performance decrements (32,142) as a result of

circadian rhythm disruption and disturbed sleep. A

more detailed discussion of the shipboard schedules

used in the military is presented in chapter 9.

Sleeping and Napping Strategies

One of the major problems facing shift workers is

loss of sleep and the resulting on-the-job sleepiness

(5,29). Sleeping and napping strategies designed to

optimize sleep could be useful interventions for the

worker. It has been noted that the majority of night

shift workers sleep after work, while day shift

workers most often sleep before work (151). It has

been hypothesized that delaying sleep after working

a night shift is preferable, since such a schedule

would maintain a normal work-off-sleep sequence

and sleep would occur during a period in the

circadian cycle more conducive to longer sleep (45).

However, there is little empirical evidence available

regarding this strategy. One survey of 328 workers

at a surface mine and two powerplants found that

those who delayed their sleep after a night shift were

less sleepy than those who slept earlier, but they

were also more likely to report health complaints

(45). Since this was a survey study, it could not be

determined if there was a causal relationship between the sleep schedule employed and the incidence of health complaints.

Napping strategies may be useful in two ways.

Brief naps taken during temporary periods of

extended work may enhance subsequent performance, and naps taken during time off may

help to offset the sleep debt typically associated

with shift work. With respect to on-duty napping, it

is known that a sleep period of 1 to 4 hours can lessen

sleepiness during a 24-hour period of continuous

activity (44,91). One study has shown that airline

pilots who were allowed to nap for a short time

during a slack period in a flight were more alert when

their workloads increased (during landings) than

pilots who did not nap (68). Other studies have

shown that naps taken early in a period of extended

work (42,44) may be more effective in preventing

sleepiness than naps taken later during the work

period are in recovering from sleepiness (133). In

prolonged work schedules (over 24 hours), measures

of performance were improved following prophylactic naps, although performance did not return to

normal levels (42,44). This indicates the usefulness

of prophylactic napping during temporary periods of

extended work. The placement of the naps in relation

to the circadian cycle was not a factor in the ability

of the naps to produce their effects. Also, the

enhanced performance occurred only after the residual effects of sleep had worn off: performance

decrements can persist for up to an hour after

awakening (9) and may be a limiting factor in the use

of naps in work settings where a worker must be

fully alert on awakening.

Napping at appropriate times during time off may

also enhance performance by offsetting the sleep

debt that typically accompanies rotating shift work.

Recent findings indicate that napping may be an

integral component of the circadian sleep-wake

cycle (22,25,26,41). Workers who cannot sleep for

more than 4 to 5 hours during their initial attempt (a

common complaint among shift workers trying to

sleep during the day) (60,172) may be able to obtain

a couple of additional hours if sleep is attempted

again later in the day (9). It has been suggested that

a rotating shift worker should not take a nap if the

next major sleep period after a work shift is to be at

night. A nap under these conditions could interfere

with that night’s sleep. If the next night is going to

be another period of work, however, a nap maybe

beneficial (9). Also, a nap taken regularly at the same

time of day could act as an anchor, or synchronizing

point, for circadian rhythms and might slow the

adaptation of the rhythms to a new schedule. This

could be advantageous to a worker on a rapidly

rotating schedule but detrimental to one on slowly

rotating shifts (135). Thus, naps can be beneficial

and provide a period of additional sleep for shift

workers under some conditions; however, napping

during the day ultimately interferes with the ability

of permanent night workers to get an adequate,

extended period of sleep (154).

Light

As discussed in chapter 3, laboratory studies have

confirmed that bright light (i.e., light that is equivalent to outdoor light at dawn) can act as a resynchronizing agent for the human circadian system

(34,98,177). This has led to the investigation of

whether exposure to light can facilitate the circadian

adjustment of an individual to shift work (box 5-D).

Rigorous use of goggles, lightproof bedrooms, and

banks of bright lights has in some cases entrained

subjects to non-24-hour routines (50,52).

A recent study of simulated shift work has shown

that a fixed schedule of exposure to bright light
108 . Biological Rhythms: Implications for the Worker

during night work, combined with complete dark- (body temperature, cognitive performance, urine

ness during daytime sleep, enhanced circadian production) and psychological (subjective alertness,

readjustment to night work, compared to exposure to cognitive performance) measures. While it has been

normal room light at night and unrestricted sleep noted that the design of this study did not preclude

conditions during the day (35) (figure 5-1 1). The other factors, such as activity and sleep-wake

adjustment was observed in both physiological schedules, from contributing to the circadian re-
Chapter 5--Biological Rhythms and Work Schedules ● 109

Figure 5-1 l—Effects of Bright Light on the Adjustment of One Worker to Shift Work

.

37.5

37.0 P

J

37.5 1

36.5 1

I

A. Control study

/v

37.5 1

First 37.0

night

shift 36.5

Standard

room light

during night

work

37.5

Sixth 37.0

L

night

shift 36.5

—

4 pm Mid- 8 am 4 pm Mid- 8 am

night night

Time of day

r“

B. Treatment study

El

First

night

shift

\

Bright light

during night work

and darkness

during day sleep

Sixth

night

shift

1

4 pm Mid- 8 am 4 pm Mid- 8 am

night night

Time of day

The body temperature of a worker on the first and sixth nights of work A) with exposure to normal levels of light and B) with exposure to

bright light during the second to fifth night of work. Exposure to bright light led to a shifting of the body temperature cycle to coincide with

the night work schedule (midnight to 8 a.m.).

SOURCE: Adapted from C.A. Czeisler, M.P. Johnson, J.F. Duffy, et al., “Exposure to Bright Light and Darkness To Treat Physiologic Maiadaptation to Night

WorlG” New England Journal of Medicine 322:1253-1259, 1990.

adjustment (24), the results do indicate a role for

exposure to light and darkness in circadian adaptation to night work. It is likely that exposure to light

and darkness as well as activity levels can interact to

affect circadian readjustment (164). It has been

proposed that circadian adjustment to shift work

might be facilitated by manipulating both sleep

schedules and exposure to light (5 1). Another study

of exposure to bright light during the night and

complete darkness during day sleep showed that the

timing of the exposure to bright light determined the

direction of the phase shift in circadian rhythms

(52,53).

Exposure to bright light may also enhance certain

types of performance (23,61) during rotating shift

work or extended duty hours. Thus, there is some

initial evidence for the usefulness of bright light

to enhance adjustment to work schedules; however, practical application in the workplace must

await additional research.

Medication and Drug Therapies

Drugs might be helpful in counteracting the sleep

and fatigue problems common to shift work. One

possible intervention, then, would be to improve

sleep by the use of hypnotic medication; however,

there are two major problems associated with the use

of hypnotics.

The first problem is that of residual effects, which

leave a person drowsy after awakening. These

effects (which are characteristic of long-acting

hypnotics) can affect the person’s performance and

could therefore cause problems in shift work. The

development of the short-acting benzodiazepines

such as triazolam and brotizolam, which have a
110 . Biological Rhythms: Implications for the Worker

half-life of only a few hours (145), has to some

extent overcome these problems. It has been shown

that triazolam significantly increases the duration of

day sleep, although this increase did not appear to

increase phase adjustment of the circadian clock,

which would have decreased the tendency to fall

asleep in the early morning hours (169). This

tendency was unaffected by triazolam. Although

triazolam will improve daytime sleep for individuals

on night shifts, it does little to improve alertness at

night (associated with improved daytime sleep) and

nothing to improve nighttime performance (170,171).

The second problem regarding the use of hypnotics by workers relates to the chronic nature of the

sleep problems associated with shift work. No

hypnotic drugs are recommended for anything other

than occasional insomnia. The dual problems of

tolerance and dependence make it likely that workers would derive little or no benefit from anything

other than intermittent use of short-acting benzodiazepines. Moreover, long-term high doses of triazolam have in some cases been associated with

amnesia and mood changes (l), effects to which shift

workers are especially vulnerable. Thus, for a

hypnotic drug to provide any lasting benefit, it

would have to be totally benign when administered

chronically. In specialized situations-for example,

in the military-occasional use of hypnotics can be

helpful in inducing sleep during a period of extended

duty (e.g., to induce sleep during rest breaks for

aviation crews exposed to extended periods of

combat) (91). Residual effects are still a concern,

however.

An alternative to more potent hypnotics may be

mild over-the-counter sedatives, such as antihistamines. These drugs are used by millions of

Americans and may aid individuals who have

difficulty sleeping (30,92), though these drugs do

have side effects which could limit long-term use.

An essential dietary amino acid, tryptophan, has

been shown to be helpful in promoting the onset of

sleep when administered in sufficient quantities

(73,74) without causing a significant impairment in

performance (99). Tryptophan is thought to “set the

stage for more rapid sleep onset” (147) rather than

directly inducing sleep. While tryptophan is a

naturally occurring substance and is considered safe,

the chronic nature of the sleep problems associated

with shift work could limit its use. Whether the

intake of a high dose of a single amino acid over an

extended period can still be regarded as natural is

debatable and has not been tested. Recently, there

have been reports of increased incidence of a rare

blood disorder associated with the use of tryptophan.

This side effect has been traced to the presence of a

contaminant that was inadvertently introduced during the manufacture of the compound and not to

tryptophan itself. Currently, the sale of tryptophan in

the United States is prohibited until its safety can be

confined.

The regular use of stimulant drugs to maintain

alertness (as opposed to maintaining or inducing

sleep) in shift work also raises concerns. While there

is some evidence that the use of caffeine can increase

vigilance (99) and may help to increase alertness and

performance on the night shift (18,168), its use can

have detrimental effects on sleep and may cause

anxiety, nervousness, and gastrointestinal discomfort in high doses. As with hypnotics, the occasional,

controlled use of more powerful stimulants (e.g.,

methamphetamine, dextroamphetamine) has been

studied to meet the demands of extended duty in

military situations (39,91). But concerns about the

possible abuse of these drugs and about the side

effects associated with them, such as irritability,

distorted perception, apprehension, rebound effects

(e.g., depression, fatigue), and psychosis after longterm exposure, make their general use inappropriate.

Further study is needed to determine the efficacy of

short-term use of stimulants such as caffeine in shift

work, especially in occupations in which optimal

performance is necessary (e.g., pilots). Any potential

benefits would have to be weighed against the

problems associated with use.

As described in chapter 3, the ability to affect

biological rhythms directly and facilitate the resetting of the body clock with drugs is being explored.

Such drugs could be used to help the circadian

system adjust to changes in work schedules. Both

melatonin and triazolam have been studied for their

ability to affect biological rhythms. While neither

has been conclusively shown to have any such action

in humans, there is initial evidence that melatonin

has an effect on the circadian system (97,143). In the

case of triazolam, the circadian effects that have

been observed in experiments with hamsters (161,162)

may be an indirect result of the effects the drug has

on activity (114).

Currently, no effective pharmacological agents

are available to assist workers in adapting to shift
Chapter 5--Biological Rhythms and Work Schedules ● 111

work. Long-term use of drugs to counteract fatigue

and to ease sleep problems is probably not desirable,

and to date no drugs have been conclusively shown

to have an effect on the circadian system.

Monitoring

Another possible intervention is the use of

monitoring devices and instruments to detect

individuals who may pose a risk to themselves or

others because their performance is impaired.

A number of tests have been designed to detect

decrements in performance. Some are being used in

the workplace to identify individuals who are

impaired due to substance abuse, but many are

sensitive to other causes of decreased performance.

The Automated Performance Test System is a

computerized battery of tests that measures alertness

and cognitive and psychomotor factors related to job

performance. The system can detect impairment

caused by sleep loss, drugs, and alcohol, but it does

not indicate the cause of the impairment (77,78,124).

Another computerized test batter-y is the Walter

Reed Performance Assessment Battery (157). This

battery is designed to examine the effects of sleep

deprivation, sustained performance, heat stress,

physical fatigue, and physical conditioning in workers. Subjects are asked to undertake a variety of

tasks, including ones that measure choice reaction

time, time estimation, visual research, pattern recognition, sustained attention, short-term memory, mental arithmetic, and logical reasoning.

Other instruments to measure performance are

geared more directly toward determiningg the effects

of fatigue and sleep loss (43,136). The National

Institute for Occupational Safety and Health, of the

Centers for Disease Control in the Department of

Health and Human Services, has developed a

Fatigue Test Battery and a Daily Sleep and Habits

Questionnaire. Included in the computerized Fatigue

Test Battery are a number of brief performance tasks

designed to evaluate a range of psychological

functions, including cognitive abilities, perceptualmotor functions, motor skills, and sensory acuity

(136-139). The Daily Sleep and Habits Questionnaire contains information on sleep and other

personal factors known to be affectedly work hours.

Some questions relate to the times of retiring and

arising (including nap times), sleep latency, number

of awakenings, depth of sleep, and quality of sleep

for the 24 hours preceding the work shift. The

workers are also asked to give their subjective

evaluation of psychological stress and of gastrointestinal conditions, to report on personal schedule

adjustments attributable to shift, adjustments of

mealtimes, and exercise periods (138).

These testing instruments are designed to screen

individuals to determine if their performance on a

task is suboptimal. Other types of monitoring

devices are designed to measure and record physiological and performance parameters as an individual

actually goes about performing his or her job. These

monitoring instruments are valuable for the collection of research and medical data (104). In addition,

they provide real-time, on-the-job feedback to the

worker, alert the worker to any decrements in

performance that may occur, and enable the worker

to respond appropriately. Such systems could be

particularly useful in job settings where reduction in

performance might have negative safety consequences. An example would be a detector that

individuals could wear to alert them if they began to

fall asleep (117). While such a device would not

reverse the person’s sleepiness, the feedback it

would provide could be crucial in certain settings

(e.g., truck drivers, railroad engineers). The design

of workplace systems to provide workers with

information to judge their performance and to

respond to anomalous events would also be valuable

(66).

While all of these monitoring procedures might be

useful, it has been noted that on-the-job monitoring

itself can induce stress (163). Such stress could

compound the stress associated with work schedules. Additional research is needed to develop

monitoring instruments and systems and to determine the role they could play in various job settings.

Employee Education and Clinical Support

Given the inherent nature of the stress caused

by circadian rhythm disruption and the other

factors associated with shift work, an important

intervention is educational programs that provide workers with strategies to deal with the

problems they face and to ease some of the

consequences (109). Information such as the best

timing of sleep, meals, and other activities to

coincide with a given schedule could be helpful.

Guidance on ways to make the home more conducive to daytime sleep and the need for cooperation

among family members to ensure that the worker is
112 ● Biological Rhythms: Implications for the Worker

able to get as much sleep as possible would also be

beneficial. Finally, providing the entire family with

support and guidance that will help them deal with

problems that occur could result in a more supportive domestic environment for the worker. Further

research is needed to determine what types of

educational programs are most effective in helping

workers cope with their schedules.

Support for shift workers is largely lacking in U.S.

workplaces. Although sleep disorder clinics are

available, most of these facilities are not designed to

diagnose and handle the underlying problems that

cause sleep and other related disorders arising from

work schedules.

Fitness

The possibility that improved physical conditioning can increase the rate of adjustment to shift work

or increase an individual’s tolerance to it has been

examined in a few studies (70,71). These studies

were conducted on 75 female nurses engaged in shift

work and sought to determine whether improving

levels of overall fitness would facilitate their ability

to cope with shift work. The 4-month exercise

training program that was implemented elevated

respiratory efficiency by 7 percent. Improvements

were noted in self-reports of sleep length, night shift

alertness, and general fatigue. Another study failed

to show any effect of physical conditioning on the

adaptation of wake-sleep and body temperature

rhythms to a change in work schedule (135). Thus,

the data collected so far suggest that the benefits of

physical conditioning may be related to an increase

in general strength and more positive subjective

reports rather than to any direct facilitation of

adjustment to shift work. While these studies

indicate that physical fitness might be helpful,

additional research is needed to confirm these results

and to delineate clearly what mechanisms produce

the observed effects. It has also been noted that while

physical fitness may lessen the effects of physical

and mental fatigue, it cannot protect against the

effects of sleep loss (16).

RESEARCH NEEDS

Substantial progress has been made in understanding the underlying physiological mechanisms

involved in the generation, entrainment, and expression of circadian rhythms in animals over the last

two decades. Similar advances in the application of

these data to workplace issues have not been made

or supported in this country. A principal need is for

research into how to apply basic knowledge on

circadian rhythms and sleep to field studies in the

workplace. Since demands differ from one

workplace to another, research is needed to establish

common chronobiological principles, as well as

task-specific applications, that can be transferred

from the laboratory to the workplace. While some

research programs, notably those of the Department

of Defense and NASA, use this approach, it is

necessary to apply it also to civilian shift work—and

not only in industrial settings, but in other settings as

well (e.g., police work, long-distance transportation,

and medical care). Physiological parameters, such as

brain activity, temperature, and endocrine levels,

need to be monitored and associated with psychological states and performance measures in order to

better understand how functioning is perturbed and

how perturbations could be ameliorated. While

laboratory studies can attempt to mimic and isolate

relevant variables, they cannot fully identify or

simulate all the factors present in natural situations.

Research designs need to incorporate enough

people over enough time to obtain statistically and

biologically meaningful data. Furthermore, analytic

models similar to those developed for operations

research are needed to take into account the multiple

input and output variables. The traditional experimental-control design may not be adequate for many

of the research questions that need to be addressed.

Research is needed on the variables that contribute to difficulties in adjusting to shift work. Factors

such as individual differences in circadian rhythms,

sleep patterns, personality, and age may play a role

in the ability of an individual to cope with a work

schedule. Studies of the roles of familial and

nonwork social demands on the shift worker are also

needed. Living in a society that has a different

timetable can impose extra burdens on the worker,

producing additional stresses on his or her health and

well-being.

Sleep loss and fatigue induced by shift work are

dependent not only on duration of work, but also on

time of day and time of cycle. These parameters need

to be documented, and their roles in the ability of

workers to perform safely and effectively need to be

established. The complex effects of biological

rhythms, health status, and drug and alcohol use on

performance of workers exposed to the additional

physiological stresses of disturbed sleep and cir-
Chapter 5--Biological Rhythms and Work Schedules .113

cadian rhythms have largely been ignored by researchers.

In addition, there is a compelling need for more

research on the interaction between work schedules

and safety in the workplace. Central to this endeavor

is more thorough collection of workplace data

regarding hours of work and the occurrence of

on-the-job accidents. Increased data collection by

relevant Federal agencies would greatly facilitate

this process.

All of the previously stated areas of research will

contribute to the final area of research activity-the

development of appropriate intervention techniques

or countermeasures to promote coping and improve

adaptation to shift work. Linked to this is the need

for adequate surveillance of workplace performance

and evaluation of the effectiveness of potential

interventions.

SUMMARY AND CONCLUSIONS

The disruption of biological rhythms that occurs

as a result of nonstandard work schedules can

interact with other factors to degrade the sleep,

health, performance, and well-being of individuals.

Although the degree to which different schedules

have these effects, which types of tasks are affected

most, what variables make an individual susceptible

to them, and what interventions can be taken to

lessen the effects have not been clearly delineated,

some general conclusions can be drawn.

The stresses associated with disruption of circadian cycles, sleep deprivation, and social disharmony interact and affect a number of areas. Shift

work is associated with increased incidence of

gastrointestinal problems, may be a risk factor for

other health problems, and for some workers results

in a general, chronic malaise. Performance on some

types of tasks can be diminished, especially in those

settings where sleep loss and fatigue compound the

effects of circadian disruption. These performance

decrements can compromise the safety of the worker

and can threaten public safety as well.

While the most direct intervention is to devise

schedules that do not lead to these consequences, the

development of a single best type of schedule is not

possible. The demands of a given job will help

dictate what might be best in that situation. The

avoidance of weekly rotating schedules maybe most

preferable from a circadian perspective, and schedules that incorporate extended duty hours which

result in sleep loss and fatigue should be avoided.

Beyond managing schedules, implementing educational and support programs regarding biological

rhythms, sleep, and family counseling may be a

good way to improve the coping ability of shift

workers. The development and use of such mechanisms as bright light and drugs to help the circadian

system desynchronize and napping strategies to

counteract the effects of sleep loss and fatigue would

also be beneficial to workers. Finally, the development of monitoring devices and systems that could

be used to assess performance capabilities could also

play a role in intervention.

Thus, while general information is available on

biological rhythms and shift work, specific information is lacking. There area number of areas in which

there are gaps in the base of knowledge. The

information derived from additional research will

define the nature, characteristics, and magnitude of

the effects caused by work schedules. This knowledge will guide the design and implementation of

intervention measures, which are necessary to reduce job-related stress, health effects, and fatigue

and to improve alertness and safety.

1.

2.

3.

4.

5.

6.

7.

CHAPTER 5 REFERENCES

Adam, K., and ”Oswald, I:, “Can a Rapidly Eliminated Hypnotic Cause Daytime Anxiety?” Pharmacopsychiatry 22:115-119, 1989.

Akerstedt, T., “A Questionnaire Study of Sleep/

Wake Disturbances and Irregular Work Hours,”

Sleep Research 12:358, 1983.

Akerstedt, T., “Adjustment of Physiological Circadian Rhythms and the Sleep/Wake Cycle to Shift

Work,” Hours of Work: Temporal Factors in Work

Scheduling, S. Folkard and T.H. Monk (eds.) (New

York, NY: John Wiley & Sons, 1985).

Akerstedt, T, “Sleep/Wake Disturbances in Working Life,” Electroencephalograph and Clinical

Neurophysiology 39(supp.):360-363, 1987.

Akerstedt, T., “Sleepiness as a Consequence of

Shift Work,” Sleep 11:17-34, 1988.

Akerstedt, T., and Gillberg, M., “Sleep Disturbances and Shift Work” Night and Shift Work:

Biological and Social Aspects, A. Reinberg, N.

Vieux, and P. Andlauer (eds.) (Oxford: Pergamon

Press, 1981).

Akerstedt, T., and Gillberg, M., “Displacement of

the Sleep Period and Sleep Deprivation: Implications for Shift Work” Human Neurobiology 1 :163-

171, 1982.
114 ● Biological Rhythms: Implications for the Worker

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

Akerstedt, T., Patkai, P., and Dahlgren, K., “Field

Studies of Shift Work: II. Temporal Patterns in

Psychophysiological Activation in Workers Alternating Between Night and Day Work,’ Ergonomics

20:621-631, 1977.

Akerstedt, T., Torsvall, L., and Gillberg, M., “Shift

Work and Napping,” Sleep and Alertness: Chronobiological, Behavioral, and Medical Aspects of

Napping, D.F. Dinges and R.J. Broughton (eds.)

(New York NY: Raven Press, 1989).

Angerspach, D., Knauth, P., Loskant, H., et al., “A

Retrospective Cohort Study Comparing Complaints

and Diseases in Day and Shift Workers,” lnternational Archives of Occupational and Environmental

Health 45:127-140, 1980.

Angus, R.G., and Heslegrave, R.J., “Effects of

Sleep Loss on Sustained Cognitive Performance

During a Command and Control Situation,’ Behavior Research Methods, Instruments, and Computers

17:55-67, 1985.

Armstrong, B. G., Nolin, A.D., and McDonald,

A.D., “Work in Pregnancy and Birth Weight for

Gestational Age,” British Journal of Industrial

Medicine 46:196-199, 1989.

Aschoff, J., Hoffman, K., Pohl, H., et al., “ReEntrainment of Circadian Rhythms After Phase

Shifts of the Zeitgeber,” Chronobiologia 2:23-78,

1975.

Axelsson, G., Rylander, R., and Molin, I., “Outcome of Pregnancy in Relation to Irregular and

Inconvenient Work Schedules,” British Journal of

Industrial Medicine 46:393-398, 1989.

Baker, D., “The Use and Health Consequences of

Shift Work,” International Journal of Health

Services 10:405-420, 1980.

Balkin, T.J., Department of Behavioral Biology,

Walter Reed Army Institute of Research, Walter

Reed Army Medical Center, Washington, DC,

personal communication, Dec. 19, 1990.

Bjerner, B., and Swensson, A., “Shift Work and

Rhythm,” Acta Medicine Scandinavia 278:102-

107, 1953.

Borland, R.G., Rogers, A. S., Nicholson, A.N., et al.,

“Performance Overnight in Shift Workers Operating a Day-Night Schedule,” Aviation, Space, and

Environmental Medicine 57:241-249, 1986.

Borowsky, M. S., and Wall, R., “Naval Aviation

Mishaps and Fatigue,” Aviation, Space, and Environmental Medicine 54:535-538, 1983.

Breithaupt, H., Hildebrandt, G., Dohre, D., et al.,

“Tolerance to Shift of Sleep, as Related to the

Individual’s Circadian Phase Position,” Ergonomics 21:767-774, 1978.

Browne, R. C., “The Day and Night Performance of

Tele-Printer Switchboard Operators,’ Occupational

Psychology 23:121-126, 1949.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

34.

Campbell, S., “Duration and Placement of Sleep in

a ‘Disentrained’ Environment,” Psychophysiology

21:106-113, 1984.

Campbell, S., and Dawson, D., “Enhancement of

Nighttime Alertness and Performance With Bright

Ambient Light,’ Physiology andBehuvior48:317-

320,1990.

Campbell, S., Eastman, C.I., and Lewy, A.J., “Light

Treatment for Shift Work,” Light Treatment and

Biological Rhythms--Bulletin of the Society for

Light Treatment and Biological Rhythms 2:9-10,

1990.

Campbell, S., and Zulley, J., “Ultradian Components of Human Sleep/Wake Patterns During Disentrainment,” Ultradian Rhythms in Physiology and

Behavior, H. Schulz and P. Lavie (eds.) (Berlin:

Springer-Verlag, 1985).

Campbell, S., and Zulley, J., “Napping as a

Biological Rhythm: Disentrainment of the Human

Sleep/Wake System,” Sleep ’86, W.P. Koella, F.

Obal, H. Schulz, et al. (eds.) (New York NY:

Gustav Fischer Verlag, 1988).

Coffey, L. C., Skipper, J.K., Jr., and Jung, F.D.,

“Nurses and Shift Work: Effects on Job Performance and Job-Related Stress,’ Journal of Advanced

Nursing 13:245-254, 1988.

Colligan, M.J., “Shift Work: Health and Performance Effects,” Environmental and Occupational

Medicine, W.N. Rom (cd.) (Boston, MA: Little,

Brown, 1983).

Colligan, M.J., and Tepas, D.I., “The Stress of

Work Hours,” American Industrial Hygiene Association Journal 47:686-695, 1986.

Comperatore, C.A., U. S.Army Aeromedical Research Laboratory, Fort Rucker, AL, personal communication, Feb. 15, 1991.

Comperatore, C.A., and Krueger, G.P., “Circadian

Rhythm Desynchronosis, Jet Lag, Shift Lag, and

Coping Strategies,’ Shift Work, Occupational Mealicine State-of-the-Art Reviews, A.J. Scott (cd.)

(Philadelphia, PA: Hanley & Belfus, 1990).

Condon, R., Colquhoun, P., Plett, R., et al., “Work

at Sea: A Study of Sleep, and of Circadian Rhythms

in Physiological and Psychological Functions, in

Watchkeepers on Merchant Vessels: IV. Rhythms

in Performance and Alertness,” International Archives of Occupational and Environmental Health

60:405-411, 1988.

Costa, G., Lievore, F., Casaletti, G., et al., “Circadian Characteristics Influencing Interindividual

Differences in Tolerance and Adjustment to Shift

Work” Ergonomics 32:373-385, 1989.

Czeisler, C.A., Allan, J. S., Strogatz, S.H., et al.,

“Bright Light Resets the Human Circadian Pacemaker Independent of the Timing of the Sleep/

Wake Cycle, “ Science 233:667-671, 1986.
Chapter 5--Biological Rhythms and Work Schedules ● 115

35.

36.

37.

38.

39.

40.

41.

42.

43.

44.

45.

Czeisler, C.A., Johnson, M.P., Duffy, J.F., et al.,

“Exposure to Bright Light and Darkness to Treat

Physiologic Maladaptation to Night Work” New

England Journal of Medicine 322:1253-

1259, 1990.

Czeisler, C.A., Moore-Ede, M. C., and Coleman,

R.M., “Rotating Shift Work Schedules that Disrupt

Sleep Are Improved by Applying Circadian Principles, “ Science 217:460-463, 1982.

Czeisler, C.A., Moore-Ede, M. C., and Coleman,

R.M., “Resetting Circadian Clocks: Applications to

Sleep Disorders Medicine and Occupational

Health,” Sleep/Wake Disorders: Natural History,

Epidemiology andLong-Terrn Evolution, C. Guilleminault and E. Lugaresi (eds.) (New York NY: Raven

Press, 1983).

Dahlgren, K., “Adjustments of Circadian Rhythms

and EEG Sleep Functions to Day and Night Sleep

Among Permanent Night Workers and Rotating

Shift Workers,” Psychophysiology 18:381-391,

1981.

DeJohn, C.A., Effects of Psychophysiological Countermeasures on Performance Decrement During

Sustained Flight Operations, Research and Technology Work Unit Summary FY 89 Addendum,

Accession No. DN 248502 (Pensacola, FL: U.S.

Department of the Navy, Medical Research and

Development Command, Aerospace Medical Laboratory, 1989).

DeVries-Griever, A.H.G., and Meijman, T.F., “The

Impact of Abnormal Hours of Work on Various

Models of Information Processing: A Process

Model on Human Costs of Performance,” Ergonomics 30:1287-1299, 1987.

Dinges, D.F., “The Influence of the Human Circadian Timekeeping System on Sleep,” Principles

and Practice of Sleep Medicine, M. Kryger, T. Roth,

and W.C. Demerit (eds.) (Philadelphia, PA: W.B.

Saunders, 1989).

Dinges, D.F., Orne, M.T, Whitehouse, W.G., et al.,

“Temporal Placement of a Nap for Alertness:

Contributions of Circadian Phase and Prior Wakefulness,” Sleep 10:313-329, 1987.

Dinges, D.F., and Powell, J.W., “Microcomputer

Analyses of Performance on a Portable, Simple

Visual RT Task During Sustained Operations,”

BehaviorResearch Methods, Instruments, and Cornputers 17:652-655, 1985.

Dinges, D.F., Whitehouse, W. G., and Orne, E. C.,

“The Benefits of a Nap During Prolonged Work

and Wakefulness,’ Work and Stress 2:139-153,

1988.

Duchon, J. C., and Keran, C.M., “The Effects of

Sleep Strategies on the Health, Length and Quality

of Sleep of Rotating Shift Wokers on the Night

Shift,” Studies in Industrial and Organizational

46.

47.

48.

49.

50.

51<

52.

53.

54.

55.

56.

57.

58.

59.

J

Psychology. Shift Work: Health, Sleep and Performance, vol. 9, G. Costa, G. Cesana, K. Kogi, et

al. (eds.) (Frankfurt am Main: Verlag Peter Lang,

1989).

Duchon,J.C., and Keran, C.M., “The Adjustment to

a Slowly Rotating Shift Schedule: Are Two Weeks

Better Than One?” Proceedings of the Human

Factors Society 34th Annual Meeting (Santa Monica,

CA: Human Factors Society, 1990).

Duchon, J.C., and Keran, C.M., “Relationships

Among Shift Worker Eating Habits, Eating Satisfaction, and Self-Reported Health in a Population of

U.S. Miners,” Work and Stress 4:111-120, 1990.

Duchon, J. C., Wagner, J., and Keran, C.M., “Forward vs. Backward Shift Rotation,’ Proceedings of

the Human Factors Society 33rd Annual Meeting

(Santa Monica, CA: Human Factors Society, 1989).

Dwyer, T., Industrial Accidents and Nightwork in

the Manufacturing Sector--A Research Project

(Wellington, New Zealand: Department of Labour,

Research and Planning Division, 1981).

Eastman, C.I., “Bright Light in Work/Sleep Schedules for Shift Workers: Application of Circadian

Rhythm Principles,” Temporal Disorder in Human

Oscillatory Systems, L. Rensing, U. an der Heiden,

and M.C. Mackey (eds.) (New York, NY: SpringerVerlag, 1987).

Eastman, C. I., “Circadian Rhythms and Bright

Light: Recommendations for Shift Work,” Work

and Stress 4:245-260, 1990.

Eastman, C.I., “Bright Light on the Night Shift:

Circadian Rhythms Can Advance or Delay,” Sleep

Research 20:318, 1991.

Eastman, C.I., and Miescke, K.J., “Entrainment of

Circadian Rhythms With 26-Hr Bright Light and

Sleep-Wake Schedules,” AmericanJournal of Physiology 259: R1189-1197, 1990.

Ely, D.L., and Mostardi, R.A., “The Effect of

Recent Life Events, Stress, Life Assets, and Temperament Pattern on Cardiovascular Risk Factors

for Akron City Police Officers,” Journal of Human

Stress 12:77-91, 1986.

Fitzpatrick, D.T., surgeon, U.S. Army Safety Center, Fort Rucker, AL, personal communication, Feb.

4, 1991.

Folkard, S., Minors, D. S., and Waterhouse, J.M.,

“Chronobiology and Shift Work: Current Issues

and Trends,” Chronobiologia 12:31-54, 1985.

Folkard, S., and Monk, T.H., “Shift Work and

Performance,” Human Factors 21:483-492, 1979.

Folkard, S., Monk, T.H., and Lobban, M. C., “Shortand Long-Term Adjustment of Circadian Rhythms

in ‘Permanent’ Night Nurses,’ Ergonomics 21 :785-

799, 1978.

Folkard, S., Monk, T.H., and Lobban, M.C., “Towards a Predictive Test of Adjustment to Shift
116 ● Biological Rhythms: Implications for the Worker

60.

61.

62.

63.

64.

65.

66.

67.

68.

69.

70.

71.

72.

Work” Ergonomics 22:79-91, 1979.

Foret, J., Bensimon, G., Benoit, O., et al., “Quality

of Sleep as a Function of Age and Shift Work,”

Night and Shift Work: Biological and Social Aspects, A. Reinberg,N. Vieux, and P. Andlauer(eds.)

(Oxford: Pergamon Press, 1981).

French, J., Hannon, P., and Brainard, G. C., “Effects

of Bright Illuminance on Body Temperature and

Human Performance,” Annual Review of Chronopharmacology 7:37-40, 1990.

Frese, M., and Semmer, N., “Shift Work, Stress and

Psychosomatic Complaints: A Comparison Between Workers in Different Shift Work Schedules,

Non-Shift Workers, and Former Shift Workers,”

Ergonomics 29:99-114, 1986.

Gadbois, C., “Women on Night Shift: Interdependence of Sleep and Off-the-Job Activities,” Night

and Shift Work: Biological and Social Aspects, A.

Reinburg, N. Vieux, and P. Andlauer (eds.) (Oxford: Pergamon Press, 1981).

Gander, P., and Graeber, R. C., “Sleep in Pilots

Flying Short-Haul Commercial Schedules,” Ergonomics 30:1365-1377, 1987.

Gordon, N.P., Cleary, P.D., Parker, C.E., et al.,

‘‘ThePrevalence and Health Impact of Shift Work,”

American Journal of Public Health 76:1225-1228,

1986.

Graeber, R. C., “HumanPerformance Issues in Shift

Work and Extended Duty Hours,” statement prepared for the Office of Technology Assessment

workshop Shift Work and Extended Duty Hours,

Washington, DC, May 23, 1990.

Graeber, R. C., Connell, L.J., Schreiber, H.G., et al.,

“Aircrew Sleep and Fatigue in Long-Haul Flight

Operations,” paper presented at the 40th Flight

Safety Foundation International Air Safety Seminar, Tokyo, Japan, Oct. 26-29, 1987.

Graeber, R. C., Rosekind, M.R., Connell, L.J., et al.,

“Cockpit Napping,” ICAO Journal 45:6-10, 1990.

Hamelin, P., “Lorry Driver’s Time Habits in Work

and Their Involvement in Traffic Accidents,”

Ergonomics 30:1323-1333, 1987.

Harma, M.I., Ilmarinen, J., Knauth, P., et al.,

“Physical Training Intervention in Female Shift

Workers: I. The Effects of Intervention on Fitness,

Fatigue, Sleep and Psychosomatic Symptoms,”

Ergonomics 31:39-50, 1988.

Harma, M. I., Ilmarinen, J., Knauth, P., et al.,

“Physical Training Intervention in Female Shift

Workers: II. The Effects of Intervention on the

Circadian Rhythms of Alertness, Short-Term Memory, and Body Temperature,’ Ergonomics 31:51-

63,1988.

Harrington, J.M., Shift Work and Health: A Critical

Review of the Literature (London: Her Majesty’s

Stationery Office, 1978).

73.

74.

75.

76.

77.

78.

79.

80.

81.

82.

83.

84.

85.

Hartmann, E., and Spinweber, C.L. “Sleep Induced

by L-tryptophan: Effects of Dosages Within the

Normal Dietary Intake,” Journal of Nervous and

Mental Diseases 167:497-499, 1979.

Hartman, E., Spinweber, C.L., and Ware, C.,

“L-tryptophan, L-lucine and Placebo: Effects on

Subjective Sleepiness,” Sleep Research 5:57, 1976.

Hildebrandt, G., Rohmert, W., and Rutenfranz, J.,

“Twelve- and 24-Hour Rhythms in Error Frequency of Locomotive Drivers and the Influence of

Tiredness,” International Journal of Chronobiology 2:175-180, 1974.

Jones, 1. S., and Stein, H. S., Effect of Driver Hours

of Service on Tractor-Trailer Crash Involvement

(Arlington, VA: Insurance Institute for Highway

Safety, 1987).

Kennedy, R. S., Wilkes, R.L., Dunlap, W.P., et al.,

“Development of an Automated Performance Test

System for Environmental and Behavioral Toxicology Studies,” Perceptual and Motor Skills 65:947-

962, 1987.

Kennedy, R. S., Baltzley, D.R., Wilkes, R.L., et al.,

“Psychology of Computer Use: IX. A Menu of

Self-AdministeredMicrocomputer-basedNeurotoxicology Tests,“ Perceptual and Motor Skills 67:1255-

1272, 1989.

Keran, C. M., and Duchon, J. C., “Age Differences

in the Adjustment to Shift Work” Proceedings of

the Human Factors Society 34th Annual Meeting

(Santa Monica, CA: Human Factors Society, 1990).

Kerkhof, G., ‘Individual Differences and Circadian

Rhythms,” Hours of Work: Temporal Factors in

Work Scheduling, S. Folkard and T.H. Monk (eds.)

(New York NY: John Wiley & Sons, 1985).

Klein, K.E., Wegmann, H.M., and Hunt, B. I.,

“Desynchronization as a Function of Body Temperature and Performance Circadian Rhythms, as a

Result of Outgoing and Homecoming Transmeridian Flights, ’ Aerospace Medicine 43:119-132,

1972.

Knauth, P., Erode, E., Rutenfranz, J., et al., “ReEntrainment of Body Temperature in Field Studies

of Shift Work,” International Archives of Occupational and Environmental Health 49:137-

149, 1981.

Knauth, P., and Kiesswetter, E., “A Change From

Weekly to Quicker Shift Rotations: A Field Study

of Discontinuous Three-Shift Workers,’ Ergonomics 30:1311-1321, 1987.

Knauth, P., and Rutenfranz, J., “Circadian Rhythm

of Body Temperature and Re-Entrainment at Shift

Change,” International Archives of Occupational

and Environmental Health 37:125-137, 1976.

Knauth, P., and Rutenfranz, J., “Development of

Criteria for the Design of Shift Work Systems,”
Chapter 5--Biological Rhythms and Work Schedules . 117

86.

87.

88.

89.

90.

91.

92.

93.

94.

95.

96.

97.

98.

Journal of Human Ergonomics 11(supp):337-36’7,

1982.

Knauth, P., Rutenfranz, J., Hermann, G., et al.,

“Re-entrainment of Physiological Functions in

Experimental Shift Work Studies,” Ergonomics

21:775-783, 1978.

Knutsson, A., Akerstedt, T., and Orth-Gomer, K.,

“Increased Risk of Ischaemic Heart Disease in Shift

Workers,” Lancet 2:89-92, 1986.

Keller, M., Kundi, M., and Cervinka, R., “Field

Studies of Shift Work at an Austrian Oil Refinery:

I. Health and Psychosocial Well-Being of Workers

Who Drop Out of Shift Work,” Ergonomics

21:835-847, 1978.

Kristensen, T. S., “Cardiovascular Diseases and the

Work Environment-A Critical Review of the

Epidemiologic Literature on Nonchemical Factors,” Scandinavian Journal of Work and Environmental Health 15;165-179, 1989.

Kroemer, K. H.E., Kroemer, H.J., and KroemerElbert, K. E., Engineering Physiology--Bases of

Human Factors/Ergonomics (New York, NY: Van

Nostrand Reinhold, 1990).

Krueger, G.P., “Sustained Work, Fatigue, Sleep

Loss and Performance: A Review of the Issues,”

Work and Stress 3:129-141, 1989.

Krueger, G.P., and Lieberman, H.R., U.S. Army

Research Institute of Environmental Medicine,

Natick, MA, personal communication, Feb. 15,

1991.

Lauber, J.K., and Kayten, P.J., “Keynote Address:

Sleepiness, Circadian Dysrhythmia, and Fatigue in

Transportation System Accidents,” Sleep 11:503-

512, 1988.

Lee, K.A., “Sleep-Related Problems Among Female Shift Workers,” Sleep Research 18:369, 1989.

Levin, L., Oler, J., and Whiteside, J.R., “Injury

Incidence Rates in a Paint Company on Rotating

Production Shifts,” Accident Analysis and Prevention 17:67-73, 1985.

Lewis, P.M., and Swarm, D.J., “Effect of a 12-Hour/

Day Shift on Performance,” Proceedings of the

Fourth Institute of Electrical and Electronics Engineers Conference on Human Factors and Powerplants, E.W. Hagen (cd.) (New York, NY: Institute

of Electrical and Electronics Engineers, 1988).

Lewy, A., Sack, R., and Latham, J., “Circadian

Phase Shifting of Blind and Sighted People With

Exogenous Melatonin Administration: Evidence

for a Phase Response Curve,” Second Annual

Conference of the Society for Light Treatment and

Biological Rhythms, New York, NY, 1990.

Lewy, A., Sack, R., Miller, L., et al., “Antidepressant and Circadian Phase-Shifting Effects of Light,’

Science 235:352-354, 1987.

99.

100.

101.

102.

103.

104.

105.

106.

107.

108.

109.

110.

111.

112.

113.

Lieberman, H.R., Corkin, S., Spring, B.J., et al.,

“The Effects of Dietary Neurotransmitter Precursors on Human Behavior,” American Journal of

Clinical Nutrition 42:366-370, 1985.

Mackie, R.T., and Miller, J. C., Effects of Hours of

Service, Regularity of Schedules and Cargo Loading on Truck and Bus Driver Fatigue (Washington,

DC: U.S. Department of Transportation, National

Highway Traffic Safety Administration, 1978).

Mahan, R.P., Carvalhais, A.B., and Queen, S.E.,

“Sleep Reduction in Night-Shift Workers: Is It

Sleep Deprivation or a Sleep Disturbance Disorder?” Perceptual and Motor Skills 70:723-730,

1990.

Meers, A., “Performance on Different Turns of

Duty Within a Three-Shift System and Its Relation

to Body Temperature-Two Field Studies,” Experimental Studies of Shift Work, P. Colquhoun, S.

Folkard, P. Knauth, et al. (eds.) (Opladen, Germany:

Westdeutscher Verlag, 1975).

Melbin, M., “Night as Frontier,” American Sociology Review 43:2-22, 1978.

Miles, L.E., and Broughton, R.J. (eds.), Medical

Monitoring in the Home and Work Environment

(New York NY: Raven Press, 1990).

Monk, T.H., “Advantages and Disadvantages of

Rapidly Rotating Shift Schedules-A Circadian

Viewpoint, “ Human Factors 28:553-557, 1986.

Monk, T.H., “Coping With the Stress of Shift

Work” Work and Stress 2:169-172, 1988.

Monk, T.H., and Embrey, D.E., “A Field Study of

Circadian Rhythms in Actual and Interpolated Task

Performance,” Night and Shift Work: Biological

and Social Aspects, A. Reinberg, N. Vieux, and P.

Andlauer (eds.) (Oxford: Pergamon Press, 1981).

Monk, T.H., and Folkard, S., “Shift Work and

Performance,’ Hours of Work: Temporal Factors

in Work Scheduling, S. Folkard and T.H. Monk

(eds.) (New York, NY: John Wiley& Sons, 1985).

Monk, T.H., Moline, M.L., and Graeber, R.C.,

“Inducing Jet Lag in the Laboratory: Patterns of

Adjustment to an Acute Shift in Routine,” Aviation

and Space Environmental Medicine 59:703-710,

1988.

Moog, R., “Optimization of Shift Work: Physiological Contributions,” Ergonomics 30:1249-1259,

1987.

Moore-Ede, M. C., and Richardson, G. S., “Medical

Implications of Shift Work,” Annual Review of

Medicine 36:607-617, 1985.

Moretz, S., “Rotational Shifts: Are They Harmful

to Workers’ Health?” Occupational Hazards October:54-57, 1987.

Morgan, J.N., “Child Care When Parents Are

Employed,” Five Thousand American Families:

Patterns of Economic Progress, vol. 9, S. Hill, D.H.
118 . Biological Rhythms: Implications for the Worker

114.

115.

116.

117.

118.

119.

120.

121.

122.

123.

124.

125.

126.

127.

Hill, and J.N. Morgan (eds.) (Ann Arbor, MI:

University of Michigan Press, 1981).

Mrosovsky, N., and Salmon, P.A., “A Behavioral

Method for Accelerating Reentrainment of

Rhythms to New Light-Dark Cycles,” Nature

330:372-373, 1987.

Mullaney, D.J., Fleck, P.A., Okudaira, et al., “An

Automated System for Administering Continuous

Workload and for Measuring Sustained Continuous

Performance,’ Behavior Research Methods, Instruments, and Computers 17:16-18, 1985.

Nachreiner, F., Brand, G., Ernst, G., et al., “Zur

Kontrolle von Hawthorne-Effekten in Feldexperimenten,” Zeiter Arbeitswissenschaft 32:172-175,

1977.

National Transportation Safety Board, Safety Study--

Fatigue, Alcohol, Other Drugs, and Medical Factors in Fatal-to-the Driver Heavy Truck Crashes,

vol. 1, NTSB/SS-90/01 (Springfield, VA: National

Technical Information Service, 1990).

Novak, R.D., Smolensky, M.H., Fairchild, E.J., et

al., “Shift Work and Industrial Injuries at a Chemical Plant in Southeast Texas, ’ Chronobiology

International 7:155-164, 1990.

Nurminen, T., “Shift Work, Fetal Development and

Course of Pregnancy,” Scandinavian Journal of

Work and Environmental Health 15:395-403, 1989.

Olson, C.M., “Shift Work,” Journal of Emergency

Medicine 2:37-43, 1984.

Ong, C.N., Phoon, W. O., Iskander, N., et al., “Shift

Work and Work Injuries in an Iron and Steel Mill,”

Applied Ergonomics 18:51-56, 1987.

Orth-Gomer, K., “Intervention on Coronary Risk

Factors by Adapting a Shift Work Schedule to

Biologic Rhythmicity,” Psychosomatic Medicine

45:407-415, 1983.

Ottman, W., Karvonen, M.J., Schmidt, K.H., et al.,

“Subjective Health Status of Day and Shift Working Policemen,’ Ergonomics 32:847-854, 1989.

Parth, P., Kennedy, R. S., Lane, N.E., et al., “Motor

and Cognitive Testing of Bone Marrow Transplant

Patients After Chemoradiotherapy,” Perceptual

and Motor Skills 68:1227-1241, 1989.

Presser, H.B., “Working Women and Child Care,”

Women: A Developmental Perspective, NIH Pub.

No. 82-2298, P.W. Berman and E.R. Ramey (eds.)

(Washington, DC: U.S. Government Printing Office, 1982).

Presser, H.B., “Some Economic Complexities of

Child Care Provided by Grandmothers,’ Journal of

Marriage and the Family 51:581-591, 1989.

Prokop, O., and Prokop, L., “Ermunudung und

Einschlafen am Steuer,” Zentralblatt fur VerkehrsMedizin, Verkehrs-Psychologie und Angrenzende

Gebiete 1:19-30, 1955.

128.

129.

130.

131.

132.

133.

134.

135.

136.

137.

138.

139.

Redmond, D.P., and Hegge, F.W., “Observations

on the Design and Specification of a Wrist-Worn

Human Activity Monitoring System,” Behavior

Research Methods, Instruments, and Computers

17:659-669, 1985.

Reinberg, A., Andlauer, P., DePrins, J., et al.,

“Desynchronization of the Oral Temperature Circadian Rhythm and Intolerance to Shift Work,”

Nature 308:272-274, 1984.

Reinberg, A., Andlauer, P., Guillet, P., et al., “Oral

Temperature, Circadian Rhythm Amplitude, Aging

and Tolerance to Shift Work” Ergonomics 23:55-

64,1980.

Reinberg, A., Motohashi, Y., Bourdeleau, P., et al.,

“Alteration of Period and Amplitude of Circadian

Rhythms in Shift Workers, With Special Reference

to Temperature, Right and Left Hand Grip

Strength,” European Journal of Physiology 57:15-

25,1988.

Reinberg, A., Motohashi, Y., Bourdeleau, P., et al.,

“InternalDesynchronization of Circadian Rhythms

and Tolerance of Shift Work” Chronobiologia

16:21-34, 1989.

Rogers, A.S., Spencer, M.B., Stone, B.M., et al.,

“The Influence of a 1 h Nap on Performance

Overnight,” Ergonomics 32:1193-1205, 1989.

Rosa, R.R., and Bonnet, M.H., “Performance and

Alertness on 8-Hour and 12-Hour Rotating at a

Natural Gas Utility,” Ergonomics, in press.

Rosa, R.R., Bonnet, M.H., Bootzin, R.R., et al.,

‘‘Intervention Factors for Promoting Adjustment to

Nightwork and Shift Work,” Shift Work, OccupationalMedicine State-of-the-Art Reviews, A.J. Scott

(cd.) (Philadelphia, PA: Hanley & Belfus, 1990).

Rosa, R.R., and Coil.igan, M.J., The NIOSHFatigue

Test Battery: Laboratory Validation of a Portable

System for Field Study of Extended Workdays and

Work Scheduling, NIOSH internal report (Cincinnati, OH: U.S. Department of Health and Human

Services, National Institute for Occupational Safety

and Health, 1986).

Rosa, R.R., and Colligan, M.J., “Long Workdays

vs. Rest Days: Assessing Fatigue and Alertness

With a Portable Performance Battery,” Human

Factors 30:305-317, 1988.

Rosa, R.R., Colligan, M.J., and Lewis, P, “Extended Workdays: Effects of 8-Hour and 12-Hour

Rotating Shift Schedules on Performance, Subjective Alertness, Sleep Patterns, and Psychological

Variables,” Work and Stress 3:21-32, 1989.

Rosa, R.R., Wheeler, D.D., Warm, J. S., et al.,

‘‘Extended Workdays: Effects on Performance and

Ratings of Fatigue and Alertness,” Behavior Research Methods, Instruments, and Computers 17:6-

15, 1985.
Chapter S-Biological Rhythms and Work Schedules .119

140.

141.

142.

143.

144.

145.

146.

147.

148.

149.

150.

151.

152.

Rutenfranz, J., Colquhoun, W.P., Knauth, P., et al.,

“Biomedical and Psychosocial Aspects of Shift

Work A Review,” Scandinavian Journal of Work,

Environment and Health 3:165-182, 1977.

Rutenfranz, J., Haider, M., and Keller, M., “Occupational Health Measures for Night Workers and

Shift Workers,” Hours of Work: Temporal Factors

in Work Scheduling, S. Folkard and T.H. Monk

(eds.) (New York, NY: John Wiley& Sons, 1985).

Rutenfranz, J., Plett, R., Knauth, P., et al., ” Work at

Sea: A Study of Sleep, and Circadian Rhythms in

Physiological and Psychological Functions, in Watchkeepers on Merchant Vessels: II. Sleep Duration

and Subjective Ratings of Sleep Quality,’ International Archives of Occupational and Environmental

Health 60:331-339, 1988.

Sack, R.L., and Lewy, A.J., “Melatonin Administration Phase Advances Endogenous Rhythms in

Man,” Sleep Research 17:396, 1988.

Scherr, J., “Man’s Work and Circadian Rhythm

Through the Ages,” Night and Shift Work: Biological and Social Aspects, A. Reinberg, N. Vieux, and

P. Andlauer (eds.) (Oxford: Pergamon Press, 1981).

Seidel, W.F., Roth, T., Roehrs, T., et al., “Treatment of a 12-Hour Shift of Schedule With Benzodiazepines,” Science 224:1262-1264, 1984.

Smith, P., “A Study of Weekly and Rapidly

Rotating Shift Workers,’ International Archives of

Occupational and Environmental Health 43:211-

220,1979.

Spinweber, C. L., L-Tryptophan, Sleep and Performance, NHRC Rep. No. 87-17 (San Diego, CA: U.S.

Department of the Navy, Medical Research and

Development Command, Health Research Center,

March 1987).

Staines, G.L., and Pleck, J.H., The Impact of Work

Schedules on the Family (Ann Arbor, MI: University of Michigan, Institute for Social Research,

1983).

Tarquini, B., Cecchettin, M., and Cariddi, A.,

‘‘Serum Gastrin and Pepsinogen in Shift Workers,”

International Archives of Occupational and Environmental Health 58:99-103, 1986.

Taste, D.L., and Colligan, M.J., Health Consequences of Shift Work, Project URU-4426, Technical Rep. (Menlo Park, CA: Stanford University,

Stanford Research Institute, 1978).

Tepas, D. I., Department of Psychology, University

of Connecticut, Storrs, CT, personal communication, Jan. 9, 1991.

Tepas, D.I., Armstrong, D.R., Carlson, M.L., et al.,

“Changing Industry to Continuous Operations:

Different Strokes for Different Plants,” Behavior

Research Methods, Instruments, and Computers

17:670-676, 1985.

153.

154.

155.

156.

157.

158.

159.

160.

161.

162.

163.

164.

165.

Tepas, D.I., and Mahan, R.P., “The Many Meanings of Sleep,” Work and Stress 3:93-102, 1989.

Tepas, D.I., Popkin, S.M., and Dekker, D.K., “A

Survey of Locomotive Engineers on Irregular Schedules and Their Spouses: A Preliminary Report,”

Studies in Industrial and Organizational Psychology. Shift Work: Health, Sleep and Performance,

vol. 10, G. Costa, G. Cesana, K. Kogi, et al. (eds.)

(Frankfurt am Main: Verlag Peter Lang, 1990).

Tepas, D.I., Walsh, J.K., and Armstrong, D.R.,

“Comprehensive Study of the Sleep of Shift

Workers,” The Twenty-Four Hour Workday: Proceedings of a Symposium on Variations in WorkSleep Schedules, L.C. Johnson, D.I. Tepas, W.P.

Colquhoun, et al. (eds.) (Cincinnati, OH: U.S.

Department of Health and Human Services, National Institute of Occupational Safety and Health,

1981).

Tepas, D.I., Walsh, J.K., Moss, P.D., et al., “Polysomnographic Correlates of Shift Worker Performance in the Laboratory,” Night and Shift Work:

Biological and Social Aspects, A. Reinberg, N.

Vieux, and P. Andlauer (eds.) (Oxford: Pergamon

Press, 1981).

Thorne, D.R., Genser, S.G., Sing, H. C., et al., “The

Walter Reed Performance Assessment Battery,”

Neurobehavioral Toxicology and Teratology 7:415-

418, 1985.

Tilley, A.J., Wilkinson, R.T., Warren, P. S.G., et al.,

“The Sleep and Performance of Shift Workers,”

Human Factors 24:629-641, 1982.

Torsvall, L., and Akerstedt, T., “Sleepiness on the

Job: Continuously Measured EEG Changes in Train

Drivers,” Electroencephalograph and Clinical

Neurophysiology 23:143-148, 1987.

Turek, F.W., “Circadian Principles and Design of

Rotating Shift Work Schedules,” American Journal of Physiology 251: R636-638, 1986.

Turek, F.W., and Losee-Olson, S., “A Benzodiazepine Used in the Treatment of Insomnia PhaseShifts the Mammalian Circadian Clock” Nature

321:167-168, 1986.

Turek, F.W., and Van-Reeth, O., “Altering the

Mammalian Circadian Clock With the Short-Acting

Benzodiazepine, Triazolam,” Trends in Neuroscience 11:535-541, 1988.

U.S. Congress, Office of Technology Assessment,

The Electronic Supervisor: New Technology, New

Tensions, OTA-CIT-333 (Washington, DC: U.S.

Government Printing Office, 1987).

Van Cauter, E., and Turek, F.W., “Strategies for

Resetting the Human Circadian Clock,” New England Journal of Medicine 322:1306-1308, 1990.

Van Loon, J.H., “Diurnal Body Temperature

Curves in Shift Workers,” Ergonomics 6:267-272,

1963.
120 ● Biological Rhythms: Implications for the Worker

166.

167.

168.

169.

170.

171.

172.

173.

Wagner, J.A., “Time-of-Day Variations in the

Severity of Injuries Suffered by Mine Shift Workers,” Proceedings of the Human Factors Society

32nd Annual Meeting (Santa Monica, CA: Human

Factors Society, 1988).

Walker, J., “Social Problems of Shift Work,”

Hours of Work: Temporal Factors in Work Scheduling, S. Folkard and T.H. Monk (eds,) (New York

NY: John Wiley & Sons, 1985).

Walsh, J., Muehlbach, M., Humm, T.M., et al.,

“Effect of Caffeine on Physiological Sleep Tendency and Ability to Sustain Wakefulness at

Night,” Psychopharmacology 101:271-273, 1990.

Walsh, J. K., Muehlbach, M.J., and Schweitzer,

P.K., “Acute Administration of Triazolam for the

Daytime Sleep of Rotating Shift Workers,” Sleep

7:223-229, 1984.

Walsh, J., Schweitzer, P. K., Anch, A. M., et al.,

“Sleepiness/Alertness on a Simulated Night Shift

Following Sleep at Home With Triazolam,” Sleep

14:140-146, 1991.

Walsh, J., Sugerman, J., Muehlbach, M., et al.,

“Physiological - Sleep Tendency on a Simulated

Night Shift: Adaptation and Effects of Triazolam,”

Sleep 11:251-264, 1988.

Walsh, J., Tepas, D. I., and Moses, P., “The EEG

Sleep of Night and Rotating Shift Workers,”

Biological Rhythms, Sleep and Shift Work, L.C.

Johnson, D.I. Tepas, W.P. Colquhoun, et al. (eds.)

(New York NY: Spectrum Publications, 1981).

Watson, A.P., “The Importance of Work Shift in

Determining Risk of Fatal and Lost Work Day

Injury Accidents,” Annals of the American Conference of Governmental Industrial Hygienists 14:125-

130, 1986.

174.

175.

176.

177.

178.

179.

180.

181.

182.

Wedderburn, A., Studies of Shift Work in the Steel

Industry (Edinburgh: Department of Business Organization, Heriot-Watt University, 1975).

Weitzman, E.D., and Kripke, D.F., “Experimental

12-Hour Shift of the Sleep/Wake Cycle in Man:

Effects on Sleep and Physiologic Rhythms,” Advances in Sleep Research, vol. 7, Variations in

Work-Sleep Schedules: Effects on Health and Performance, L.C. Johnson, D.I. Tepas, W.P. Colquhoun, et al. (eds.) (New York NY: Spectrum

Publications, 1982).

Wever, R.A., The Circadian System of Man: Results

of Experiments Under Temporal Isolation (New

York, NY: Springer-Verlag, 1979).

Wever, R.A., Polasek, J., and Wildgruber, C.M.,

‘ ‘Bright Light Affects Human Circadian

Rhythms,” Pflugers Archives 396:85-87, 1983.

White, L., and Keith, B., ‘‘The Effect of Shift Work

on the Quality and Stability of Marital Relations, ”

Journal of Marriage and the Family 52:453-462,

1990.

Williamson, A.M., and Sanderson, J. W., “Changing the Speed of Shift Rotation: A Field Study,”

Ergonomics 29:1085-1096, 1986.

Wojtczak-Jaroszowa, J., and Jarosz, D., “TimeRelated Distribution of Occupational Accidents,”

Journal of Safety Research 18:33-41, 1987.

Wojtczak-Jaroszowa, J., Makowska, Z., Rzepechi,

A., et al., “Changes in Psychomotor and Mental

Task Performance Following Physical Work in

Standard Conditions, and in a Shift Working

Situation,” Ergonomics 21:801-809, 1978.

Wojtczak-Jaroszowa, J., and Pawlowska-Skyba, K.,

“Night and Shift Work: I. Circadian Variations in

Work” Medical Practice 18:1, 1967.
Chapter 6

Legal and Regulatory Issues
Contents

Page

CURRENT AREAS OF REGULATORY ACTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Hours of Service Act . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......................*.,.*,.**.***

Motor Carrier Safety Act of 1984 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Civil Air Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maritime Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

National Transportation Safety Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Nuclear Powerplant Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fair Labor Standards Act . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

State Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

AREAS OF POTENTIAL REGULATORY ACTION . .*.....,.*....,....,..,.**,.+*..,.,

Occupational Safety and Health Laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

State Plans ... ... ... ... ... ... .*. ..** * . . . . . . . . . . * . . . * . . . . . . . + * * * * . + * * * * * * . * * * ..+***...

Mine occupational Safety and Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Other Safety and Health Statutes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Relationship of OSHA to Other Laws . .............,......*.......,**.*...**..**.*,..

Fair Labor Standards Act . . . . . . . . . .

Labor Relations Statutes . . . . . . . . . . .

GOVERNMENT EMPLOYEES . . . . . .

Federal Employees . . . . . . . . . . . . . . . .

State Employees . . . . . . . . . . . . . . . . . .

SUMMARY AND CONCLUSIONS . .

CHAPTER 6 REFERENCES

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Box

6-A. Evolution

6-B. Employer

. . . . . . . . .

Workday

Liability . . . . . . . . . . . . ~.

Boxes

123

123

125

126

127

127

128

128

130

130

131

133

133

134

135

136

136

138

138

139

139

140

Page

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

●
Chapter 6

Legal and Regulatory Issues

This chapter addresses legal and regulatory issues

related to work schedules and hours of work,

referred to generally as work schedules. In particular, it discusses Federal and State regulation, including statutes and regulations currently in place and

potential areas of regulation under existing authority. The discussion will consider several categories

of statutes:

●

●

●

statutes relating directly to work schedules and

hours of employment;

safety and health regulatory statutes not dealing

directly with work schedules (to the extent that

work schedules are shown to affect the safety

and health of employees and the public, these

statutes could be an important source of legal

authority to regulate schedules); and

statutes that protect the collective rights of

employees (work schedules are included in

collective bargaining agreements).

The chapter also addresses a number of legal

issues related to work schedules, among them:

●

●

●

the relationship between Federal and State

regulation;

various types of mechanisms to enforce the

legal requirements, as well as their advantages

and disadvantages; and

the regulation of public employees.

CURRENT AREAS OF

REGULATORY ACTION

A distinction in Federal regulatory structure

should be emphasized at the outset. In some cases,

such as the Hours of Service Act in the railroad

industry, requirements regarding work schedules are

included in the statute itself and therefore could be

modified only by legislative action. In other instances, the statutes give an administrative agency

quasi-legislative authority, and the requirements are

promulgated in rules issued by the agency, for

example, the regulation of hours of work of air

personnel by the Federal Aviation Administration

(FAA), in the Department of Transportation (DOT).

Changes in these requirements could therefore be

made by the agency through amendments to the

rules.

Hours of Service Act

It is not surprising that the earliest Federal

regulation of work schedules took place in industries

where public safety is an important factor. Early

Federal regulation of railroads was concerned with

the integrity of the physical equipment and imposed

requirements for safety equipment on railroad engines and cars (see Safety Appliance Act, 45 U.S.C.

1 et seq.). However, it was clear that significant

hazards to employees and travelers existed because

of the failure of some employees responsible for

operations to discharge their responsibilities in a

safe manner. This led to enactment of the Hours of

Service Act (HSA) in 1907 (45 U.S.C. 61 et seq.).

The Supreme Court has recognized that the purpose

of this statute was to avoid dangers to employees and

to the public when employees do hazardous work for

such long periods hat-they are unfit and their

judgment is compromised (3). Responsibility for

enforcement of this statute originally rested with the

Interstate Commerce Commission. When DOT was

created in 1966, this responsibility was transferred to

the Secretary of Transportation and the Federal

Railroad Administration (FRA) [Public Law 89-670

(1966); 49 U.S.C. 1655(e)(2); 49 U.S.C. 102 (DOT);

49 U.s.c. 103 (m)].

Although the HSA has been amended several

times since 1907, its basic requirements have

remained the same. In addition to the work schedule

requirements in the law itself, FRA has issued rules

under the act that impose requirements for recordkeeping and reporting and govern construction of

employee sleeping quarters (49 CFR 228).

The HSA applies to any common carrier engaged

in interstate or foreign commerce by railroad [45

U.S.C. 61(a)]. Employees commonly covered include locomotive engineers, firefighters, conductors, train operators, and switch operators (49 CFR

228, app. A). The act makes it unlawful for a

common carrier to require or permit an employee

who has been continuously on duty for 12 hours to

continue on duty or go on duty until he or she has had

at least 10 consecutive hours off duty [45 U.S.C.

2(a)(l)]. The act also makes it unlawful to permit or

require an employee to continue or go on duty when

he or she has not had at least 8 consecutive hours off

–123–

297-935 - 91 - 5 QL 3
124 ● Biological Rhythms: Implications for the Worker

duty during the preceding 24 hours [45 U.S.C.

62(a)(2)]. The act includes as on-duty time all time

that the employee spends in connection with train

movement, as well as all time in the service of the

common carrier [45 U. S. C. 62(b) (1990 pocket

part)]. Time on duty begins when an employee

reports for duty and ends when he or she is released

from duty. It includes periods for rest at other than

designated terminals [45 U.S.C. 61(b)(3)]. An exception to these limitations is provided for crews of

a wreck or relief train when the crew’s work is

related to an emergency, in which case employees

may remain on duty for 4 additional hours in any

period of 24 consecutive hours [45 U.S.C. 62(c)].

The HSA specifies that the common carrier must

also provide sleeping quarters for employees which

afford an opportunity for rest free from interruption

caused by noise under the control of the railroads [45

U.S.C. 62(a)(3)]. Similarly, sleeping quarters may

not be constructed in or near areas where railroad

switching and humping operations are performed

[45 U.S.C. 62(a)(4)]. These requirements have been

interpreted in FRA rules, which, among other things,

define the distance requirements for sleeping quarters and specify procedures for approval by FRA of

construction plans for sleeping quarters (49 CFR

228, subpart C).

The HSA also limits hours for other categories of

employees, that is, those not actually engaged in or

connected with train movements. It is unlawful for

any employee who uses electrical or mechanical

devices to dispatch, transmit, or receive orders

affecting train movements to remain on duty for

more than 9 hours in a 24-hour period in a place

where two or more shifts are employed [45 U.S.C.

63(a) and 1990 pocket part]. The same is true for 12

hours in a 24-hour period where one shift is

employed [45 U.S.C. 63(a)(2)]. Special authorization is given for 4 hours of additional service in a

24-hour period in case of emergency, but not

exceeding 3 days in 7 consecutive days [45 U.S.C.

63(c)]. Other work schedule requirements are imposed for individuals engaged in installing, repairing, or maintaining signal systems. An individual

who has been on duty continuously for 12 hours may

not continue on duty without at least 8 consecutive

hours off duty during the preceding 24 hours [45

U.S.C. 63a (a)].

These provisions are the maximum permissible

hours of service consistent with safety (45 U.S.C. 64

and 1990 pocket part). However, the HSA also

provides that they are proper subjects for collective

bargaining under the National Labor Relations Act

and the Railway Labor Act (discussed later). That is,

a carrier and employee representative may agree to

further limit employee work schedules (45 U.S.C. 64

and 1990 pocket part).

A related statute, but one designed for an entirely

different purpose, is the Adamson Act, enacted in

1916 and codified together with the HSA (45 U.S.C.

65). The Adamson Act establishes a day’s work to be

8 hours, for the purpose of compensation for services

(45 U.S.C. 65). Thus, the act does not bar workdays

of more than 8 hours, it simply provides that 8 hours

is the basis for calculating overtime under the Fair

Labor Standards Act and under collective bargaining

agreements. The Adamson Act may provide economic incentives for limiting work schedules, but it

does not regulate them directly.

Enforcement of the HSA, as noted, is assigned to

the Secretary of Transportation (49 CFR 209.1). The

Administrator of the FRA is appointed by the

President with the advice and consent of the Senate

and reports directly to the Secretary of Transportation. The provisions of the HSA relating to manner

of enforcement were amended significantly by the

Rail Safety Improvement Act of 1988 (45 U.S.C.

64A). The enforcement scheme of the FRA under the

HSA and related safety statutes will be discussed in

more detail below.

Persons violating requirements of the HSA are

liable for civil penalties. The penalties for willful

violations may be as high as $1,000 per violation [45

U.S.C. 64a(a)(l)]. The FRA decides whether a

penalty is to be assessed. Where no compromise is

reached with the offending party, it is the duty of the

U.S. Attorney to sue to collect the penalty in a

Federal court under the Federal Claims Collection

Act [45 U.S.C. 64a(a)(l)].

The FRA’s most sweeping enforcement tool,

although one that it has used only rarely, is its

authority to issue emergency safety orders halting

conditions or practices that create a hazard of death

or injury to persons [45 U.S.C. 432(a)]. After

issuance of the order, it must be reviewed in a

trial-like hearing (49 CFR 211.47, 216.21-27). This

emergency authority is unique in that it can be used

to address unsafe practices and conditions whether

or not they contravene an existing regulatory or

statutory requirement (49 CFR 209, app. A). The
Chapter 6--Legal and Regulatory Issues ● 125

provision has been held by a U.S. court of appeals to

apply to conditions or practices that are hazardous

under the HSA respecting sleeping accommodations,

even though HSA requirements are enforced in court

by the U.S. Attorney and not the FRA (21).

The Railroad Safety Act, which became law in

1970 (45 U.S.C. 421 et seq.), authorizes the Secretary of Transportation, through FRA, to issue rules

for all areas of railroad safety to supplement laws

and rules already in effect, including those under the

Hours of Service Act. To date, the FRA has not

issued any. The FRA’s potential to regulate work

schedules will be discussed below.

Motor Carrier Safety Act of 1984

The Motor Carrier Safety Act of 1984 (MCSA) is

an example of a statute that gives an administrative

agency quasi-legislative authority to regulate safety.

Congress stated in the preamble to the MCSA that

the purpose of the law was to:

promote the safe operation of commercial

motor vehicles;

minimize dangers to the health of the operators

of those vehicles and of other employees whose

employment directly affects motor carrier safety;

and

assure increased compliance with traffic laws

and with various regulations issued under the

act (49 U.S.C. App. 2501).

MCSA covers commercial motor vehicles

defined as:

●

●

●

vehicles with gross weight exceeding 10,001

pounds;

vehicles designed to transport more than 15

persons (including the driver); and

vehicles used to transport certain hazardous

materials [49 U.S.C. App. 2503(1)].

Federal, State, and local government employers are

not covered by the act.

The Secretary of Transportation is required to

issue regulations that, at a minimum, ensure that the

physical condition of operators of commercial motor

vehicles is adequate to safe operation and that the

operation of the vehicles does not have deleterious

effects on the physical condition of the operators [49

U.S.C. App. 2505(a)(3),(4)]. Regulations regarding

motor carrier safety are exercised by the Federal

Highway Administration (FHWA) through the Office of Motor Carriers.

The Secretary of Transportation’s responsibility

to issue regulations under MCSA has been implemented in part by FHWA regulations entitled Hours

of Service of Drivers (49 CFR 395). These regulations relate to maximurn on-duty and driving time,

drivers’ records of on-duty status, and provisions for

special circumstances. The regulations also contain

provisions for the use of automatic on-board recording devices (49 CFR 395.15) and provide that these

devices not be used to harass operators (the latter

provision stemming from concern that the devices

might be used to spy on drivers). The on-board

devices record such things as engine revolutions per

minute, vehicle speed, oil temperature and pressure,

distance traveled, driving time, breaks, daily rest

periods, and compliance with speed limits.

Hours of Service Regulations for Drivers

The basic work schedule limitation in FHWA

regulations is that no driver may be required or

permitted to drive:

●

●

●

●

The

more than 10 hours following 8 consecutive

hours Off duty;

for any period after having been on duty 15

hours following 8 consecutive hours off duty;

for any period after having been on duty 60

hours in any 7 consecutive days if the motor

carrier does not operate every day of the week;

for any period after having been on duty 70

hours in any period of 8 consecutive days if the

motor carrier operates every day of the week

(49 CFR 395.3).

regulations define on-duty time to include

waiting-time; inspection time; time spent loading,

unloading, or repairing equipment; and time in any

motor vehicle, even if not driving. It does not include

time spent resting in a sleeper berth meeting FHWA

requirements.

In an emergency, a driver may complete a run

without violating the regulations if the run can

reasonably be completed without such a violation. In

the event of adverse driving conditions, such as

snow, sleet, or fog, a driver may drive for 2

additional hours to complete a run or reach a safe

place; however, a driver may never drive for more

than 12 hours following 8 consecutive hours off duty

or after being on duty 15 hours following 8
126 ● Biological Rhythms: Implications for the Worker

consecutive hours off duty (49 CFR 395.10). These

regulations do not apply to carriers transporting

passengers or property in order to provide relief in

the event of a natural disaster (49 CFR 395.12).

The regulations contain two methods for determining a driver’s hours of service. Under the first,

the carrier requires the driver to record his or her

duty status for each 24-hour period on a specified

grid or on a previously approved daily log, in

combination with any company forms. Under the

other, the carrier requires drivers to use an automatic

on-board recording device in lieu of manual recording. The recording device produces on demand an

electronic display or printout of the driver’s hours of

service, including the sequence of duty status

changes and each day’s starting time (49 U.S.C.

395.15).

Enforcement

Regulations issued under the Motor Carrier Safety

Act are enforced by FHWA through periodic random inspections and inspections conducted in response to complaints (49 U.S.C. App. 2509-2511).

The FHWA is authorized to impose civil penalties

for violations of MCSA in amounts specified in

DOT’s authorization statutes (49 U.S.C. 521). A

penalty of up to $500 may be imposed for violations

of recordkeeping requirements. Where there has

been a serious pattern of safety violations other than

recordkeeping, a civil penalty of up to $1,000 for

each offense may be assessed; however, total

penalties may not exceed $10,000. If FHWA determines that a health or safety violation resulted or

reasonably could have resulted in serious physical

injury or death, a civil penalty of up to $10,000 may

be imposed for each offense. No penalty may be

imposed on an employee except for gross negligence

or reckless disregard of safety, in which case the

penalty may not exceed $1,000 [49 U.S.C. 521(b)

(l)(B)]. A person is entitled to be given notice when

charged and to be given an opportunity for a hearing

before the penalty becomes final.

The FHWA can order a vehicle out of service or

order an employer to cease all or part of its

commercial motor vehicle operations if it finds that

a violation or combination of violations poses an

imminent hazard to safety [49 U.S.C. 521(b)(5)].

Criminal penalties may be imposed on anyone who

knowingly or willfully violates the statute or regulations; if the violator is an employee, the penalty is

limited and may be applied only if the unlawful

activity could have led to death or serious injury.

Special agents of FHWA can also declare a driver

out of service and therefore ineligible to drive if they

determine that the driver has been on duty longer

than the maximurn period permitted in the regulations (49 CFR 395.13).

Civil Air Safety

The Secretary of Transportation has the statutory

duty to promote the safety of commercial airlines by

prescribing and revising reasonable rules and regulations governing maximum’ hours or periods of

service of airmen and other employees of air carriers

[49 U.S.C. App. 1421(a)(5)]. The FAA has issued

numerous safety regulations under its statutory

authority, including limitations on duty and flight

time and rest requirements for various categories of

covered employees [14 CFR 121(P-S)]. Enforcement of FAA safety rules is governed by provisions

of the Federal Aviation Act (49 U.S.C. App. 1471 et

seq.) and the implementing regulations (14 CFR

13.15,13.16) and includes agency authority to impose civil penalties, orders of compliance, criminal

penalties, punitive damages, and injunctions (49

U.S.C. App. 1471,1472,1523).

Work Schedule Limitations

FAA has issued rules prescribing duty and flight

limitations for pilots, air traffic controllers, engineers, and crew members of various kinds of air

carriers [14 CFR 121(P-S)]. Because the rules are

detailed and complex, only the flight time limitations and rest requirements for crew members of

domestic air carriers will be summarized here.

Under the rules, a domestic air carrier is not

permitted to issue, and a flight crew member may not

accept, an assignment for flight if the crew member’s

total flight time will exceed:

. 100 hours in a calendar month;

. 30 hours in 7 consecutive days; or

. 8 hours between required rest periods.

In addition, a flight crew member may not be

assigned flight time during the 24 consecutive hours

preceding the scheduled completion of any flight

segment unless he or she has a scheduled rest period

of at least:

. 9 consecutive hours for less than 8 hours of

scheduled flight time;
Chapter 6--Legal and Regulatory Issues ● 127

. 10 consecutive hours for 8 to 9 hours of

scheduled flight time; or

. 11 consecutive hours for 9 or more flight hours.

These rest requirements may be reduced if a rest

period of a specified length is scheduled to begin no

more than 24 hours after the reduced rest period.

The rules further require that the crew member be

relieved of all duty for at least 24 hours during any

7 consecutive days and prohibits the assignment or

acceptance of any duty during any scheduled rest

period. The rules also provide that flight time does

not include:

time spent in transportation provided to the

crew member by the carrier to and from the

airport; and

time when the airplane does not reach its

destination within the scheduled time because

of circumstances beyond the control of the

carrier [14 CFR 121(Q)].

Separate FAA rules prescribe flight time limitations

for pilots and other crew members of flag air carriers

[14 CFR 14 (R)] and of supplemental air carriers and

commercial operators [14 CFR 121 (5)].

Limitations on duty time for air traffic controllers

are also important to safety. Except in emergency

situations, a certified air traffic tower operator may

not be required to work in excess of:

. 10 consecutive hours or

. 10 hours during a 24-hour period unless he or

she has been allowed a rest period of at least 8

hours before or at the end of the first 10 hours

of duty.

In addition, an air traffic controller must be allowed

at least 1 day off during each consecutive 7-day

period (14 CFR 65.47).

Enforcement

The FAA is authorized to enforce the safety

requirements of the Federal Aviation Act by means

of civil and criminal penalties. Where the FAA

believes that an emergency exists, it is authorized,

either on its own initiative or on a complaint, to issue

an order promptly [49 U.S.C. App. 1485(a)].

Maritime Safety

The U.S. Coast Guard has been part of DOT since

1966, when the Department was created (49 U.S.C.

108). The shipping statute related to work schedules

contains specific requirements on the manning of

vessels (46 U.S.C. 8101-8105). In particular, the

provisions on watches limit hours of service. An

officer may take charge of a deck watch on a vessel

only if that officer has been off duty for at least 6 of

the 12 hours immediately before departure [46

U.S.C. 8 104(a)]. On certain oceangoing or coastwise

vessels (vessels that only go along the coast), a

seaman cannot be required to work more than 9 of 24

hours when in port or more than 12 of 24 hours at

sea, except when life or property is endangered [46

U.S.C. 8104(b)]. Similarly, a seaman in a deck or

engine department cannot work more than 8 hours in

1 day on a towing vessel, except in an emergency or

on certain merchant vessels [46 U.S.C. 8104(c),(d)].

On certain towing vessels, an individual cannot

work for more than 12 hours in a consecutive

24-hour period except in an emergency [46 U.S.C.

8104(h)]. Additional statutory requirements related

to watches may affect hours of service indirectly,

such as provisions concerning the number of watches

into which personnel must be divided [46 U.S.C.

8104(1)]. The statute also prescribes certain rest

periods and prohibits unnecessary work on Sundays

and certain holidays [46 U.S.C. 8104(e)(2)]. In some

circumstances, however, such as when work is

necessary for the safety of the vessel or saving a life

on board another vessel, these restrictions are not

applicable [46 U.S.C. 8104(f)].

National Transportation Safety Board

The National Transportation Safety Board (NTSB)

is a separate and independent agency made up of five

members appointed by the President with the advice

and consent of the Senate. The NTSB’s primary

responsibility is to investigate railway, aircraft,

highway, marine, pipeline, and hazardous material

accidents in order to determine the probable cause of

an accident and to make recommendations concerning safety (49 U.S.C. App. 1903, 1906). Although

NTSB has no direct regulatory authority and

cannot require compliance, its recommendations

are publicized and may be influential in a

number of arenas. Indeed, the law requires the

Secretary of Transportation to respond to NTSB

safety recommendations, including giving a statement of intent to address the recommendations,

together with a proposed procedure and a timetable for adopting them. The Secretary must give

a detailed explanation for his or her refusal to adopt

NTSB recommendations. NTSB accident reports
128 ● Biological Rhythms: Implications for the Worker

and other reports have addressed issues related to

hours of service in all modes of transportation.

Nuclear Powerplant Regulation

The Nuclear Regulatory Commission (NRC) was

created in 1974 under the Energy Reorganization

and Development Act (42 U.S.C. 5841 et seq.). It has

the authority to regulate the possession and use of

nuclear materials, nuclear power reactors and facilities, and persons who use nuclear materials [42

U.s.c. 2201(b); 10 CFR 55].

The NRC has issued a policy statement regarding

working hours for nuclear powerplant staff [47 FR

23,836 (1982)]. NRC policy statements are enforceable only if a plant voluntarily incorporates them

into its technical specifications as part of the NRC

licensing procedure. The policy statement addresses

the need to establish controls to prevent situations in

which fatigue could reduce the ability of personnel

to operate a reactor safely. The controls, which focus

on shift staffing and the use of overtime, apply to

staff who perform safety-related functions and

ensure that such staff are not assigned to shift duties

while in a fatigued condition, which might reduce

their mental alertness or their decisionmaking ability. The objective is for plants to employ enough

personnel so that operating staff work a normal

8-hour day, 40-hour week. However, where unforeseen problems or special circumstances arise necessitating major overtime, the policy offers certain

guidelines to be followed. According to the policy

statement, an individual, even in emergency situations, should not be permitted to work:

. more than 16 consecutive hours;

● more than 16 hours in a 24-hour period;

● more than 24 hours in a 48-hour period; or

● more than 72 hours in any 7-day period.

In addition, a break of at least 8 hours should be

allowed between work periods, and licensed operators at controls should be relieved periodically and

given noncontrol responsibilities during their tour of

duty [47 FR 23,836 (1982)]. Nuclear powerplant

control room operators are discussed in greater detail

in chapter 7.

Fair Labor Standards Act

The Fair Labor Standards Act (FLSA), a centerpiece of New Deal employment legislation enacted

in 1938, originally:

. mandated a minimum wage rate for covered

employees (29 U.S.C. 206);

. required employers to pay an overtime premium for each hour worked in excess of 40

hours in a single week (29 U.S.C. 207); and

● imposed penalties on employers for oppressive

child labor (29 U.S.C. 212).

In 1963, the FLSA was amended to provide for equal

pay for equal work regardless of sex [29 U.S.C.

206(d)]. The act has also been amended to expand its

coverage. It originally imposed statutory requirements only on employers engaged in commerce or in

the production of goods for commerce [29 U.S.C.

206(a); 29 U.S.C. 207(a)(l)], but it now includes

certain agricultural employees and State and local

government employees.

The statutory and regulatory provisions of FLSA

relating to who is covered are detailed and complex.

Thus, for example, employees in a bona fide

executive, administrative, or professional capacity

are exempt from FLSA’s requirements [29 U.S.C.

213(a)(l)]. Other employees may be exempt from

the maximum hour requirements alone [29 U.S.C.

213(b)] and still others from the child labor requirements [29 U.S.C. 213(c)]. The Department of Labor

has issued regulations and statements of general

policy relating to the coverage of FLSA. Of particular relevance is the extent to which FLSA overtime

provisions apply to employees of railroads, motor

carriers, airlines, and maritime transportation.

The FLSA is implemented by the Wage and Hour

Division of the Department of Labor. The act is

enforced primarily through suits brought by the U.S.

Government and by private individuals. Criminal

penalties, enforced by the Department of Justice, are

authorized in some cases [29 U.S.C. 216(a)], and

violations of the child labor requirements are enforced by a system of administratively determined

civil penalties [29 U.S.C. 216(e)].

Child Labor Provisions

Child labor laws protect children from mistreatment in employment settings and ensure that employment will not interfere with their schooling.

Children between 14 and 16 may not work in certain

occupations, such as those connected with transportation, under any circumstances [29 CFR 570.33(f)

(l)]. In other occupations, employment of 14- to

16-year-olds is permitted if confined to the following times:
Chapter 6-Legal and Regulatory Issues ● 129

Box 6-A—Evolution of the 8-Hour Workday

The 8-hour workday began as a key demand of the labor movement in the United States during the last quarter

of the 19th century. The shortened day was advocated as a means of increasing leisure time for workers and as a

way to offset the unemployment of workers whose jobs were being taken over by machines. Labor leaders, such

as Samuel Gompers, believed that shortening the workday to 8 hours would provide more jobs for those whose tasks

were threatened by automation. This did not prove to be true, however, since increased automation led to heightened

production, even with fewer workers.

Despite this, the movement for an 8-hour workday continued. In 1938, the concept was codified in the Fair

Labor Standards Act under the section regulating maximum hours for workers (29 U.S.C. 207). This section limited

the standard workweek to 40 hours, indirectly creating the 8-hour workday. Any work beyond the initial 40 hours

required compensation at one and one-half times the employee’s regular rate (29 U.S.C. 207).

Reasons for this limitation of hours included the desire for more leisure time and improved morale within the

working population, the health benefits of shorter hours, and increased general well-being. Economic factors also

enhanced the acceptability of the 8-hour day to the employer. It was thought that shorter hours would ultimately

lead to increased health and a reduction of social ills, which would bolster productivity and increase profits.

Furthermore, philosophical and societal goals entered into the reasoning behind the legislation. President

Franklin D. Roosevelt stated in a message to Congress on May 24,1937, “[a] self-supporting and self-respecting

democracy can plead no economic reason for chiseling workers’ wages or stretching workers’ hours. , . .

[e]nlightened business is learning that competition ought not to cause bad social consequences which inevitably

react upon the profits of business itself. . . . Government must have some control over maximum hours. . . to protect

the fundamental interests of free labor and a free people,’

SOURCIIS: Office of TednologyAssessmen4 1991; Uuitetl&atesO& Congressional ttl AdministrativeNews, Wt.bCongress, vol. 2 (SLPWL

MN: West PublM@, 1%7), pp. 3002-3003; ?JnitedStates Code Congressional 4iAdm’nistrative news, 93rd (!ongress, vol. 2 (St.

Paul, MN: West PablisMng, 1975), pp. 2814-2819; Unit&States Code Congressional &Adnu”nistrative Akmw, IOlst Congress, vol.

2 (St. Pa~ MN: West Publishing, 1990), pp. 69tk697.

● outside school hours; an employer to pay each employee meeting certain

● not more than 40 hours per week when school

is not in session;

. not more than 18 hours per week when school

is in session;

. not more than 8 hours per day when school is

not in session;

. not more than 3 hours per day when school is in

session; and

s between 7 a.m. and 7 p.m. in any 1 day, except

during the summer, when the evening hour will

be 9 p.m. [29 CFR 570.35(a)].

The regulations also provide for employment of

children between 14 and 16 in school-related work

and career exploration programs meeting certain

requirements. Among those requirements is that the

employment shall not exceed 23 hours in 1 week or

3 hours in 1 day when school is in session [29 CFR

570.35A(d)].

Overtime Provisions

Unlike the child labor provisions of FLSA, which

directly limit the work schedules of minors, the

minimum wage and overtime provisions have only

an indirect impact on regulation. The FLSA requires

requirements a minimum wage (29 U.S.C. 206).

Under the overtime provisions, an employer may not

employ a worker for more than 40 hours per week

unless the worker is paid at one and one-half times

his or her regular rate (29 U.S.C. 207). Thus this

statute does not prohibit employers from requiring

or permitting employees to work more than 40 hours

a week, but it does regulate the basic hourly rate and

the resulting regular rate on which overtime is based.

Box 6-A explains the origin of the 8-hour workday.

Central to both minimum wage and overtime

provisions is the determination of hours worked.

This can become complicated when it involves

issues such as waiting time, rest and meal periods,

preparatory and concluding activities, lectures, meetings, training programs, and travel time (29 CFR

785, subpart C). Of particular relevance is its

application to sleeping time. An employee who is

required to be on duty for less than 24 hours is

working even though he or she is permitted to sleep

or engage in personal activity when not busy (29

CFR 785.20, 785.21). However, for employees

required to be on duty for 24 hours or more, the

employer and employee may agree to exclude from
130 ● Biological Rhythms: Implications for the Worker

hours worked a regularly scheduled sleeping period

of not more than 8 hours, as long as adequate

sleeping facilities are furnished by the employer and

the employee can usually enjoy an uninterrupted

sleep [29 CFR 785.22(a)]. No more than 8 hours

sleep time can be excluded, however [29 CFR

785.22(a)]. If the sleep period is interrupted to such

an extent that the employee cannot get a reasonable

amount of sleep, the entire period must be counted

as hours worked. According to Wage and Hour

Division guidelines, if 5 hours of sleep are not

provided, the entire time is work time [29 CFR

785.22(b)]. In a recent case involving overnight

relief workers at residential facilities for the mentally retarded, the court held that the employees,

though on duty for more than 24 hours, were entitled

to compensation for sleep time because of the nature

of their accommodations and the frequent need to

attend to clients at the facilities (8).

State Regulation

There is a substantial body of State regulation in

the area of employee hours and conditions of work,

some of which relates directly or indirectly to work

scheduling. Because of the extensive nature of the

material, only a few examples will be discussed. In

considering State legislation, one should bear in

mind the possible preemptive effect of Federal

regulation of the same subject matter.

A number of States have legislation paralleling

the FLSA. An example is Michigan’s minimum

wage law, enacted in 1964 (11) and last amended in

1980. This law establishes a minimum wage and

overtime pay and provides for exemptions for

certain categories of employees. Michigan also has

in effect a work scheduling law for motor truck and

tractor operators (sec. 480.12, 480.13 of Compiled

Laws of 1970). Under the law, a person may not

drive a motor truck or tractor more than 10 hours in

15 hours, and then only following 8 hours off duty.

The law defines duty time as beginning with the

person’s reporting for duty and ending with the

person’s release. It further provides that off-duty

time may be accumulated in a sleeping berth in two

periods of at least 2 hours each (1 1).

Michigan has also enacted a child labor statute,

which imposes work schedule limitations on certain

minors. The law does not apply to:

. children over age 15 who have graduated from

high school;

● children over 16 who have passed a certain

development test; and

. emancipated minors.

In addition to prohibiting certain work entirely, the

law makes it unlawful for a person under 18 to be

employed in a covered occupation for:

. more than 6 days in 1 wink;

● more than a weekly average of 8 hours per day;

and

● more than 48 hours in 1 week or more than 10

hours in 1 day.

In addition, the minor may not be employed between

10:30 p.m. and 6 a.m. when school is in session, or

between 11:30 p.m. and 6 a.m. when school is not in

session. A minor in school may not be employed a

combined school and workweek of 48 hours when

school is in session. Children under 16 have the same

restrictions, except they may not be employed

between 9 p.m. and 7 a.m. (11).

Other State legislation focuses generally on work

schedule limitations for specific categories of employees, such as minors, and requirements for

premium pay for overtime. A notable exception that

has attracted wide attention is the recently enacted

New York State statute regulating the work schedules of attending physicians and certain postgraduate trainees in hospitals [N.Y. State Code, Title 10,

sec. 405.4(a)(6)]. This matter is discussed in more

detail in chapter 8. Box 6-B discusses employer

liability for accidents caused by a sleep deprived

employee in a recent Oregon case.

AREAS OF POTENTIAL

REGULATORY ACTION

Regulatory action can arise from the enactment of

new (or amended) legislation covering work schedules or from the promulgation of new regulations

under existing statutory authority. With respect to

the enactment of new Federal legislation, there is no

serious question regarding the power and authority

of the Congress to take legislative action to regulate

work schedules. Along line of Supreme Court cases

has established the plenary power of Congress to

regulate economic matters, including labor regulation, under the commerce clause of the U.S. Constitution. While Federal legislation could apply

work schedule requirements selectively, that is, to

some categories of employees but not to others, there

would have to be a satisfactory explanation for its
Chapter 6---Legal and Regulatory Issues ● 131

Box 6-B—Employer Liability

‘‘Employment,” according to Black’s Law Dictionary, includes the actual act of working and may include a

reasonable amount of space and time necessary to travel to and from the work site. An employer who allows an

employee to work too many hours without rest may be found negligent in cases where this employee causes an

accident, even after leaving the job site.

Faverty v. McDonald’s Restaurants of Oregon, Inc.: The jury found McDonald’s liable for allowing its

employee to drive home after working an all-night shift and awarded Frederic M. Faverty $170,000 for medical

expenses and lost wages and $230,000 in general damages. The employee, Matthew A. Theurer, an 18-year-old high

school senior, left McDonald’s at the end of a 12-hour split shift after asking the manager to schedule another worker

for his next shift because he was tired. Theurer began the 19-mile drive to his home but fell asleep behind the wheel

and struck Faverty’s car head on. Faverty suffered serious injuries. Theurer was killed. Theurer had worked a

51/z-hour shift on Sunday night from 6 p.m. to 11:30 p.m. and had attended a full day of school on Monday. On

Monday afternoon he began a 12-hour split shift that ran from 3:30 p.m. to 7:30 p.m., resumed at midnight, and

lasted until 8:20 a.m. Tuesday. According to testimony, Theurer had complained at school and work that he was

tired. He had had less than 7 hours of sleep in the 48 hours before the accident and had not slept at all in the 24 hours

preceding the crash.

Faverty sued McDonald’s for his injuries stemming from the automobile accident. The jury found that

McDonald’s knew, or should have known, of Theurer’s exhaustion and that he planned to drive home by himself.

According to this decision, it should have been foreseeable to McDonald’s that Theurer would be operating a motor

vehicle and would be a danger to himself and others since he had been awake more than 24 hours. McDonald’s is

appealing this decision.

SOURCES: Office of Technology Assessment, 1991; based on Associated Press, “McDonaId’s Loses Worker’s Collision Case,” New York

Times, Apr. 1, 1991, p. A12; Case No. 90-0100394, Circuit Court of the State of Oregon for the County of Muhnomah; B2ack’s L.uw

Dictionq, 5tb ed. (St. Paul, MN: West Publishing Co., 1979); M. Lowe~, attorney, legal department, McDonald’s Corp.,

Oakbrootq IL, personal communicatio~ June 18, 1991.

.—— .— ————

doing so. This explanation could consist of data

showing particular danger from fatigue in specific

industries. Such an explanation would probably be

upheld, particularly sine legislation singling out

certain industrial groups for regulatory purposes has

substantial precedent.

At the same time. it should be emphasized that

some distinctions in regulatory coverage may be

problematic under the equal protection clause of the

U.S. Constitution and State constitutions and under

civil rights statutes. Distintions based on gender

and race would be subject to particular scrutiny.

Thus, for example. a statute that limited night

work for women but not men would be scrutinized very carefully by the court. The argument

that women are in need of special protection is no

longer acceptable and probably would not stand

up in court (17). Where Federal statutes already

include specific work schedule requirements, as for

example railroad employees, modification of these

requirements may be necessary.

With regard to State legislation, the issue is

somewhat more complex. While State legislatures

generally have authority to regulate economic matters, they are subject to both Federal constitutional

limitations (e.g., due process and equal protection)

and State constitutional limitations. In addition, any

State regulatory action, whether in the form of a

statute, regulation, order, or decision, may be

preempted by Federal regulatory action in the same

area, The issue of Federal preemption is a complex

area of law involving constitutional principles,

Federal statutory language and intent, and a substantial body of precedent. Any potential State legislative action or other regulatory action would have to

take into account this body of law.

occupational Safety and Health Laws

The most likely source of authority in regulating work schedules would be safety and health

statutes. Some of these deal specifically with occupational safety and health, notably the Federal

Occupational Safety and Health Act (OSH Act) (29

U. S.C. 651).

The Occupational Safety and Health Administration (OSHA) was created to implement the provisions of the OSH Act, which covers all private

employees [29 U.S.C. 652(5)]. Although Federal

and some State and local employees are not covered
132 . Biological Rhythms: Implications for the Worker

by the basic OSHA program, they are covered by

separate provisions [29 U.S.C. 652(5), 668]. Covered employers have two basic obligations:

. to comply with occupational safety and health

standards issued by OSHA; and

. to comply with the general duty clause (see

later discussion) (29 U.S.C. 654).

OSHA enforces those obligations through a system

of workplace inspections, the issuance of civil

penalties of up to $70,000, and citations with

abatement requirements [29 U.S.C. 666(a)-(d)]. The

OSH Act also includes authority for limited criminal

penalties [29 U.S.C. 666(e)].

OSHA Standards

OSHA has issued a large body of standards,

generally separated into safety standards and health

standards (29 CFR 1900 et seq.), but none deals with

work scheduling. If, however, OSHA determined

that hours of work pose a safety or health hazard

to employees, it could regulate work schedules by

issuing a standard. In considering whether OSHA

should take regulatory action on work schedules

through the promulgation of standards, a number of

factors must be kept in mind:

●

●

●

The standard’s purpose must be to protect

employee safety and health; OSHA has no

authority to issue standards directed solely

toward public safety (2).

OSHA’s jurisdiction is broad, and many serious

hazards are competing for its regulatory attention. OSHA would have to determine that

regulation of work schedules was particularly

important before it would take action. With

such subjects as AIDS, ergonomic hazards, the

hazards of blood-borne diseases to health care

workers, and various carcinogens on its agenda,

there is serious question whether OSHA is

likely to tackle the work schedule issue in the

near future. Interested parties may petition

OSHA to begin rulemaking on an issue, may

make use of political or other means to persuade the agency to act, and may sue in court to

force OSHA to act. In some cases, courts have

ordered OSHA to undertake rulemaking, but

this has been in the context of carcinogens or

other special circumstances (15).

OSHA rulemaking is typically slow, with years

elapsing before a final standard is issued and

upheld in court. While priority items are often

speeded up, such special treatment would not

necessarily be accorded to work schedule

regulation. On occasion, courts have forced

OSHA to complete rulemaking, but this is

unusual and takes place only in special situations (16).

General Duty Clause

The general duty clause of the OSH Act [sec. 5 (a)

(l)] requires that an employer provide employees

with a workplace free from recognized hazards

likely to cause death or serious physical harm [29

U.S.C. 654(a)(l)]. Like standards, the general duty

clause is enforced through workplace inspections,

citations, and penalties. However, enforcement differs in several important respects. When OSHA

enforces a standard, the employer’s obligations are

defined by the standard, which has already entailed

a public participation phase and has usually been

upheld by a court. Thus, in the enforcement proceeding OSHA need only establish the facts and show

that the standard was violated in order to uphold the

citation and penalty.

In general duty proceedings, however, the burden

on OSHA is greater. There is no specific obligation

to be enforced; there are only the more generalized

requirements of section 5 (a)(l). To establish a

general duty violation, OSHA must show the

following:

●

●

●

The

There is a recognized hazard. On this, there is

considerable case law, and while OSHA generally need not prove that the employer recognized the hazard, it is still necessary to show

that the hazard has been recognized by industry

or safety experts (14).

The hazard is likely to cause death or serious

physical harm.

Feasible methods of abatement of the hazard

exist.

general duty clause is usually not applicable

where a standard covering the hazard involved

already exists, even when it can be shown that the

existing standard is generally recognized as inadequate.

Employer obligations under the general duty

clause are established on a case-by-case basis. This

means that employers would have to sift through

OSHA announcements and Occupational Safety and

Health Review Commission and court decisions to

determine what work schedule requirements are
Chapter 6--Legal and Regulatory Issues ● 133

considered by OSHA to be recognized as a possible

hazard. OSHA would have to establish, and reestablish, the recognition of these hazards in each

individual case to be enforced. Thus, use of the

general duty clause to regulate work schedule

hazards would probably lead to less effective

compliance and would be more burdensome for

the agency. In short, if OSHA decides to regulate

employee work schedules; the requirements

should be defined by a standard issued after

rulemaking. Despite the possible length of the

standards proceedings, standards afford the only

reliable basis for regulation. Until a standard is

issued, the general duty clause would be available to

deal with particularly egregious hazards (12).

State Plans

The OSH Act contains specific provisions dealing

with State plans (29 U.S.C. 667). State occupational

safety and health enforcement is expressly preempted

by OSHA standards on the same issue, unless a State

plan is in effect. States may submit their own

programs for State occupational safety and health

enforcement and, if found at least as effective as

Federal standards, the State program will be approved. On approval, the State is entitled to escape

preemption and to enforce its own program with 50

percent financial assistance from OSHA. Ultimately, a State may be granted final approval, at

which time Federal enforcement legally ends and the

State alone enforces safety and health obligations;

however, the State must maintain its program at a

level at least as effective as OHSA’s. It also would

be required to issue at least as effective a standard if

OSHA were to promulgate a new standard for work

schedules. OSHA continues to monitor the effectiveness of State programs, even after final approval,

and may withdraw approval of a State plan [29

U.S.C. 667(f)].

There are at present 26 approved plans submitted

by States and other jurisdictions, and 14 of these

have been granted final approval. In these, there is no

Federal enforcement, with States having jurisdiction

over most occupational safety and health enforcement under their plans.

In sum, if OSHA undertook regulation of work

schedules, the Federal standard and enforcement

would cover fewer than half the States; the remainder would be covered by State standards and

enforcement. This State activity must be at least as

effective as OSHA’s and, with limited exceptions,

may be more effective [29 U.S.C. 667(c)(2)].

Mine Occupational Safety and Health

In 1977, Congress enacted the Federal Mine

Safety and Health Act (30 U.S.C. 801 et seq.). This

statute assigned enforcement of its standards to the

Mine Safety and Health Administration (MSHA) in

the Department of Labor. The act covers all coal and

other mines and authorizes the issuance of mine

safety and health standards (30 U.S.C. 803). The

procedures for issuance of standards are similar to

the OSHA procedure, including authority to issue

emergency temporary standards (30 U.S.C. 811).

MSHA is required to enforce these standards, but in

a number of respects its enforcement provisions are

more stringent than those in the OSH Act. Thus, for

example, MSHA in some circumstances has administrative close-down authority (30 U.S.C. 817), and

the mine safety statute provides for a mandatory

minimum number of inspections per year for various

kinds of mines (30 U.S.C. 813). The Supreme Court

has held that, unlike OSHA, MSHA is not obligated

to obtain a search warrant before conducting amine

inspection (6). The greater stringency of MSHA

statutory procedures is due largely to congressional

recognition of the seriousness and immediacy of

hazards at mines.

The act does not provide for State plans, but State

standards that provide for more stringent protection

than Federal standards or provide protection where

no applicable Federal standard exists may be enforced (30 U.S.C. 955). Provisions are also made for

Federal grants to States for the purpose of developing and enforcing effective mine safety and health

standards (30 U.S.C. 953).

MSHA is given explicit authority to issue mandatory health and safety standards for the protection of

life and the prevention of injury in coal and other

mines [30 U.S.C. 81 l(a)]. This authority parallels

OSHA’s authority, and on a satisfactory showing

that work schedules create safety and health hazards

for employees, MSHA would have authority to issue

mandatory standards protecting employees from

work schedule hazards (12).

OSHA is preempted by the OSH Act from

applying to any working condition covered by

another statutory program [29 U.S.C. 653(b)(l)].

Since mine employees are covered comprehensively
134 ● Biological Rhythms: Implications for the Worker

by MSHA standards and enforcement, OSHA does

not apply to them or to mine working conditions.

Other Safety and Health Statutes

In addition to statutes dealing with protection of

employees, there are mixed-purpose statutes designed to protect both public and employee safety.

An example is the Federal Railroad Safety Act of

1970 (45 U.S.C. 421 et seq.), designed to protect

both railroad employees and passengers and members of the public who may be affected by railroad

operations.

Federal Railroad Safety Act

The Federal Railroad Safety Act is designed to:

●

●

●

promote safety in all areas of railroad operations;

reduce railroad-related accidents; and

reduce deaths and injuries to persons caused by

accidents involving any carrier of hazardous

materials (45 U.S.C. 421).

Under the law, the Secretary of Transportation,

acting through the Federal Railroad Administration,

is required to prescribe rules, regulations, orders,

and standards for all areas of railroad safety,

supplementing those laws and regulations already in

effect (45 U.S.C. 431). The statute expressly provides that FRA is not authorized to issue rules

related to qualifications of employees except when

qualifications are specifically related to safety [45

U.S.C. 431(a)]. The act further authorizes carriers

and unions to enter into bargaining agreements

related to qualifications of employees, consistent

with FRA rules issued under the statute. The statute

contains a timetable for FRA issuance of safety rules

and provides for court review of the rules.

The act authorizes railroad safety rules to supplement those contained in earlier statutes and in

previously issued administrative rules. Thus, while

the Hours of Service Act (45 U.S.C. 61 et seq.)

prescribes specific limitations on the hours of

service of specific categories of railroad employees,

the Railroad Safety Act would authorize FRA to

issue safety rules for additional categories of railroad

employees or prescribe additional requirements.

These new rules could impose limitations on employee work schedules as long as the rules were

specifically related to safety.

FRA has promulgated regulations on the control

of alcohol and drug use by railroad employees to

prevent accidents and casualties resulting from

impairment of employees (49 CFR 219). Accordingly, it could be argued that FRA would have

authority to regulate work schedules if it could be

proved that regulation would prevent railroad accidents resulting from such conditions as fatigue and

inattention.

Motor Carrier Safety Act

Under the MCSA, the Secretary of Transportation

is authorized to issue regulations establishing minimum Federal safety standards for commercial motor

vehicles. At a minimum, these standards must

ensure that:

. the responsibilities imposed on operators of

vehicles do not impair their ability to operate

the vehicles safely;

● the physical condition of operators is adequate

to enable them to operate vehicles safely; and

. the operation of vehicles does not have deleterious effects on the physical condition of operators (49 U.S. App. 2505).

This authority is broad enough to include work

schedule regulation. Indeed, FHWA has already

issued hours of service regulations and regulations

on alcohol and drug use of operators, which have

been upheld (22). Accordingly, FHWA could amend

existing hours of service regulations or issue additional regulations on work scheduling.

Federal Aviation Act

Under this statute, the FAA has specific authority,

in the interests of safety, to issue reasonable rules

and regulations governing the maximum hours or

periods of service of airmen and other employees of

air carriers. The FAA is also authorized to issue

reasonable rules and regulations or minimum standards governing other practices, methods, and procedures it finds necessary to provide adequately for

safety in air commerce [49 U.S.C. App. 1421(a)(5),(6)].

As already discussed, FAA has issued hours of

service regulations for various categories of employees in air commerce, and it would have the authority

to modify or add to these regulations, subject to court

review.
Chapter 6--Legal and Regulatory Issues . 135

U.S. Coast Guard

The Coast Guard supervises the merchant marine

of the United States and merchant marine personnel.

It has specific statutory authority to take action

governing vessels and shipping in the interests of

marine safety and seamen’s welfare (46 U.S.C.

2103). The statute also contains specific requirements for the reaming of vessels, including limitations on hours of service for certain types of

employees, particularly in relation to watches on

ships. The Coast Guard has general authority to issue

interpretations of the manning requirements (46

CFR 15) and hours limitations and to issue regulations limiting hours beyond those stipulated by the

statute, based on its authority to regulate marine

safety and seamen’s welfare.

Energy Reorganization and Development Act

The NRC has authority to issue regulations

governing nuclear materials in order to protect

health or to minimize danger to life or property [42

U.S.C. 2201(b)]. This could provide sufficient

authority for the agency to regulate work schedules

of covered employees. NRC has already issued

regulations related to fitness for duty of employees

of licensees, prescribing a program of drug and

alcohol testing (10 CFR 26). Work schedule regulations could be analogous, as they, too, impose

requirements for fitness for duty. The relevance of

schedule restrictions to fitness has been recognized

explicitly by NRC in a policy statement.

Relationship of OSHA to Other Laws

Broadly speaking, where an agency has general statutory authority to regulate employee

safety or health, or both, this authority ordinarily

includes regulation of work schedules if the

connection between safety and health and the

regulatory requirements can be shown. There

may be more limited authority over work schedules

under specific statutes, and conclusions on the

extent of that authority can be drawn from the

statutory language, its legislative history, and relevant decisions. The OSH Act covers occupational

safety and health in all private industries. In addition, there are other statutes which provide regulatory authority over both public and occupational

safety and health; these include several statutes

administered by the Secretary of Transportation (45

U.S.C. 2121; 49 U.S.C. App. 1421). These statutes

may also provide agency authority over work

schedules of employees.

There remains the issue of the jurisdictional

overlap between OSHA’s broad employee safety

and health coverage and the coverage of industryspecific statutes relating to employee safety and

health. Thus, for example, employees of private

railroads are covered by OSHA under the Railroad

Safety Act and the Hours of Service Act. The OSH

Act [29 U.S.C. 653(b)(l)] deals with this issue and

provides that the act does not apply to working

conditions when other Federal agencies exercise

statutory authority to prescribe or enforce standards

or regulations affecting occupational safety and

health. While the language of this section is not

entirely clear, its purpose is to prevent redundant

regulation of occupational safety and health, while

avoiding any gaps in employee protection. OSHA

has issued an interpretative regulation of this provision (29 CFR 1955), which contains the following

general principles:

●

●

●

It

The act applies only when specific working

conditions are regulated by another Federal

agency. OSHA would not be preempted in an

entire industry merely because some working

conditions in that industry were regulated by

another Federal agency (20). The only industrywide preemption that has taken place is in

mining, which is regulated comprehensively

under the Mine Safety and Health Act.

The regulation of working conditions by another Federal agency would be preemptive,

even where the relevant statute is not directed

exclusively to employee safety and health (for

example the Railroad Safety Act, which also

deals with public safety). However, the statute

must intend to include employees in the class of

persons to be protected under it (7).

In order to preempt OSHA, another Federal

agency must have exercised its statutory authority to protect employees (19).

is apparent, therefore, that it would be necessary

to study the statutes and regulations of both OSHA

and other Federal agencies to determine, in the event

of overlapping jurisdiction, which regulations would

apply. Even after study, the answer may not be

apparent, and court decisions sometimes add to the

confusion. In order to clarify jurisdictional issues for

the public and the agencies themselves, OSHA has

entered into a series of agreements with other
136 ● Biological Rhythms: Implications for the Worker

Federal agencies to define more accurately their

respective jurisdictions.

Fair Labor Standards Act

As discussed, the child labor provisions of FLSA

authorize the Department of Labor’s Wage and Hour

Division to issue regulations respecting the employment of children 14 to 16 years old to ensure that

their employment in permissible occupations will

not interfere with their schooling or their health and

well-being [29 U.S.C. 203(1)(2)]. The Wage and

Hour Division has issued such regulations (29 CFR

570.35) and has authority to amend or replace them,

but it does not appear to have authority to regulate

the hours of employment of other minors. Thus,

FLSA prohibits the employment of children 16 to 18

years old in an occupation which the Division

determines is particularly hazardous and detrimental

to their health and well-being [29 CFR 570(E)]. The

Division’s discretion, therefore, relates to defining

the particularly hazardous occupations and not to

determining permitted hours of employment [29

CFR 570(E)]. For children under 14, the statute bars

any employment [29 U.S.C. 203(1)] except under

specific circumstances in agriculture and the entertainment industry [29 U.S.C. 213(c)].

The overtime provisions of FLSA would not

provide authority for direct regulation of shift

schedules. Under the act, an employer is prohibited

from employing workers for more than 40 hours a

week unless a premium wage is paid. It follows that

if the appropriate time-and-a-half wage rates are

paid, there would be no barrier to employment under

FLSA for hours beyond the 40-hour week in any

arrangement that is otherwise in accordance with

law. This conclusion is underscored by a consideration of the main purpose of the overtime provisions

of FLSA, which was to spread the work among more

workers. While the law had an additional purpose,

namely, to promote health among workers by

limiting excessive work hours and thus providing for

more rest and leisure, this further goal was achieved

by providing a financial penalty for employers who

imposed lengthy hours on the existing work force.

Any argument that FLSA authority extends to direct

shift regulation could persuasively be answered by

citing the OSH Act, passed 22 years after FLSA,

which was designed expressly to protect employee

health and which provides clear authority for direct

shift regulation. On the other hand, the Wage and

Hour Division would have authority to modify its

interpretations of hours worked and thus indirectly

affect work schedules.

Labor Relations Statutes

So far, this chapter has considered shift regulation

under command and control type regulatory statutes,

which impose direct and enforceable obligations on

employers. The Labor-Management Relations Act

(LMRA), originally enacted as the National Labor

Relations Act in 1935, amended and renamed in

1947, and amended twice since then, provides a

regulatory framework for employee exercise of

collective rights, including the right to bargain

collectively and to enter into collective bargaining

agreements (29 U.S.C. 141 et seq.). These bargaining agreements may, and often do, contain provisions on limitations of hours and shift restrictions,

which are enforceable as a matter of contract law

through private remedies.

Labor-Management Relations Act

The LMRA is administered by a five-member

National Labor Relations Board (29 U.S.C. 153).

The coverage of the act is broad, applying to

virtually all private employers (29 U.S.C. 152).

Under the act, the employer and the union are

obligated to bargain collectively with each other,

and a refusal to bargain in good faith is an unfair

labor practice [29 U.S.C. 158(a)(5),(b)(3),(d)]. The

obligation to bargain in good faith relates only to

mandatory subjects of bargaining, that is, wages,

hours, and other terms and conditions of employment (13). There is a considerable body of case law

on the issue of what subjects are mandatory, but

there is little doubt that hours of employment,

including work schedules, are among them.

The LMRA does not regulate shift schedule

limitations directly. However, at least partly because

of the legal requirements imposed by the act, parties

regularly enter into collective bargaining agreements that include hours and shifts. Bargaining

agreements with such clauses may be reached

voluntarily by parties not covered by LMRA.

While LMRA covers the bulk of private employees, several other labor-management statutes should

be mentioned. The Railway Labor Act (45 U.S.C.

151 et seq.) governs the labor relations of railroads

and their employees. Like LMRA, the Railway

Labor Act requires carriers and employees to exert

every reasonable effort to make and maintain
Chapter 6-Legal and Regulatory Issues . 137

agreements (45 U.S.C. 152). This obligation covers

rates of pay, rules, and working conditions. While

hours are not expressly mentioned, the obligation to

bargain over them could be encompassed by working conditions.

There is a wide range of clauses in collective

bargaining agreements relating to hours of work.

These have been collected in the Bureau of National

Affairs’ Collective Bargaining, Negotiation and

Contracts (5). According to this survey, virtually all

contracts contain hours and overtime provisions;

typical provisions include:

● daily and weekly work schedules;

. overtime premium pay;

@ distribution of overtime work; and

. length of lunch and rest periods (5).

Many contracts state the length of the workday and

workweek, and some specify the days of the week on

which work may be performed. Management, however, may retain scheduling rights, frequently with a

requirement for advance consultation with the union

(5).

Some contracts provide specific restrictions on

scheduling, such as no split shifts (5) and limits on

switching employees from one shift to another (5).

The bargaining agreement between a steel company

and a chemical workers’ union (5) provides that

employees are not permitted to work more than 16

hours within any 24-hour period unless an employee

is awaiting replacement and is willing to stay or

needs 2 additional hours to finish a job.

Various contract clauses deal with overtime,

covering both scheduling and premium compensation. One contract for aluminum and steel workers

(5) limits the amount of employee overtime. Except

in cases of emergency, no employee may be

permitted or required to work:

●

●

●

●

more than 16 consecutive hours in a workday;

16 overtime hours in a workweek;

more than two consecutive 16-hour work periods; or

more than 16 hours in any 24-hour period.

In another contract for industrial workers, no

employee may be required to work more than 12

continuous hours and may not be penalized for

leaving after that time (5). Other provisions relate to

rest periods with pay during regular shifts (5).

In sum, there are many clauses concerning shift

scheduling that may appropriately be part of the

mandatory collective bargaining process.

State Labor Relations Legislation

A number of States have labor relations statutes

addressing mandatory bargaining issues. For example, the Connecticut Labor Relations Act (Corm.

Gen. Stat., 1958 rev. sec. 31-101-111, CCH Rep.,

47,000) contains:

provisions defining the rights of employees

(sec. 31-104);

provisions prohibiting unfair labor practices by

employers (sec. 31-105);

procedures for employee election of representatives (sec. 31-106); and

procedures for the handling of unfair labor

“practices cases (sec. 31-107).

In some cases, State labor relations statutes are

applicable only to a specific industry, for example,

the California Agricultural Labor Relations Act

(Third Extraordinary Sess., L. 1975, amended, ch.

1292, L. 1980; CCH Rep.,47,400). In any event, the

scope of these labor relations laws depends both on

their language and interpretation and, significantly,

on the extent to which they” are preempted by the

Federal LMRA.

Federal preemption in the field of labor relations

has been much litigated and has been the subject of

numerous Supreme Court decisions. The purpose of

Federal preemption is to avoid duplicative or inconsistent State regulation of conduct regulated by the

Federal Government under the U.S. Constitution’s

supremacy clause. Preemption depends in the first

instance on the intent of Congress as expressed in the

Federal statute. In the case of LMRA, Congress

expressly provides that the States are free to regulate

with respect to employers over whom the National

Labor Relations Board lacks legal jurisdiction or

declines to exercise its jurisdiction [29 U.S.C.

164(c)]. Otherwise, since Congress has not indicated

its intention to preempt State regulation completely,

the courts must decide the extent of the preemption.

The Supreme Court has developed three tests for

deciding whether State regulation is preempted in

the field of labor relations (1, 10, 18). Early in the

history of the LMRA, the Supreme Court applied the

tests quite strictly, often finding State regulations

preempted (18). More recently, the Court has found

preemption inapplicable, for a variety of reasons (4).
138 ● Biological Rhythms: Implications for the Worker

The important point here is that State regulation of

labor relations cannot be considered separately from

the Federal requirements and the preemptive effect

of the Federal regulatory structure (9).

GOVERNMENT EMPLOYEES

The government as employer determines the

working conditions of its employees. Its authority

may be limited by certain authorizing statutes or by

other regulatory statutes insofar as they apply to

government employees, for example, FLSA. In

addition, both the Federal and many State governments may have bargaining obligations under labor

relations statutes specifically applicable to government employees.

Federal Employees

Under Federal law, each executive agency is

required to establish a basic administrative workweek of 40 hours for full-time employees and to

require that work be performed within a period of not

more than 6 of any 7 consecutive days [5 U.S.C.

6101(a)(2)]. The law further imposes certain limitations on work scheduling, except in cases where the

agency head determines that agency operations

would be seriously handicapped or costs would be

substantially increased by them. These limitations

are:

●

s

●

●

●

●

assignments to tours of duty are scheduled in

advance, over periods of not less than 1 week;

the basic workweek is scheduled on 5 days,

Monday through Friday when possible, and the

2 days outside the basic workweek are consecutive;

the working hours in each day in the basic

workweek are the same;

the basic nonovertime workday does not exceed 8 hours;

the occurrence of workdays does not affect the

basic workweek; and

breaks of more than 1 hour may not be

scheduled in a basic workday [5 U.S.C. 6101

(a)(3)].

An important innovation in Federal employee

work scheduling took place with enactment of

legislation providing for flexible and compressed

work schedules for Federal employees. This law was

originally passed in 1978 [Public Law 95-390

(1978)] and amended several times, most recently in

1982 [Public Law 97-221 (1982); 5 U.S.C. 6121 et

seq.]. Under the statute presently in effect, an agency

is authorized to establish programs of flexible

schedules, which include:

. designated hours during which an employee

must be present for work; and

. designated hours which an employee may elect

as the time for his or her arrival or departure,

solely . . . for the purpose of accumulating

credit hours to reduce the length of the workweek or another workday [5 U.S.C. 6122(a)].

The head of an agency may cancel all or part of a

flexible scheduling program if he or she determines

that the program is substantially disrupting agency

operations or is incurring additional costs [5 U.S.C.

6122(b), 6131].

The statute also authorizes an agency to establish

programs which use a 4-day workweek or other

compressed schedules (5 U.S.C. 6127). It provides

for excepting an employee from a compressed

schedule program or transferring the employee if the

program imposes personal hardship. In addition, the

head of an agency may decide not to establish or to

discontinue a flexible or compressed schedule if it

would have an adverse impact on the agency, as

defined in the statute [5 U.S.C. 6131(a)].

The OSH Act does not apply directly to Federal

and State employees [29 U.S.C. 652(5)]; therefore,

OSHA standards and the statute’s enforcement

provisions are not used by the Department of Labor

to enforce safety and health requirements in the

Federal workplace. However, the OSH Act contains

a separate provision, section 19 (29 U.S.C. 668),

covering safety and health programs for Federal

agencies. The section assigns to the head of each

Federal agency the responsibility for establishing

and maintaining an effective and comprehensive

safety and health program that is consistent with the

standards promulgated by OSHA covering private

employees [29 U.S.C. 668(a)]. If OSHA issues

requirements for private employers concerning safety

and health (as, for example, limitations on hours of

work), the heads of the Federal agencies would be

required to impose similar limitations, except to the

extent that circumstances differ, as determined by

OSHA.

The FLSA applies to most Federal Government

employees, including civilians in the military and

employees of the executive, judicial, and legislative

branches of the Federal Government [29 U.S.C.
Chapter 6--Legal and Regulator Issues ● 139

203(e)]. Thus, the wages, hours, and working

conditions set by the Federal Government for

Federal employees must meet the minimum wage,

overtime, and child labor requirements of the FLSA.

In 1966, Congress passed the Federal LaborManagement Relations Act (5 U.S.C. 7101 et seq.),

establishing a program of labor relations for Federal

employees. The program is administered by the

Federal Labor Relations Authority (5 U.S.C. 7104).

The basic rights of employees include the right to

join or assist a union, or to refrain from such activity,

and through their own representatives to engage in

collective bargaining with respect to conditions of

employment (5 U.S.C. 7102). However, because the

Federal Government is the employer, and because

Federal employees may not strike to enforce their

demands (5 U.S.C. 1819), the obligation of the

Federal agency to bargain with Federal employee

unions is defined in a more limited manner than the

bargaining obligation of private employers (5 U.S.C.

7106, 7117). For example, with certain exceptions,

the agency’s obligation to bargain collectively must

be consistent with any Federal law or any Government rule or regulation [5U.S.C.7117(a)(l), (2)]. A

Federal agency’s authority to fix hours of work for

its employees may be affected by its statutory

bargaining obligation. Many bargaining agreements

between Federal agencies and Federal employee

unions are in effect, and some contain provisions on

hours of work of Federal employees.

State Employees

State governments and their agencies are authorized to set the hours and working conditions of State

employees in accordance with the provisions of

State law. State law is applicable to the extent that

it is not preempted by Federal law and does not

contravene any specific constitutional prohibition or

statutory prohibitions in Federal or State law.

The OSH Act does not cover State employees [29

U.S.C. 652(5)]. However, in order for a State to

qualify for Federal approval or financial assistance,

its employees must be covered by an occupational

safety and health plan that is as effective as the plan

covering private employees [29 U.S.C. 667(c)]. In

addition, OSHA regulations allow States to develop

and obtain approval for plans covering State employees alone. Under these laws and regulations, if

the OSH Act were to limit the hours and shifts of

employees, States with approved plans would be

required to do likewise for both private and State

employees.

The FLSA currently applies, with some exceptions, to State and local employees [29 U.S.C.

203(e)(2)(C)]. While the child labor provisions

apply without change to State employees, FLSA

now allows States to grant compensatory time

instead of overtime pay under some circumstances

for State employees [29 U.S.C. 207(0)]. In addition,

FLSA contains provisions directed specifically toward employees engaged in fire protection and law

enforcement activities for State public agencies [29

U.S.C. 207(K)].

The LMRA does not apply to State employees [29

U.S.C. 152(2)]. However, a number of States have

their own labor relations statutes governing State

and local employees, and these statutes impose

collective bargaining obligations on the parties. An

example is the Massachusetts State labor relations

act, which includes a requirement that the State

bargain with employee representatives (CCH Labor

Law Rep., Massachusetts 47,000). However, because the State is the employer, the bargaining

obligation is defined more narrowly than under the

LMRA, which is applicable to private employees

(CCH Rep., 47,019, 47,025).

SUMMARY AND CONCLUSIONS

The protection of the safety and health of American working men and women is the central goal of

a variety of Federal and State regulatory statutes.

The best known of these is the Federal Occupational

Safety and Health Act.

Since early in 20th century, the protection of

employees and the public from the hazards resulting

from certain work scheduling practices in the

transportation industry has been the subject of

specific regulatory action. At present, enforceable

statutes or regulations are applicable to various

groups of railroad, motor carrier, air carrier, and

maritime employees. In addition, the Federal minimum wage law limits the working hours of certain

minors.

Under the Federal Labor-Management Relations

Act, employees are guaranteed the right to organize

and to bargain collectively. Additional protection

against the hazards to employees of work scheduling

is also afforded under a number of voluntarily

negotiated collective bargaining agreements.
140 ● Biological Rhythms: Implications for the Worker

States provide parallel protection to employees

against work scheduling risks under statutes and

regulations, subject, however, to the limitations

imposed by the doctrine of Federal preemption.

In general, currently effective Federal and State

statutes provide a broad base of authority for the

issuance and implementation of regulations to

strengthen the protection of employees in this area.

Particularly noteworthy in this regard is the OSH

Act, with its pervasive coverage of all private

employers. Acting under this statute, the Department of Labor has authority, on a showing of

significant risk to employees, to issue and enforce

regulations relating to work scheduling. States with

approved occupational safety and health plans

would be required to provide protection that is at

least as effective as that under the OSH Act.

While no additional statutory authority is necessary to enhance employee protection, it should be

recognized that the enactment of an industrywide

statute dealing expressly with the regulation of work

scheduling would constitute a strong declaration of

governmental policy and would provide a considerable impetus to protective progress in this area.

1.

2.

3.

4,

5,

6,

CHAPTER 6 REFERENCES

Allis-Chalmers v. Lueck, 471 U.S. 202 (1985).

American Textile Manufacturers Institute, Inc. v.

Donovan, 452 U.S. 490 (1981).

Atchison Topeka & Santa Fe Railway Co. v. United

States, 244 U.S. 336 (1917).

Belknap v. Hale, 463 U.S. 491 (1983).

Bureau of National Affairs, Collective Bargaining,

Negotiation and Contracts (Washington, DC: 1990).

Donovan v. Dewey, 452 U.S. 594 (1981).

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21,

22.

Fineberg Packing Co., 10SHC 1598 (Rev. Commission 1974).

Hultgren v. County of Lancaster, 913 F.2d 498 (8th

Cir. 1990).

Local 24, International Brotherhood of Teamsters v.

Oliver, 358 U.S. 283 (1959).

bcal 76, Machinists v. Wisconsin Employment

Relations Commission, 427 U.S. 132 (1976).

Michigan Act 154 L. 1964, Commerce Clearing

House, State Labor Law Reports (Michigan sec.

48,000).

Mintz, B. W., Professor of Law, Catholic University

of America, Washington, DC, personal communication, February 1991.

Nationul Lubor Relations Board v. Borg-Warner

Corp., 356 U.S. 342 (1958).

National Realty and Construction Co. v. Occupational Safety and Health Review Commission, 489

F.2d 1257 (D.C. Cir. 1973).

Public Citizen Health Research Group v. Auchter,

702 F.2d 1150 (D.C. Cir. 1983).

Public Citizen Health Research Group v. Brock, 823

F.2d 1479 (D.C. Cir. 1987).

Rosenfeld v. Southern Pacific Co., 444 F.2d 1219

(9th Cir. 1971).

San Diego Building Trades Council v. Garmon, 359

U.S. 236 (1959).

Southern Pacijic Transportation Co. v. Usery, 539

F.2d 386 (5th Cir. 1976), cert. denied, 434 U.S. 874

(1977).

Southern Railway v. Occupational Safety and Health

Review Commission, 539 F.2d 335 (4th Cir. 1976),

cert. denied, 429 U.S. 99 (1976).

United Transportation Union v. Lewis, 699 F.2d

1109 (C.A. 5, 1983).

Yellow Freight System, Inc. v. Amestoy, 736 F. Supp.

44 (D. Vt. 1990).
Chapter 7

Case Study: Nuclear Powerplant

Control Room Operators
Contents

Page

WHO ARE THE WORKERS? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

WORKING HOURS AND OVERTIME . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . 144

NRC Oversight ......., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

The NRC and Shift Schedules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

Overtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

THE JOB OF THE CONTROL ROOM OPERATOR.. . . . . . . . . . . . . . . . .,,.+... . . . . . . . . . . 147

Control Room, Operator Tasks, Performance, and Fatigue . . . . . . . . . . . . . . . .*...,.. . . . . . . . 148

MONITORING OPERATORS FOR PERFORMANCE CAPABILITIES . . . . . . . . . . . . . . . . . 149

SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

CHAPTER PREFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . 151

Figures

Figure Page

7-l. Example of an 8-Hour-per-Day Work Schedule Used in the Nuclear Power Industry . . . 146

7-2. Example of an Every-Other-Weekend-Off 12-Hour Shift Schedule Used

in the Nuclear Power Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

7-3. Example of a 4-Days-On, 4-Days-Off Rotating Schedule Used in the

Nuclear Power Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

7-4+ Example of a Control Room Configuration Used in a Nuclear Power Utility . . . . . . . . . . . 148
Chapter 7

Case Study: Nuclear Powerplant Control Room Operators

In March 1987, the U.S. Nuclear Regulatory

Commission (NRC) was notified that several control

room operators at the Peach Bottom atomic power

station had been found sleeping while on the job and

not performing their duties; 7 days later, the NRC

shut down the Peach Bottom powerplant, marking

the first time the NRC had ordered a plant shut down

for operator deficiencies. The NRC found:

●

●

●

At times during various shifts, particularly

during the 11 p.m. to 7 a.m. shift, one or more

of the operations control room staff (including

licensed operators, senior licensed operators,

and shift supervisors) periodically slept or had

been otherwise inattentive to licensed duties

while on shift during at least the past 5 months.

Management at the shift supervisor and shift

superintendent levels either knew about and

condoned the facts set forth above or as a part

of their duties should have known of these facts

and taken action to correct the situation.

Plant management above the shift superintendent position either knew about and condoned

the facts set forth above or should have known

the facts and taken action to correct this

situation (18).

The Peach Bottom nuclear powerplant reopened

in April 1989, after a costly, 2-year shutdown. What

occurred at Peach Bottom was a situation in which

a breakdown in management, combined with disruptions of circadian rhythms and fatigue effects,

created conditions in which the safe operation of the

plant was jeopardized. In particular, lack of management oversight during the night shift (11 p.m. to 7

a.m.), when performance and alertness decrements

are most likely, resulted in the behavior observed by

the NRC. Though no accident resulted from operator

inattentiveness at Peach Bottom, other accidents and

incidents, such as that at Three Mile Island in 1979,

have occurred during these hours of operation.

This case study examines the job of nuclear

powerplant control room operators, a job characterized by continuous, routine monitoring tasks that

must be carried out 24 hours a day, usually on a

rotating shift schedule. It is an example of an

occupation in which the adverse effects that can

result from shift work may have negative implications not only for the worker, but for the public as

well.

WHO ARE THE WORKERS?

According to the NRC, there were 111 nuclear

power reactors licensed for operation by the Commission in the United States in 1989. Five additional

reactors are scheduled to be completed by 1995 (21).

The NRC has estimated that there are 5,290 licensed

control room operators in the United States, consisting of 1,969 licensed reactor operators and 3,321

senior reactor operators.

Nuclear power operator trainees come from three

primary sources: 1) fossil fuel powerplant personnel;

2) U.S. Navy nuclear programs; and 3) interested

young people, typically possessing a high school

education, starting a career. Training for the novice

is carried out by individual utility companies and

consists of many months of classroom work on the

necessary theories, skills, and knowledge required to

operate a facility. This process may be partially

waived for persons with equivalent training (e.g.,

former operators at another facility or persons

trained in reactor operations by the Navy). Some

experience credit is given to individuals who have

worked at fossil fuel plants. Subsequent training

consists of actual experience at various nonlicensed

operator positions, which familiarizes the trainee

with the equipment and control system characteristics. Operators also train on high-fidelity simulators.

The NRC licensing examiners conduct plantspecific oral, written, and simulator examinations of

the trainees to ensure that candidates are prepared

for, and capable of, performing the tasks of a nuclear

reactor operator or of supervising the powerplant

control room operations as a senior reactor operator.

Continuing training throughout the operator’s career

is provided by the utility companies through their

programs for maintaining and upgrading personnel

skills. It takes up to 6 years to complete the training

program. Individuals with previous related experience may require 3 years’ training. Operators’

licenses are renewed every 6 years through NRC

testing.

–143–
144 ● Biological Rhythms: Implications for the Worker

WORKING HOURS AND

OVERTIME

NRC Oversight

All nuclear powerplants must be licensed by the

NRC. The licenses are legally binding and place

numerous conditions on nuclear reactor design,

construction, and operations. Part of the licensing

process is the implementation of a plant’s technical

specifications, which describe all aspects of that

plant’s operations. Besides the licensing process, the

NRC has authority to issue policy statements or

promulgate regulations related to the operation of

nuclear powerplants. NRC policy statements ‘‘urge

or strongly recommend” that a nuclear powerplant

follow a given course (7). The NRC’s policy

statements are not enforceable per se, and a plant

is not required to incorporate them into its

technical specifications and administrative procedures. However, if a plant does incorporate

NRC policy statements into its technical specifications or administrative procedures, the plant

must follow that policy. The NRC may then issue

notices of violations of the technical specifications

(7).

Powerplants must comply with NRC regulations. In response to violations of regulations, the

NRC may require a plant to change its administrative procedures, perform operations differently,

enforce standard operating procedures, or change its

design. In cases of repeated violations or failure to

comply with NRC directives, the NRC may shut

down a facility.

The NRC’s resident inspectors are its primary

means of monitoring compliance with regulations.

These inspectors are assigned to all nuclear powerplants to ensure: 1) that the facility is being operated

safely and in conformance with licensing and

regulatory requirements, and 2) that the licensee’s

management is effectively discharging its responsibilities for continued safe operation (24).

Guidelines for the NRC and OSHA

Responsibility for safety and health at nuclear

powerplants is divided between the Occupational

Safety and Health Administration (OSHA), within

the U.S. Department of Labor, and the NRC. OSHA

has regulatory jurisdiction for health and safety

matters in the workplace, including nuclear powerplants. The NRC, on the other hand, has regulatory

oversight of the operations of all utilities licensed to

operate by the Commission. In October 1988, in an

effort to clarify and coordinate the roles of these two

Federal agencies, OSHA and the NRC collaborated

on a memorandum of understanding to provide

general guidelines regarding worker protection at

NRC-licensed facilities (53 FR 43950-43952). The

memorandum specifically defines the roles and

responsibilities of each agency for achieving worker

safety and health at NRC-licensed plants. For

example, OSHA investigates worker injuries at

nuclear powerplants, as it does for other industries,

while the NRC is responsible for regulating hours of

work. This memorandum also provides general

procedures for the coordination of activities and

exchange of information between the two agencies.

The NRC and Shift Schedules

Currently, there are no NRC regulations specifically covering shift scheduling or working hours for

nuclear powerplant operators; however, there are

NRC policy statements regarding total working

hours for operators. Shift schedules at nuclear

powerplants are implemented by the plant management and are sometimes the result of managementlabor negotiations. Control room operators can work

several types of shift schedules. Many work an

8-hour-per-day shift schedule; however, more powerplants are switching to a 12-hour-per-day schedule

(2).

The development of policies on work schedules

for control room operators is relatively new. The

NRC published its first policy on overtime and

working hours in a letter in July 1980 (13). In

November 1980, the NRC revised this policy to

make it more flexible (14), and in 1982, additional

revisions provided further clarification and established a formal policy statement, which was transmitted in Generic Letter 82-12 (15) and Generic

Letter 82-16 (16) (47 FR 7353). The Generic

Letters provide guidance on how to implement

the policy statements on shift scheduling and

working hours for nuclear powerplant control

room operators. They consist of the following

guidelines:

An individual should not be permitted to work

more than 16 consecutive hours (excluding

shift turnover time).

An individual should not be permitted to work

more than 16 hours in any 24-hour period, more
Chapter 7--Case Study: Nuclear Powerplant Control Room Operators ● 145

●

●

than 24 hours in any 48-hour period, or more

than 72 hours in any 7-day period (all excluding

shift turnover time).

A break of at least 8 hours should be allowed

between work periods (including shift turnover

time).

The use of overtime should be considered on an

individual basis, not for the entire staff on a

shift.

In addition to these guidelines, the NRC urged

that licensed operators be periodically relieved and

assigned to duties away from the control board, in

order to reduce fatigue during a shift (47 FR 7353).

The NRC policy statement embodied in the Generic

Letters indicates that all nuclear powerplants should

establish controls to prevent situations in which

fatigue could reduce the ability of control room

operators to run the reactor safely. Thus, workers

should not be assigned to shift duties while in a

fatigued condition, because fatigue could significantly reduce their alertness and decisionmaking

capabilities.

The NRC recommends that plants hire enough

staff to work shift hours without continuous, burdensome use of overtime and that workers routinely

work an 8-hour day and 40-hour week while the

plant is in operation. The NRC policy statement also

applies to situations in which the operations of the

facility require overtime or the plant has been shut

down for refueling, major maintenance, or major

modifications. To date, approximately 77 of the 111

licensed nuclear powerplants have incorporated

these policy statements into their technical specifications.

8-Hour-per-Day Shift Schedules

In 1985 the NRC contracted with a private

laboratory to set up an expert panel to study NRC

policy related to scheduling (17). The panel’s

recommendations for a routine 8-hour-per-day shift

schedule consist of various suggestions designed to

reduce excessive working hours, including:

●

●

●

limiting the schedule to a maximum of 7 consecutive days of work,

maintaining a schedule that does not exceed21

days of work (including training) in any 4-week

period,

ensuring that the schedule includes at least

2 consecutive full days off in any period of

9 consecutive days,

. ensuring at least 2 full days of rest following

night shifts, and

● rotating the schedule forward, not backward.

To date, these recommendations are still under

review by the NRC.

Features of 8-Hour Schedules

Most plants use rotating shifts to apportion the

more desirable morning and afternoon shifts and the

least favored night shifts equally among all staff

members (5). However, there are other reasons for

using a rotating shift system. First, locating people

willing to work on a permanent night shift is often

difficult; second, when seniority governs the choice

of which shift is to be worked (as often occurs in

permanent shift systems), the older, most experienced people usually opt for day work; and third, the

precedent for rotating shifts was set at fossil fuel

powerplants.

Control room operators typically rotate through

three 8-hour shifts (5):

. a morning shift (usually 8 a.m. to 4 p.m.),

. an afternoon shift (usually 4 p.m. to midnight),

and

. a night shift (usually midnight to 8 a.m.).

Continuous three-shift systems usually have four,

five, or six crews of workers in order to have workers

on duty over weekends and still provide rest periods.

Most nuclear powerplants operate with six crews.

The Institute of Nuclear Power Operations conducted a survey in 1989 on the number of operating

crews commonly used. Of the 75 plants surveyed,

50 reported that they were using six crews. The

remaining 25 plants operated with five crews, but

two of these indicated that they were preparing to

change to a six-crew operations system (4).

As described in chapters 4 and 5, 8-hour shift

schedules can vary in their direction and speed of

rotation. As in other work settings, many types of

schedules are used at nuclear powerplants, although

weekly rotating schedules are typical. Figure 7-1 is

one example of an 8-hour shift schedule.

12-Hour-per-Day Shift Schedules

Within the last few years, 12-hour work schedules

have become more popular in nuclear powerplants.

Twenty-three plants now operate under 12-hour

schedules (25). If a plant has incorporated its shift

schedules into its technical specifications and ad-
146 . Biological Rhythms: Implications for the Worker

Figure 7-l—Example of an 8-Hour-per-Day Work Schedule Used in the Nuclear Power Industry

Day of the week

Crew A

Crew B

Crew C

Crew D

Crew E

The world training schedule for five crews (A, B,C,D,E) over a 5-week period is illustrated.

KEY: D= day shift; A= afternoon shift; N= night shift; T= training; — = day off.

SOURCE: U.S. Nuclear Regulatory Commission, fW/REG/CR-4248, Recommendations for NRC Policy on Shiff Schechding and Overtime at Nuclear Power

P/ants (Richland, WA: Pacific Northwest Laboratory, 1985).

ministrative procedures, it must frost get NRC

approval before implementing a 12-hour schedule; if

it has not, NRC notification is not required. Currently there is no NRC guidance regarding the

implementation of 12-hour schedules. The expert

panel on scheduling, described earlier, also developed the following guidelines for 12-hour work

schedules (17):

●

●

●

●

●

Adoption of a routine 12-hour-per-day schedule must be authorized by the NRC.

The schedule should contain a maximum of

4 consecutive 12-hour workdays.

Four consecutive 12-hour workdays should be

followed by no fewer than 4 days off.

The basic 12-hour-per-day schedule could be

one of several types: 2 days on, 2 days off;

3 days on, 3 days off; 4 days on, 4 days off.

Another possible schedule would be the everyother-weekend-off schedule, which combines

2 days on, 2 days off with 3 days on, 3 days off.

The general safety record of the plant should be

satisfactory, based on criteria such as those

used in NRC’s Systematic Assessment of

Licensee Performance ratings.

The plant should have the capability to cover

unexpected absences satisfactorily without requiring any individual to work more than 12

hours per day.

The round trip commute times for the operators —

should not exceed 2 1/2 hours.

Features of 12-Hour Schedules

A number of 12-hour work schedules are in use at

present. An advantage of these schedules is that the

worker has more nonworking days during the week,

thus allowing more time for rest and leisure. A

potential drawback is that the 4 additional hours per

shift may produce fatigue and decrements in alertness (2,9-1 1).

Typically there are three types of 12-hour shift

schedules (8,12):

1. every other weekend off (EOWEO);

2.3 days on, 3 days off rotating schedule; and

3.4 days on, 4 days off rotating schedule.

Figure 7-2—Example of an Every-other-Weekend-Off 12-Hour Shift Schedule Used in the Nuclear Power Industry

Day of the week

Nights

Days

o f f

o f f

S M T W T F S IS M T W T F S S M T W T F S S M T W T F S

A B B D D c c c A A B B D D D c c A A B B B D D c c A A

D c c A A B B B D D c c A A A B B D D c c c A A B B D D

B A A B B A A A B B A A B B B A A B B A A A B B A A B B

c D D c c D D D c c D D c c c D D c c D D D c c D D c c

The work schedule for four crews (A, B,C,D) over a 4-week period. For example, during week 1, crew A works Sunday night, has Monday

and Tuesday off, works days Wednesday and Thursday, and then Friday and Saturday has off.

SOURCE: H.R. Northrup, J.T. Wilson, and K.M. Rose, “The Twelve-Hour Shift in the Petroleum and Chemical Industries,” /ndustria/ and Lalxx Re/ations

Review 32:312-316, 1979.
Chapter 7-Case Study: Nuclear Powerplant Control Room Operators ● 147

Figure 7-3—Example of a 4-Days-On, 4-Days-Off Rotating Schedule Used in the Nuclear Power Industry

Day of the week

Day

Night

The work schedule for four crews (A, B,C,D) over a 16-week period. For example, crew A works the day shift on 4 consecutive days during

week 1, has 4 days off, then works the night shift for 4 consecutive days before having another 4 days off.

SOURCE: H.R. Northn.m, J.T. Wilson. and K.M. Rose, “The Twelve-Hour Shift in the Petroleum and Chemical Industries,” Industrial and Labor Re/afions

Review 32:3i2-316, 1979.

Figure 7-2 is an example of an EOWEO schedule,

and figure 7-3 is an example of a 4 days on, 4 days

off rotating schedule, both of which are commonly

used for control room operators.

Overtime

Nuclear powerplants have used a variety of

overtime schedules for operators. The NRC recommends, but does not require, that plants have an

overtime policy. In 1988, 76 plants had a specific

overtime policy written in their technical specifications; 32 plants did not (6). As described earlier, the

1982 Generic Letters provide guidance regarding the

maximum number of hours of work for 24-hour,

48-hour, and 7-day periods. The expert panel on

scheduling developed further guidelines for overtime

●

●

scheduling (7), which include:

The approval of the plant manager should be

required before individuals are allowed to

exceed the following limits: 60 hours of work

in 7 days, 112 hours of work in 14 days, 192

hours of work in 28 days, and 2,260 hours of

work in 1 year.

NRC approval should be required before individuals are allowed to exceed the following

limits: 72 hours of work in 7 days, 132 hours of

work in 14 days, 228 hours of work in 28 days,

and 2.300 hours of work in 1 year.

As with the panel’s recommendations on 8- and

12-hour schedules, its recommendations on overtime are still under review by the NRC.

Overtime is necessary in outage situations, when

every day off-line (not functioning) will result in lost

revenues for the utility company. Employees often

work 12-hour days in these situations. Overtime also

increases when there are staff shortages, typically

when someone fails to come to work. In such cases,

workers may be required to work double shifts (if

they are 8-hour shifts) or split the second shift with

another worker. This type of shift activity may have

negative effects on the worker, leading to performance decrements and interpersonal problems (l).

Currently, there are few effective techniques for

minimizing the physiological, psychological, and

performance effects of overtime (see ch. 5).

THE

CONTROL

JOB OF THE

ROOM OPERATOR

This section describes the work environment in

the control room, the typical tasks for a control room

operator, and the effects environmental and physiological factors can have on the performance of these

, — tasks.
148 ● Biological Rhythms: Implications for the Worker

Figure 7-4-Example of a Control Room Configuration Used in a Nuclear Power Utility

~Entr’~~‘n’r’= “l____– J”

/’Y--l – – - r---lA

I I

~ l_-! H ~ ‘, Nonoperational\

A

D

w

~ control board ~

 –

Unit 2

Main control boards

1 I

SOURCE: Electric Power Research Institute, Human Enaineetina Guide fbrEnhancing Nuc/ear Cantro/ Rooms, Rep.

No. NP-2411-project 501-4 (Palo ”Alto, CA: El&Xric P;wer Research lnstit~e, 1982).

Control Room, Operator Tasks,

Performance, and Fatigue

The nuclear powerplant control room consists of

a panel board that operates each unit (i.e., the reactor

containment building and associated systems). In

facilities that have two reactors, there will be two

control boards, which can be located either in the

same or in separate control rooms. Figure 7-4

illustrates a typical control board configuration that

is used in a nuclear utility.

The control board is made up of many switches,

indicators, computer display systems, and alarm

panels, each performing different functions. The two

categories of personnel authorized to operate control

units, reactor operators and senior reactor operators,

are licensed by the NRC. Reactor operators are

required to be alert and responsive at all times during

the shifts. Their duties typically include monitoring

the information displayed on the control board and

overseeing the operations of all of the components of

the control unit. They are required to execute a

variety of monitoring tasks that require low-level,

sustained vigilance but no physical activity. Thus,

performing such tasks may result in sleepiness or

fatigue, or both. Reactor operators’ duties also

include responding to a variety of alarms indicating

that adjustments need to be made. If an emergency

arises, they must be able to assess the situation and

select appropriate procedures to mitigate it.

Senior reactor operators are responsible for overseeing the activities of the reactor operators in the

control room. They are supervisors and have administrative, work control, and other company-related

tasks. In addition, they must be ready at all times to

back up the reactor operator.

Studies of tasks that require high levels of

alertness and attentiveness have repeatedly found

that human error increases after about half an hour of
Chapter 7--Case Study: Nuclear Powerplant Control Room Operators ● 149

continuous vigilance (2). Since working on the same

task and not moving around for along period of time

can cause fatigue, experts suggest that managers

should attempt to vary operators’ work tasks every

2 hours (2). Reactor operators are sometimes required to perform additional tasks outside of the

control room, such as noting water level temperatures, checking the operations of radiation monitors,

and performing general tasks for generator, turbine,

and reactor upkeep. The more active nature of these

duties can reduce fatigue. Experts have also suggested several other strategies to minimize sleepiness and fatigue (2). These include interventions that

can be initiated by the operator:

. taking short walks during periods of low

alertness,

. spending time each hour standing up and

walking,

. avoiding getting too comfortable, and

. interacting with colleagues on the shift to help

stay alert;

and interventions that would have to be implemented by management:

scheduling tasks that involve physical activity

on night shifts;

allowing operators to take scheduled breaks

away from the control panel;

balancing the workload across shifts and days

of the week to eliminate long periods of intense

activity and stress;

redesigning job responsibilities to maximize

completeness, variety, and feedback in an effort

to make jobs more interesting;

not allowing individuals to work beyond their

scheduled shift or to monitor the control board

for over 2 hours without some relief (during the

night shifts); and

scheduling the shift workload so that difficult

mental tasks are not required during periods of

predictably low alertness.

Effects of Environmental and Physiological

Factors on Vigilance

Several other factors can influence the vigilance

of nuclear powerplant control room operators. These

include lighting in the control room, ambient noise

from the control panels and other machinery, ambient temperature, humidity, and ventilation, and

the design of the work station. Each of these in

some way or another can affect an operator’s ability

Photo credit: DavkiLiskowsky

Control board at a nuclear powerplant.

to carry out the job. Improper design of these

variables can lead to fatigue, sleepiness, reduced

attention span, and changes in mood that can result

in errors in performance (2).

While there is a substantial body of literature on

the effects these factors can have on performance,

there is little information available on the interaction

of such effects with shift work schedules or the

application of that information to the nuclear powerplant environment. Such research could greatly

benefit the operators of nuclear powerplants.

MONITORING OPERATORS FOR

PERFORMANCE CAPABILITIES

The primary responsibility for monitoring employees on the job rests with the management of the

utility that operates the powerplant. The NRC’s role

is to ensure that the management control system at

a plant is carrying out its responsibilities. One task

of NRC resident inspectors is to monitor control

room activities, including observation of control

room personnel (24). In addition, the inspectors are

required to spend approximately 10 percent of their

time conducting unannounced control room inspections on the night shift. If an inspector observes that

individuals are not performing their duties adequately, he or she notifies the appropriate supervisor.

Beyond the supervision provided by the utility

management and the observational oversight of the

NRC resident inspectors, there are no specific

guidelines or regulations set forth by the NRC for

monitoring control room operators for possible

performance deficiencies related to sleepiness, fa-
150 ● Biological Rhythms: Implications for the Worker

tigue, or disruption of biological rhythms. The

NRC’s Policy on Conduct of Nuclear Powerplant

Operators (54 FR 1489-1498) and Regulatory Guide

1.114 (20) both state the Commission’s expectation

that operators be alert; moreover, since the Three

Mile Island and Peach Bottom incidents, there has

been a greater awareness among plant operators of

the need to monitor control room operators. As a

result, some plants have voluntarily carried out more

comprehensive monitoring programs.

The purpose of such monitoring programs is to

ensure that operators are capable of carrying out

their duties on a routine basis. These programs use

test batteries that are sensitive to decrements in

performance caused by fatigue or disrupted biological rhythms. There is no one test battery capable of

adequately measuring decrements in performance

specifically for the control room operator. However,

many general test batteries that are available assess

deficiencies in performance, and these maybe used

for control room operators (see ch. 5).

It is not known how frequently voluntary monitoring programs are being carried out at nuclear

powerplants. However, when monitoring occurs, it

is usually a result of one of two circumstances: either

a plant’s management has noticed problems in

control room operators’ work practices and has

requested a private testing organization to come to

the facility and monitor the operators to help

determine the nature of the problem, or a testing

organization may approach the management of a

nuclear powerplant and ask if it can run a series of

tests on the workers to measure performance deficiencies and fatigue using its test battery. The latter

affords the testing organization an opportunity to

field test and market its test battery.

As previously mentioned, no NRC guidance

exists regarding the use of formal testing procedures

to monitor control room operators. In response to

concerns about decreased performance due to substance abuse, however, the NRC has instituted

regulations regarding a fitness-for-duty program for

nuclear powerplant operators (54 FR 24468-24508).

The fitness-for-duty program is intended to ensure

that “all operators and plant personnel are reliable,

trustworthy, and not under the influence of any

substance (legal or illegal), or mentally or physically

impaired from any cause, that would affect their

ability to safely and competently perform their

duties in any manner” (54 FR 24468-24508) (19,

22,23). Currently, the program is designed only to

detect individuals using legal or illegal substances,

not to determine decrements in performance caused

by sleepiness, fatigue, or circadian desynchronization.

However, if deemed necessary or desirable, this

program represents an existing mechanism that

could be modified to include monitoring for

decrements in performance due to the effects of

shift work.

SUMMARY AND CONCLUSIONS

NRC guidance related to overtime and shift length

for nuclear powerplant control room operators is

provided in Generic Letters 82-12 (15) and 82-16

(16); currently the Commission provides no guidance or policy regarding the design of work schedules. Recommendations have been made by a panel

convened by a private laboratory under contract to

the NRC, but no action has been taken on them to

date and they remain under consideration by the

NRC. Many nuclear powerplants use an 8-hour-perday shift schedule; however, the trend is toward a

12-hour-per-day schedule.

Control room operators are responsible for the

safe operation of the nuclear utility. Their duties

involve engaging in continuous monitoring of all

indicators on the control board and responding to

numerous alarms. This generally does not require a

great deal of physical movement. Furthermore,

operators must be ready to respond to any emergency situation that may arise. This requires operators to be alert and attentive at all times while on

duty.

Since working on the same tasks and remaining

stationary for along period of time can cause fatigue,

experts suggest that managers who design work

assignments attempt to vary operators’ tasks every

2 hours. Experts have also recommended several

strategies to reduce fatigue and sleepiness, since

remaining awake late at night is often difficult.

These may include allowing operators to take

scheduled breaks away from the control panel and

balancing the workload across shifts to eliminate

continuous periods of stress.

Operators are sometimes required to work two

consecutive 8-hour shifts, depending on the circumstances, or, especially in an outage situation, they

may be required to work additional overtime. Such

activities may have negative effects on the workers,

leading to decrements in their performance.
Chapter 7--Case Study: Nuclear Powerplant Control Room Operators . 151

In addition to shift work, several factors related to

the environment and design of the control room can

influence the vigilance of operators. Improper design of these factors can lead to fatigue, sleepiness,

and reduced attention span, which could result in

errors in performance. Research on the interaction of

these factors with shift work effects in the nuclear

powerplant control room environment could provide

useful information to aid in plant operations.

Although the problems of fatigue and decreased

performance capability in connection with shift

work cannot be entirely eliminated, several steps can

be taken to deal with them. One researcher (3) has

suggested several possibilities, including:

. . . make stricter regulations regarding shift work

scheduling; designing schedules to meet the health

and safety needs of the plant and its workers;

improve the design and lighting of the control room;

improving incident reporting systems and incident

analysis to ensure that proper remedies are applied

regarding the problems associated with 24-hour

operations; and continued research and further

studies to gain more knowledge and understanding

of the impacts from circadian disruption due to shift

work on the safety and health of nuclear powerplant

control room operators.

One of the duties of the NRC’s resident inspectors

is to oversee the supervision of operators by the

utility. Currently, there is no NRC guidance or

policy regarding the monitoring of control room

operators for specific performance deficiencies related to fatigue or disruptions of biological rhythms.

In some cases, powerplants voluntarily institute a

monitoring program using standardized test batteries administered by outside organizations, although

it is unclear how frequently this occurs. The NRC’s

fitness-for-duty program is designed to detect workers who are using legal or illegal substances, not to

determine decrements in performance due to decreased attention span and alertness that could be

associated with work schedules. The NRC could

require that the fitness-for-duty program be restructured to include measures of performance deficiencies resulting from shift work.

CHAPTER 7 REFERENCES

1. Biotechnology, Inc., Survey and Analysis of Work

Structure in Nuclear Power Plants, prepared for

Electric Power Research Institute, EPRI Rep. No.

NP-3141-project 2167-1 (Palo Alto, CA: Electric

Power Research Institute, 1983).

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

Circadian Technologies, Inc., Control-Room Operator Alertness and Performance in Nuclear Power

Plants, prepared for Electric Power Research Institute, EPRI Rep. No. NP-6748-project 2184-7 (Palo

Alto, CA: Electric Power Research Institute, 1990).

Dahlgren, K., “Shift Work Work Scheduling and

Their Impact on Operators in Nuclear Power Plants,’

1988 IEEE Fourth Conference on Human Factors

and Power Plants, June 5-9, 1988, Monterey, CA

(New York, NY: Institute of Electrical and Electronics Engineers, 1988).

Institute of Nuclear Power Operations, 1989 Survey

of Nuclear Related Employment in United States

E/ectric Utilities, INPO Rep. No. 89-011 (Atlanta,

GA: 1989).

hwis, P. M., Shljit Scheduling and Overtime: A

Critical Review of Literature, PNL-5391 (Richland,

WA: Pacific Northwest Laboratory, 1985).

kwis, P.M., and Mullen, M.F., ‘Overtime, Staffing

Levels, and Shift Scheduling in Nuclear Reactors,”

Proceedings of the Institute of Nuclear Materials

Management 18:941-948, 1989.

Morisseau, D., U.S. Nuclear Regulatory Commission, personal communication, October 1989.

Nolthrup, S.E., ‘‘The 12-Hour Shift in the Petroleum

and Chemical Industries, ” Industrial and Labor

Relations Review 32:312-326, 1979.

Rosa, R.R., and Colligan, M. J., The NIOSH Fatigue

Test Battery: Laboratory Vali&tion of a Portable

System for Field Study of Extended Workalzys and

Work Scheduling, NIOSH internal report (Cincinnati,

OH: U.S. Department of Health and Human Services,

National Institute for Occupational Safety and

Health, 1986).

Rosa, R. R., Colligan, M.J., Lewis, P., et al., “Extended Workdays: Effects of 8-Hour and 12-Hour

Rotating Shift Schedules on Performance, Subjective

Alertness, Sleep Patterns, and Psychological Variables,” Work and Stress 3:21-32, 1989.

Rosa, R.R., Wheeler, D.D., and Warm, J. S., “Extended Workdays: Effects on Performance and Ratings of Fatigue and Alertness, ’ Behavior Research

Methods, Instruments, and Computers 17:6-15,

1985.

U.S. Department of Health and Human Services,

Public Health Service, Centers for Disease Control,

National Institute for Occupational Safety and

Health, Alternative Worker Schedules (Cincinnati,

OH: Lieb, Id3cowitz & Associates, 1981).

U.S. Nuclear Regulatory Commission, “Letter to all

Licensees of Operating Plants and Applicants for

Operating Licenses and Holders of Construction

Permits-Interim Criteria for Shift Staffing,” from

Darrell G. Eisenhut, director, Division of Licensing,

Washington, DC, July 31, 1980.
152 ● Biological Rhythms: Implications for the Worker

14.

15.

16.

17.

18.

19.

U.S. Nuclear Regulatory Commission, NUREG0737, Clarification of TMIAction Plan Requirements

(Washington, DC: 1980).

U.S. Nuclear Regulatory Cornrnission, Generic btter No. 82-12, from Darrell G. Eisenhut, director,

Division of Licensing, Washington, DC, June 15,

1982.

U.S. Nuclear Regulatory Commission, Generic ktter No. 82-16, from Darrell G. Eisenhut, director,

Division of Licensing, Washington, DC, Sept. 20,

1982.

U.S. Nuclear Re@atory Commission, NUREG/CR4248, Recommendations for NRC Policy on Shift

Scheduling and Overtime at Nuclear Power Plants

(Richland,WA: PacificNorthwestLaboratory, 1985).

U.S. Nuclear Regulatory Commission, Shutdown

Order Issued Because Licensed Operators Asleep

While on Duty, NRC Information Notice No. 87-21

(Washington, DC: Office of Nuclear Reactor Regulation, May 11, 1987).

U.S. Nuclear Regulatory Commission, NUREG/C’R5227, Fitness for Duty in the Nuclear Power

20.

21.

22.

23.

24.

25.

Industry: A Review of Technical Issues (R.ichhincl,

WA: Pacflc Northwest Laboratory, 1988).

U.S. Nuclear Regulatory Commission, GuideZina on

Being an Operator at the Controls of a Nuclear

Power Plant, Regulatory Guide 1.114, rev. 2 (Washington, DC: 1989).

U.S. Nuclear Regulatory Commission, NUREG1350, vol. 1, Nuclear Regulatory Commission 1989

Information Digest (Washington, DC: 1989).

U.S. Nuclear Regulatory Commission, NUREG1354, Fitness for Duty in the Nuclear Power

Industry: Responses to Public Comments (Washington, DC: 1989).

U.S. Nuclear Regulatory Commission, NUREG/CR5227, supp. 1, Fitness for Duty in the Nuclear Power

Industry: A Review of Technical Issues (Richland,

WA: Pacific Northwest Laboratory, 1989).

U.S. Nuclear Regulatory Commission, NRC Inspection Manual (Washington, DC: 1990).

Ybder, J., Office of Safety Policy, U.S. Department

of Energy, Washington, DC, personal communication, Jan. 11, 1991.
Chapter 8

Case Study: Registered Nurses

and Resident Physicians
Contents

Page

SHIFT WORK IN NURSING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Registered Nurses: An Overview . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Prevalence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Evidence of Dissatisfaction With Shift Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Consequences of Shift Work in Nursing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..

EXTENDED DUTY HOURS AND GRADUATE MEDICAL

EDUCATION PROGRAMS . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Libby Zion Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Current Status of Graduate Medical Education Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Regulation of Residents’ Hours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Effects of Extended Duty Hours on Residents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CHAPTER PREFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Boxes

Box

155

155

156

157

158

159

166

168

170

170

176

178

179

Page

8-A. Impact of Shift Work on Nursing in Great Britain.... . . . . . . . . . . . . . . . . . . . . . . . ● .,..... 158

8-B. Limitations on Residents’ Hours in Great Britain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

8-C. Reduction of Residents’ Hours in New Zealand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

Figure

8-1. Prevalence of Hospitals With

Table

Figure

Page

on Residents’ Hours . . . . . . . . . . . . . . . . . . . . . . . . . . 170

Tables

Page

8-1. Studies of Health Consequences of Shift Work in Nursing . . . . . . . . . . . . . . . . . . . . . . . . . . .

8-2. State Legislative Action Regarding Residents’ Work Hours . . . . . . . . . . . . . . . . . . . . . . . . . .

8-3. Residents’ Working Hour Requirements in the Residency Review Committee’s

Updated Accreditation Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

163

171

174
Chapter 8

Case Study: Registered Nurses and Resident Physicians

Health care is a 24-hour-a-day business. People

get sick and need care around the clock, and

hospitals must be staffed with health care professionals ready to meet those needs. This means that

some health care employees, such as nurses and

residents, l must work at night, on weekends, and on

holidays. Extended duty hours and circadian rhythm

disruption play a major role in the training of

residents. Historically, that training has been marked

by long, intensive hours over several years. Some

residents have worked more than 130 hours per week

in shifts of 12 to 60 hours, with every other night on

call (58). The resulting sleep deprivation is a major

source of stress in residency (23). Likewise, many

nurses must work nondaytime shifts and endure the

resulting circadian rhythm disruption for the duration of their professional lives.

Although the issues discussed in this case study

affect some portion of virtually every group working

in hospitals (e.g., laboratory and x-ray technicians,

pharmacists, transport teams, chaplains, social workers, runners, admitting clerks, housekeepers), the

focus here will be limited to nurses and residents.

This case study examines the effects of shift work on

the health and well-being of nurses and the quality

of care they deliver and how the structure of resident

training programs may result in sleep deprivation

that can affect the health and well-being of residents

and their patients.

SHIFT WORK IN NURSING

Jane Doe . . . worked as a registered nurse (R.N.)

at a hospital on the West Coast. She had been

working all night and was in the 12th hour of a

12-hour shift. She was under time pressure to

complete her work She was disconnecting a patient’s I.V. and had to dispose of a used I.V. needle.

In the process, she was accidentally stuck by the

needle, which turned out to contain HIV-infected

blood. Jane Doe seroconverted and is now HIVpositive. The fact that she was tired at the end of a

12-hour shift, that the hospital was understaffed, and

that the hospital did not have proper containers

accessible to dispose of sharp needles all combined

to create a hazardous working condition, with tragic

results (88)0

A nurse at a Northeastern hospital was on

restricted duty due to a heart condition but eventually

was required to work 18 hours straight. She was on

medication and increased the dosage to help cover

the demands of her work situation. She became ill,

and her case, along with 14 others, was submitted to

labor arbitration (105). The case was settled just

prior to the arbitration hearing (98).

A malpractice case was filed against a nurse in the

Northeast because a patient died during the nurse’s

second continuous 8-hour shift (105).

Registered Nurses: An Overview

Anecdotes such as these are easy to find, but the

contribution work hours may play in them is difficult

to document. Several explanations for this seem

plausible. First, statistics on the relationship between hours of work and adverse events for nurses

are not tallied by the U.S. Department of Labor, and

there is no statutory requirement that unions or

employers collect such data. As illustrated by the

case of Jane Doe, extended duty hours may be only

one of several factors contributing to an incident,

and a nurse may therefore not interpret an incident

as related to shift work. Even if nurses do believe

that shift work is causing problems, they may find it

difficult to prevail when they file grievances over

shift work issues unless these issues are covered in

their collective bargaining agreements. Nonunion

nurses often work at facilities without formal

grievance procedures and, thus may have less opportunity to pursue shift work concerns through a

structured complaint process (89).

A number of unions representing nurses, including the American Nurses Association, Service Employees International Union, American Federation

of State, County and Municipal Employees, and the

Federation of Nurses and Health Professionals (a

division of the American Federation of Teachers),

bargain over shift assignments, length of time

between shifts, shift of choice, split shifts, and shift

~For tie ~Wo~e~ of ~~ ~ha~ter, a resident is my post~duate medi~ &fiee, inclu~g interns, in ~fi rnedic~ ~(i swgkal specialties. Residents

are also referred to as house officers or house staff.

–155–

297-935 - 91 - 6 QL 3
156 ● Biological Rhythms: Implications for the Worker

rotations for nurses. In the words of one union

employee, however:

. . . our success at limiting shift work through the

collective bargaining process has been modest at

best. We attribute this in part to the lack of any legal

or regulatory framework on shift work and extended

hours. It is very difficult to persuade employers to

adopt measures that exceed existing legal requirements. In addition, in many of these industries, shift

work and night work are unavoidable. In these cases,

we attempt to give the employees more of a choice

and more control over their hours of work (88).

Some nurses must work extended hours as a

condition of their employment, while others welcome the opportunity to mass their hours. Both

situations may present challenges to the well-being

of nurses, their families, and their patients. This

section reviews research on shift work in nursing and

the consequences of shift work for family and social

life, health, and work performance of nurses.

R.N.s are the largest health care profession.2

According to a recent survey, there were 2,033,032

R.N.s licensed to practice in the United States in

1988, of whom 1,627,035 (80 percent) were employed in nursing positions (67). Nursing is predominantly a woman’s profession; in 1988, only

3 percent of registered nurses were men. In

addition, 71 percent of R.N.s were married, and

54 percent had at least one child living at home.

One-half of all R.N.s in 1988 were under age 40, and

63 percent were under age 45. Thus the majority of

nurses have families or are in their childbearing

years, sociodemographic factors that bear on shift

work.

Of those employed in nursing in 1988,68 percent

were working full-time and 32 percent were working

part-time. Hospitals traditionally have been the principal employer of R.N.s. In 1988, 68 percent of employed registered nurses worked in hospitals, and no

other single type of employment setting accounted

for more than 8 percent of employed nurses. Nursing

homes and other long-term care facilities employed

only 7 percent of R.N.s in 1988. Ninety percent of

R.N.s employed in hospitals in 1988 worked in nonFederal, short-term care hospitals, 6 percent worked

in Federal Government hospitals, and 4 percent

worked in non-Federal, long-term care hospitals.

Among R.N.s working in hospitals in March 1988,

2.7 percent (or 30,358 nurses) were working through

a temporary employment service (67).

Prevalence

No national survey of R.N.s provides estimates of

the prevalence of shift work or the number of years

the typical R.N. spends in shift work during her or

his career. However, since the organizations that

employ the vast majority of nurses—hospitals, nursing homes, and other extended care

facilities—require 24-hour operations, it is likely

that a sizable proportion of R.N.s are engaged in

shift work. Moreover, many nurses also work

overtime, since they draw time-and-a-half pay for

overtime (62). Data from one survey show that

among 764 responding community hospitals, an

average of71 percent of R.N.s were reported to work

some nondaytime hours, and an average of 33 percent of R.N.s worked some combination of day,

evening, and night shifts, including rotating all three

shifts; furthermore, only 7 percent of R.N.s had

every weekend off (l).

Another survey reported that 46 percent of R.N.s

employed in nursing homes in 1985 worked nonstandard hours, and 9 percent worked rotating shifts

(107). The smaller proportion of R.N.s on rotating

shifts in nursing homes compared with hospitals

could be attributed to the fact that nursing home

R.N.s are more likely to be in supervisory positions

than in staff positions.

Estimates for the total U.S. labor force suggest

that shift work is more prevalent among nurses

than women workers in general (see ch. 4). Data

collected in 1985 on wage and salary workers age

16 and over revealed that 13 percent of full-time

women workers and 43 percent of part-time women

workers were involved in some type of shift work.

Among full-time workers in health assessment and

treatment occupations (the category that includes

R.N.s), 31.3 percent were in some type of shift work.

Rotating shifts were the most frequent kind of shift

work in these occupations. (Ch. 4 gives a more

thorough discussion of the extent of shift work in the

labor force.)

2 ~~ ~epofi pefi~ to@~te~d~~es.N~sing perso~el in the us. he~th c~e fidustry include @s&d n~ses, licensd pmCtiCd-VOCdiOlld

nurses, and unlicensed ancillary personnel, including nursing aides. It is estimated that these three occupations included over 3 million persons employed

in health care in 1984 (108).
Chapter 8-Case Study: Registered Nurses and Resident Physicians ● 157

Photo credit: Joint Commission on the Accreditation of Healtheare Organizations

Nurses tend to patients within view of the nursing station.

Patterns

Traditionally, hospitals and nursing homes have

operated on three 8-hour shifts (day, evening, and

night shifts), with nurses typically working five

8-hour shifts per week on either a freed or rotating

basis, including weekend work.3 Shifts typically

overlap for one-half hour, in order that nurses

leaving the unit can communicate with those arriving regarding patient status or anticipated admissions. The pattern of activity in hospitals varies by

time of day, so the tasks and workloads of nurses can

vary by shift. Night shifts are generally considered

to be slower and to require a smaller complement of

nurses, since most patients are asleep and fewer

procedures take place at night. A possible exception

might be the emergency room, where activity can be

frenetic during the night shift. On the other hand,

night nurses are expected to be able to manage

emergencies when other services are not readily

available.

Shift patterns (e.g., timing and length of shifts,

patterns of rotation), the method of shift assignment

(the degree to which nurses can control their

assignments by bidding on preferred shifts or trading

shifts), and compensation for shift work (e.g., higher

hourly wages for undesirable shifts) are determined

by the employing organization and vary widely. In

some decentralized organizations, these policies are

determined at the unit level. Some aspects of shift

work, such as requirements regarding rotation,

mandatory overtime, or pay differentials, become

issues in collective bargaining by nurses, although

only 20 percent of hospitals report having organized

collective bargaining for R.N.s (predominantly

through State nurses’ associations) (l).

Typically, nursing coordinators or nursing managers have authority over shift assignments for staff

nurses and resolve scheduling conflicts. Assignments to undesirable shifts (e.g., night or weekend

work or rotating shifts as opposed to fixed shifts) are

often an inverse function of seniority. Some nursing

3 In nursing, the day shift typic-ally refers to the 8-hour shill occnrring during daytime hours (e.g., 7 a.m. to 3:30 p.m.), as contrasted with evening

(e.g., 3 p.m. to 11:30 p.m.) and night shifts (e.g., 11 p.m. to 7:30 a.m.). In this chapter, nurses who workfmed day shifts are not regarded as shift workers.
158 ● Biological Rhythms: Implications for the Worker

administrators reward seniority with more desirable

shifts as a retention strategy (61).

Six distinct hospital scheduling alternatives appear to exist, although some are used in very few

hospitals. The models are:

●

●

●

●

●

●

the traditional five 8-hour shifts per week,

including rotation within a l-week cycle;

the “Baylor Plan,” consisting of two or three

12-hour shifts for separate weekend staff, with

the regular staff working traditional 8-hour

shifts;

‘‘4 to 40,’ consisting of four 10-hour shifts per

week;

“7-on, 7-off,” consisting of seven 10-hour

shifts on alternative weeks;

“ 12-hour shifts,” consisting of three 12-hour

shifts one week, four 12-hour shifts the next;

and

‘‘customized schedules," involving choice of

various shift lengths (47). -

Traditional 8-hour shifts continue to predominate in

nursing. Community hospitals report that nearly 79

percent of R.N.s, on average, work 8-hour shifts, 17

percent work 12-hour shifts, and 4 percent work

other types of shifts, including partial shifts of 4 to

6 hours (l). Although a number of experiments with

hospital shift lengths and patterns have been reported, these appear to affect a relatively small

proportion of R.N.s. For example, one hospital in

North Carolina has reported a 12-hour shift system

in which nurses work seven 12-hour days in succession, followed by 7 days off (40). Urban hospitals

appear to be more innovative with regard to shift

issues because they face greater competition for

nursing staff (61). At Johns Hopkins Hospital, a

professional practice model, in which the nurses

agree to provide 24-hour coverage of their unit in

exchange for self-management and annual salaries,

has been in place on some nursing units since 1981.

The model permits nurses to design their own shift

systems and to make and monitor their own shift

assignments (27).

Differentials in pay for shift work are used widely

by U.S. hospitals. In a 1988 survey, over 97 percent

of hospitals reported paying more to full-time and

part-time R.N.s for evening and night shifts (l).

However, only 41 percent of hospitals reported paying more for weekend shifts (l). In 1987, the

average hourly differential paid for the evening

shift by U.S. hospitals was $0.79, for the night

Box 8-A—Impact of Shift Work on Nursing

in Great Britain

A recent study for the British Department of

Health entailed a survey of the shift schedules in

effect in large (400+ beds) general hospitals in

England and Wales. Over 50 percent of all such

hospitals supplied details of their shift schedules.

Only a small minority of hospitals (less than 20

percent) had a regular shift schedule, The majority

of hospitals (65 percent) claimed to have a flexible

system in which the individual nurses’ requests

were taken into account when drawing up the duty

rosters. The remainder had an irregular system in

which no account was taken of nurses’ requests.

Despite these differences, timing and duration of

shifts were remarkably consistent among hospitals.

Approximately 80 percent of the early morning

shifts started between 7:30 a.m. and 8 a.m. and

lasted for 8 to 8.5 hours. The starting time, but not

the duration, of the late afternoon shift was slightly

more variable. Ninety percent started between

12:30 p.m. and 2 p.m. Similarly, most night shifts

started between 8:30 p.m. and 9:30 p.m. and lasted

between 10 and 12 hours. Perhaps more important,

while new schedules involved more than two or

three successive early or late shifts, spans of seven

or eight successive night shifts were not uncommon, These data contrast with U.S. patterns,

presumably reflecting national differences.

SOURCES: OffIce of Technology Assessment, 1991; based on

S. Folkard, Department of psychology, University

of Shefileld, Sheffkld, United Kingdom, personal

communicatio~ January 1991.

shift $1.02 (5). Nonfinancial compensation for shift

work (e.g., extra days off or childcare) is rare. The

effectiveness of pay differentials in attracting nurses

to undesirable shifts is unknown. Box 8-A discusses

shift work schedules for nurses in Great Britain.

Evidence of Dissatisfaction With Shift Work

A number of polls and research studies conducted

during the last decade provided evidence that shift

work, or the nurse’s perceived lack of control over

scheduling, was associated with job dissatisfaction

and turnover. However, few prospective studies of

job satisfaction have distinguished between the

effects of shift work and other job, organizational, or

personal attributes. Results of a 1981 Texas survey

of 3,500 nurses suggested that work overload and

shift work issues were intermingled and that, in

general, nurses desired greater control over work

assignments and scheduling (1 13). (The job condi-
Chapter 8--Case Study: Registered Nurses and Resident Physicians ● 159

tion eliciting the most dissatisfaction, however, was

salaries.)

In one 1987 poll, 1,643 nurses were asked what

caused them the greatest dissatisfaction with their

jobs:

●

●

●

76 percent of nurses responding said increased

work hours;

51 percent of nurses responding said increased

shift rotation; and

43 percent of nurses responding said increased

weekend work due to the current nursing

shortage.

In addition, 65 percent of nurses responding said that

a minimum of every other weekend off was most

important in evaluating their present jobs, and 53

percent reported that a permanent shift assignment

was most important. (Salary and benefits were

ranked equal in importance with a permanent shift

assignment) (30).

A l-year prospective study of nursing job satisfaction and turnover asked R.N.s in two large universityaffiliated hospitals to report their satisfaction with

scheduling of work hours. Overall, nurses were

dissatisfied with their scheduling (114). In one

hospital, working rotating shifts, as opposed to fried

shifts, was found to lower nurses’ perceptions of

their control over the work environment. Lower

perceived control, in turn, was the strongest predictor of job dissatisfaction. In the second hospital, shift

work had no significant impact on perceived control

(115).

A study of job satisfaction of R.N.s in five

short-term acute care hospitals measured satisfaction at two points, 8 months apart. Assignment to the

day shift was associated with higher job satisfaction

(12). A study of 146 nursing units in 17 hospitals

examined unit-level determinants of turnover rates.

Greater shift rotation among R.N.s in a unit was seen

as an indicator of less staff cohesiveness, which was

predicted to produce higher rates of turnover. In fact,

extent of shift rotation was found to be a marginally

significant predictor of turnover rates (2).

Only one randomized trial of different shift

patterns in nursing has been reported. In a 788-bed

tertiary-care hospital (i.e., a hospital that provides

highly intensive, sophisticated care for medical

conditions that are difficult to manage in a community hospital), 12 randomly selected medicalsurgical units staffed by both R.N.s and licensed

practical nurses (L.P.N.s) were assigned at random

to one of four schedules:

●

●

●

●

fixed shifts;

computer-assisted scheduling in which nurses’

shift preferences were considered;

select-a-plan, in which unit nurses designed

their own scheduling system, typically combining 8- and 12-hour shifts; and

a control group.

Descriptions of job attitudes were obtained from 98

percent of nurses before and after the shift assignments, but the length of the followup period is

unspecified. The results did not indicate substantial

variations by schedule in R.N.s’ job attitudes or

turnover at followup (20).

A number of commissions and task forces in

recent years have recommended that health

service organizations address the issue of shift

work. A 1981 study of nursing and nursing education noted flexible scheduling as a strategy to

increase nursing labor supply to hospitals and

nursing homes (48). A 1983 report recommended

that flexible scheduling be developed as a component of models for organizational change in nursing

(68). A study of magnet hospitals found that flexible

scheduling and elimination of rotating shifts were

among the four most important factors promoting

recruitment and retention of nursing staff (3).

A consensus appears to have developed regarding

the need to provide shift work alternatives for nurses

and to increase nurses’ involvement in scheduling

decisions. A 1988 report cited work scheduling as a

major source of stress among hospital R.N.s (108).

Most recently, the authors of a study of 421 hospitals

and over 15,000 nurses in six urban areas recommended that hospitals offer varied and flexible

schedules as a means of responding to the work

preferences of nurses and resolving the current

nursing shortage (91).

Consequences of Shift Work in Nursing

While there is a body of research that addresses the consequences of shift work on the

health, well-being, and performance of workers

in a variety of industries, these industries employ

mostly men; relatively little research has been

conducted specifically on women shift workers

(24). As a result, it is difficult to generalize about

nurses from existing studies. (The consequences of
160 ● Biological Rhythms: Implications for the Worker

Photo credit: Harvati Community Health Plan

Patient getting his blood pressure checked by a nurse.

shift work are discussed more fully in ch. 5.) In

nursing, type of shift is often confounded by age,

because younger, less experienced nurses tend to be

assigned to rotating shifts. This discussion of

consequences focuses on studies in which nurses

have been subjects, but it will allude occasionally to

studies of other women shift workers or to the

absence of information about women shift workers.

Work Performance

Studies of the work performance of shift workers

have generally focused on lost productive time as a

consequence of health problems (e.g., absenteeism

due to illness or use of health services) and on errors

and injuries as a consequence of fatigue or disrupted

circadian rhythms. A few studies of nurses have

reported results for sick days, use of health services,

self- or supervisor-reported performance levels, and

various indicators of quality of patient care.

Sick Days and Use of Health Services—A 1977

study of the health consequences of shift work

conducted by the Stanford Research Institute for the

National Institute for Occupational Safety and

Health (NIOSH) used employee records to study

sick days and clinic visits by nurses on four shifts.

(The number of sick days alone is not a reliable

indicator of health problems, since sick days are

limited by personnel policies.) Nurses on a rotating

schedule tended to take more sick days than

nurses on fixed shifts, and rotating nurses tended

to have more serious reasons for taking sick days

(e.g., acute respiratory infection, upper gastrointestinal tract distress). With regard to clinic

visits, rotating nurses attended workplace clinics

during work hours more frequently than fixed shift

nurses and for a wider array of complaints (103),

indicating that rotating nurses lose more time from

work (due to both sick days and clinic visits) and

could be less productive on the job.

Job Performance Ratings-A few studies of the

effects of shift work on the job performance of

individual nurses have used self-reports of performance or the reports of supervisors. The NIOSH study

found that nurses on fixed afternoon-evening and

rotating shifts reported lower levels of satisfaction

with their work performance than did freed night and

day shift nurses (103). Another study found that

nurses on rotating shifts received lower job performance ratings by their supervisors, compared to nurses

on freed shifts (49).

In a recent study of job performance and jobrelated stress among 482 R.N.s in five hospitals in

the Southeastern United States, self-reported job

performance was examined in relation to type of

shift worked. On overall job performance, nurses on

rotating shifts reported the lowest performance

level, followed by freed afternoon nurses, freed

night nurses, and freed day nurses. The investigators

found that only one of a number of dimensions

studied was significantly associated with shift: for

performance with regard to professional development, rotating and freed afternoon nurses scored

themselves lower than fixed day and freed night

nurses. There were no significant differences by shift

for leadership, teaching-collaboration, planningevaluation, or interpersonal relations-communications. Rotating nurses also reported the highest

levels of job-related stress. These relationships held

when anticipated turnover, position level, and length

of time on the present shift schedule were controlled

(21).

Quality of Patient Care—Very little research

has been conducted on the relationship between

shift work and quality of patient care by nurses.

The few studies that have addressed the effects of

shift work on quality have been small-scale evaluations of shift work demonstration projects.

In nursing studies in general, quality of care is

typically measured in terms of the nursing care

process rather than patient outcomes. Process meas-
Chapter 8-Case Study: Registered Nurses and Resident Physicians . 161

ures of quality usually take place at the unit level and

involve chart audits, in which raters examine nursing

care plans to determine whether specific procedures

have been recorded. An alternative method is direct

observation of nursing procedures, in which a rater

assesses performance along a number of dimensions. Other indicators of quality include incident

reports (medication errors, accidents, or injuries)

and patient satisfaction. One should remember,

however, that quality of care as defined by provider

and quality of care as defined by patient may not be

the same (15).

Research to date implies two mechanisms by

which shift patterns might affect quality of nursing

care. First, shift work patterns that are more compatible with circadian rhythms would be expected to

result in less fatigue and increased alertness on the

job. Second, shift work patterns that are more

satisfying to nurses would be expected to result in

greater nurse retention, unit cohesiveness, and continuity of care across shifts.

A 4-month trial of the 4 to 40 workweek (four

10-hour days per week) in a pediatrics unit employing both R.N.s and L.P.N.s was conducted in Seattle,

Washington. The new scheduling system, compared

to the traditional 8-hour, 5-day shift system, was

expected to improve quality of care, defined in terms

of intershift continuity of care. Process measures of

nursing care quality revealed little change from the

traditional system. Staff reports of quality, however,

did show improvement (50).

In another program, a 12-hour shift system was

introduced on an intensive care unit and evaluated

over a 6-month period. The impact of the 12-hour

shift, compared to the traditional 8-hour shift

pattern, was measured with regard to nurses’ job

satisfaction, interpersonal relations in the work

environment, nurses’ health status, nurses’ fatigue

and alertness, and quality of patient care. No

significant differences were found between types of

shift for alertness (reaction times) or fatigue, although in the 12-hour shift system reaction time was

faster for day shift than for night shift nurses. Using

retrospective analysis, the investigators found no

significant difference between the quality of nursing

care at the time studied and that during a corresponding period of the previous year. Data from incident

reports showed no change in the rate of incidents

with the switch to 12-hour shifts (29).

In a pilot study of 12-hour shifts in a surgical

intensive care unit, quality of patient care prior to

implementation of 12-hour shifts was compared to

quality of care 1 year later. Some increase in

subjective feelings of fatigue and decreased accuracy on performance tests was reported, but evidence

from chart audits revealed no significant changes,

and nurses perceived that their performance improved (63).

One small study compared 10 R.N.s working

8-hour shifts with 10 R.N.s working 12-hour shifts

in the intensive care units of two Midwestern

hospitals. The Quality Patient Care Scale (QUALPACS) was administered by an observer to provide

concurrent ratings of patient care provided by each

nurse. Only one of five behavior categories rated by

the QUALPACS demonstrated a statistically significant difference between 8- and 12-hour shift workers, although nurses on 12-hour shifts scored lower

than nurses on 8-hour shifts on all of the dimensions.

Since most of the 12-hour nurses volunteered

comments about the fatigue they experienced, the

investigators interpreted these results as indicating

potential problems with quality of care on 12-hour

shifts (69).

It is not known how extended workdays and

compressed workweeks affect patients’ satisfaction with nursing care. Conceivably, patients could

react differently to various shift schedules, depending on the availability of their primary care nurse.

One study reports anecdotal evidence of patient

satisfaction with a 12-hour shift system in which

nurses worked 7 consecutive 12-hour days followed

by 7 days off (40). However, patients who do not see

their primary nurse for days at a time may experience

this as discontinuity in their care.

Health

As discussed in chapter 5, shift work can affect

health. Disruption of circadian rhythms because of

shift work could have differing effects on men and

women due to hormonal differences between the

sexes. Differences between men’s and women’s

circadian rhythms and adjustment of these rhythms

to shift work have been studied, but no definitive

conclusions have been drawn (8). Congressional

interest in research on women’s health, as exemplified by the Women’s Health Equity Act of 1991,

supports the theory that the results of research on

male subjects cannot be assumed to apply to women.
162 . Biological Rhythms: Implications for the Worker

Table 8-1 lists recent studies of health outcomes

of shift work in nursing. The key findings are

discussed below. Research has demonstrated that

nurses working night and rotating shifts suffer

more sleep disturbances than other nurses and

may be at higher risk for various other health

problems (89).

Sleep Disturbances—Deficits in the quantity or

quality of sleep are associated with physical or

emotional disorders and with problems in alertness

and performance that can produce injuries on the

job. All but one of the studies summarized in tabl e

8-1 measured quantity or quality of sleep as a

function of nurses’ shift work. Outcomes studied

included amount of sleep, sleep stages and rapid eye

movement (REM) sleep, interruptions of sleep, and

subjective fatigue. A frequent focus has been the

adaptation of sleep patterns to different amounts of

night work. In general, nurses working rotating

shifts and night shifts involving only a few nights on

duty had more sleep disturbances than other nurses,

although few studies compared nurses on a variety

of shifts or controlled for such variables as age, shift

work history, and family circumstances. None of the

studies examined the effects of chronic sleep disruption on nurses’ health or work performance.

Several of the studies made a distinction between

part-time and full-time night nurses (e.g., those

working only 2 nights a week or 2 nights in

succession compared to those working more than 2

nights a week or in succession) in an effort to study

short-term compared to long-term sleep adjustment

to shift work. These studies found that full-time

night nurses were better adjusted than part-time

night nurses in terms of quantity and quality of sleep

(34,64,65). Such adjustment was attributed in part to

greater commitment to night work among full-time

night nurses, as well as to greater compatibility of

family situations with night work and day sleep

among these nurses (e.g., no children at home).

The dual issues of a selection effect (i.e., nurses

selecting shift work based on compatibility with

lifestyle) and family roles as mediating variables in

adjustment to night work were noted in most of the

studies. For women night shift workers more than

for men, family responsibilities (e.g., child care,

carpooling, housework) during nonworking hours

take precedence over the need to compensate for

lost sleep (39). Duration of sleep was found to be

greater among unmarried subjects than among

married subjects with children (39). Nurses' lifestyles, not just their shift patterns, determine

sleep patterns (39). Another study found that

fatigue in nurses working nights (in a sample of

nurses who worked various shifts at irregular

intervals) appeared to be due to social factors

(number of children, age, and being married or living

with a partner) (45). Greater number of children also

decreased the amount of sleep achieved by nurses

after work on the night shift.

The NIOSH study mentioned earlier (103) found

that nurses on fixed night shifts and on rotating

shifts generally reported more problems with

sleep, as compared with nurses on fixed day or

fixed afternoon or evening shifts. These included

subjective reports on the overall adequacy of sleep,

trouble falling asleep, awakening during sleep and

falling asleep after awakening, waking up feeling

tired, and feeling tired during work. Although

nurses on all four types of shifts reported desiring

the same amount of sleep, nurses on fixed night

shifts reported getting the least sleep. Further,

rotating shift nurses, compared with those on

fixed shifts, showed significantly higher incidence of fatigue and inadequate sleep patterns

when the effects of age and marital status were

controlled (103).

Digestive Disorders—The NIOSH study reported

data on nutritional intake, appetite, and digestive

problems among nurses by type of shift. Nurses on

fixed afternoon or evening shifts reported better

appetites than nurses on other shifts. Night shift

nurses reported needing fewer meals in a 24-hour

period than other nurses, and day shift nurses

reported needing the most. Rotating shift nurses

reported more snacking. Day nurses reported the

most meals eaten with family or fiends.

Rotating and day nurses reported significantly

more bloating or feeling full; rotating and afternoon

nurses reported more gastritis; and rotating nurses

had higher incidence of trouble digesting food.

Rotating shift nurses showed a significantly

higher incidence of digestive trouble than other

nurses, when age and marital status were controlled (103).

In another study, nurses working three or more

consecutive nights exhibited greater adjustment in

their meal times during a period of 12 consecutive

days than nurses working single nights or only 2

nights in succession. Nurses working more nights
Table 8-l-Studies of Health Consequences of Shift Work in Nursing

study Sample Shifts compared Major findings

Bryden and Holdstock, 12 nursing students in 1 hospital in

1973 South Africa (all female)

Felton, 1976 39 nurses in Hawaii (all female)

Folkhard et al., 1978

Gadbois, 1981

Harma et al., 1988

30 nurses in 1 hospital in England

(all female)

898 nurses and nursing auxiliaries

in 61 hospitals in France (all

female)

128 nurses and nursing aides in 1

hospital in Finland (all female)

Hildebrandt and Stratmann, 6 nurses in Germany

1979

lnfante-Rivard et al.,

1989

418 nurses and nursing aides in 1

hospital in Canada (all female)

Day shift, night shift in same

nurses

Night shift, postnight duty in same

nurses

Early and late day shifts,

permanent nightshirt (full-time,

4 nights/week; part-time,

2 nights/week)

Fixed night work only (varied

number of nights on duty)

Irregular rotating shifts only

(combinations of day, evening,

night shifts in 3-week cycles)

7-to 18-day period of night work

compared with 10-day

recovery period in same

nurses

Fixed day, fixed evening (within

both groups, comparisons

between those with and

without prior night work)

Daytime sleep was shorter than night sleep and had more

interruptions. REMa sleep occurred sooner in day sleep

than in night sleep.

Peak body temperature; excretion of sodium, potassium, and

creatinine in the urine; and osmolality (concentrations of

these substances in the urine) occurred later in the day in

nurses on night duty. After returning to day shift, nurses’

urinary sodium, creatinine, and osmolality cycles returned

to baseline pattern, but temperature and potassium did not

after 10 days of followup. Fewer hours of sleep and poorer

quality of sleep reported while on night duty.

Circadian rhythms (oral temperature, subjective alertness and

well-being) of full-time night nurses showed greater

adjustment than those of part-time nurses, both on first

night shift and in adjustment from first to second nights.

Part-timers reported less sleep and less “calmness” on

waking.

Self-reported sleep duration was shorter, and sleep

interruptions more frequent, for married women with

children than for unmarried women. Mothers with young

children went to bed later in the day.

Neuroticism and morningness were found to increase shiftcycle fatigue, and greater maximal oxygen consumption

decreased it. Morningness, older age, and having children

decreased sleep duration after night shift. Shift work

experience and morningness decreased sleep quality after

night work, and oxygen consumption increased it.

Gastrointestinal symptoms were increased by neuroticism,

marriage, and older age. Neurovegetative symptoms were

increased by marriage and neuroticism. Musculoskeletal

symptoms were increased,by marriage, neuroticism, and

physical activity and were decreased by oxygen

consumption and muscle strength.

Three “evening type” nurses reacted to night work with

flattening of circadian amplitude (temperature and heart

rate) and greater tolerance. Three “morning type” nurses

developed increased amplitude, higher amounts of

subjective complaints (e.g., headache, nervousness,

irritation), greater compensation for lost sleep, and lower

subjective vigilance.

Prevalence of 9 sleep disorder symptoms ranged from 6

percent to 53 percent. Evening workers were at higher risk

of not being alert and receptive at rising and at lower risk of

early morning awakening. Prior night work was associated

with day tiredness and quantity of sleep.
Table 8-l-Studies of Health Consequences of Shift Work in Nursing-Continued

Study Sample Shifts compared Major findings

Kuchinski, 1989 146 R.N.sb in 1 hospital in Cincinnati (all female)

LeClerc et al., 1988 824 nurses in 10 hospitals in

France

Matsumoto, 1978 5 nurses in 1 hospital in Japan

Minors and Waterhouse,

1983

Minors and Waterhouse,

1985

Tasto et al., 1978;

Smith et al., 1979

Verhagen et al., 1987

Webb, 1983

26 nurses

14volunteernurses in 1 hospital in

England (11 female)

1,219 full-time nonsupervisory

R.N.s and L. P.N.sC in 12 U.S.

hospitals (1,195 female)

167 nurses in 6 hospitals in Belgium (all female)

19 nurses age 50 to 60 in 3

hospitals in Florida compared

with forty 50- to 60-year-old

female university employees

with no history of shift work

Fixed shifts, rotating shifts

Permanent day, permanent night,

rotating without night, rotating

with <5 nights/month, rotating

with 5+ nights/month

Day shift, night shift in same nurses

Single nights, paired nights, nights

in blocks of 3+

Short-term night shift (1 to 3 successive nights), long-term night

shift (3 successive nights)

Fixed day, fixed afternoon/evening, fixed night, rotating

Permanent night (full-time and parttime), 2-shift rotation with some

nights

Current night shift with 10 years of

rotating shift experience; nurses

not on current shift work but

extensive night or rotating shift

experience; nurses not on current night shift and limited prior

shift experience

No differences by shift were found in menstrual interval,

duration of flow, amount of flow, dysmenorrhea, intermenstrual bleeding, or secondary amenorrhea.

For 38 health variables, including symptoms and health

services utilization, type of shift had poor explanatory

power.

Time in bed and total sleeping time were lower in daytime than

nighttime sleep. Number of awakenings was greater in day

sleep. Daytime sleep differed qualitatively from night sleep

in appearance of REM and non-REM sleep.

Nurses working single nights maintained a conventional

diurnal routine. Nurses working a number of consecutive

nights showed changes in routine, including afternoon

napping and different meal times.

Nurses working 3 successive nights were better adjusted to

nocturnal activity and diurnal sleep, as reflected in amount

of sleep, afternoon naps, and fewer subjective complaints.

Nurses who rotate shifts took more sick days than nurses on

fixed shifts, suffered more injuries, and reported more

digestive trouble, leg and foot cramps, colds, nervousness

and shaky feelings, fatigue and exhaustion, use of stimulants, use of beer and liquor, tension or anxiety, depression

or dejection, confusion or bewilderment, neuroticism, sleep

disturbances, and problems adjusting work schedules and

family life.

Rotating nurses reported more health complaints. Permanent

nurses slept less than rotating nurses.

Little evidence of enduring effect of night shift experience on

sleep patterns. Some evidence of moderately changed

REM sleep.

aREM, rapid eye movement.

bR.N., registered nurse.

%.P.N., licensed practical nurse.

SOURCE: Office of Technology Assessment, 1991.
Chapter 8--Case Study: Registered Nurses and Resident Physicians ● 165

tended to have their evening meal around midnight,

indicating a commitment and long-term adaptation

to night shift work (64).

Being married increased the reported incidence of

gastrointestinal symptoms (poor appetite, gaseous

distention, heartburn, constipation, and diarrhea),

nervous and psychological symptoms (nervousness

and tautness, headache, nightmares, giddiness and

nausea, palpitation or irregular heartbeat, hand

sweating, pricking or numbness of body parts,

decrease in libido), and musculoskeletal symptoms

(back symptoms, neck, shoulder or hip symptoms,

knee or ankle symptoms) (45).

Psychological and Nervous Symptoms—Psychological variables may be interpreted as outcomes

of shift work or as outcomes of mediating variables.

The NIOSH study used the Profile of Mood States

(POMS) to measure psychological state and the

Eysenck Personality Inventory (EPI) to assess personality traits. Psychological state changes over

time, while personality trait is more or less constant

(25,54). On the POMS subscales:

●

●

●

●

nurses on a rotating shift reported significantly

higher tension and anxiety than afternoonevening and night workers;

rotating nurses reported significantly more

depression and dejection than day or night

workers;

rotating nurses reported significantly less vigor

and more fatigue than nurses on all other shifts;

and

rotating nurses reported significantly more

confusion and bewilderment than nurses on all

other shifts.

On the EPI, nurses on a rotating shift were significantly more anxious and irritable than nurses on

other shifts. Interestingly, day shift nurses scored

lower on sociability than afternoon-evening and

night nurses (103).

Anxiety, irritability, and nervousness increase

shift-cycle fatigue in nurses and contribute to a

higher reported incidence of gastrointestinal, nervous, psychological, and musculoskeletal symptoms,

regardless of shift (45). A measure of morningness

(preferring daytime activity) as opposed to eveningness (preferring nighttime activity) was also predictive:

●

●

The

morningness decreased reported fatigue in morning shift nurses and increased it in evening shift

nurses; and

morningness also decreased the duration and

quality of sleep after night shift work (45) (see

ch. 5).

relationship between specific psychological

symptoms and degree of social interaction, which

may be reduced by shift work, is not known.

Menstrual Dysfunction-Few studies have examined the relationship between shift work and

reproductive health in nurses, although environmental and occupational conditions can contribute to menstrual dysfunction (51). The NIOSH

study included some indicators of menstrual dysfunction and found that nurses on fixed day shifts

reported more irregular menstrual periods than other

nurses and that nurses on all types of freed shifts

reported more menstrual cramps than did rotating

nurses. Night and rotating nurses, however, reported

spending more time lying down due to menstrual

cramps, and rotating nurses reported more tension,

nervousness, weakness, and sickness at menstruation, as well as longer periods, than did nurses on

other types of shifts (103).

In a recent study of the menstrual characteristics

of 146 R.N.s age 20 to 40 in a university hospital, 43

percent of the nurses studied worked fixed shifts and

57 percent worked rotating shifts. No significant

differences between these two groups of nurses were

found for self-reported length of the menstrual

period, duration of flow, amount of flow, dysmenorrhea, intermenstrual bleeding, or secondary amenorrhea (55).

Substance Use and Abuse-Only the NIOSH

study has reported differences in nurses’ substance

use by type of shift:

●

●

●

●

●

The

rotating nurses, compared with nurses on freed

shifts, were more likely to use stimulants;

rotating and afternoon shift nurses drank more

beer;

rotating nurses drank more alcohol of all kinds;

rotating and day shift nurses were more likely

to drink on workdays; and

night nurses were more likely to drink before

going to work.

information obtained on quantity of alcohol

consumed was limited, and no conclusions can be

drawn regarding alcohol dependency. Similarly, it is
166 ● Biological Rhythms: Implications for the Worker

not possible to determine from the reported data

whether “drinking on workdays occurs during or

outside of work hours or whether drinking on

workdays causes problems in performance (103). It

also is not possible to determine whether people who

drink more prefer different shifts (25,54).

Injuries—Fatigue and impaired cognitive and

psychomotor function during shift work can result in

injuries. As mentioned in chapter 5, laboratory

studies have shown that speed, reaction time, and

accuracy decline after evening hours, suggesting

that more accidents and injuries are likely to occur

at night (33). Only the NIOSH study and a reanalysis

of those data (97) have reported injuries by type of

shift worked by nurses. Rotating shift workers

suffered more injuries than fixed shift workers.

Injury rate was not influenced by age, length of

employment, or marital status. Furthermore, cuts,

bruises, and punctures (mainly to fingers) were the

most frequent category of injury on all shifts, and

rotating nurses had significantly more such injuries

than nurses on freed shifts (97).

Family and Social Life

The NIOSH study provides some information

about the effects of shift work on the family and

social life of nurses. Questionnaires were administered to 1,219 fill-time, nonsupervisory R.N.s and

L. P.N.s in 12 U.S. hospitals; 98 percent of the nurses

were female, the average age was 32.9 years, and 45

percent were married. The sample was fairly evenly

distributed across four work schedules: fried day

shift, freed afternoon or evening shift, fixed night

shift, and rotating shift (generally, rotation occurred

between two shifts only) (103).

Results showed that the greatest disruption of

family and social life occurred for nurses on

rotating shifts. Regarding degree of satisfaction

with the amount of time spent with their spouses,

rotating and night shift nurses were most dissatisfied. Night shift nurses reported the most interference with sexual activities, whereas nurses on

rotating shifts reported the most complaints from

spouses regarding their work schedules. As for

amount of time spent with children, nurses on

rotating shifts were the least satisfied, although

afternoon and evening shift nurses reported that they

assumed the least responsibility for child rearing and

disciplining. Finally, rotating and afternoon shift

nurses were least satisfied with the time available for

personal activities, sports, and social activities

(103).

EXTENDED DUTY HOURS AND

GRADUATE MEDICAL

EDUCATION PROGRAMS

“Shifts” implies that there is a preset beginning

and end to your work hours, however long they may

be. We do not work shifts. We just work, When the

work is done we can go. If that’s 36 hours later, so

be it. During my internship year, I routinely spent

120 hours a week in the hospital. These hours were

largely devoted to menial, nonmedical tasks called

scut work, a catch-all term for patient-care-related

work that does not require a medical degree (i.e.,

inserting I.V.s, doing blood cultures, transporting

patients, or scheduling tests) (31).

I entered medical school with lofty aspirations of

selfless dedication to the sick, a life of joyful

altruism. Like many of my colleagues, I saw these

worthy aspirations transformed into cynicism under

the pressure of sleepless call nights in a pediatrics

internship. My love for children became a loathing.

As an intern in 1984, I worked over 135 hours a

week taking short call (until 10 p.m.) one night, long

call (40 hours) the next night, and 8 hours off the next

night. I felt that sleep deprivation dangerously

impaired my judgment, giving me the sensation of a

sleep-walking nightmare. I remembered the story of

the resident in our program a few years before I came

who had been so impaired by her sleep deprivation

that she fell asleep at the wheel after returning from

a 40- to 45-hour shift. She is now quadriplegic and

will never be able to practice medicine again (62).

I was on call for the hospital trauma and code

teams eight times during a 14-week chaplaincy

internship. Like the medical staff, I worked 28- to

31-hour shifts, with the most intense work during

nights of little or no sleep. Like them, I alternated

between adrenalin-charged highs when an ambulance or helicopter arrived and crushingly weary

lows when patients died or were transferred. I

counted on the calm, alert time in between to do my

best work. Yet that period shrank as the shift

progressed. My mind slowed after 2 a.m., and my

empathy tumbled. Medical staff seemed to react the

same way. Sometimes tempers frayed as the night

wore on, and we all cut corners. No one was a very

cheery friend for a couple of days after a night on call

(117).

Graduate medical education, or residency, is

formal medical education beyond the M.D. degree.

This training incorporates substantial clinical expe-
Chapter 8-Case Study: Registered Nurses and Resident Physicians ● 167

rience and prepares the residents for practice in

recognized medical or surgical specialties. Residents who complete this training become eligible to

take the appropriate board certification examination.

Resident training programs began at the Johns

Hopkins School of Medicine roughly 100 years ago.

In those early days, residents, as the title implies,

were expected to live at the hospital, were on

permanent call, and were discouraged from marrying (83,100). The first-year trainee was called an

intern; now, that year is often referred to as

postgraduate year one, PGY1. The training period

was lengthened t o include additional years-junior resident (PGY2), senior resident

(PGY3), and chief resident (PGY4).4 Some specialties have a fifth year of residency (PGY5), and

others, such as neurosurgery, require 7 years. The

typical resident has changed since the early days of

resident training. Today the resident is older, more

likely to be a woman, and more likely to have a

family or other commitments outside the hospital

(59).

Although extended hours for resident training

date back to the early 1900s, when residents lived on

hospital grounds and were on permanent call, in

more recent times some residents have rotated the

night shift every other night in addition to their daily

duties (100). In 1975, when the Committee of Interns

and Residents, a union, struck New York City’s

hospitals, many programs revised this requirement

and allowed an on-call schedule of every third night

(100). According to the Association of American

Medical Colleges (AAMC):

. . . the resident benefits by being exposed to patients

throughout the course of their illnesses. This allows

observation of both the natural history of the illness

and the impact of the medical intervention. To

experience all of the learning opportunities, the

resident would have to be on duty 7 days a week, 24

hours a day. Clearly, such a schedule is unrealistic

and does not recognize the possible adverse impacts

of fatigue or the resident’s commitments to other

activities and interests. Therefore, assignment schedules for residents must be balanced between competing objectives and constraints (82).

Long hours are a necessary part of resident

training. They enable residents to follow the progression of a disease and to provide continuity of

care. This has been the custom and practice in

postgraduate medical education for nearly 100

years. However, questions and concerns have been

raised about the work schedules that have traditionally been used in resident training. It has been argued

that the progression of a disease can no longer be

learned in a hospital setting, since patients remain in

hospitals for much shorter periods of time than they

did 20 or 30 years ago (10). In addition, some

maintain that long hours are a bow to tradition and

an initiation into the profession-a rite of passage—

that all would-be doctors must endure (6,100,1 12).

Supporters of extended hours for residents argue that

labels such as “rite of passage” are irresponsible

and destructive (95). Four additional points have

been identified to support the current system of

extended duty hours with night call hours:

●

●

●

●

sleep-depriving night call is a valid learning

experience;

individual idiosyncrasies, not night hours and

sleep deprivation, make night call a negative

experience;

night call does not cause permanent distortion

of personal and professional sensitivities; and

quality of care is not compromised by sleepdeprived physicians (7).

It has been noted that due to the many recent

advances in medical knowledge and technology, the

practice of medicine is not what it was 100 years ago,

when the concept of residency was created. Patients

today come into the hospital sicker, and there are

many more drugs and technologies available to treat

them. In fact, the medical problems of patients are

more severe today than they were even a few years

ago (106). Prior to modern advances in medical

technology and pharmacology, physicians were very

limited in what they could do for patients. Physicians did their best to make patients comfortable and

relieve suffering, but few diseases could be cured.

There were no intensive care units, only a handful of

antibiotics, and patients were admitted for observation (a practice not routinely performed today

because of insurance regulations and reimbursement

schedules) (16). Today, both the intensity of medical

treatment and the pressure from patients for a

positive outcome are higher.

qN~t ~ pGY4~ ~chief msiden~. ~stm refers t. the resident who devises the schedule and resigns cM. ody hI medicine ad pe&&iCS, ~d

perhaps psychiatry, is the PGY4 automatically chief. In other specialties, such as pathology and surgery, usually one of the PGY5s is made chief. The

other PGY5s are called senior residents.
168 . Biological Rhythms: Implications for the Worker

According to one chief resident:

In reality, a resident does not sit at the bedside and

watch the progression of a disease process. After

admitting a patient, the resident scurries about,

drawing blood on another patient, checking lab

values, or admitting the next patient. Therefore, long

hours for residents provide a cheap source of labor

and less real teaching benefit, with very little

continuity. Furthermore, once residency finishes,

rarely does a physician spend the whole night at the

bedside of a patient, ready to pounce on the next

development of disease. In fact, many physicians

alternate call schedules with other physicians or

members of their group. Very often the person who

‘‘covers’ for a physician has never seen the patient

before and only has a short description of the patient

and the current medical problems. What happens to

continuity of care in this situation? (17).

In addition, in some diseases, such as cancer, a

period of weeks, months, or years is necessary to

follow disease progression in patients (117). There

is also the position that it is not the resident but the

R.N. who is constantly at the patient’s bedside; a

resident may check on a patient frequently during a

shift but usually does not spend more than a few

minutes with the patient (101).

One legal expert rejects the notion that injuries

may result because doctors are fatigued by long

shifts of duty and maintains that, despite being on

duty for long stretches at a time, doctors are able to

sleep during slack periods (71). A chief resident

argues that, although there may be times when there

is a lull in the admissions process, it is during such

lulls that the resident tries to catchup on all his or her

other work (I.V.s, drawing blood, assessing other

sick patients on the floor, etc.) (17). A resident on

call at night is often responsible for the care of 40 to

60 patients, and in some busy inner-city hospitals,

first-year residents may have as many as 15 new

admissions each night (17). One senior resident

points out that in many programs if a resident is

caught sleeping during slack hours, he or she is

reprimanded (62). Further, sleeping during slack

periods does not take into account the likelihood that

such sleep may be short, unpredictable, and repeatedly interrupted. Prior to the implementation of the

new regulations of hours of work in New York, it had

been reported that first-year residents averaged 2.6

hours of sleep per day (44).

Libby Zion Case

An incident that recently caused the public to

focus on the issue of residents’ hours was the death

of a patient, Libby Zion, in a New York hospital. In

1984, Libby Zion, an 18-year-old woman, was

admitted to New York Hospital-Cornell University

Medical Center through the emergency room and

died a few hours later. Her father, an attorney and a

former reporter for the New York Times, charged that

his daughter had received substandard care at the

hands of residents. Zion was treated by an intern and

a junior resident. Both of them had been on duty for

some 18 hours prior to her admission.

During the 8 hours between her admission and her

death, Zion was not examined by an emergency

room attending physician (a physician who has

completed all phases of the medical education

process and whose job is teaching interns and

residents), because none was on duty. Telephone

discussions were held with her private attending

physician, although he did not examine her in

person. Further, it is argued that the intern and

resident who were on duty failed to provide adequate

monitoring of the patient and prescribed medications that were contraindicated in light of Zion’s

history of drug and medication use.

Grand Jury Findings

A grand jury convened to examine the circumstances surrounding Libby Zion’s death determined

that there were five contributing factors. Four factors

involved supervision and treatment (85). In addition, the grand jury concluded that the number of

hours that interns and residents are required to

work is counterproductive to providing quality

medical care (85). While this practice may be

cost-effective for hospitals, providing them with a

cheap source of labor, the corresponding cost is a

diminished quality of health care (85). Physicians

must be in full command of their mental faculties in

order to provide proper care for patients and to

continue the learning process (85). The grand jury

investigation found that major medical decisions

made by inexperienced physicians acting alone and

unsupervised can result in medical mistakes, sometimes with fatal consequences. The likelihood that

such mistakes will occur is increased by the long

hours that interns and residents must work (85).

Moreover, the wee hours of the morning are when

the attending physician coverage is routinely sparse.
Chapter 8--Case Study: Registered Nurses and Resident Physicians . 169

Hence, not only are residents tired and sleepdeprived, but they often have no senior person

available for a second opinion or backup (10,31). In

addition, physicians who are sleep-deprived and

overworked cannot make a commitment to continuity of care (9). Accordingly, the grand jury proposed

that regulations be promulgated to limit consecutive

working hours for interns and residents. The grand

jury failed to hand down any criminal indictments

concerning Libby Zion’s treatment and subsequent

death, but it severely criticized the graduate medical

education system in New York and made five

recommendations to improve the system. Concerning resident work hours, the grand jury recommended that the State department of health

promulgate regulations to limit consecutive working hours for interns and junior residents in

teaching hospitals.

In response to the grand jury and other public and

political pressures, the New York State Department

of Health convened an Ad Hoc Advisory Committee

on Emergency Services, which issued 19 recommendations to the health department (73). Three of these

related to residents’ hours:

●

●

●

a 12-hour limit was to be placed on emergency

room shifts;

residents in acute care specialties not on

emergency room services should work no more

than 80 hours per week averaged over a 4-week

period and should not be scheduled to work as

a matter of course for more than 24 consecutive

hours, with one 24-hour period of nonworking

time per week; and

no moonlighting would be allowed.

The commissioner of health promulgated regulations in 1988 modifying the overall organization and

operations of hospitals and staffs, including supervision of residents and their hours:

●

●

as of October 1, 1988, the emergency room shift

for both house staff and attending physicians

should not exceed 12 hours (there are certain

exceptions if the hospital meets certain criteria); and

as of July 1, 1989, the scheduled workweek for

other house staff in designated acute care

specialties should not exceed an average of 80

hours over a 4-week period. No scheduled shift

should exceed 24 consecutive hours. On-duty

Photo credit: George Washington University Media lCenter

Surgery is the specialty with the most demanding hours.

assignments should be separated by at least

8 hours, with one 24-hour nonworking period

per week.5

The cost of implementing these new regulations was determined to be $226 million by the

New York Health Department, an increase of

about 3 percent in its annual budget. The hospitals

asked for additional funding. Approximately $65

million is needed for additional ancillary support

—phlebotomists (technicians who withdraw blood

from patients’ veins), housekeepers, intravenous

teams, messengers, and transport teams. It has been

reported that this ancillary support work can take up

as much as 50 percent of a resident’s work hours

(31). In some teaching hospitals, 70 to 80 percent of

a resident’s working hours at night have been found

to be devoted to such work (4). To replace work

hours lost from resident physicians, $80 million is

s~me were special guidelines for smgew.
170 . Biological Rhythms: Implications for the Worker

needed for additional residents, nurses, attending

physicians, and physician assistants. The balance is

to cover the costs of new supervision requirements,

which are also part of the new regulations. It is

estimated that the cost will be $3.1 billion over the

next 10 years and $5.7 billion over the next 15

years. This cost was to be distributed between the

State and other third-party payers. Medicare (the

Federal program for the aged and disabled) was not

obligated to pay its proportional share of the cost

(99). The health commissioner allocated Medicare

costs to all other payers controlled by the State—

Medicaid, Blue Cross, and the commercial payers

(99). Blue Cross subsequently filed a successful suit

to avoid payment of the Medicare costs apportioned

to it (72). The commercial payers, and the State’s

Medicaid program, also refused to pay the Medicare

share apportioned to them, leaving the system

$50 to $60 million short (99).

Although the intent of the regulations was to limit

residents’ work hours, the wording of the regulations

is that no resident should be scheduled to work more

than 12 hours in the emergency room or scheduled

to work more than 80 hours in a 4-week period (10).

It has been reported that some hospitals in New York

have not fully implemented the new regulations, and

some residents are still working hours in violation of

them (38). Not enough time has elapsed to determine

whether the regulations will have any effect on the

number of malpractice incidents in New York, since

a malpractice action may be filed several years after

the alleged incident, and the regulations have been

in effect for only 2 years. No broad-based analysis of

the effect of the preexisting working hours on

successful malpractice claims or quality of care was

ever done (99).

While there have been some legislative and

regulatory efforts involving the work hours of

residents throughout the country, there have been no

mandated or involuntarily enforced changes in any

State other than New York (99). Massachusetts’

teaching hospitals have undertaken a voluntary

effort to change the working conditions of residents

in that State (99). Table 8-2 discusses the current

status of residents’ work hours in some States. Box

8-B discusses limitations on residents’ hours in

Great Britain. Box 8-C explains reductions in

residents’ hours in New Zealand. And figure 8-1

shows the percentage of American hospitals, by

ownership, that have implemented policies which

set a maximum number of resident work hours.

Figure 8-l—Prevalence of Hospitals With Policies

on Residents’ H-ours

Percent

100

8 0 - r-1

All COTH V A Church Other Municipal State

n ■ 307 n ■ 55 n . 30 non- n ■ 41

profit

n D 57

= 1988-89 ~ 1989-90 m 1990-9 1

Percent of Council on Teaching Hospitals (COTH) with hours for

house staff, by ownership, 1988-91.

SOURCES: “Council on Teaching Hospitals Survey Shows Increase in

Stipends, Prevalence in Housestaff Hours Policies,” Association of American Medical Colleges W-k/y Report, Oct. 19,

1990, p. 1; S. Zimmerman, “VA Leads COTH Hospitals in

Resident Hours Policies,” COTHReport24:5, 1990.

Current Status of Graduate Medical

Education Programs

As of January 1,1990, there were 6,591 accredited

resident training programs in the United States in

24 major specialties and 38 subspecialties (94). Of

the approximately 85,330 residents in training programs, nearly 40 percent were in training for internal

medicine, family practice, or pediatrics (94).

Regulation of Residents' Hours

Regulation of residents’ hours has traditionally

been under the control of the Accreditation Council

for Graduate Medical Education (ACGME), which

has five member organizations:

American Board of Medical Specialties;

American Hospital Association;

American Medical Association;

Association of American Medical Colleges;

and

Council of Medical Specialty Societies.

Each member organization appoints four representatives to ACGME, and the Council also has a resident

representative, a public representative, and a nonvoting representative of the Federal Government. ACGME

sets standards and procedures for accreditation that
Chapter 8--Case Study: Registered Nurses and Resident Physicians ● 171

Table 8-2—State Legislative Action Regarding Residents’ Work Hours

California: The legislature is vigorously debating whether to Michigan: There are plans to reintroduce a bill that died in 1990.

control hours by legislation or through voluntary restrictions The State’s hospital association contends that such legislation

enforced by the medical schools themselves. An hours bill, is not necessary, since all but three teaching hospitals already

calling for an 80-hour workweek with 2 days off every 2 have policies on this issue.

weeks and no more than 1 day in 3 on call, was defeated in

the Senate in 1990 but will be considered by the Assembly

Minnesota: The legislature has no active bill, but the topic is being

Ways and Means Committee in January 1992.

overseen by two senators, one of whom may reintroduce an

earlier bill if not satisfied with residents’ working conditions.

Connecticut: A bill was introduced in March 1988 but it did not Missouri: The legislature is not considering a bill during the 1991

get out of committee. A new version was introduced in 1991. term. A 1988 bill regarding residents’ hours and working

Hawaii: There has been no active bill in 3 years. A bill was renditions died in committee.

introduced in 1988 but will not be reintroduced since the Nevada: The University of Nevada School of Medicine at Reno,

sponsor now believes that ACGME guidelines will be the State’s only academic medical center, has executed its

sufficient to control residents’ hours. own hours limitations on residents.

Illinois: A bill was introduced in 1988 that would have required

the Department of Public Health to examine residents’

New Jersey: The legislature has never considered a bill regarding

working conditions, but the Illinois Hospital Association

residents’ hours. The State health department discussed

lobbied strongly against it. The sponsor of the bill is

possible guidelines several years ago but never implemented

changes.

considering reintroducing it in a future session.

Iowa: There are no plans to introduce legislation in this area, but

New York: It is still the only State that has implemented rules

in 1988 a preliminary request for a draft bill on residents’

regarding residents’ hours and supervision. New York passed

working conditions was made to the legislative service

its law administratively in 1989, while the legislature merely

bureau.

passed a bill for its funding. During 1990 the State began to

enforce the rules.

Massachusetts: For the first time in 3 years, the legislature

does not plan to consider a bill in this area. Legislators say

Pennsylvania: For the first time in 3 years, no legislator has plans

they are optimistic about proposed regulations by the State’s

to introduce a bill on this issue. No reason for this change was

given.

medical centers themselves.

SOURCES: Office of Technology Assessment, 1991; based on L. Page, “Resident Hours Legislation Has Slowed Down,” American Medical News, Mar. 11,

1991, pp. 49-52.

BoX 8-B—Limitations on Residents’ Hours in Great Britain

In an effort to end the potential dangers posed by overworked resident physicians, the English minister for

health recently announced that the Ministerial Group on Junior Doctors’ Hours has developed an agreement to

reduce the maximum workweek for resident physicians to 72 hours. The Ministerial Group includes representatives

of the United Kingdom’s health departments, National Health Service management, consultant physicians, resident

physicians, and medical colleges.

The agreement calls for a short-term goal of 83 hours of work per week and a long-term goal of 72 hours of

work per week for all residents, especially those in the most overworked positions. In the first step of the agreement’s

enactment, the government will fund the creation of an additional 200 consultant and 50 staff grade positions during

1991 and 1992. Next, the agreement will be translated into practical measures to be carried out on the local level.

It calls for the immediate formation of regional committees to analyze local problems and suggest solutions.

The agreement strongly supports various types of shift work, especially in busy areas, and lists several methods

for change. These include the sharing of duties by residents, additional coverage in the busiest posts, and a

reorganization of work schedules to allow for more part-time doctors and time off after night duty. Examining how

to maximize the use of other staff, such as nurses and midwives, will also be important.

This announcement came 2 days before the English Court of Appeal refused to dismiss a claim by a doctor

who sued the Bloomsburg Health Authority for damages caused by the health authority’s requirement that he work

at least 88 hours a week. The doctor claimed that these hours were unbearable and that they deprived him of

necessary sleep to the point of posing a danger to his own health and that of his patients.

SOURCES: officttof Technology Assessrneng 1991; J. BurkhsrL “Englaud Imposes 72-HouI Limit on Residents,’* Jourwdof theA~rica~

Medicd Association 265:2742, 1991. ,.
172 ● Biological Rhythms: Implications for the Worker

Box 8-C—Reduction of Residents' Hours in New Zealand

In 1985, the New Zealand Resident Medical Officers’ Association was successful in reducing residents’ hoursfrom 100 per week to a maximum of 72 hours per week. In April 1988, three doctors who aided in implementing

these changes spoke at a convention of the National Federation of Housestaff Organizations in Boston. They

explained the reasons for this reduction, how the new hours system is structured, and the results of the decreased

hours:

Rationale Behind the Reduced Hours:

The system as it existed before 1985 produced sleep-deprived doctors who were unfairly paid and open to

abuse by hospital administrations.

Doctors who were the most sleep-deprived tended to work the longest hours and care for the sickest patients.

Studies showed that two-thirds of residents were working over 72 hours per week and a large number were

working over 90 hours per week.

The ability to learn and the motivation to work were reduced by insufficient sleep,

Continuity of care is already broken by changes in shifts; therefore, the question becomes one of when it

is best to break the continuity, not whether to break it.

Other professions that take responsibility for human lives and safety (e.g., airline pilots) have regulated their

workers through shortened shifts.

Generally, the night shift is the quietest, and residents’ work between midnight and 8 a.m. is focused on new

patients and organizing work rather than on continuing work on old patients.

Quantity of residents’ work does not equal quality.

The benefit of shortened hours to patients greatly outweighs administrative difficulties in implementing

different schedules.

Limits on Hours:

A resident’s shift may be no longer than 16 hours, and there must be an 8-hour break before the next

scheduled shift can begin.

Residents may work a maximum of 72 hours per week averaged over no more than 4 weeks.

Emergency rooms have been targeted as high-pressure areas; thus, a resident’s shift there can last no longer

than 10 hours, and there must be a 9-hour break before the next shift begins.

Emergency room residents may work a maximum of 60 hours per week, with a 50-hour-per-week average

over 3 months.

Under normal circumstances, only one shift may be worked per day.

Adequate handover time must be provided between shifts.

No resident shall be on duty or on call for more than 12 days without a scheduled rest period of at least

48 hours.

Exceptions may be made on a case-by-case basis, but in considering extensions of hours, priority must be

given to adequacy of rest and sleep for the resident involved.

Results:

*

●

☛

☛

●

●

☛

●

☛

Residents’ hours have decreased significantly: a study conducted in Auckland showed approximately

1 percent of residents working 72 hours per week; the average number of hours worked now is 54 per week,

a 19 percent decrease.

Contrary to predictions before the regulations went into effect, few problems with scheduling have arisen.

Doctors are more awake, alert, and enthusiastic about their jobs.

Patients have noted improved care, since they are no longer treated by sleep-deprived doctors.

There is nothing to stop a resident from following a particular patient, but he or she does so without the

ongoing responsibility for that patient’s care.

Productivity has increased, especially on the night shift.

Residents on the night shift are expected to do more, such as keep up patient records, than they were when

working longer hours.

Nurses find the residents easier to work with, especially on the night shift.

Residents have more time with their families and have time to pursue outside interests.

SOURCES: 0.ff3ce of Technology Assessment, 1991; J. Cooper, J. Mawsom and B. SWi.nbq past presidents, New Zealand Rmidtmt Medical

Oftlcers’ Associatkxl exeerptsfrorapresentations given at the National Federation of HousestaffOrgardzations, Bosto% MA, April

1988; J. Stoke, Acting Chief Medical Officer, Workforce Development, Department of Healm Wellington New Zealand, personal

communication June 12, 1991.
Chapter 8--Case Study: Registered Nurses and Resident Physicians . 173

apply to all training programs for residents. These

standards have the force of law, since resident

training programs cannot operate without ACGME

accreditation (76). Under ACGME rules, resident

training programs must be in “substantial compliance’ with standards in order for their accreditation

to continue.

The American Medical Association (AMA) House

of Delegates passed two resolutions in early 1988

regarding conditions in resident training programs,

which are monitored by a Residency Review Committee (RRC) in each of the 24 specialties:

one asking each RRC to develop guidelines for

residents’ work hours and conditions, taking

into account the intensity of the particular

service environment; and

one directing each RRC to develop guidelines

regarding standards for achieving clinical competence, with a specific focus on weekly or

continuous work hours, adequate time off, an

average of no more than every third night on

call, and one 24-hour period off every 7 days.

(106).

Of the 24 specialty boards, 16 have adopted specific

language addressing residents’ work hours. The

other eight are in areas where there is little night

work (e.g., nuclear medicine, physical medicine and

rehabilitation, radiation oncology, preventive medicine), thus the issues of extended hours and night call

are not as great.

Accreditation Council for Graduate Medical

Education

As described above, within the past few years, the

ACGME has moved to revise its requirements for

programs regarding supervision and hours and has

directed the RRCs to introduce new standards on

residents’ work hours. Responses of the RRCs

ranged from specific (emergency medicine mandating no more than 60 hours per week, with 12-hour

shifts) to general (thoracic surgery giving the

program director responsibility for ensuring reasonable in-house duty hours) to no response (general

surgery and psychiatry) (see table 8-3). According to

the Association of American Medical Colleges,

guidelines vary because of differences in the demands and patient care requirements among specialties (102). For example, the surgical RRCs are

unwilling to accept the one 24-hour period free of

patient care responsibilities because of a strong

belief that surgical residents should see their preand postoperative patients every day. On the other

hand, residents in pathology have little patient

contact and do not require extended hours (41).

The RRC for internal medicine, under the auspices of the ACGME, implemented new rules that

took effect in October 1989 (76). Internal medicine

residents must observe a maximum workweek of

80 hours averaged over 4 weeks. Residents are also

to spend, on average, 1 day a week away from the

hospital, and their continuous duty in the emergency

room should not exceed 12 hours (76). The rules call

for adequate opportunity to rest and sleep when on

call for 24 hours or more, and residents should be on

call no more than once every third night. In addition,

limits were placed on the number of patients

assigned to residents.

The American Board of Medical Specialties

recently vetoed a proposal to let residents have 1 day

off per week and to be on call no more than once

every third night (77). Continuity of care was cited

as the reason for such action. As a result of this veto,

the Council of Medical Specialty Societies (CMSS),

one of the other ACGME member organizations,

recently failed to take a position on proposed work

hours limits for residents. In a panel discussion

before the CMSS deadlock vote, an AMA executive

vice president argued that universal limits on hours

would show Government regulators that the house of

medicine was taking care of the problem of resident

hours and overwork (78). According to this same

AMA executive vice president, the ACGME hopes

to adopt language on hours revisions that applies to

all specialties, but this probably will not happen in

the near future (106).

As a means of informing medical students about

the work environment, including the hours requirement, at various residencies, the AMA has instituted

a computerized information system called Fellowship in Residency Electronic Interactive Database

Access System (FREIDA). Through FREIDA, medical students who are selecting a graduate program

can determine the program’s:

average number of hours per week on duty

during the first year;

average number of 24-hour periods per month

off duty;

maximum number of consecutive hours permitted on duty; and

whether moonlighting is allowed (93).
Table 8-3-Residents’ Working Hour Requirements in the Residency Review Committee’s Updated Accreditation Guidelines

Specialty Specific hourly requirements

Hours not

General guidelines addressed

Allergy and immunology Adequate backup should be provided if workload may

create resident fatigue sufficient to jeopardize patient care.

Emergency medicine

Family practice

Internal medicine

Anesthesiology 1 full day out of 7 away from hospital; on call no more

than every third night; off-duty time should be

sufficient to avoid fatigue.

Dermatology On average, 1 day/week should be free from hospital

duties; no more than once every third night should

be spent on call; rest and sleep should be provided

when on call for at least 24 hours.

On average, no more than 60 hours/week; at least 1

day/week away from hospital; no more than 12

hours/shift; at least an equivalent amount of time off

between duty periods.

Should be adequate resident staff to prevent excessive

workloads; suggest the following: on average, 1

day/week away from residency program; on call no

more than every third night; ensuring backup available if there is a sudden increase in workload.

In no case should resident go off duty until proper care

of patient is ensured. No more than 80 hours/week

averaged over 4 weeks; on average, 1 day/week out

of hospital; on call no more than once every third

night and have adequate backup; should be adequate opportunity and facilities to rest when on for

24 hours or more.

Neurological surgery

Neurology

Child neurology

Nuclear medicine

Obstetrics-gynecology

Ophthalmology

Orthopedic surgery

Continuity of care is most important; should have

adequate backup; scheduling should avoid prolonged and excessive duties on a regular basis.

Should be allowed 1 day/week away from hospital; on

call not more than every third night; should be

adequate physician coverage.

x

x

1 day/week away from hospital; on call no more than

every third night; adequate backup must be provided.

80 hours/week limit averaged over 4 weeks; 1 day/

week away from hospital; on call no more than every

third night.

On average, an 80-hour/week limit for direct patient

care.
Otolaryngology

Pathology

Pediatrics

Physical medicine and

rehabilitation

Plastic surgery

Preventive medicine

Psychiatry

Radiology (diagnostic,

pediatric, neuroradiology)

Residents should not be required to perform excessively difficult or prolonged duties regularly; they

should have the opportunity to spend an average of

1 day/week free of hospital duties; on call no more

than every third night, except to maintain continuity

of care; adequate opportunity and facilities for rest

when on call for 24 hours or more.

On average, 1 day/week free of hospital duties; on call

no more than every third night; backup should be

provided when patient care responsibilities are

heavy.

Resident should be on call on an average of every third

or fourth night in any year; schedule should have a

monthly average of 1 day/week without assigned

duties in the program.

No hour limits, but should have 1 day/week free from

hospital duties; should be on call no more than once

every third night; must recognize patient duties are

not discharged at any given time.

1 day/week off; on average, every other night off duty;

annual vacation time is additional time off; adequate

backup if excessive patient care could lead to

resident fatigue or jeopardize patient care; support

systems, including counseling to minimize stress

and fatigue, should be provided.

1 day/week off; on average, on call no more than once

every third night; must have adequate backup.

Radiology (nuclear, oncology) Residents should have 1 day/week off; on call no more

than once every third night.

General surgery

Thoracic surgery

Resident hours on duty should be scheduled to avoid

excessive stress and fatigue.

Residents must not be regularly required to perform

excessively prolonged duties; responsibility of program director to ensure reasonable in-hospital duty

hours.

x

Responsibility of program director to ensure reasonable

in-house duty hours so residents do not have to

perform excessively prolonged periods of duty

regularly.

Urology On average 1 day/week free of hospital duties; on call

no more than every third night; adequate opportunity to rest when on call for 24 hours or more;

adequate backup if work volume jeopardizes quality

of patient care.

SOURCE: Office of Technology Assessment, 1991.
176 ● Biological Rhythms: Implications for the Worker

It has been pointed out by one resident that some

specialties, such as pediatrics, dermatology, radiology, and obstetrics-gynecology, are attracting more

women. These women, as part of the old guard and

as new recruits, are insisting on changes to make the

current system more manageable (31). Some programs are beginning to implement a system known

as night float to assist residents with hours coverage

(74,104). Night float can take several forms, but

basically the house staff on call will admit patients

until 10 p.m., for example, and then leave the

hospital when their workups are completed. At 10

p.m. the night float team comes on duty (they have

been off duty all day) and covers admissions and

calls until the next morning, when duties will again

be turned over to the house staff. This arrangement

can also be used for a day float system. It has been

reported that not all programs have the funds to

implement this type of system (74).

Effects of Extended Duty Hours on Residents

Research on sleep deprivation began as early as

1896 (79). In 1961 a researcher concluded that

interns had little time for sleep and spent only a small

proportion of their time on direct patient care (81).

Ten years later, another study reported similar

findings regarding the daytime activities of interns

in California (42). A more recent study observed

internal medicine interns and residents for 5 nights

at three teaching hospitals. It determined that:

●

●

●

●

●

●

●

●

●

the interns and residents admitted between

three and eight patients each night;

each house officer received 16 to 25 calls per

night:

up to 12 percent of their time was spent doing

procedures such as inserting I.V. catheters or

drawing blood specimens, most of which could

have been done by nonphysicians;

from 87 to 175 minutes of on-call time were

spent in direct patient evaluation;

the mean time spent on each new patient

evaluation ranged from 17 to 31 minutes;

the mean time before the evaluation was

interrupted ranged from 7 to 11 minutes;

66 to 187 minutes per night were spent documenting new patient evaluations in the hospital

record;

the average sleep time ranged from 122 to 273

minutes; and

the mean time before sleep was interrupted

ranged from 40 to 86 minutes.

While no finding was made as to whether these

house officers were sleep-deprived because of their

work schedules, the researchers concluded that

house officers:

. spend relatively little time in direct patient

contact;

. spend considerable time charting; and

● are frequently interrupted while working and

trying to sleep (59).

The results of studies examining the effects of

extended hours on residents’ performance are equivocal. One study noted deficits in grammatical

reasoning in a group of five physicians after sleep

deprivation (84). These researchers found that in

another 15 subjects deprived of sleep, the ability to

compensate for fatigue led to improved performance

on a more complicated reading test; however,

additional time was needed to maintain accuracy and

complete the test. They concluded that physicians

can compensate for the effects of sleep loss in the

performance of both simple and complex psychomotor and cognitive functions (84). In another study,

33 surgical residents were given a comprehensive

psychometric test battery (87). Results showed no

differences in performance between sleep-deprived

and rested residents.

A recent study of the effects of sleep deprivation

on the performance of residents assigned to three

services (trauma, vascular, and cardiothoracic) of a

major teaching hospital failed to support the idea

that sleep deprivation impairs cognitive and motor

performance of residents (26). Results of this study

indicated that sleep deprivation did not affect

performance, as measured by a series of five

psychomotor tests of visual and auditory attention,

reasoning ability, spatial visualization ability, and

fine motor coordination. Moreover, analysis of the

correlation between certain sleep parameters (total

sleep and longest period of uninterrupted sleep) and

performance on each component of the psychometric test battery identified changes in performance on

some tests but only insignificant effects due to sleep

loss (26). The results of this study are controversial

and have been challenged on the basis of the

measures and experimental design used (13,14,18,

19,32,43,60,66,75,80,90,96,1 10).

Other studies have found decrements in some

measures of performance. For example, a study in

England found decreased mathematical abilities

among sleep-deprived residents (57). Other studies
Chapter 8-Case Study: Registered Nurses and Resident Physicians ● 177

Photo credit: George Washington University Medical Center

Being able to confer with other residents and attending physicians is a critical part of graduate medical education.

involving sleep-deprived interns have found increased errors in reading electrocardiograms (EKGs)

and increased time required to complete the task

(36,37,11 1). In one of these studies, a mood scale

was administered simultaneously, and results indicated that the rested interns felt more elation, social

affection, egotism, and vigor and less fatigue and

sadness than sleep-deprived interns (11 1). In another

study, rested and fatigued anesthesiology residents

showed a difference in response time to abnormalities appearing on a simulated monitor (28), while a

study of sleep-deprived and rested interns assessing

speed of information processing, decisionmaking,

recent memory, and mood showed that the sleepdeprived interns had less ability to retain information, longer response latencies, and greater mood

disturbances, including hostility, than the rested

interns (46).

Family and Personal Consequences

There are a great number of stresses associated

with graduate medical education, and working

long duty hours is one of them. Cultivating and

maintaining a healthy relationship with a spouse or

significant other can be difficult when a resident is

constantly tired. Recognizing that sleep deprivation

can be a stressor, one study detected no relationship

between gender and stress among internal medicine

residents (56), while a separate study found that

women residents reported more stress than men

residents but were more likely to mobilize external

support to cope with it (11).

Divorce and broken relationships often result

from the stresses of residency (23). One survey of

family practice residents determined that 41 percent

believed their performance was impaired because of
178 ● Biological Rhythms: Implications for the Worker

marital problems (70). Another survey found that 17

percent of residents felt that their current relationships were in jeopardy because of job stresses (53).

The outcome of pregnancy during residency for

1,293 residents and 1,494 wives of residents who

served as controls was the subject of a recent study

(52). It was determined that there were no significant

differences in the proportion of pregnancies ending

in miscarriage, ectopic gestations, and stillbirths.

The rate of voluntary termination of pregnancy

among women residents was three times higher than

among the wives. The women residents reported

working twice as many hours per week as the wives

(in some residents’ cases more than 100 hours per

week), with pregnant residents averaging 6 to 7

on-call nights per month. Premature labor requiring

bed rest or hospitalization was nearly twice as

common among the residents as among the wives, as

was preeclampsia or eclampsia. However, placental

abruption was less likely to occur in residents. The

study concluded that there were no significant

differences in pregnancy outcome between women

residents and wives of male residents.

It has been alleged that sleep deprivation is the

cause of numerous automobile accidents among

house staff (22,92). Anxiety and depression are

common among residents (23), and several studies

have documented incidents of significant depression

(53,86,109). Women house staff may be at greater

risk of depression than men (35), in part because

residents who are mothers may have primary responsibility for child rearing when they are not on duty

at the hospital. Drug dependency and alcohol

dependency are also prevalent in the medical profession (116). Many hospitals are implementing programs to help ‘‘impaired physicians’ cope with

stress.

While many stressors may combine to affect a

resident’s home life, it is unclear that extended

duty hours in themselves are responsible for

negative consequences. No studies have focused

solely on the impact of extended duty hours on

home life.

SUMMARY AND CONCLUSIONS

Both nursing and resident training are characterized by shift work. Information about shift work in

nursing is limited by the absence of national data on

nurses’ shift prevalence and career experience with

shift work; few studies of the short- or long-term

consequences of shift work for nurses’ family and

social life, health, and work performance; and few

studies of the impact of various schedules on the

quality of patient care. These limitations are due in

part to a general lack of research attention to shift

work. However, available data may also reflect

prevailing assumptions about the effectiveness of

pay differentials in solving shift-specific staffing

problems and about the ease with which resigning

nurses can be replaced, at least until recently, by a

steady stream of new graduates who will be willing

to work shifts early in their careers. Increased

demand for R.N.s could prompt more health care

administrators to examine shift work policies and to

experiment with alternatives as a means of improving recruitment and retention of nurses.

While more research is needed on the short- and

long-term effects of shift work on a range of nurses’

health outcomes and on work performance, some

adverse effects of shift work have been established.

The findings of the NIOSH study associate rotating

shift work with more digestive problems, more

tension and stress, and a higher rate of injury. While

the NIOSH study was an important examination of

a number of health consequences of shift work in a

large sample of R.N.s, it was cross-sectional, relied

primarily on self-reported symptoms, and contained

few measures of other job attributes that could be

confounded with type of shift worked (e.g., workload, degree of control over work-related decisions,

method of shift assignment).

Furthermore, working conditions of hospital nurses

have changed since the NIOSH study was conducted

in 1977. Hospital nurses today are coping with

decreased lengths of patient stay and increased

severity of illness as a result of prospective reimbursement of hospitals. These factors may exacerbate work stress and health problems in general,

independent of shift work, or they may interact with

shift work to produce extremely high stress levels

among those nurses working undesirable shifts and

confronting patients who require more intensive

nursing care. These factors may also offset any

positive effects of alternative shift schedules as a

recruitment or retention strategy. More research is

needed on various shift work issues, including the

impact of changes in the health care system on

workload, shift work, job stress, and related issues.

Graduate medical education as a training process

subjects young doctors-in-training to many stresses,
Chapter 8-Case Study: Registered Nurses and Resident Physicians ● 179

one of which is long hours. This has been the case for

many generations of doctors. Some have begun to

question the wisdom of this system, arguing that

with advances in medical technology doctors have

many more treatment decisions to make, and the

sleep deprivation and fatigue that result from long

hours can reduce the resident’s ability to make

timely and appropriate decisions. The Libby Zion

case demonstrated how long hours may contribute to

errors in patient care. This case focused attention on

the issue of extended duty hours for house staff.

New York has responded with limitations on scheduling of house staff hours. The ACGME has also

established guidelines for reduction of residents’

hours. The problem that has yet to be resolved is how

these new changes will be funded in a health care

economy that is financially strapped.

There have been a number of studies on extended

duty hours and sleep deprivation in medical residency, but results are inconclusive. Proponents of

revision argue that, despite study conclusions, it is

difficult to function at maximurn proficiency when

one is sleep-deprived and fatigued. Almost no

research has been done to determine the effect that

extended duty hours have on the personal lives of

residents.

1.

2.

3.

4.

5.

6.

7.

CHAPTER 8 REFERENCES

Adams, C., 1988 Report of the Hospital Nursing

Personnel Surveys (Chicago, IL: American Hospital

Association, 1989).

Alexander, J.A., “The Effects of Patient Care Unit

Organization on Nursing lhrnover, ” HeaZth Care

Management Review 13:61-72, 1988.

American Academy of Nursing, Task Force on

Nursing Practice in Hospitals, Magnet Hospitals:

Attraction and Retention of Professional Nurses

(Kansas City, MO: American Nurses Association,

1983). ‘

American College of Surgeons, “Fundamental

Characteristics of Surgical Residency Programs,”

American College of Surgeons Bulletin 73(8):22-

23,1988.

American Hospital Association, Report of the

Hospital Nursing Personnel Survey, 1987 (Chicago, IL: American Hospital Association, 1987).

Asch, D.A., and Parker, R.M., “The Libby Zion

Case: One Step Forward or Two Steps Backward?”

New England Journal of Medicine 318:771-775,

1988.

Asken, M.J., and Raham, D.C., ‘Resident Performance and Sleep Deprivation: A Review,’ Jourrud of

Medical Education 58:382-388, 1983.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

Asso, D., “Cyclical Variations,” Sex Differences in

HurnanPeformance, M.A. Baker (ed.) (Chichester:

John Wiley & Sons, 1987).

Bell, B., “The New Hospital Code and the Supervision of Residents,” New York State Journal of

Medicine 88:617-619, 1988.

Bell, B., Chairman, Bell Committee, New York

NY, personal communication, April 1991.

BlackWell, B., “Prevention of Impairment Among

Residents in Training,” Journal of the American

Medical Association 255:1177-1178, 1986.

Blegen, M. A., and Mueller, C.W., “Nurses’ Job

Satisfaction: A Ixmgitudinal Analysis,” Research

in Nursing and Health 10:227-237, 1987.

Blocker, D., letter, Journal of the American Medical

Association 261:862, 1988.

Bonnet, M.H., Veterans’ Administration Hospital,

Long Beach, CA, personal communication, December 1990.

Brown, T., Association of American Railroads,

Washington, DC, personal communication, March

1991.

Burke, K., “Rite of Passage for the Wrong Reasons,” Baltimore Sun, Sept. 25, 1990.

Burke, K., Chief Resident, Department of Internal

Medicine, Prince George’s Hospital Center, Cheverly, MD, personal communication, April 1991.

Burlingarne, M.W., letter, Journal of the American

Medical Association 261:860, 1988.

Chelmowski, M.K., letter, Journal of the American

Medical Association 261:860, 1988.

Choi, T, Jameson, H., Brekke, M., et al., “Effects

on Nurse Retention: An Experiment With Scheduling,” Medical Care 24:1029-1043, 1986.

Coffey, L. C., Skipper, J.K., Jr., and Jung, F.D.,

“Nurses and Shift Work: Effects on Job Performance and Job-Related Stress,’ Journal of Advanced

Nursing 13:245-254, 1988.

Cohen, B.D., “Must Residents Work Exhausting

36-hour Shifts?” Baltimore Sun, Sept. 4, 1990.

Colford, J.M., and McPhee, S.J., “The Raveled

Sleeve of Care: Managing the Stresses of Residency

Training,’ Journul of the America nMedicalAssociation 261:889-893, 1989.

Colligan, M.J., “Methodological and Practical Issues Related to Shift Work Research,” Journal of

Occupational Medicine 22:163-166, 1980.

Comperatore, C.A., U.S. Army Aeromedical Research Laboratory, Fort Rucker, AL, personal communication, February 1991.

Deaconson, TF., O’Hair, D.P., I_Jwy, M.F., et al.,

“Sleep Deprivation and Resident Performance,”

Journal of the American Medical Association 260:

1721-1727, 1988.

Dear, M.R., Weisman, C. S., and O’Keefe, S.,

‘‘Evaluation of a ‘Contract’ Model for Professional
180 ● Biological Rhythms: Implications for the Worker

28.

29.

30.

31.

32.

53.

34.

35.

36.

37.

38.

39.

40.

41.

42.

43.

Nursing Practice,” Health Care Management Review 10:65-77, 1985.

Denisco, R. A., Drummond, J.N., and Gravenstein,

J. S., “The Effect of Fatigue on the Performance of

a Simulated Anesthetic Monitoring Task,’ Journal

of Clinical Monitoring 3:22-24, 1987.

Eaton, P., and Gottselig, S., “Effects of Imnger

Hours, Shorter Week for Intensive Care Nurses,”

Dimensions in Health Service 57(8):25-27, 1980.

Editors, “Nursing Shortage Poll Report,” Nursing

88 18:3341, 1988.

Eghrari, J., Resident Physician, Childrens’ National

Medical Center, Washington, DC, personal communication, May 1991.

Feldman, J. M., letter, Journal of the American

Medical Association 261:862, 1988.

Finn, P., “The Effects of Shift Work on the Lives of

Employees,” Monthly Labor Review 104:31-35,

1981.

Folkard, S., Mo* T.H., and Lmbban, M. C., “Shortand Imng-Terrn Adjustment of Circadian Rhythms

in ‘Permanent’ Night Nurses,’ Ergonomics 21 :785-

799, 1978.

Ford, C. V., and Wentz, D. K., “The Internship Year:

A Study of Sleep, Mood States, and Psychophysiologic Parameters, 99 SouthernMedicalJourna177: 1435-

1442, 1984.

Friedman, R. C., Bigger, TJ., and Kornfeld, D. S.,

“The Intern and Sleep Imss,” New England Journal of Medicine 285:201-203, 1971.

Friedman, R. C., Kornfeld, D. S., and Bigger, TJ.,

“Psychological Problems Associated With Sleep

Deprivation in Interns,’ Journal of Medical Educa -

tion 48:436-441, 1973.

Friedman, T.H., attorney, private practice, New

York, NY, April 1991.

Gadbois, C., “Women on Night Shift: Interdependence of Sleep and Off-the-Job Activities,” Night

and Shljl Work: Biological and Social Aspects.

Proceedings of the 5th International Symposium on

Night and Shljl Work, Permanent Commission and

International Association on Occupational Health

(Oxford: Pergamon Press, 1981).

Ganong, W.L., Ganong, J.M., and Harrison, E.T,

“The 12-Hour Shift: Better Quality, Imwer Cost,”

Journal of Nursing Administration 6~2):17-29,

1976.

Gienapp, J. C., Executive Secretary, Accreditation

Council for Graduate Medical Education, Chicago,

IL, personal communication, January 1991.

Gillanders, W., and Heiman, M., “Time Study

Comparisons of 3 Intern Programs,” Jourrud of

Medical Education 46:142-149, 1971.

Goodman, S., letter, Journal of the American

Medical Association 261:861-862, 1988.

44.

45.

46.

47.

48.

49.

50.

51.

52.

53.

54.

55.

56.

57.

58.

59.

60.

Greater New York Hospital Association, Recommendations of the New York State Department of

Health’s Ad Hoc Advisory Committee on Emergency Services: A Preliminary Analysis Prepared

by the Greater New York Hospital Association

(New York NY: August 1987).

Harma, M., Ilmarinen, J., and Knauth, P., “Physical

Fitness and Other Individual Factors Relating to the

Shift Work Tolerance of Women,” Chronobiology

International 5:417-424, 1988.

Hart, R.P., Buchsbaum, D.G., Wade, J. B., et al.,

“Effect of Sleep Deprivation on First-Year Residents’ Response Times, Memory and Mood,”

Journal of Medical Education 62:940-942, 1987.

Health Care Advisory Board, Nurse Recruitment

and Retention (Washington, DC: November 1987).

Institute of Medicine, Nursing and Nursing Education: Public Policies and Private Actions (Washington, DC: National Academy Press, 1983).

Jamal, M., and Jamal, S.M., “Work and Nonwork

Experiences of Employees on Fixed and Rotating

Shifts: An Empirical Assessment,” Journal of

Vocational Behavior 20:282-293, 1982.

Kent, L.A., “The 440 Workweek on Trial,”

American Journal of Nursing 72:683-686, 1972.

Keye, W.R., “Environmental Exposure and Altered

Menstrual Function,” Reproduction: The New Frontier in Occupational and Environmental Health

Research (New York, NY: Alan R. Liss, 1984).

Klebanoff, M.A., Shiono, P.H., and Rhoads, G. C.,

“Outcomes of Pregnancy in a National Sample of

Resident Physicians,” New England Journal of

Medicine 323:1040-1045, 1990.

Koran, L., and Litt, I., ‘‘House Staff Well-Being,”

Western Journal of Medicine 148:97-101, 1988.

Krueger, G.P., and Lieberman, H.R., U.S. Army

Research Institute of Environmental Medicine,

Natic~ MA, personal communication, February

1991.

Kuchinski, B. B., “The Effects of Shift Work on the

Menstrual Characteristics of Nurses,” doctoral

dissertation, Johns Hopkins University, 1989.

Landau, C., Hall, S., Wartman S.A., et al., “Stresses

and Supports During Residency Training,” Division of Educational Measurement and Research:

Research in Medical Education (Chicago, IL:

American Medical Association, 1984).

Leighton, K., and Livingston, M., “Fatigue in

Doctors,” Lizncet 1:1280, 1983.

Litwin, M. S., letter, New York Times, Jan. 10,1990.

Lurie, N., Rank, B., and Parenti, C., “How Do

House Officers Spend Their Nights?’ New England

Journal of Medicine 320:1673-1677, 1989.

McCall, T. B., letter, Journal of the American

Medical Association 261:859, 1989.
Chapter 8-Case Study: Registered Nurses and Resident Physicians ● 181

61.

62.

63.

64.

65.

66.

67,

68.

69.

70.

’71.

72.

73.

74.

75.

76.

McLaughlin, B., and Mohr, P., “Approaches to

Shift Work in Non-Nursing Occupations and Nursing,” Final Report, vol. 2: Support Studies and

Background Information, U.S. Department of

Health and Human Services, Secretary’s Commission on Nursing (Washington, DC: U.S. Government Printing Office, December 1988).

Martin, A.A., attorney and Senior Resident (PGY3), Department of Pathology, 7Mane University

Medical Center, New Orleans, LA, personal communication, March 1991.

Mills, M.E., Arnold, B., and Wood, C.M., “Core12: A Controlled Study of the Impact of 12-Hour

Scheduling,” Nursing Research 32:356-361, 1983.

Minors, D. S., and Waterhouse, J.M., “Circadian

Rhythm Amplitude-Is It Related to Rhythm Adjustment and/or Worker Motivation?” Ergonomics

26:229-241, 1983.

Minors, D. S., and Waterhouse, J.M., “Circadian

Rhythms in Deep Body Temperature, Urinary

Excretion and Alertness in Nurses on Night Work,”

Ergonomics 28:1523-1530, 1985.

Monk, T.H., and Buysse, D. J., letter, Journal of the

American Medical Association 261:860-861, 1988.

Moses, E., Selected Findings From the 1988 Sample

Survey of Registered Nurses, U.S. Department of

Health and Human Services, Health Resources and

Services Administration, 1989, and unpublished

data from the survey.

National Commission on Nursing, Summary Report

and Recommendiztions (Chicago, IL: Hospital Research and Educational Trust, 1983).

Nelson, B.J., and Blasdell, A.L., “Comparing

Quality on Eight-and Twelve-Hour Shifts,” Nursing Management 19(11 ):64A-64H, 1988.

Nelson, F., and Henry, W., “Psychosocial Factors

Seen as Problems by Family Practice Residents and

their Spouses,’ Journal of Family Practice 6:581-

589,1978.

New York Law Journal, “Report Finds Better

Practice May Have Saved Woman’s Life,” New

York Law Journal, Jan. 27, 1987, p. 1.

New York State Department of Health, FinuZReport

of the New York State Ad Hoc Advisory Committee

on Emergency Services (Albany, NY: 1987).

New York State Conference of Blue Cross and Blue

Shield Plans v. Axelrod, 145 Misc. 2d 336 (1989).

Nolan, J., “New Regulations and Their Cost

Implications,’ paper presented at the Regulation of

Physician Training Programs Conference, Coral

Gables, FL, March 1989.

Nowack, D.H., and Reuben, D.B., letter, JournaZ of

the American Medical Association 261:861, 1988.

Page, L., “ACGME Review Panel Sets Up Hour

Limits for Internist Residents,’ American Medical

News, Nov. 18, 1988, p. 2.

77.

78.

79.

80.

81.

82.

83.

84.

85.

86.

87.

88.

89.

90.

91.

92.

93.

Page, L., “ABMS Nixes University Residents’

Work Reforms,” American Medical News, Sept.

28, 1990, p.1.

Page, L., “Surgeons’ Votes Deadlock CMSS,”

American Medical News, Apr. 1, 1991, p. 4.

Patrick, G., and Gilbert, J., “Studies From the

Psychological Laboratory of the University of

Iowa,” Psychology Review 3:475-483, 1896.

Pawel, B.R., letter, Journal of the American Medical Association 261:860, 1988.

Payson, H.E., Gaenslen, E. C., Jr., and Stargardter,

F.L., “Time Study of an Internship on a University

Medical Service,’ New England Journal of Medicine 264:439-443, 1961.

Petersdorf, R.G., Memorandum No. 88-12, Association of American Medical Colleges, Washington,

DC, Mar. 8, 1988.

Petersdorf, R.G., and Bentley, J., “Residents’

Hours and Supervision,’ AcademicMedicine 64(4):

175-181, 1989.

Poulton, E. C., Hunt, G. M., Carpenter, A., et al.,

“The Performance of Junior Hospital Doctors

Following Reduced Sleep and bng Hours of

Worlq” Ergonomics 21:279-295, 1978.

Report of the Fourth Grand Jury for the April/May

Term of 1986 Concerning the Care and Treatment

of a Patient and the Supervision of Interns and

Junior Residents at a Hospital in New York County,

New York Supreme Court, New York County, Dec.

31,1986.

Reuben, D., “Depressive Symptoms in Medical

House Officers: Effects of I.xwel of Training and

Work Rotation,” Archives of Internal Medicine

145:286-288, 1985.

Reznick, R.K., and Folse, J.R., “Effect of Sleep

Deprivation on the Performance of Surgical Residents,” American Journal of Surgery 154:520-525,

1987.

Rhinehart, L., writer-researcher, Health and Safety

Department, Service Employees International Union,

letter to W. Pachter, Office of Technology Assessment, July 20, 1990.

Rhinehart, L., writer-researcher, Health and Safety

Department, Service Employees International Union,

personal communication, January 1991.

Ritchie, K., letter, Journal of the American Medical

Association 261:859-860, 1988.

Roberts, M., Minniclq A., Ginzberg, E., et al., What

To Do About the Nursing Shortage (New York M:

Commonwealth Fund, 1989).

Rovner, S., “The Battle Over Limiting Residents’

Hours,” Washington Post, Oct. 16,1990, Health, p.

42.

Rowley, B.D., Director, Department of Data Systems, American Medical Association, Chicago, IL,

personal communication, Nov. 19, 1990.
182 ● Biological Rhythms: Implications for the Worker

94.

95.

96.

97.

98.

99.

100.

101.

102.

103.

104.

105.

Rowley, B.D., Baldwin, D. C., McGuire, M. B., et

al., “Graduate Medical Education in the United

States,’ Journal of the American Medical Association 264:822-832, 1990.

Scherr, L., “Residency Under Scrutiny-A Case

Report,’ American College of Physicians Observer

7(7):3, 1987.

Schwartz, C. E., letter, Journal of the American

Medical Association 261:859, 1989.

Smith, M.J., Colligan, M.J., Frockt, I.J., et al.,

“Occupational Injury Rates Among Nurses as a

Function of Shift Schedule,” Journal of Safety

Research 11:181-187, 1979.

Smith, R., Assistant Director, Professional, &onomic and General Welfare, Massachusetts Nurses

Association, letter to W. Pachter, Office of Technology Assessment, June 8, 1990.

Sommers, E., Senior Vice President, Greater New

York Hospital Association, testimony before the

Committee on Health, City Council of New Yorlq

NY, January 1991.

Stone, M., “New York Hospital on the Spot: Three

Baffling Deaths Jolt a Proud Institution,’ New York

Times, June 22, 1987, pp. 4047.

Sundt, F., Registered Nurse, Georgetown University Hospital, Washington, DC, personal communication, Apr. 30, 1991.

Swanson, A.G., Vice President for Graduate Medical Education and Vice President for International

Programs, Association of American Medical Colleges, Washington, DC, personal communication,

Apr. 25, 1991.

Taste, D.L., Colligan, M. J., Skjei, E.W., et al.,

Health Consequences of Shifi Work (Cincinnati,

OH: U.S Department of Health and Human Services, National Institute for Occupational Safety and

Health, March 1978).

Teich, D. L., Assistant Professor of Medicine,

George Washington University, Washington, DC,

personal communication, April 1991.

Tepas, D., Professor and Director, Division of

Industrial and Organizational Psychology, Department of Psychology, University of Connecticut,

personal communication, Apr. 2, 1990.

106.

107.

108.

109.

110.

111.

1120

113.

114.

115.

116.

117.

Told, J. S., Executive Vice President, American

Medical Association, Chicago, IL, personal communication, May 1991.

U.S. Department of Health and Human Services,

Public Health Service, National Center for Health

Statistics, “Characteristics of Registered Nurses in

Nursing Homes: Preliminary Data From the 1985

National Nursing Home Survey,” Advance Data

From Vital and Health Statistics, No. 152, DHHS

Pub. No. (PHS)88-1250, G. Strahan (cd.) (Hyattsville, MD: Public Health Service, Apr. 14, 1988).

U.S. Department of Health and Human Services,

Secretary’s Commission on Nursing, Find Report,

VOIS. 1 and 2 (Washington, DC: December 1988).

Valko, R., and Clayton, P., “Depression in the

Internship,” Diseases of the Nervous System 36:26-

29, 1975.

Walbroehl, G. S., letter, Journal of the American

Medical Association 261:861, 1988.

Walerstein, S.J., Rosner, F., and Wallace, E.Z.,

“House Staff Stress,” New York State Journal of

Medicine 89:454-457, 1989.

Wallis, C., “Re-Examining the 36-Hour Day: New

York State hads a Movement to Change the Way

U.S. Doctors Are Trained,” Time, Aug. 31, 1987,

p. 54.

Wandelt, M. A., Pierce, P.M., and Widdowson,

R. R., “Why Nurses ~ave Nursing and What Can

Be Done About It,” American Journal of Nursing

81:72-77, 1981.

Weisman, C. S., “Recruit From Within: Hospital

Nurse Retention in the 1980s,” Journal of Nursing

Administration 12:24-31, 1982.

Weisman, C. S., Alexander, C. S., and Chase, G.A.,

‘‘Determinants of Hospital Staff Nurse hover,”

Medical Care 19:431443, 1981.

Western Medical Journal, “Medical Staff Conference: Stress and Medical Training,” Western Medical Journal 142:814-819, 1985.

Windle, P., Senior Associate, U.S. Congress, Office

of Technology Assessment, Washington, DC, personal communication, May 1991.
Chapter 9

Case Study: The Military
Contents

Page

THE NATURE OF MILITARY OPERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

Military Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

OPERATIONS REQUIRING 24-HOUR MANNING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

Army Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...,*. 188

Air Force Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

Navy Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ...+,..... 190

Marine Corps Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

CHAPTER 9 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ● .*.**.* .*** 193

Tables

Table Page

9-1. Crew Endurance Guide for Flight Operations, U.S. Army . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

9-2. Maximum Flight Duty Periods, U.S. Air Force .,...., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190

9-3. Maximum Accumulated Individual Flight Times, U.S. Navy . . . . . . . . . . . . . . . . . . . . . . . . . 192
Chapter 9

Case Study: The Military

As Operation Desert Storm illustrated, technological advances have dramatically increased the ability

of the military to carry out operations at night. In

addition, many military situations demand that

personnel engage in operations that require 24-hour

manning and around-the-clock work. These operations can lead to circadian rhythm disruption, sleep

loss, and other stressors (13). Many military settings

that require continuous manning (e.g., command and

control, medical, security, communications, ship

navigation and propulsion, most transportation system operations) have civilian equivalents; others do

not. For the most part, military work that has no

direct civilian counterpart is performed on a continuous basis. This case study focuses on operations and

work settings that are unique to the military and

examines the typical duty schedules employed by

the U.S. armed forces for carrying out those operations.

THE NATURE OF MILITARY

OPERATIONS

An important characteristic of military activity is

the context in which operations and tasks are being

carried out. That context determines the tempo at

which tasks are to be performed and the nature of the

stressors associated with job performance. A task

being performed during routine operations or in

training can be very different when performed under

actual or simulated combat conditions. Routine

operations are those that are characteristic of peacetime and usually involve regular duty and rest

schedules for continuous reaming of tasks. In

continuous operations, work is unceasing, but the

demands on the individual are not; in sustained

operations, the individual has to maintain performance for long periods (usually more than 12 hours).

Sustained operations are characteristic of combat or

high-alert conditions and are often characterized by

sharply increased tempo (surge conditions). As a

result, in sustained operations individuals have

inadequate opportunity for rest, making sleep loss

and fatigue limiting factors in an operation. In

sustained operations, sleep loss often results from

the need for an individual to perform some vital

function almost continuously for an extended period

of time. The amount and tempo of work (especially

mental work requiring attention and concentration)

and the availability of nonsleep rest periods will

determine the rate at which performance degrades,

with faster work tempos causing faster degradation

of performance (l). Although this report is concerned with the factors limiting personnel endurance, other factors, such as having enough materiel

(munitions, fuel, other supplies), equipment (servicing and repair requirements), or information (command and control decisionmaking, communication

limitations, or intelligence and situation assessments) can also limit the duration of fast-paced

combat or training activities.

The nature of work and rest schedules can also be

altered when military units are transported to different areas. The extra tasks involved in relocation

operations disrupt individual schedules, and transmeridian relocations add jet lag to other disruptions.

Rapid aerial deployment of military units overseas

results in jet lag, and the first day or two at sea often

involves extra tasks. Relocation of forces can also

occur under surge conditions (the beginning of

combat operations, combat reinforcement operations, and major training exercises), in which case

disruptions and stressors associated with both normal relocation and surge conditions are present.

Various disruptions of biological rhythms and

stressors that lead to performance decrements are

associated with these situations. Short-term desynchronization of circadian rhythms can result from

changes in operations (e.g., relocation overseas) or

changes in operating tempo (e.g., at the onset of

hostilities or at the start of a major operation). As in

shift work in the civil sector, chronic disruption of

circadian rhythms may result from constantly shifting schedules and schedules that require daylight

rest and night duty, such as the 18-hour duty cycle

often found in submarines, the 12-hour duty cycle

often used on ships, or the deployment of nightfighter teams on the battlefield. Both acute and

chronic sleepiness may occur in these situations,

especially under sustained operating conditions, and

these, in concert with circadian disruption or on their

own, can lead to degradations in performance.

Training and operational readiness exercises are a

constant fixture in the military. These exercises are

–185–
as realistic as possible, replicating as closely as

possible the conditions and schedules that would be

encountered during combat. Although training exercises cannot duplicate the stress and fear encountered in actual combat, they do mimic the nature and

tempo of such operations. As a result, military

personnel are routinely and repeatedly exposed to

the various conditions described.

Activities that occur in conjunction with combat

or combat training are usually marked by an

increased tempo and sustained hours of duty. Another factor which can impinge on military duty

hours are manpower limitations. For example, in the

Navy there are manpower documents that outline the

level of manning of a ship necessary for a given

operation. A loss of manpower due to casualties or

sickness will result in a mismatch between manpower resources and mission requirements. This

situation would require that the available crew work

extended duty hours to successfully complete the

mission (21).

There are few specific regulations or guidelines in

the military related to hours of service and scheduling. Regulations limit flight hours and length of duty

for aviators in all the services; however, decisions

regarding hours of duty and work schedules for all

other military personnel are generally left up to

commanding officers, who base their decisions on

their knowledge of mission requirements and on the

condition and limitations of their personnel. Under

routine post, camp, and station operating conditions,

in which service members can go home to their

families at the end of each workday, military work

schedules tend to resemble civilian work schedules.

For personnel deployed in the field or at sea, work

schedules tend to be about 70 hours per week. In

training and operational readiness exercises, work

often continues until individuals are unable to go on.

The existing guidelines for rest requirements in

peacetime are not binding in combat (29,38,40) and

are frequently relinquished in order to accomplish

the mission (3,16).
Chapter 9--Case Study:The Military ● 187

Military Tasks

A variety of tasks have to be carried out at any

time, day or night, and are therefore susceptible to

the effects of disrupted biological rhythms and sleep

loss. Since sustained operations are integral to

modern military operations, some of the most salient

problems for an individual are sleepiness (inclination for sleep) and fatigue (weariness due to physical

or mental exertion). Both sleepiness and fatigue

affect performance. As with studies of task performance in a civilian setting, studies of the effects of

around-the-clock operations in military settings

have revealed that the nature of the task determines

its sensitivity to circadian disruption, sleep loss, and

fatigue. For example, studies of sustained operations

over several days with little or no opportunity to

sleep show that vigilance, memory, and cognitive

task performance of infantry soldiers, tank crews,

and artillery fire direction teams are degraded (13).

Although most people need 6 to 8 hours of sleep

daily to maintain normal levels of alertness and

performance, 4 hours of sleep can offer some

protection from the deleterious effects of sustained

operations (13).

Tasks that require physical activity and effort

(e.g., infantry marches, preparing fortifications,

handling supplies) are not significantly affected by

the time of day, moderate sleep loss, or other

circadian disruptions (2,8,26,41) However, the perceived effort required to do a physical task is

sensitive to the time of day the task is performed,

with greatest fatigue perceived between 2 a.m. and

6 a.m. (11). If personnel are quite fatigued, as they

often are during sustained operations, their ability to

perform physical tasks can be reduced (2,10,13).

Physical conditioning is important in all the services, because fit personnel have more endurance in

the performance of physical tasks, even though

physical fitness does not protect against the effects

of sleep loss.

Military operations also involve many tasks that

require constant vigilance, often under conditions

not conducive to alertness. These include air defense

radar and electronic surveillance, sonar, sentries,

pickets, and so on. The performance of many tasks

requiring vigilance (sonar operation, for example)

degrades-measurably after less than an hour of duty

(13,24). Performance is also degraded by sleep loss

and being required to work at inappropriate times

during the circadian cycle, regardless of amount of

rest (13,18-20,22). When vigilance is required in

sustained operations, naps can be effective, especially if taken during the predawn period, from

2 a.m. to 6 a.m. (13); however, relief from the task

(i.e., simple rest) and sleep are the most effective

means of combating decrements in vigilance.

The operation and control of vehicles is also a

common characteristic of military operations. Studies of the effects of fatigue on the performance of

aircraft pilots indicate that physical coordination

seems little degraded, even in conditions of extreme

sleepiness (15); however, judgment degrades fairly

quickly with the onset of fatigue (7,12,42). This

effect is compounded when tasks are performed near

the nadir of the circadian alertness cycle. There are

regulations to guide aircraft operations (described

later) but no crew rest guidelines for land or water

vehicle operators. The use of pharmacological

agents to enhance performance in aircraft operations, especially after long flights or during sustained operations, is being investigated (5).

The performance of other types of tasks associated with military operations, such as the maintenance, preparation, and operation of equipment (e.g.,

weapons systems, communication systems, construction equipment), may also be affected by

circadian, fatigue, and sleepiness factors associated

with time and duration of duty. As with the other

tasks described, this is especially true in the case of

sustained operations (13,23).

Finally, the task of commanding, which involves

judgment and planning, is vulnerable to performance degradation caused by sleep loss and biological

rhythm disruption. In fact, judgment is usually the

first faculty to be degraded, and it is a very difficult

one for the individual to monitor (2,9,12). There are

no regulations or guidance regarding the duty hours

associated with command. Leaders and command

and control personnel generally stay awake and are

involved during continuous and sustained combat

operations to see to their responsibilities. However,

since effective leadership depends on unimpaired

judgment, and fatigue, sleep loss, and other biological rhythm disruptions impair judgment, avoiding or

minimizing such effects is critical to successful

combat leadership and command and control. The

implementation of sleep discipline plans, a relatively new military innovation, is critical for combat

leaders (14).

297-935 - 91 - 7 QL 3
188 ● Biological Rhythms: Implications for the Worker

OPERATIONS REQUIRING

24-HOUR MANNING

Military operations that could be affected when

personnel are exposed to biological rhythm disruption or sleep loss include combat operations (immediate involvement in fighting) and combat support

(supply, communications, or medical aid), as well as

combat training exercises. This includes all aspects

of land combat (in-place, reinforcement, and expeditionary), support logistics operations, air operations

(tactical and logistic), high-readiness operations of

strategic forces, and the operation of naval vessels at

sea. The most salient disruption in such cases is

fatigue and sleep loss, exacerbated by various kinds

of stress. Circadian disruption can also occur in

combat operations: events such as strikes and

assaults are often planned for the time at which the

enemy is expected to be least effective. Momentum

is very important in offensive operations (especially

in land combat), and sustaining it for days or weeks

entails many human endurance problems. Also,

some element of surprise is always desirable in

combat actions. The conduct of extended combat

operations (over days and weeks) tends to be more

effective if there is no discernible routine to the

action. The need to carry out operations in which

routines and predictability are minimized will have

a negative effect on personnel duty-rest schedules.

Army Operations

With the exception of Army Aviation, there are no

specific guidelines for work schedules and duty

hours for most Army activities and operations. In

their planning of operations, it is the responsibility

of individual commanders to ensure that the personnel under their command are rested and fit for duty.

Deployment

Most military units are based in the United States;

military units outside the United States are usually

deployed for some limited period and then replaced.

This deployment is usually scheduled well in

advance. Individual jet lag can best be mitigated by

allowing for recovery periods at the destination.

Surge deployment is usually in response to some

new military requirement (e.g., the need to show

force to support foreign policy in a time and place of

tension) and is done on short notice. It usually

involves transmeridian movement by aircraft, so jet

lag effects would be present. The requirement to

pack up, load, unload, and set up at a destination

causes additional transient disruptions. Since these

temporary tasks are not part of what is usually

thought of as combat or mission tasks, they are not

included in the planning of operations (35,38).

Reinforcement

Reinforcement is adding more personnel and

equipment to units already deployed. Usually, reinforcement would be more urgent than relocation and

would require new personnel to begin operations

immediately on arrival at the same operating tempo

as existing forces. Reinforcement is most likely to

occur under surge conditions. The same disruptions

in biological rhythms that would be encountered

during initial troop deployment could also occur

during reinforcement operations.

Special Operations

Special operations are difficult to characterize,

given their inherent irregularity and classified nature. Special forces can be subjected to unpredicta-
Chapter 9--Case Study:The Military ● 189

Table 9-l-Crew Endurance Guide for Flight Operations, U.S. Army

Maximum duty Maximum flight

Time period (hours) period (hours) time (hours) Environmental factor

24 16 8 Day

48 27 15 Day contour/low level

72 37 22 Instrument

168 (7 days) 72 37 Night

720 (30 days) (peacetime) 288 90 Day NOE

720 (30 days) (mobilization) 360 140 Night terrain

Night vision devices

Chemical MOPP

1.0

1.3

1.4

1.4

1.6

2.1

2.3

3.1

EXAMPLE : The stress and fatigue experienced in 1 hour of day nap-of-the-Earth (NOE) flight (e.g., extreme low-level, Contour flight) is

equal to 1.6 hours of standard day flight. If a crew member flies day NOE in chemical mission-oriented protective posture

(MOPP), the larger factor (3.1) will be used. The flight time shown in column 3 will be adjusted by the factors in column 4.

SOURCE: U.S. Department of the Army Regulation AR 95-3, Aviation, General Provisions, Training, Standardization, and/7esource Management.

ble and unanticipated requirements and must respond on short notice to anything from military

search and rescue missions to counterterrorism.

Frequently these situations require rapid deployment and the crossing of time zones. Planned or

programmed duty-rest schedules usually are difficult to implement in such situations (17). Special

operations forces tend to train at a continuous

operations tempo, interspersed with periods of

sustained operations, combined with relocations on

short notice (often involving transmeridian travel).

Combat

For planning purposes, Army regulations specify

that combat personnel (those doing the fighting)

should have 6 hours each day for rest (35). In actual

combat situations, as in the reinforcement and

special operations outlined above, the nature and

scheduling of rest periods would be dictated by the

conditions of the moment.

Army Flight Operations

Army regulation 95-3 (36) governs scheduling

limits for flight operations of both fixed-wing and

rotary aircraft. These regulations provide guidance

for duty period and flight time limits for air crews

(table 9-l). The limits are adjusted for the conditions

under which the operations occur. For example,

flying 1 hour at night is considered the same as

flying 1.3 hours during the day. In addition, the

regulations recommend that commanders consult

the unit’s flight surgeon and aviation safety officer

when setting limits for specific operations or time

periods.

Air Force Operations

Tactical and Transport Forces

Air Force tactical and transport flight operations

are guided by a number of regulations that provide

requirements for scheduling (27-29,32,33). Tactical

forces engage in air combat, support land warfare

(close air support, interdiction of enemy supply

lines, surveillance), and consist largely of fighters,

bombers, and helicopters. Transport forces carry

personnel and materiel from the United States

overseas and from overseas supply depots to more

remote distribution points. These aircraft consist

primarily of tanker and transport craft. Exercises are

conducted routinely to provide experience with

various combat and readiness scenarios.

Rest and flight duty limitations for all personnel

who operate Air Force aircraft are delineated in

several Air Force regulations (29-31,33). These

regulations specify:

● maximum allowable flight duty periods for

basic and augmented crews,

. maximum monthly and quarterly flying hours

for aircrews,

● minimum crew rest periods, and

. conditions necessary to waive the requirements.

The maximum allowable flight duty period is the

maximum number of hours crew can fly in a certain

type of aircraft in a 24-hour period (table 9-2). Total

flying time for tactical forces is limited to 75 hours

per 30 consecutive days and 200 hours per 90

consecutive days (31). A minimum rest period of 12

hours is mandated between flights and must include

8 hours of uninterrupted, continuous rest. If a crew
190 . Biological Rhythms: Implications for the Worker

Table 9-2—Maximum Flight Duty Periods,

U.S. Air Force

Basic Augmented

Aircraft aircrew aircrew

Fighter, attack or reconnaissance

Single control . . . . . . . . . . . . . .

Dual control . . . . . . . . . . . . . . .

Bomber or reconnaissance

Single control . . . . . . . . . . . . . .

Dual control . . . . . . . . . . . . . . .

Transport . . . . . . . . . . . . . . . . . . .

Sleeping provisions . . . . . . . . .

Tanker . . . . . . . . . . . . . . . . . . . . . .

Sleeping provisions . . . . . . . . .

Trainer . . . . . . . . . . . . . . . . . . . . .

Rotary wing (no automatic

flight control system). . . . . . . .

Rotary wing (automatic flight

control system) . . . . . . . . . . . .

Utility . . . . . . . . . . . . . . . . . . . . . .

12

12

12

24

16

16

20

20

12

12

14

12

16

30

24

30

16

14

18

18

SOURCE: U.S. Department of the Air Force Regulation AFR 60-1, EUght

Management.

member is interrupted and cannot get 8 hours of rest,

he or she must be afforded 8 more hours of

uninterrupted rest plus reasonable time for other

activities (e.g., dressing, eating, traveling) (31).

These regulations also specify that the relationship

between crew rest and limitations on flight duty

hours be considered when planning and scheduling

missions. For transport crews, total flying time is

limited to 125 hours per 30 consecutive days and 330

hours per 90 days (33). Based on the timetable

established for a deployment operation, a unit’s

commander and flight surgeon may develop a

schedule prior to departure that will adjust crew

members’ body clocks (6). Finally, the regulations

authorize commanders to waive maximum flight

duty periods for high-priority missions and during

impending or actual hostilities.

Nonflight Air Force support units (airfield operations, communications facilities, logistic support,

aircraft repair) are generally operated on a continuous basis. The factors affecting their operating

tempo and conditions are similar to Army combat

support activities.

Maximum limits on duty hours for all Air Force

personnel (i.e., flight and nonflight) in a wartime

setting have been set at 247 hours per month (10

hours per day, 6 days a week) during continuous

operations and 309 hours per month (12 hours per

day, 6 days a week) for a maximum of 30 days during

sustained operations (6).

Strategic Forces

Strategic forces are the nuclear deterrent intercontinental bomber and missile forces. These forces

operate on a routine carefully designed and controlled to sustain operations without decrements in

performance. The primary concern is to ensure that

personnel with access to nuclear weapons are

reliable and can carry out their duties without

impairments to their judgment or performance.1

Flight operations are guided by the general Air

Force flight regulations previously described and

others specific to strategic forces operations (30).

These regulations include the requirement that,

when possible, missions with late-night departures

(which cause the crew to fly through normal sleeping

hours and to rest during normal working hours) be

scheduled for less than maximum duty periods.

Also, the regulations stipulate that crew members

who cross more than three time zones on route to a

permanent location should normally not be required

to perform any additional flight duty for the first 48

hours after arrival at their destination (30).

The crews manning intercontinental ballistic missile silos are on alert duty for 24-hour periods.

Regulations stipulate that the minimum rest-sleep

period for each crew member is 6 hours (34). In

general, these crews are on duty every third day.

When relieved of duty, a crew member will have a

minimum rest period of 12 hours.

Navy Operations

Nonshipboard operations are similar to Army or

Air Force nonflight operations as far as scheduling

is concerned. Ships in port maintain duty-rest

schedules very much like those of activities ashore,

nominally modeled on a 40-hour workweek, with

limited personnel standing watch around the clock

(see later discussion). When deployed, there is a

transition to the at-sea routine, which typically

consists of a 70- to 80-hour workweek (38).

l~ch semice has a tighfly con~o~~ pmsonnel Reliability Program which covers all persons who have duties invOlvkg aCCeSS tO nUckXU wmpo~

(from the technicians who put them together and do maintenance on them, to the crews who prepare them to fue or be dropped, to the CXEWS who fm

or drop them). The program involves background checks, regular reviews by medical officers and commariders, and annual certification of behavioral

reliability for each person in the program.
Chapter 9--Case Study:The Military ● 191

Shipboard operations require that some tasks be

performed on a continuous basis. Unlike land-based

facilities, where there may be local resources to draw

on, each ship must be entirely self-sufficient. The

crew must not only carry out the mission of the ship

but also perform all housekeeping and maintenance

tasks associated with it. Thus, normal operations on

a ship have the character of continuous operations.

Typically, jobs on board ship are divided into two

types. Work that is general in nature, such as

maintenance and repair tasks, is routinely carried out

on board ships at sea using a 12-hour shift schedule

(12 hours on, 12 hours off’) (38,39). Tasks that

require an individual to operate a specific piece of

equipment or be at a specific station (sonar, radar,

communication operators, engine room personnel)

are manned using a watch schedule. A person who

is on watch is at his or her station for a certain period

of time and is then relieved by the next person

standing watch. The specific watch schedules for

submarines and surface ships are described later;

however, they often result in personnel constantly

changing the hours they are active and the hours that

they are sleeping. Thus, these schedules cause

substantial circadian disruption. A study that examined the effects of watch schedules on merchant

ships has shown that these schedules are associated

with sleep disturbances, decreased alertness, and

decreases in measures of performance (4,25).

Several conditions of readiness modulate a ship’s

work schedule. Condition I Battle Readiness is the

equivalent of sustained operations; all systems are

manned and operating, and no maintenance is

conducted except maintenance associated with keeping watch and urgent repairs. The crew does not have

any rest period and is expected to be able to endure

Condition I for 24 continuous hours. Condition II

Battle Readiness means that required operational

systems are continuously reamed and operating, but

the crew does have 4 to 6 hours of rest per person per

day. Urgent preventive maintenance and support

functions are carried out. Other conditions are

Wartime Cruising Readiness, Peacetime Cruising

Readiness, and Inport Readiness, as well as readiness for specific types of ships (e.g., mine countermeasures, amphibious operations, supply ships)

(21).

Submarines

The essence of submarine operations is to remain

undetected, and that, in turn, depends on maintaining

a very high state of vigilance. Undersea is a

significantly more hostile environment than the

surface, with much less time available to respond to

mechanical problems that arise, so propulsion and

control (and related systems) vigilance must be high

and sustained as well. There are two types of

submarines, ballistic missile and attack submarines.

Ballistic missile submarines carry nuclear missiles

and operate in a mode that is essentially a combination of independent operations and Air Force strategic forces operations. Their task is to remain in their

assigned area, undetected, and be ready to launch

their missiles if so ordered. Attack submarines have

more varied tasks, including defense of a group of

surface ships, information gathering, and attacks on

enemy shipping. Both ballistic and attack submarine

operations at sea use 18-hour watch schedules,

consisting of three sections of personnel rotating

6 hours on, 12 hours off. Generally, the 6-hour on

period is the time an individual is engaged in his or

her specific job (e.g., sonar operator, radio operator).

The 12-hour off period is used for sleep and rest as

well as other activities, including meals, maintenance, training, and administration. Typically, a

crew member averages 4 hours of sleep during an

18-hour cycle, depending on the tempo of the

operations, training, and maintenance, with each

sleep period occurring 6 hours earlier than the

previous one (37). Analogous to a rotating shift

schedule, watch scheduling results in individuals

who will always be active and sleeping at different

times of the day and whose sleep periods will

generally be shorter than normal.

Surface Ships

Naval surface ships include combat vessels and

supply ships. During routine operations at sea, the

watch schedules depend on the size of the crew,

which will determine how many sections of personnel are used. Usually, schedules are based on duty

cycles of 12 hours (two sections with 6 hours on

watch, 6 hours off; three sections with 4 hours on

watch, 8 hours off), 16 hours (four sections with 4

hours on watch, 12 hours off), or 18 hours (three

sections with 6 hours on watch, 12 hours off). The on

period is the time when the crew member is engaged

in a specific job, while off time is divided among

other tasks, eating, and sleeping. Crew members on
192 ● Biological Rhythms: Implications for the Worker

surface ships average 6 hours of sleep per 24 hours

(37), and their watch schedules require them to

constantly change their hours of activity and rest.

Supply ships replenish combat ships with fuel,

foodstuffs, parts, and munitions. Replenishing supplies while at sea can upset the duty-rest routine of

a large portion of the crew on the ship being supplied

because of the extra tasks required (e.g., tending

lines, standing extra lookout watches, stowing

supplies). The frequency of underway replenishment

depends on the activity of the ship, but replenishment every 3 or 4 days is not uncommon, principally

because combat ships are maintained as nearly full

of fuel and other supplies as possible all of the time.

Under combat conditions, when the crew of a ship

is at general quarters for extended periods, acute

fatigue can become a problem. In combat there is a

constant threat of attack from the air, submarines,

and other ships. The entire crew is on duty without

relief in order to carry out all of the defensive and

other operations required. Activity under these

conditions is fast-paced and continuous; sleep and

rest are often sporadic and irregular.

Aircraft carrier operations involve the same tasks

as other combat surface vessels but include tasks

involved in flight operations. These tasks include

moving aircraft around, preparing them for flight,

operating catapults and arresting gear, air traffic

control, and all other operations that support air

combat mission preparation and control. Generally,

aircraft carriers carry enough personnel to make up

one complete shift to operate the equipment and do

the tasks required to conduct flight operations.

During continuous flight operations, this shift is

split; thus, flight operations do not involve the kind

of rotating work-sleep schedules so common on

other ships. Crews ordinarily work about 14 to 16

hours each day; during periods of sustained activity,

they may work nearly continuously (20 hours or so

each day) for several days. Operating for extended

periods at general quarters is even more disruptive

aboard an aircraft carrier than other surface combat

ships because of the far greater amount of movement

of men and materiel from one part of the ship to

another in conducting flight operations. Crew members are effectively in a sustained operations mode

(none returns to sleeping quarters).

Table 9-3--Maximum Accumulated Individual Flight

Times, U.S. Navy

Maximum hours

Aircraft 30 days 90 days 365 days

Single-piloted. . . . . . . . . . . . . . . . 65 165 595

Multipiloted (pressurized,

ejection seat) . . . . . . . . . . . . . . 80 200 720

Multipiloted (nonpressurized) . . . 100 265 960

Multipiloted (pressurized) . . . . . . 120 320 1,120

SOURCE: U.S. Department of the Navy, “Military Planning and the Impact

of Circadian Rhythms on Military Operations,” briefing materials

provided to D. Liskowsky, Offioe of Technology Assessment,

Washington, DC, 1989.

Flight Operations

The Navy’s flight crew regulations are similar to

the Air Force’s in that they may not constrain

operations in wartime (40). These regulations specify maximum hours of flight time: 6.5 hours per day

for single-seat aircraft and 12 hours for other aircraft.

They also specify that flight personnel should not be

assigned to flight duty on more than 6 consecutive

days. The regulations indicate that 8 hours of sleep

time should be made available every 24-hour period

and that flight personnel should not be scheduled for

continuous alert or flight duty (which requires the

person to be continuously awake) for more than 18

hours. If the 18-hour rule is exceeded, 15 hours of

continuous off-duty time must be provided to the

individual. The maximum number of accumulated

hours of flight time for various aircraft is also

specified (table 9-3). Finally, the regulations state

that if the tempo of operations requires an individual’s flight time to exceed any of the guidelines, that

person should be closely monitored and specially

cleared for flight by the commanding officer, with

the advice of the flight surgeon. In situations where

jet lag might occur (changing local sleep-awake

periods, transmeridian flights), flight crews are not

grounded, but the guidelines suggest that closer

observation of the individuals by the flight surgeon

may be warranted (37,40).

Marine Corps Operations

Amphibious Assault

The opposed landing (coming ashore against

armed opposition) is the essence of Marine Corps

operations. It is a very intense period of sustained

operations that changes to continuous operations in

a day or two. Although seas and tides are important

factors in the timing of amphibious assaults, most
Chapter 9--Case Study:The Military . 193

operations are planned to begin before dawn, when

the enemy is expected to be least vigilant and

effective. As with Army combat operations, there

are no specific guidelines regarding duty hours for

Marine combat units. The planning of operations

and the monitoring of the condition of troops are left

to the discretion of commanding officers. The

Marine air forces, which provide air support for

amphibious assaults and other Marine ground operations, are governed by the same flight crew duty-rest

cycle regulations as Navy flight crews (40). Under

actual combat conditions, the limitations on flight

hours imposed by these regulations may be exceeded. For example, in the case of amphibious

assaults, which tend to be fairly short in duration,

these limits may be exceeded for the first 36 to 48

hours of the operation.

SUMMARY AND CONCLUSIONS

The nature of many military operations requires

that personnel be engaged in activity at all hours and

often for extended periods of time. Within the

context of these operations, personnel are required to

carry out a variety of tasks, the performance of which

can be degraded as a result of disruptions in

biological rhythms, sleep loss, fatigue, and other

factors. Decisions concerning the schedules used

and the duration of duty are generally left to

commanding officers, who base their judgments on

their knowledge of the limitations of their personnel

under various conditions. There are few specific

regulations or guidelines in the military related to

hours of service and scheduling. An exception is the

regulations that direct flight operations in all services. These regulations specify maximum allowable

hours of flight duty and may include stipulations

regarding transmeridian flight, minimum necessary

rest periods, and the scheduling of flight operations.

In the Navy there are specific guidelines, which have

a long-standing tradition, for the scheduling of

watches on board ships. They require that personnel

standing watch constantly vary their hours of

activity and sleep, which results in a constant state

of circadian desynchronization.

Finally, the overriding priority in all military

operations is the successful completion of the

mission. As a result, regulations regarding duty

hours are generally waived in wartime operations.

There may be battle circumstances in which all

available forces are needed, even if they will not be

functioning at optimal levels and even if their

effectiveness in the near future will be even more

degraded. Decisions concerning the disposition and

activities of personnel are guided by the demands of

a given situation, and the effects of performance

decrements due to biological rhythm upset, fatigue,

and other factors may be accepted rather than

mediated in some wartime circumstances. A better

understanding of those decrements and their effects

will ultimately aid military commanders in balancing the various factors that go into making such

decisions.

CHAPTER 9 REFERENCES

1.

2.

3.

4.

5.

6.

7.

8.

Balkin, T.J., Department of Behavioral Biology,

Walter Reed Army Institute of Research, Walter

Reed Army Medical Center, Washington, DC, personal communication, Dec. 19, 1990.

Belen@, G.L., Krueger, G.P., Balkin, T.J., et al.,

Effects of Continuous Operations (CONOPS) on

Soldier and Unit Pe~orrnance: Review of the Literature and Strategies for Sustaining the Soldier in

CONOPS, Rep. No. WRAIR BB-87-1 (Washington,

DC: U.S. Department of the Army, Medical Research

and Development Command, Walter Reed Army

Institute of Research, April 1987).

Comperatore, C.A., U.S. Army Aeromedical Research Laboratory, Fort Rucker, AL, personal communication, Feb. 15, 1991.

Condon, R., Colquhoun, P., Plett, R., et al., “Work

at Sea: A Study of Sleep, and of Circadian Rhythms

in Physiological and Psychological Functions, in

Watchkeepers on Merchant Vessels. IV. Rhythms in

Performance and Alertness,’ International Archives

of Occupational and Environmental Health 60?105-

411, 1988.

DeJohn, C. A., Effects of Psychophysiological Countermeasures on Pe~orrnance Decrement During

Sustained Flight Operations, Research and Technology Work Unit Summary Fiscal Year 1989 Addendum, Accession No. DN 248502 (Pensacola, FL:

U.S. Department of the Navy, Medical Research and

Development Command, Aerospace Medical Laboratory, 1989).

Garnbrell, B., Major, U. S.’ Department of the Air

Force, Washington, DC, personal communication,

July 17, 1989.

Graeber, J. G., Rollier, R.L., and Salter, J. A., Continuous Operations SOP for BIFV Units, USA.RI Research Note 86-60 (Fort Benning, GA: U.S. Department of the Army, Research Institute for the Behavioral and Social Sciences Field Unit, 1986).

Haslarn, D.R., “Sleep Ims, Recovery Sleep, and

Military Performance,” Ergonomics 25:163-178,

1982.
194 ● Biological Rhythms: Implications for the Worker

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

Hegge, F.W., The Future Battlefield: Human Dimensions and Implications for Doctrine and Research,

Rep. No. WRAIR NP-82-1 (Washington, DC: U.S.

Department of the Army, Medical Research and

Development Command, Walter Reed Army Institute of Research, December 1982).

Hegge, F.W., and Tyner, C. F., Deployment Threats to

Rapid Deployment Forces, Rep. No. WRAIR NP-82-

2 (Washington, DC: U.S. Department of the Army,

Medical Research and Development Command,

Walter Reed Army Institute of Research, December

1982).

Johnson, L. C., Freeman, C.R., Spinweber, C.L., et

al., The Relationship Between Subjective and Objective Measures of Sleepiness, NHRC Rep. No. 88-50

(San Diego, CA: U.S. Department of the Navy,

Medical Research and Development Command,

Naval Health Research Center, December 1988).

Kopstein, G., Siegel, A., Corm, J., et al., SoZdier

Peq60rrnance in Continuous Operations, USARI

Research Note 85-68, prepared by Applied Psychological Services, Inc. for the U.S. Army Research

Institute for the Behavioral and Social Sciences

(Wayne, PA: Applied Psychological Services, July

1985).

Krueger, G.P., ‘Sustained Work, Fatigue, Sleep Imss

and Performance: A Review of the Issues,’ Work

and Stress 3:129-141, 1989.

Krueger, G.P., “Sustained Military Performance in

Continuous Operations: Combatant Fatigue, Rest

and Sleep Needs,” Handbook of Military Psychology, R. Gal and A.D. Manglesdorff (eds.) (London:

John Wiley & Sons, 1991).

Krueger, G.P., Armstrong, R.N., and Cisco, R.R.,

“Aviator Performance in Week-Long Extended

Flight Operations in a Helicopter Simulator,’ Behavior Research Methods, Instruments, and Computers

17;68-74, 1985.

Krueger, G. P., and Liebennan, H.R., U.S. Army

Research Institute of Environmental Medicine,

Natick, MA, personal communication, Feb. 15,1991.

Lindsay, J. J., General, Office of the Commander in

Chief, U.S. Special Operations Command, MacDill

Air Force Base, FL, personal communication, June 7,

1989.

Mackie, R.R., Wylie, C. D., and Evans, S. M., “Fatigue Effects on Human Performance in Combat: A

Literature Review,’ draft working paper prepared for

the Institute for the Behavioral and Social Sciences,

Medical Research and Development Command, U.S.

Department of the Army, Goleta, CA, and Ann

Arbor, MI, October 1988.

Morgan, B. B., Brown, B.R., Coates, G. D., et al.,

Sustaining Pe@ormance During 36 Hours of Continuous Work and Sleep, F’RL Rep. No. ITR-75-31

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

34.

(Louisville, KY: University of Imisville, Performance Research Laboratory, 1975).

Morgan, B. B., and Coates, G.D., Sustained Per$ormance and Recovery During Continuous Operations,

PAL Rep. No. JT’R-74-2 (Norfolk, VA: Old Dominion University, Performance Assessment Laboratory,

1974).

Naitoh, P., Naval Health Research Center, San Diego,

CA, personal communication, Jan. 21, 1991.

Naitoh, P., Englund, C.E., and Ryman, D.H., Sleep

Management in Sustained Operations: User’s Guide,

NHRC Rep. No. 86-22 (San Diego, CA: U.S.

Department of the Navy, Medical Research and

Development Command, Health Research Center,

July 1986).

Naitoh, P., Englund, C.E., and Ryman, D. H., Sustained Operations: Research Results, NHRC Rep.

No. 87-17 (San Diego, CA: U.S. Department of the

Navy, Medical Research and Development Command, Health Research Center, June 1987).

Poulton, E. C., The Effects of Fatigue Upon Sonar

Detection, MRC NPRC Rep. No. OES 20-72 (I.xmdon: Royal Naval Personnel Research Committee,

1972).

Rutenfranz, J., Plett, R., Knauth, P., et al., “Work at

Sea: A Study of Sleep, and Circadian Rhythms in

Physiological and Psychological Functions, in Watchkeepers on Merchant Vessels. II. Sleep Duration, and

Subjective Ratings of Sleep Quality,” International

Archives of Occupational and Environmental Health

60:331-339, 1988.

Ryman, D. H., Naitoh, P., and Englund, C. E., PerceivedExertion Under Conditions of Sustained Work

and Sleep Loss, NHRC Rep. No. 87-9 (San Diego,

CA: U.S. Department of the Navy, Medical Research

and Development Command, Health Research Center, 1987).

U.S. Department of the Air Force Regulation AFR

28-40, Mobility for Tactical Air and Strategic

Aerospace Defense Forces.

U.S. Department of the Air Force Regulation

AFR 2842, Mobility for Military Airlijit Command

Forces.

U.S. Department of the Air Force Regulation AFR

60-1, Flight Management.

U.S. Department of the Air Force Regulation AFR

60-1, Flight ManugementlSAC Supplement 1.

U.S. Department of the Air Force Regulation AFR

60-1, Flight ManagementlTAC Supplement 1.

U.S. Department of the Air Force Regulation MACR

28-2, Contingency Planning Policies and Procedures.

U.S. Department of the Air Force Regulation MACR

55-1, Airlifi Operations.

U.S. Department of the Air Force Regulation SACR

55-66, ICBM Operations.
Chapter 9--Case Study:The Military ● 195

35.

36.

37.

38.

39.

U.S. Department of the Army Regulation AR 570-2, 40.

Manpower Requirements Criteria (MARAC)-

Tables of Organization and Equipment.

U.S. Department of the Army Regulation AR 95-3, Al

Aviation, General Provisions, Training, Stanahd- “

ization, and Resource Management.

U.S. Department of the Navy, “Military Planning

and the Impact of Circadian Rhythms on Military

Operations,” briefing materials providedtoD. Liskowsky, Office of Technology Assessment, Washington,

DC, 1989. 42.

U.S. Department of the Navy Directive OPNAVINST 1000.16F, Manual of Navy Total Force Management.

U.S. Department of the Navy Directive OPNAVINST 3501 (series), Squadron Manning Document.

U.S. Department of the Navy Directive OPNAVINST 3710.7M, NATOPS General Flight and Operating Instruction.

Vogel, J.A., Sampson, J. B., Wright, J.E., et al., E~ect

of Transatlantic Troop Deployment on Physical

Work Capacity and Work Performance, USARIEM

Rep. No. T 3/79 (Natick, MA: U.S. Department of the

Army, Research Institute of Environmental Medicine, 1979).

Word, L.E., Observations From Three Years at the

National Training Center, USARI Research Product

87-02 (Alexandria, VA: U.S. Department of the

Army, Medical Research and Development Command, Research Institute for the Behavioral and

Social Sciences, 1987).
Appendixes
Appendix A

International Regulation of Shift Work

Policies and regulations on shift work vary widely from

country to country. This appendix examines regulation of

wages, hours, rotation schedules, and rest periods in other

nations. It also reports on special provisions for women

and specific industries (e.g., the transportation industry),

as well as social support services for night and shift

workers. The International Labor Organization’s (ILO)

global role in encouraging and coordinating protective

legislation is also discussed.

An estimated 7 to 15 percent of the work force in

industrialized countries is engaged in some form of night

work (6). As of 1988, 13.3 percent of workers in France,

5.4 percent in Sweden, 12.5 percent in Switzerland, and

15 percent in Norway engaged in some form of night

work.

The degree to which various countries address the

needs of their shift workers via regulation varies. Most

governments regulate basic matters such as extra pay for

night work. Some governments, however, address the

physiological dangers of night and shift work directly. For

example, Bulgarian laws prescribe reduced hours for

night work on the assumption that “the performance of

night work is harmful to the human organism, as a result

of changes in the normal cycle of the physiological

functions in the human body which are caused by its

performance” (3). In Bolivia, the statutes reflect a belief

that “night work is contrary to man’s physiology,

exhausting and dangerous to the health if practiced as a

normal system” (3). In France, the laws allow someone

who has been working at night for a long period (5 years’

continuous night work or 10 years total) to receive top

priority for openings on the day shift. In Angola, a person

with medical problems gets a similar priority for openings

on the day shift (6). Other countries make different

provisions, outlined later in this appendix.

Special arrangements and regulations for shift workers

are by no means universal, however. Often, regulations do

not address all the needs of shift workers, and when they

do, efforts to meet those needs are rarely systematic.

Actual response to the needs of the workers depends on

a variety of external factors. For example, in some

countries the cost of enacting and enforcing protective

legislation could be greater than the benefit to the

workers. This may be particularly true in less-developed

countries, where strict regulations on shift work could

slow needed economic development. In other countries,

however, where high wages make automation a viable

option in some sectors, shift work could be reduced with

little economic impact. In still other countries, economics

could necessitate the hiring of more shift workers; this is

the present position of France and England (6).

In some cases, regulation of shift work did not stem

from conscious attempts to address the specific problems

of night or other shift workers, but from some other labor

initiative, such as a general campaign to reduce work

hours. In some countries, such as the United States, the

legal framework may make it difficult to enact a national

standard. In the United States, many of the regulations fall

under the jurisdiction of the States, not the Federal

Government (11). The issue of a national standard is

unresolved because there has never been an attempt by the

Federal Government to test the Constitution on this point.

In other countries, traditional methods of dealing with

labor problems without government intervention are

firmly entrenched. In the United Kingdom, for example,

labor problems have been solved through collective

agreements, and the government has traditionally not

regulated such areas, including shift work. Finally, the

absence of national regulation of shift work in the

majority of countries can be because “special rules for

shift work exist as part of plant agreements applicable to

a particular region or branch of industry’ (10). This is true

in Canada, which has regulations on the provincial level.

The end result is that some countries have extensive

regulation and support services for shift workers, and

others have virtually none. In a few nations, there are

extensive laws that cover a wide range of issues, including

leisure facilities, housing facilities, and retirement programs for workers. For the most part, though, regulations

dealing with nonstandard work schedules are limited to

hours and wages. The most common regulation seems to

be increased pay. The second most common seems to be

fewer hours.

Few countries have no guidelines. Of the countries

analyzed here, six—China, the United States, Canada, the

Dominican Republic, Tunisia, and Nigeria-have no

national regulation of night or shift work (apart from a few

specific industries such as the transportation sector). As

noted before, however, regional regulations can exist in

the absence of national regulations; therefore, absence of

national regulations does not necessarily mean absence of

all regulations. Table A-1 displays regulations of work

rest, and shift work in 49 countries.

Special night work regulations for certain industries or

segments of the population are common. In the United

States, for example, there are Federal regulations governing some sectors of the transportation industry (e.g.,

airlines and marine shipping). Transportation is regulated

in many other countries, including Greece, Ireland,

Austria, Japan, Spain, and Turkey. Agriculture, on the

other hand, is often specifically exempted from shift work

regulation, as it is in New Zealand, Norway, Finland,

–199–
200 ● Biological Rhythms: Implications for the Worker

Table A-l—Regulation of Work, Rest, and Shift Work in 49 Countries

Major source of regulation a . . . . . . . . . .

Maximum daily hourb . . . . . . . . . . . . . .

Maximum weekly hours. . . . . . . . . . . . .

Rest during the dayd... . . . . . . . . . . . . .

Minimum rest between days or shiftse. .

Minimum week/y rest f 

. . . . . . . . . . . . . .

Shift work (except night work)g 

. . . . . . .

Night work onlyh 

. . . . . . . . . . . . . . . . . . .

Data valid as of {

. . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum week/y hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum week/y rest. . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest. . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work on/y. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Argentina

Legislation

8, but maybe exceeded so long as weekly total

does not exceed 40

48

For meals (at home if possible) and for duties

such as feeding of child

12 hours

No work from 1 p.m. Saturday to midnight

Sunday

Maximum limits on daily and weekly working

hours waived, but must average no more

than 8 hours/day and 48 hours/week over

3-week period

Maximum of 7 hours/night

1984!

Austria

Legislation

10 (8); RCm

50 (40); RC

0.5 hour if work exceeds 6 hours

11 uninterrupted hours

36 uninterrupted hours, except for shift work

Maximum of 2 consecutive shifts; maximum of

40 hours/week, averaged

2 to 6 extra vacation days per year; special

pension; extra breaks

1986!

Brazil

The constitution; legislation, which may

sometimes be overridden by collective

bargaining

j~8)

No general regulations

No general regulations

1 day/week

Extra pay

Extra pay; 52.5 minutes are equal to 1 hour of

day work

 1977j

Australia

Collective bargaining; mandatory

government arbitration

No general regulations

38-40, but maybe averaged over a period

exceeding a week

Usually 0.5 hour if work exceeds 5 hours

Usually 10 hours

1.5 to 2 days

Maximumof 11 shifts in 12 days, usually

extra pay

Extra pay, RWCk

1986l

Belgium

Legislation

8, but 10 hours/day if worker is unable to

return home every day; maximum of

11 in special cases (including shift

work)

40 (50 for shift work; up to 65 hours above

average)

No general regulations

No general regulations

24 hours on Sunday

Maximum of 11 hours/day; maximum of

50 hours/week; maximum of 40 hours/

week for 13 weeks

Generally prohibited; exceptions up to 11

hours/day; up to 12 hours/day for work

that cannot be disrupted; maximum of

50 hours/week so long as it averages

40 hours/week or less over 13 weeks

1986jl 

Bolivia

Legislation

8

(48); RWC

At least 2 hours; no more than 5 hours of

work at a stretch

No general regulations

Work prohibited on Sundays

For “team work” hours averaged over 3

weeks; must meet normal daily and

weekly limits

Maximum of 7 hours; extra pay; RWC
Appendix A-International Regulation of Shift Work . 201

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum week/y hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum week/y hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum week/y rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work on/y. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum week/y rest . . . . . . . . . . . . . . .

Shift work (except night work). . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Bulgaria

Legislation

Maximum of 8.5 for 5-day workweek; maximum

of 8 for 6-day workweek; maximum of 6 days

before rest days; RC

Maximum of 42.5 for 5-day workweek; maximum

of 46 for 6-day workweek; RC

0.5 hour

12 uninterrupted hours

48 uninterrupted hours for 5-day workweek; 24

uninterrupted hours for continuous-process

workers, shift workers, and 6-day workweek

See above; no consecutive shifts, regular

rotations

For 5-day workweek, maximums of 7 hours/night

and 35 hours/week; for 6-day workweek,

maximums of 6 hours/night and 36 hours/

week

1986l

China

Legislation

8

48

Required but unspecified; extra hour for nursing

mothers for feeding

No general regulations

No general regulations

No general regulations

No general regulations

197@

Czechoslovakia

Legislation

9 (8)

46 (42.5); may be averaged; RC

0.5 hour if work exceeds 5 hours

12 uninterrupted hours; 8 for shift workers; RWn

32 uninterrupted hours

Maximum of 7.5 to 8.5 hours/shift, depending on

circumstances; maximum of 56 hours/week

for continuous shift workers; minimum of 8

hours rest between shifts

Extra pay; RWC

1986l

Dominican Republic

Legislation

8

44; not applicable to shift or continuous work

No general regulations

No general regulations

24 uninterrupted hours on Sundays; usually no

work permitted on Saturday afternoons

No general regulations

No general regulations

1986l

Canada

Provincial legislation

8

48 (40)

No general regulations

No general regulations

1 day

No general regulations

No general regulations

19861

Colombia

Legislation

Maximum of 8; not applicable to shift work

Maximum of 48; maximum of 56, when

necessary, for shift work

Required but unspecified

No general regulations

Paid rest on Sundays

Extra pay; may work over the daily and

weekly limits up to 56 hours/week;

may work on Sundays, but must

receive advance notice and must

receive a compensatory rest day

Extra pay; RWC

1976J

Denmark

Collective agreement

Usually 8, by national collective

agreement

Usually 39

No general regulations

11 hours/day; RC

1 day

Earn 3 extra hours of leave every 40

hours of work; minimum of 8 hours’

rest when changing shifts

No general regulations; RC

1986l

Ecuador

Legislation

Maximum of 8, unless 9 hours are worked

to free Saturdays; RC

44; RC

No general regulations

No general regulations

No work permitted on Sundays

No general regulations

Extra pay; RWC

1 97@
202 . Biological Rhythms: Implications for the Worker

Table A-l—Regulation of Work, Rest, and Shift Work in 49 Countries—Continued

Major source of regulation. . . . . . . . . . .

Maximum alai/y hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day, . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum week/y rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Finland

Legislation

8; 9 if weekly total is less than or equal to 40

48 (40); RC

1 hour if work exceeds 7 hours, except for shift

work; RC

12 hours

30 uninterrupted hours; RC

No general regulations

Prohibited

1986l

Germany

Legislation

10 (8); RC

48; RC

0.5 hour if work exceeds 6 hours; RWC

11 uninterrupted hours; RC

24 hours, usually on Sunday; RC

May work up to 16 hours once every 3 weeks to

change shift, but must be granted

uninterrupted rest of 24 hours at least twice

during the 3 weeks; RC

No general regulations; RW

19861

Greece

Legislation

8; 9 for 5-day week

48 (40); 56 for shift work

No general regulations

No general regulations

24 hours, usually on Sundays

Hours averaged over 8 weeks, must conform to

normal limits

Extra pay; RWC

19861

Hungary

Legislation and collective bargaining

12

40 for industry and government; 42 for the rest of

the industries

One 20-minute break/day

11 uninterrupted hours

1 day/week mandatory; 2 days usual

Extra pay; regular rotations unless worker

requests otherwise; maximum of 36 to 40

hours/week

Extra pay; regular rotations unless worker

requests otherwise; maximum of 36 to 40

hours/week

1983l

France

Legislation

10

48 (39); must average to maximum of 46

hours/week over 12 weeks; RC

No general relations; RC

No general regulations; RC

24 hours on Sundays

No consecutive shifts; maximum of 35

hours/week averaged over a year

No general regulations; RWC

1986{

Hong Kong

Legislation

No general regulations; RWC

No general regulations; RWC

No general regulations; RWC

No general regulations

24 uninterrupted hours/week; RWC

No general regulations

No general regulations; RWC

1981j

India

Legislation, but with wide powers to make

exceptions by the state governments

9, 10.5 including rest time; RC; not

applicable to shift work during change

of shifts

48; RC

At least 0.5 hour/5 hours

No general regulations

No general regulations

No general regulations; double shifts

allowed

No general regulations

1979
Appendix A-International Regulation of Shift Work . 203

Major source of regulation . . . . . . . . . . .

Maximum alai/y hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum week/y rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum week/y hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum week/y rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum alai/y hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work on/y. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum week/y hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Ireland

Legislation

11 (9); RC

60 (48); maximum of 56 for shift work; RC

0.5 hour/5 hours; RC

No general regulations; RWC

No work allowed on Sunday; Saturday short day;

shift work exempted; RC

Not allowed unless granted special license

(maximum of 48 hours/week averaged over

3 weeks) or required by the nature of the work

(maximum of 56 hours/week); minimum of 8

hours between shifts; 15-minute break required 3 to 4 hours into shift; no double shifts

Prohibited

1989! 0

ltaly

Legislation

8; RC

48; shift work can be averaged over a year

No general regulations; RC

No general regulations; RC

24 hours, usually on Sundays

No general regulations

No general regulations; RWC

19861

Japan

Legislation

8

48, averaged over 4 weeks; RC

45 minutes if work exceeds 6 hours; 1 hour if it

exceeds 8

No general regulations

1 day

Maximum of 10 hours/day; maximum of 60

hours/week averaged over 4 weeks; RC

Extra pay; RWC

19861

Netherlands

Legislation

8.5; RC

48 (40)

If work exceeds 5.5 hours, 0.5 hour within the

first 4.5 hours

No general provisions

No work allowed on Sundays or Saturday

afternoons

Prohibited; when changing shifts, up to 18-hour

shifts allowed

Prohibited without special permit; hours must be

approved by minister or fulfill either: 1)

maximum of 48 hours/week averaged over 3

weeks, maximum of 54 hours in any given

week, and maximum of 144 in any given

3-week period; or 2) maximum of 60 hours/

week averaged over 4 weeks, and maximum

of 56 hours in any given week and maximum

of 192 hours over any given 4-week period

198611

Israel

Legislation and collective agreement

8; 7 on the day before holidays and days

of rest

47

No general regulations

No general regulations

36 uninterrupted hours; 25 for shift

workers

No general regulations; lower minimum

weekly rest

Maximum of 7 hours/night; RWC

19861

Jamaica

Legislation

(8)

40

No general regulations

No general regulations

No work permitted on Sundays; usually

no work on Saturdays

No general regulations

No general regulations; RWC

19831

Morocco

legislation

(8 to 10, depending on how many days

per week worked)

48

No general regulations; RWC

No general regulations

Uninterrupted 24 hours per week, starting

from midnight

Prohibited

No general regulations; RWC

19851

New Zealand

Combination of legislation, arbitration,

and collective agreement

8

40

By collective agreement

By collective agreement

2 days

No general regulations

No general regulations; RC

19861
204 ● Biological Rhythms: Implications for the Worker

Table A-l—Regulation of Work, Rest, and Shift Work in 49 Countries-Continued

Nigeria Norway

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum alai/y hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest. . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Legislation

No general regulations

No general regulations

1 hour if work exceeds 6 hours

No general regulations

No generaI regulations

No general regulations

No general regulations

1984[

Panama

Legislation

8; 7 for night shift; 7.5 for mixed shifts

48; 42 for night workers; 45 for mixed

workers

Minimum of 0.5 hour

No general regulations

24 uninterrupted hours

After a double shift, worker must receive

12 uninterrupted hours of rest; extra

pay

Maximum of 7 hours/day; maximum of

7.5 hours/day if shift is mixed daynight shift; extra pay; RW

197@

Papua New Guinea

Legislation, collective agreements, court

awards, common rules

8

44 for rural areas, 42 for urban

No general regulations

No general regulations

No general regulations

Extra pay

No general regulations

19861

Poland

Legislation

8 for 6-day week; 9 for 5-day week

46 (42)

No general regulations

No general regulations

No work on Sundays; usually no work on three

Saturdays/month

Maximum of 42 hours/week, averaged

Extra pay

1986jl

Legislation

8

40; 38 for revolving shift work; 36 fur

continuous shift work

0.5 hour if work exceeds 8 hours

10 hours; RC

36 hours, 24 of which must be

uninterrupted

See above

No general regulations; RC

19861

Philippines

Legislation

8

48

1 hour/day for meal; short rest breaks

required but not specified

1 day, normally Sundays

No general regulations

Extra pay (10%); RWC

197@

Romania

Legislation

8; RWC

46; RWC

0.5 hour plus lunch break

12 uninterrupted hours

48 uninterrupted hours twice a month; 24

uninterrupted hours on the other weeks;

usually this rest falls on Sundays

Extra pay

Maximum of 7 hours without diminution in

pay; bonus; extra breaks; RWC

19861
Appendix A---international Regulation of Shift Work .205

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum week/y rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest. . . . . . . . . . . . . . .

Shift work (except night work). . . . . . . .

Night work only . . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum alai/y hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum week/y rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

South Africa

Legislation

9.25 for 5-day week; 8 for 6-day week; 8.5 hours

for 6-day week if work does not exceed 5

hours/day

46

1-hour meal break if work exceeds 5 hours

No general regulations

No general regulations

Maximum of 8 hours/day for continuous shift

work; maximum of 9.25 hours/day for 5

shifts/week; maximum of 8 hours/day for 6

shifts/week; if one shift does not exceed 5

hours, maximum of 8.5 hours/day

No general regulations

19851

Spain

Legislation

9

40

15 minutes/day; RW

12 uninterrupted hours

Sunday, plus either Saturday afternoon or

Monday morning

Maximum of 2 weeks at a time unless worker

volunteers

Extra pay; RC

19861

Switzerland

Legislation

No general regulations; RC

45 in industry, office, technical, and sales; 50 for

others, including craft and commerce; 52 in

shift work (60 for special cases)

15 minutes if work exceeds 5.5 hours; 0.5 hour

if it exceeds 7; 1 hour if it exceeds 9

Work permitted from 5 a.m. in summer or 6 a.m.

in the winter to 8 p.m.; RW

1 day, usually Sundays

Shifts must rotate every 6 weeks; extra pay; 52

rest days/year of 24 uninterrupted hours

each; 9 hours/day averaged over 6 weeks;

weekly rest period may be reduced to 20

uninterrupted hours

Prohibited; for exceptions, maximum of 9 hours/

day averaged over 6 weeks; maximum of 6

weeks at a stretch; RW

198910

South Korea

Legislation

8; RWC

48, but may be averaged over 4 weeks;

RWC

0.5 hour for every 4 hours

No general regulations

1 day

No general regulations

Extra pay; RWC

19841

Sweden

Legislation

8

40; may be overridden by collective

agreement

No more than 5 hours at a stretch

No general regulations

36 hours

No general regulations

Prohibited

1986j I

Tunisia

Legislation

9

48, for nonagricultural work

1 hour

10 uninterrupted hours

24 uninterrupted hours

No general regulations

No general regulations

198@
206 ● Biological Rhythms: Implications for the Worker

Table A-l—Regulation of Work, Rest, and Shift Work in 49 Countries—Continued

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Plight work only . . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum daily hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Data valid as of. . . . . . . . . . . . . . . . . . . .

Major source of regulation . . . . . . . . . . .

Maximum alai/y hours . . . . . . . . . . . . . . .

Maximum weekly hours . . . . . . . . . . . . .

Rest during the day. . . . . . . . . . . . . . . . .

Minimum rest between days or shifts . .

Minimum weekly rest . . . . . . . . . . . . . . .

Shift work (except night work) . . . . . . . .

Night work only. . . . . . . . . . . . . . . . . . . .

Turkey

Legislation, but the Minister of Labor may set

rules for night and other shift workers

7.5 for 6-day workweek, 8.5 for 5-day workweek;

maximums of 10.5 and 11.5, respectively

45

15 minutes if work exceeds 4 hours; 0.5 hour if

it lasts 4-8 hours; 1 hour if it lasts 8 hours or

more

No general regulations

35 hours, beginning at 1 p.m. on Saturday

Minimum of 8 hours of rest when changing shifts;

maximum of 1 week on night shift at a stretch

Maximum of 7.5 hours/night; RWC

19861

United States

State legislation

No general regulations; RC

40

No general regulations

No general regulations

No general regulations

Data valid as of. . . . . . . . . . . . . . . . . . . . 19861

No general regulations

No general regulations

1986l

U. S.S.R.

Legislation

10 (8)

41; RC

Maximum of 2 hours for each 4 hours worked

At least twice the number of hours in the last shift

worked

42 uninterrupted hours

No double shift; regular rotations, usually in

1 -week cycles

Extra pay; working hours shortened by 1 hour

(nonapplicable to necessary continuous work)

United Kingdom

Collective bargaining, but employers must

not require excessive hours or shift

patterns Iikely to lead to ill health or

fatigue-induced accidents

No general regulations; RC

No general regulations; RC

No general regulations; RC

No general regulations

No general regulations

No general regulations; RC

No general regulations; RWC

19890

Uruguay

Legislation; ILO conventions

(8)

48

No general regulations

No general regulations

No work on Sundays, plus another day of

rest during week; 36 uninterrupted

hours for commercial sector; RWC

No general regulations

No general regulations; RWC

198(3J

Venezuela

Legislation

8

418

0.5 hour; no more than

continuous work

No general regulations

1 day

No general regulations

5 hours of

Extra pay; maximum of 7 hours/day;

maximum of 42 hours/week for

laborer, 40 for other workers; for mixed

work (up to 4 hours of night work),

maximums of 7.5 hours/day and 45

hours/week

19841

Yugoslavia

Major source of regulation . . . . . . . . . . . Legislation; workers’ decisions

Maximum alai/y hours . . . . . . . . . . . . . . . No general regulations

Maximum weekly hours . . . . . . . . . . . . . 42

Rest during the day. . . . . . . . . . . . . . . . . 1 hour

Minimum rest between days or shifts . . Minimum of 12 hours

Minimum weekly rest . . . . . . . . . . . . . . . 24 hours, usually on Sundays

Shift work (except night work) . . . . . . . . No general regulations

Night work only . . . . . . . . . . . . . . . . . . . . Extra pay; 15 extra vacation days per year

Data valid as of. . . . . . . . . . . . . . . . . . . . 19861

——
Appendix--A-international Regulation of Shift Work ● 207

SOURCE: Office of Technology Assessment, 1991.

Ireland, Japan, Greece, the U. S. S.R., Hungary, and

Turkey. Many countries limit the hours of work in

unhealthful or dangerous occupations, including Turkey,

Czechoslovakia, Yugoslavia, and Hungary. Six countries

prohibit night work by women, and many regulate young

people’s and women’s night work much more stringently

than men’s.

Hours and Wages

Although most employers voluntarily give night workers higher wages than day workers, many countries have

laws to ensure extra pay for night work. These range from

10-percent increases (Germany and the Philippines) to

50-percent increases (Korea), with many countries in

between (25 percent in Ecuador, Greece, Ireland, Japan,

Portugal, Switzerland, and Spain). In other countries,

extra pay for night work is often achieved by collective

bargaining. Normally, employers are free to pay the

workers more than prescribed by law (6). In the United

States, the increase in pay for shift workers is between 7

and 10 percent.

Some governments mandate shorter work hours for

night work instead of higher wages, which can have the

same effect as raising wages because the workers often

receive the same pay for less work. Unlike higher wages,

however, shorter hours are directly protective, in that they

seek to reduce the strain on the workers. In Argentina, 52

minutes of work at night is considered equivalent to an

hour of daytime work. In Brazil, 52.5 minutes is

equivalent to 1 hour. These conversions from 52 or 52.5

to 60 minutes are required by law and are used to calculate

pay, overtime, and compliance with the maximum

working hour restrictions. Some countries arrange shorter

hours via collective bargaining (6). In still other countries,

such as Bolivia, shorter work hours are written into the

constitution (5). In Finland and Sweden, the maximum

length of night work is 2 hours shorter than the daytime

limit, and in Czechoslovakia it is 2.5 hours shorter.

Finally, some countries grant early retirement or longer

vacations for night workers instead of, or in addition to,

shorter workdays. Australian night workers earn an extra

week of vacation every year. Austrian night workers

receive 2 to 6 extra vacation days per year, and

Yugoslavian employees get 15 extra days (5,6). In both

Austria and Luxembourg, night workers are entitled to

early retirement by law, and Austrian night workers

receive a special pension in addition.

Sometimes extended workdays are unavoidable because of technological constraints. For example, in steel

mills using continuous casting techniques, any interruption in the production process damages the machinery.

During harvesting season, agricultural workers must work

long hours to gather all the crops on time. Mindful of such

circumstances, many countries permit some workers,

such as shift or seasonal workers, to work longer than

normal. These countries include Argentina, Belgium,

Austria, Finland, Japan, Switzerland, Bolivia, Colombia,

Israel, and India. But employers must limit total work

hours so that the average hours are equal to those of the

average worker. For example, shift workers in Finland can

work a maximum of 40 hours per week, averaged over a
208 . Biological Rhythms: Implications for the Worker

2-to 3-week period. For continuous shift work, they can

work a maximum of 90 hours over 3 weeks. Similarly, in

Argentina the average hours worked over a 3-week period

by a shift worker must conform to the limits imposed for

day workers. Thus, leeway in arranging work hours is

allowed in some countries, but only within the constraints

of maximum total hours.

As described throughout this report, for many shift

workers the arrangement of rotations is just as important

as the number of hours worked. Physiological and social

problems associated with night and shift work are affected

considerably by the scheduling of shifts (9). Thus, most

workers here and abroad strongly prefer rotating schedules to permanent night shifts (6). In response to this

preference, many countries impose limits on the number

of consecutive nights a person is permitted to work.

Furthermore, most countries (including Finland, Greece,

Hungary, Iraq, Norway, Paraguay, Turkey, the U. S. S.R.,

and Venezuela) encourage rotating schedules, usually on

I-week rotations. Iraq imposes a maximum of 1 month for

night work, and Switzerland forbids more than 6 consecutive weeks of night work. Recent research, however, has

shown that permanent night shift work may be physically,

mentally, and socially better in some situations than

rotating shifts and that l-week rotations seem to be the

most disruptive to biological rhythms (9).

Finally, another point of concern is double shifts. Some

countries permit double shifts (India, Austria, Germany,

the Netherlands, Panama), but more countries prohibit

them. Many do so indirectly, by restricting the number of

hours that can be worked consecutively, but the U. S. S.R.,

France, Ireland, Turkey, and Czechoslovakia do so

directly. According to recent research, an extra-long break

is advisable when shift workers are changing from a night

to a day shift (6). On rotation schedules of one week or

longer, shift workers build up a sleep debt during the night

shift. This debt should be alleviated by extra sleep at the

end of the night rotation (6). At present, no country

requires this type of extra rest. Also, no country regulates

the direction in which shifts rotate (i.e., forward or

backward).

Other Concerns

Apart from the issues of pay and hours, shift workers

have a host of other concerns. These include obtaining

adequate medical supervision, food, sleep, transportation,

and entertainment. Shift workers can face health problems

from continually operating out of synchrony with their

biological rhythms. Factory canteens often close at night,

and night workers must endure relatively poor food. Sleep

during the day is more likely to be interrupted than sleep

at night. Transportation and entertainment schedules are

usually designed around standard daytime work schedules.

Only a few countries have provisions for extra medical

supervision. The most common form of supervision,

where it exists, is a medical examination before a worker

engages in shift work. Such supervision is required bylaw

in France and Portugal and by collective agreement in

Germany (6).

One characteristic complaint of the shift worker is

digestive problems. Often, ulcers can be traced to the

quality and availability of food. With rotating shifts,

continual variation in meal times disrupts the digestive

system. In recognition of this, several countries have

adopted special regulations for shift workers’ meals.

French law stipulates special food arrangements. The

U.S.S.R. also requires a free or subsidized meal for its

night workers. Many other countries have food arrangements by collective agreement (6).

Another common problem is inadequate sleep. Noise

tends to be greater during the day, and sunlight can

impede sleep. The continually disturbed circadian

rhythms of rotating shift workers make it generally more

difficult to fall asleep during the day. As a result, they

often sleep less well and for a shorter time than their

daytime counterparts. This can lead to drowsiness on the

job, stress, and damage to the health of the workers.

France is unique in addressing the problem of the

quality and quantity of sleep for night workers, establishing a multiministerial committee which has provided

special arrangements for night workers’ housing. Not

only do night workers get priority in obtaining nationally

directed funding for housing, but they also receive 6

percent more money than other workers to soundproof

and lightproof their houses. People who soundproof or

lightproof their old dwellings can get 50 percent of the

expenses back from the government and qualify for

special loans to help with the balance (6).

France’s multiministerial committee has also taken

steps to arrange leisure activities for night workers.

Because most recreational and entertainment activities are

organized around daytime schedules, many night workers

are forced to engage in solitary pursuits for entertainment.

Night workers frequently complain about being on the

fringe of society and often suffer from isolation, which

may play an important role in causing biological and

psychological problems. Thus, the French committee has

provided for rebroadcasts of certain television programs

for night workers. A few other countries have also made

arrangements to facilitate leisure activities for shift

workers. In other countries, nonstatutory arrangements

exist, such as collective agreements for leisure programs

and facilities (6).

Public bus and train services often cut backer eliminate

operations at night. Getting to and from work after hours

can be difficult. Special transportation arrangements

usually come from collective agreements, such as those in
Appendix A--International Regulation of Shift Work ● 209

Australia and Canada, entitling some categories of female

night workers to free transportation between home and the

workplace (two provinces in Canada, certain jobs in

Australia). In Mauritius and Swaziland, employers must

either provide or pay for transportation for all night

workers (6).

In summary, the amount and kind of support countries

offer their shift workers vary widely. In most cases, hours

of work and pay rates are regulated. A few countries have

made efforts to extend their services further. In particular,

France has adopted extensive policies to alleviate the

problems of its night workers, who make up almost

one-seventh of its labor force.

Women’s Night Work

Restrictions on shift work are protective in nature. They

are designed to protect the worker from exposure to

unreasonable dangers or strain and to prevent employers

from taking advantage of workers. Predictably, then,

much of the legislation on shift work applies to women

and children, who are traditionally the focus of protective

labor legislation. Many countries have stricter labor

restrictions on women than men in all aspects of work

including maximum overtime, daily working hours, rest

periods, and so on. Most countries also limit young

people’s work, but these limits are not nearly as controversial as those on women, because most people accept

the necessity of protecting young people.

The first national ban on women’s night work was

passed in England in 1844. Other countries soon followed

suit. The bans were prompted by government recognition

of and concern about the exploitation of women and

children in factories, but they were eventually applied to

other areas of work as well. In 1890, the International

Congress for the Protection of Workers adopted a

resolution against women working at night. In 1906, the

Berne Convention met and proposed a ban on women’s

night work in an industry if the employer had more than

10 workers. Thirteen countries signed the ban. The ILO

has had three conventions against industrial night work

for women (6).

At one time in the United States, 20 States had laws

against women working at night, but by the 1970s all of

them had been repealed. In 1924, the Supreme Court

upheld the constitutionality of prohibiting women’s night

work (12), but the Equal Employment Opportunity

Commission has decided that such laws are discriminatory under Title VII of the Civil Rights Act (29 CFR 1990

ed. 1604.2(b)(l)).

There were many reasons for placing women under

stricter night work regulations than men. Women were

thought to need more protection because they were

thought to be physically and psychologically weaker than

men. They were thought to need protection by law

because they were unable to fight for themselves individually. In addition, it was also feared that allowing women

to work at night might take them away from their

traditional domestic duties, such as rearing children and

keeping house. Safety was also cited as a greater concern

when women worked at night, especially during the travel

to and from work. Increased opportunity for moral

degeneracy was even cited as a reason to prevent women

from working at night. Sometimes men were afraid that

women would take their jobs. In other cases, male

workers seem to have been planning to use a ban on

women’s night work as the first step toward a general ban

on night work. All these factors led to the widespread ban

on women’s work at night (6). In many countries, these

conditions still hold and the same arguments are still

advanced.

Algeria, Argentina, Austria, Bolivia, Cape Verde,

Costa Rica, Czechoslovakia, Ecuador, Egypt, Germany

(manual workers), Indonesia, Peru, Philippines, Saudi

Arabia, Thailand, Turkey, and Venezuela currently restrict night work by women. Algeria, Argentina, Bolivia,

Indonesia, Austria, and many other nations categorically

ban women’s night work. Some countries, such as

Denmark, Norway, and Sweden, ban night work by both

male and female workers, but it is much easier for men to

obtain exemptions. There are also exceptions to the ban

on women’s night work. For example, in most countries,

managerial workers, including women, are excluded from

the ban. In Austria, Ghana, Nigeria, Greece, and other

countries, the prohibition on women night workers is

suspended for certain seasonal tasks such as harvests. In

Austria, Angola, Switzerland, Iraq, and other countries,

women are permitted to work at night in emergencies. In

Zaire, Saudi Arabia, and other countries, one or more

persons in the government are authorized to issue

exemptions at their own discretion (6).

Some countries, such as Ethiopia, Singapore, and

Chile, prohibit pregnant women from working at night.

Germany, Mongolia, and Luxembourg prohibit nursing

mothers from working at night. Hungary and Mongolia

prohibit mothers with children under the age of 1 from

working at night, and Bulgaria extends the ban to the age

of 3. In Bulgaria, mothers with a handicapped child or a

child between 3 and 6 years old may refuse to work the

night shift. In Poland, pregnant women and women with

children under 1 year old may refuse night work

assignments.

In recent years, attitudes toward women’s night work

have changed. Recent evidence indicates that women are

no more susceptible to physiological or medical harm

from night work than men (4), prompting the United

Nations to pass a resolution recently calling for equality

between the sexes. The ILO has issued a convention on

equal pay, and several nations have denounced the ILO’s

convention prohibiting women from working at night.
210 . Biological Rhythms: Implications for the Worker

The reason for the change in opinion is partly social and

partly economic. Many countries are finding it necessary

to employ women at night in order to be competitive. The

United Kingdom, France, and Luxembourg have all

declared that prohibitions on women’s night work impair

economic efficiency. Some countries that have repealed

such prohibitions are Barbados, Canada, Guyana, Ireland,

Israel, New Zealand, Sri Lanka, and Surinam (6).

Some parties argue that the proper way to achieve

equality is not by lifting the ban on women but extending

it to men. Workers’ organizations in Finland, France, and

Germany have called for extending the night work ban to

men. Some workers in Japan, Netherlands, Switzerland,

and Britain also demand a prohibition on night work for

men. Others argue for the preservation of the status quo.

When Sri Lanka was considering abolishing restrictions

on women’s night work, for example, the Ceylon

Mercantile Union argued unsuccessfully for the preservation of the ban because the adverse effects of night work

are harsher on women, who also have family responsibilities. In many developing countries, ingrained social and

economic conditions make it almost impossible for

women to work at night.

In any case, there is almost unanimous agreement that

pregnant women should not work at night. In 1978, the

ILO Tripartite Advisory Meeting on Night Work unanimously called for the prohibition of pregnant women in

night jobs.

Types of Regulations

In countries where regulations exist, they take four

basic forms:

●

●

●

●

national collective agreements, where a union representing all or most of the workers in a country

negotiates the contract with an employer’s group,

resulting in consistency of working conditions

across the nation and fields;

national government legislations, where the national

government sets the rules;

local collective agreements, where small-scale bargains are struck; and

local legislation (e.g., State laws in the United

States), ‘where smaller bodies than the national

government set the standards.

Combinations of the various methods are also used. In

some countries, special systems have been set up to

resolve labor disputes. In Australia, for example, wages

are fixed by government-mandated court arbitration. The

most common form of regulation is national legislation,

followed by national collective bargaining. Unlike many

local regulations, national regulations normally apply to

all industries and to all workers; however, certain

industries, e.g., transportation, mining, or hotels, are often

governed by separate sets of regulations.

The International Labor Organization

The ILO, an agency of the United Nations, is made up

of 150 member countries (as of 1989), including the

United States. Among other things, it formulates conventions on working conditions (8). Many countries have

modeled their protective labor regulations for work hours,

children, and women on the ILO conventions. The first

convention, enacted in 1919, fixed working hours at 8

hours per day and 48 hours per week. Other conventions

address such topics as freedom of association, right to

organize and bargain collectively, equal remuneration,

asbestos, maritime regulations, medical care, insurance,

and discrimination. No country is required to abide by a

convention unless its government ratifies it. Once a nation

ratifies a convention, however, it is bound by the

convention as an international treaty and must report on

its implementation to the ILO. The number of countries

ratifying the conventions ranges from O to 128 (7).

Although the ILO has no formal powers of enforcement,

it can and does use unfavorable publicity to encourage

nations to support the labor standards which they have

ratified. The ILO aids in the implementation of labor

standards through training, technical assistance, and

special programs. This practice has been successful

because the ILO enjoys the respect of many countries and

its conventions are prominent factors in labor relations. In

1969, the ILO was awarded the Nobel Peace Prize.

Conventions are initiated by questionnaires polling

governments’ opinions. A preliminary set of proposals is

drawn up on the basis of the responses to the questionnaires and introduced at the annual conference. The actual

adoption process spans 2 years and also takes place at the

conference. Each country sends four delegates to the

conference: two government representatives, one employers’ representative, and one workers’ representative.

The conventions are debated and discussed at the first

conference and are adopted or rejected at the second. After

a convention is adopted, each government is free to ratify

or denounce it. A convention maybe denounced after 10

years. If a government fails to denounce a convention, that

government is bound for another 10 years, and the process

is repeated. The ILO can also adopt a purely advisory

recommendation which governments are free to follow or

ignore.

In 1990, the 77th session of the International Labor

Conference adopted convention 171. This convention

institutes the first regulations on general night work. All

previous night work conventions dealt with women,

young persons, or specific industries. The conference also

adopted recommendation 178 concerning general night

work, along with a protocol which revised convention 89

regarding women’s night work.

Convention 171, however, has not yet received the

required number of ratifications to be entered into force.
Appendix A--International Regulation of Shift Work ● 211

For this reason, several pertinent, older conventions still age of 18 in night work is prohibited by conventions 6,79,

control night and shift work. Convention number 47, and 90 (6). Table A-2 illustrates which countries have

adopted in 1937, reduced the working week to 40 hours. ratified various conventions on night and other shift work.

Conventions 14 and 106 provide for weekly rest. In 1979, Conventions 4, 41, and 89 prohibit industrial night

convention 153 set guidelines on work and rest for road work for women. Convention 89 is the current version and

transport workers (7). Employment of workers under the the one most widely accepted. It prohibits industrial night

Table A-2—lnternational Labor Organization Conventions Related to Night and Other Shift Work

and the Countries That Have Ratified Them

ILO Conventiona

Country 1 14 20 30 47 79 89 90 106 153

Afghanistan . . . . . . . . . . . . . . . . .

Albania . . . . . . . . . . . . . . . . . . . . .

Algeria . . . . . . . . . . . . . . . . . . . . . .

Angola . . . . . . . . . . . . . . . . . . . . .

Antigua and Barbuda . . . . . . . . .

Argentina . . . . . . . . . . . . . . . . . . .

Australia . . . . . . . . . . . . . . . . . . . .

Austria . . . . . . . . . . . . . . . . . . . . . .

Bahamas . . . . . . . . . . . . . . . . . . .

Bahrain . . . . . . . . . . . . . . . . . . . . .

Bangladesh . . . . . . . . . . . . . . . . .

Barbados . . . . . . . . . . . . . . . . . . .

Belgium . . . . . . . . . . . . . . . . . . . . .

Belize . . . . . . . . . . . . . . . . . . . . . .

Benin . . . . . . . . . . . . . . . . . . . . . . .

Bolivia . . . . . . . . . . . . . . . . . . . . . .

Botswana . . . . . . . . . . . . . . . . . . .

Brazil . . . . . . . . . . . . . . . . . . . . . . .

Bulgaria . . . . . . . . . . . . . . . . . . . .

Burkina Faso . . . . . . . . . . . . . . . .

Burma . . . . . . . . . . . . . . . . . . . . . .

Buruni . . . . . . . . . . . . . . . . . . . . . .

Belorussian SSR . . . . . . . . . . . .

Cameroon . . . . . . . . . . . . . . . . . .

Canada . . . . . . . . . . . . . . . . . . . . .

Cape Verde . . . . . . . . . . . . . . . . .

Central African Republic. . . . . . .

Chad . . . . . . . . . . . . . . . . . . . . . . .

Chile . . . . . . . . . . . . . . . . . . . . . . .

China. . . . . . . . . . . . . . . . . . . . . . .

Colombia . . . . . . . . . . . . . . . . . . .

Comoros . . . . . . . . . . . . . . . . . . . .

Congo . . . . . . . . . . . . . . . . . . . . . .

Costa Rica . . . . . . . . . . . . . . . . . .

Cuba . . . . . . . . . . . . . . . . . . . . . . .

Cyprus . . . . . . . . . . . . . . . . . . . . .

Czechoslovakia . . . . . . . . . . . . . .

Democratic Yemen . . . . . . . . . . .

Denmark . . . . . . . . . . . . . . . . . . . .

Djibouti . . . . . . . . . . . . . . . . . . . . .

Dominica . . . . . . . . . . . . . . . . . . . .

Dominican Republic . . . . . . . . . .

Ecuador . . . . . . . . . . . . . . . . . . . .

Egypt . . . . . . . . . . . . . . . . . . . . . . .

EISalvador . . . . . . . . . . . . . . . . . .

Equatorial Guinea . . . . . . . . . . . .

Ethiopia . . . . . . . . . . . . . . . . . . . .

Fiji . . . . . . . . . . . . . . . . . . . . . . . . .

Finland . . . . . . . . . . . . . . . . . . . . .

France . . . . . . . . . . . . . . . . . . . . . .

x

x

c

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

c

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

D x

c

x x

x

x

x x

x x

x x

x

x

D x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x x

x

x

x

x

x x

x

x

x

x x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x x

x x

x x

x

x

x

x x

x x

x

x x x
212 . Biological Rhythms: Implications for the Worker

Table A-2—International Labor Organization Conventions Related to Night and Other Shift Work

and the Countries That Have Ratified Them-Continued

ILO conventiona

Country 1 14 20 30 47 79 89 90 108 153

Gabon . . . . . . . . . . . . . . . . . . . . . .

Germany. . . . . . . . . . . . . . . . . . . .

Ghana . . . . . . . . . . . . . . . . . . . . . .

Greece . . . . . . . . . . . . . . . . . . . . .

Grenada . . . . . . . . . . . . . . . . . . . .

Guatemala . . . . . . . . . . . . . . . . . .

Guinea . . . . . . . . . . . . . . . . . . . . .

Guinea-Bissau . . . . . . . . . . . . . . .

Guyana . . . . . . . . . . . . . . . . . . . . .

Haiti . . . . . . . . . . . . . . . . . . . . . . . .

Honduras . . . . . . . . . . . . . . . . . . .

Hungary . . . . . . . . . . . . . . . . . . . .

Iceland . . . . . . . . . . . . . . . . . . . . .

India . . . . . . . . . . . . . . . . . . . . . . .

Indonesia . . . . . . . . . . . . . . . . . . .

Iran . . . . . . . . . . . . . . . . . . . . . . . .

Iraq . . . . . . . . . . . . . . . . . . . . . . . .

Ireland . . . . . . . . . . . . . . . . . . . . . .

Israel . . . . . . . . . . . . . . . . . . . . . . .

Italy . . . . . . . . . . . . . . . . . . . . . . .

Ivory Coast . . . . . . . . . . . . . . . . .

Jamaica . . . . . . . . . . . . . . . . . . . .

Japan . . . . . . . . . . . . . . . . . . . . . .

Jordan . . . . . . . . . . . . . . . . . . . . . .

Kampuchea . . . . . . . . . . . . . . . . .

Kenya . . . . . . . . . . . . . . . . . . . . . .

Kuwait . . . . . . . . . . . . . . . . . . . . . .

Laos . . . . . . . . . . . . . . . . . . . . . . .

Lebanon . . . . . . . . . . . . . . . . . . . .

Lesotho . . . . . . . . . . . . . . . . . . . .

Liberia . . . . . . . . . . . . . . . . . . . . . .

Libya . . . . . . . . . . . . . . . . . . . . . . .

Luxembourg . . . . . . . . . . . . . . . .

Madagascar . . . . . . . . . . . . . . . . .

Malawi . . . . . . . . . . . . . . . . . . . . . .

Malaysia . . . . . . . . . . . . . . . . . . . .

Mali . . . . . . . . . . . . . . . . . . . . . . .

Malta . . . . . . . . . . . . . . . . . . . . . . .

Mauritania . . . . . . . . . . . . . . . . . .

Mauritius . . . . . . . . . . . . . . . . . . . .

Mexico . . . . . . . . . . . . . . . . . . . . .

Mongolia . . . . . . . . . . . . . . . . . . . .

Morocco . . . . . . . . . . . . . . . . . . . .

Mozambique . . . . . . . . . . . . . . . .

Namibia . . . . . . . . . . . . . . . . . . . . .

Nepal . . . . . . . . . . . . . . . . . . . . . . .

Netherlands . . . . . . . . . . . . . . . . .

New Zealand . . . . . . . . . . . . . . . .

Nicaragua . . . . . . . . . . . . . . . . . . .

Niger . . . . . . . . . . . . . . . . . . . . . .

Nigeria . . . . . . . . . . . . . . . . . . . . .

Norway . . . . . . . . . . . . . . . . . . . . .

Pakistan . . . . . . . . . . . . . . . . . . . .

Panama . . . . . . . . . . . . . . . . . . . .

Papua New Guinea . . . . . . . . . . .

Paraguay . . . . . . . . . . . . . . . . . . .

Peninsular Malaysia . . . . . . . . . .

Peru . . . . . . . . . . . . . . . . . . . . . . .

Philippines . . . . . . . . . . . . . . . . . .

Poland . . . . . . . . . . . . . . . . . . . . .

Portugal . . . . . . . . . . . . . . . . . . . .

x

x

x

x

x

x

x

x

c

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

D

x x

x x

x

x

x

x

D x

x

x x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

D

x

x

x

x

x

D

x

x

x

D

D

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x x

x

x

x

x

x

x

x x

x

x

x

x

x

x
Appendix A--International Regulation of Shift Work ● 213

ILO convention

Country 1 14 20 30 47 79 89 90 108 153

Qatar . . . . . . . . . . . . . . . . . . . . . . .

Romania . . . . . . . . . . . . . . . . . . . .

Rwanda . . . . . . . . . . . . . . . . . . . .

Sabah . . . . . . . . . . . . . . . . . . . . . .

St. Lucia . . . . . . . . . . . . . . . . . . . .

San Marina . . . . . . . . . . . . . . . . . .

Sao Tome and Principe . . . . . . . .

Sarawak . . . . . . . . . . . . . . . . . . . .

Saudi Arabia . . . . . . . . . . . . . . . . .

Senegal . . . . . . . . . . . . . . . . . . . .

Seychelles . . . . . . . . . . . . . . . . . .

Sierra Leone . . . . . . . . . . . . . . . . .

Singapore . . . . . . . . . . . . . . . . . .

Solomon Islands . . . . . . . . . . . . .

Somalia . . . . . . . . . . . . . . . . . . . . .

South Africa. . . . . . . . . . . . . . . . .

Soviet Union... . . . . . . . . . . . . . .

Spain . . . . . . . . . . . . . . . . . . . . . . .

Sri Lanka . . . . . . . . . . . . . . . . . . .

Sudan . . . . . . . . . . . . . . . . . . . . . .

Surinam . . . . . . . . . . . . . . . . . . . .

Swaziland . . . . . . . . . . . . . . . . . . .

Sweden . . . . . . . . . . . . . . . . . . . .

Switzerland . . . . . . . . . . . . . . . . .

Syria . . . . . . . . . . . . . . . . . . . . . . .

Tanganyika . . . . . . . . . . . . . . . . .

Tanzania . . . . . . . . . . . . . . . . . . .

Thailand . . . . . . . . . . . . . . . . . . . .

Togo . . . . . . . . . . . . . . . . . . . . . . .

Trinidad and Tobago . . . . . . . . . .

Tunisia . . . . . . . . . . . . . . . . . . . . .

Turkey . . . . . . . . . . . . . . . . . . . . . .

Uganda . . . . . . . . . . . . . . . . . . . . .

Ukranian SSR . . . . . . . . . . . . . . .

United Arab Emirates . . . . . . . . .

United Kingdom.. . . . . . . . . . . . .

United States.. . . . . . . . . . . . . . .

Uruguay . . . . . . . . . . . . . . . . . . . .

Venezuela . . . . . . . . . . . . . . . . . .

Viet Nam . . . . . . . . . . . . . . . . . . .

Yemen . . . . . . . . . . . . . . . . . . . . .

Yugoslavia . . . . . . . . . . . . . . . . . .

Zaire . . . . . . . . . . . . . . . . . . . . . . .

Zanzibar . . . . . . . . . . . . . . . . . . . .

Zambia . . . . . . . . . . . . . . . . . . . . .

Zimbabwe . . . . . . . . . . . . . . . . . . .

x

x

x

x

x

x

x

x x

x x

x

x

x

x

x

x

x x x

x

x

x

x x

D

x x

x x x

x x

x x x

x x

x

x x

x D

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x x x

x x

x

x x

x

x D

x D

x x

x

x x

x x

x

x

x x

x

x x

NOTE:X—Ratified.

C-Ratified conditionally.

D-Denounced.

a Convention

1—Hours of work(industry)

14-Weekly rest(industry)

20-Nightwork(bakery)

30-Hours of work(commerce and offices)

47-40-hour week

79-Nightwork of young persons (nonindustrial)

89-Nightwork(women)

90-Nightwork of young persons(industry)

106-Weekly rest(commerce and offices)

153-Hours of work and rest periods (road transportation)

Ratifications

48

104

16

16

8

16

62

41

52

6

1919

1921

1925

1930

1935

1946

1948

1948

1957

1979

SOURCE: Office of Technology Assessmen41991.
214 . Biological Rhythms: Implications for the Worker

work by women except in family enterprises, managerial

jobs, technical tasks, nonmanual health occupations, and

nonmanual welfare work. Other exemptions include when

an emergency arises, when night work is necessary to

prevent deterioration of materials, and when a government declares a suspension in consultation with employers’ and workers’ organizations. Night is to be defined by

each government, but it must be at least 11 hours long, 7

of which must fall between 10 p.m. and 7 a.m. As of

November 1987,62 countries had ratified convention 89;

73 nations were bound by one or more of the conventions

prohibiting women’s night work.

The protocol revising the prohibitions on night work

for women retains the present restriction but allows it to

be overridden by collective bargaining. In addition, the

mandatory n-hour rest period may be varied by legislation, after due consultation with workers’ and employers’

organizations. Work at least 8 weeks before childbirth,

and for a total of 16 weeks before and after childbirth, is

prohibited except under special circumstances.

Convention 171’s articles are as follows:

●

●

●

●

●

●

●

●

●

●

Night work will be any work performed during a

period of 7 or more hours, which includes the period

from midnight to 5 a.m.

A night worker will be a person whose job requires

night work exceeding an hours limit established by

competent authority following consultation with

representative organizations of employers and workers or by collective agreements.

The convention will apply to all workers, male and

female, except those in agriculture, stock raising,

fishing, maritime transport, and inland navigation.

A country may exclude certain categories of workers

if including them would cause substantial problems,

but it must first consult the employers’ and workers’

organizations.

A country must report such excluded categories to

the ILO, explain the reasons for exclusion, and

describe measures taken to progressively extend the

convention to the workers concerned.

Workers should have a right to free medical examination before starting the night work assignment and

at periodic intervals during it.

Workers should receive advice to facilitate their

adaptation to night work, especially in regard to

sleep, meals, and out-of-work activities.

Safeguards must be provided for persons who have

medical conditions that prevent them from engaging

in night work for a given period.

Measures shall be taken to provide alternatives to

night work for pregnant female workers for a period

of at least 16 weeks, 8 weeks of which must be

provided before the expected date of childbirth.

The maternity period may be extended for medical

reasons.

●

●

●

●

●

●

During maternity leave, the worker must be protected against dismissal or financial penalization.

Compensation in pay, benefits, and working time

must recognize the nature of night work.

Appropriate social services should be provided for

night workers.

Adequate first aid and emergency medical transportation must be available.

The provisions of the convention may be implemented by laws, regulations, collective agreements,

work rules, arbitration, court decisions, a combination of these methods, or other appropriate methods.

If the convention is implemented by laws or regulations, the employers’ and workers’ organizations

should be consulted.

In addition, recommendation 178 adopts the following

nonbinding propositions:

Night work should not exceed 8 hours per 24-hour

period.

Weekly hours for night workers generally should be

fewer than, and in any case should not exceed, the

weekly hours for day workers doing the same task.

A rest period of at least 11 hours should be

guaranteed between shifts whenever possible,

Overtime should be avoided for night workers.

In tasks involving special hazards or heavy mental or

physical strain, overtime should be prohibited except

in emergencies.

Double shifts should be prohibited except in emergencies.

Night workers must be granted rest and meal breaks.

The nature of night work’s demands must be taken

into account when designing the breaks.

Night workers should be paid appropriately, and men

and women should be paid equally for the same work

or work of equal value.

If night workers receive higher wages, those wages

should be used to calculate vacation pay, holiday

pay, other paid leave, social security contributions,

and benefits.

Where available, consultation with the occupational

health services in regard to the consequences of

various schedules for night work should be provided

to the workers’ and employers’ representatives.

Night workers’ commuting time should be minimized. This can be achieved by coordinating work

hours with public transportation services, providing

transport where public transport is unavailable,

helping workers obtain means of transport, and

building housing near the workplace.

Employers should compensate night workers for

extra transportation expenses involved in traveling

between work and home at night.

Rooms suitable for resting must be provided.
Appendix A--International Regulation of Shift Work ● 215

Facilities for meals must meet the special needs of

night workers.

Night workers should have a place to prepare or heat

and eat the food they have brought.

Where possible, employers should make appropriate

food and beverages available to night workers.

The extent to which night work is performed locally

should be considered when establishing nursery

facilities.

Night workers should be considered when public

authorities or employers are encouraging recreational, cultural, or sporting activities.

When composing night crews in shift work, consideration should be given to the needs of older workers,

workers with family duties, and workers in training.

Paid educational leave and training opportunities,

where available, should be arranged so that night

workers can take part.

After a certain number of years, night workers should

receive priority for openings on the day shift for

which they have the necessary qualifications, and

any required training for day work should be

provided.

Night workers should have priority for early retirement programs, where available.

Occupational safety at night should be equal to that

during the day.

Special attention should be given to toxic substances,

noise, poor lighting, and high levels of mental or

physical strain involved in night work. The effects of

these factors should be minimized.

Night workers who are trade union representatives

should have the same rights as their daytime

counterparts.

The workers’ representative should be consulted

regularly regarding the organization of night work as

it relates to personnel and to the undertaking.

Implementation of ILO conventions varies. Most

conventions are not self-executing, therefore each government must act to promulgate each convention. The

convention on general night work is likely to be implemented in a variety of ways (see the last two points of

convention 171).

The United States and the ILO

The United States has not approved many ILO conventions. As of July 1989, it had ratified nine, almost all of

which were maritime conventions. In fact, the United

States withdrew from the ILO between 1977 and 1980. A

combination of factors is responsible for the paucity of

ratifications, but one justification has been that the United

States already has sufficient protective legislation.

One factor to be considered when dealing with ILO

conventions is the expanding multinational role of U.S.

companies. In light of this trend, uniform labor standards

could be advantageous to American firms (2). However,

if the general night work convention passes in its

proposed form, the United States is unlikely to approve it.

The restriction on pregnant women (article 10) is unacceptably discriminatory in the United States(2), and some

of the provisions of the convention appear to be within the

jurisdiction of the States, not the Federal Government

(11).

Ratification rests ultimately with the U.S. Senate, but

the evaluation process is handled by the President’s

Commission on the ILO, headed by the Secretary of Labor

and composed of government, employers’, and workers’

representatives. Under this commission is the Tripartite

Advisory Panel on International Labor Standards, which

analyzes legal issues of the conventions and makes

recommendations to the committee. The present policy

regarding ILO conventions is that they will be ratified

only if every Federal and State law is already in

compliance with the convention in question (11).

Relevance of Foreign Regulations

A word of caution is in order about comparing data

from other countries with U.S. policies. In many countries, the system of worker-employer-government relationships is different from the U.S. system. In Japan, for

example, an agreement for limiting work is often based

not on hours, but on production (l). In other words, a

collective bargain in Japan could focus on the number of

cars to be produced rather than the maximum number of

hours to be worked. In Australia, wages and hours are set

by a system of mandatory court arbitration. In Soviet and

Eastern European countries, wages and hours are usually

set by the government. Data from foreign countries,

therefore, do not always fit into the framework of U.S.

labor. Nevertheless, the data are useful because the

physiological, psychological, and social problems faced

by night workers are similar everywhere, and it may be

instructive to examine the ways that other governments

have dealt with the issues of shift work.

1.

2.

3.

4.

Appendix A References

Anderson, M., economist, Economic Research Department, AFL-CIO, Washington, DC, personal cornmunication, August 1989.

Belt, B., Regional Administrator, Employment Standards Administration, U.S. Department of Labor, and

U.S. Government Delegate to the 1989 ILO Convention, personal communication, August 1989.

Blanpain, R. (cd.), International Encyclopedia for

Labour Law and Industrial Relations (Boston, MA:

Kluwer, 1982).

Carpenter, J., and Cazamian, P., Night Work, Its

Eflects on the Health and Welfare of the Worker

(Geneva: International Labor Organization, 1977).
216 ● Biological Rhythms: Implications for the Worker

5.

6.

7.

8.

International Labor Organization, Conditions of Work

Digest, vol. 5, No. 2 (Geneva: 1986). 9.

International Labor Organization,lnternationa2Labor

Conference, 76th Session 1989, Report V: Night 10.

Work, vol. 1 (Geneva: 1988).

International Labor Organization, Chart of Interna- 11.

tional Lubor Conventions (Geneva: 1989).

International Labor Organization, The Znternationd

Labor Organization: Serving the American Employ- 12.

em (Geneva: n.d.).

Jamal, M., “Shift Work Creates Unusual Problems,”

Personnel Journal, May 1989, p. 114.

Maurice, M., Shifl Work (Geneva: International

Labor Organization, 1975).

Misner, J., Bureau of International Labor Affairs,

U.S. Department of Labor, personal communication,

August 1989.

Radice v. New York, 264 U.S. 292 (1924).
Appendix B

Federal Research Activities

Research on biological rhythms in this country has

been directed primarily at the basic mechanisms underlying those rhythms. It has produced a marked increase in

our understanding of the biology and functions of

circadian rhythms over the past two decades, as reviewed

in chapter 3. However, little effort has been made to apply

these research findings to workplace issues, as reviewed

in chapter 5. While it is clear that many of the findings

from studies on animals can lead to identification of

problems of circadian function in humans, there is a need

for research aimed at identifying appropriate interventions to alleviate these problems, which affect the health,

safety, family welfare, and productivity of U.S. citizens.

The Federal Government is the principal supporter of

research on biological rhythms in this country. Its effort

is distributed among various departments, agencies, and

institutes, based upon their missions and priorities.

Department of Health and Human Services

National Institutes of Health

The National Institutes of Health (NIH) is the principal

Federal agency supporting biomedical research. In fiscal

year 1989, NIH funded 150 research projects focused

primarily on biological rhythms, according to a search of

the NIH’s Computer Retrieval of Information on Scientific Projects (CRISP) database. Almost all were competitive grants to investigators in public and private institutions; only five were conducted by the NIH. About 40

percent of the biological rhythm research was supported

by two institutes, the National Institute of Child Health

and Human Development and the National Institute of

Diabetes and Digestive and Kidney Diseases. Most of this

research deals with the cyclic production of hormones and

their influence upon reproductive functions and energy

metabolism. Eight other NIH institutes and divisions

funded the remaining 60 percent. Almost all of this

research supported by NIH deals with the physiological

bases of biological rhythms (primarily circadian rhythms)

and their manifestations in endocrine, metabolic, reproductive, or sleep-wake functions. Many of these projects

are aimed at delineating the neural circuitry that links the

light signal to the biological clock in the hypothalamus

(the suprachiasmatic nucleus) and to the neuroendocrine

mechanisms which regulate other organ systems. Approximately half of the projects involved human subjects. This

research should also lead to further understanding of other

problems of circadian dysfunction, such as disturbed

sleep, jet lag, and shift work. Only 5 of these 150 projects

are directly related to the effects of shift work, with total

expenditures of about $250,000. Individual research

projects averaged about $112,000, and NIH expenditures

on research primarily related to biological rhythms totaled

approximately $17 million. This was about 2.5 percent of

NIH’s total budget of $6.8 billion for fiscal year 1989.

Alcohol, Drug Abuse, and Mental Health

Administration

The Alcohol, Drug Abuse, and Mental Health Administration (ADAMHA) is also a major supporter of

biomedical research in this country. It had 46 projects on

biological rhythms in fiscal year 1989, according to a

CRISP search, most of them supported by the National

Institute of Mental Health. Much of this research deals

with the desynchronization and regulation of biological

rhythms in psychiatric states, primarily depression. Goals

of studies are not only to delineate the causes of these

disturbances, but also to develop effective treatments for

them. Other research is directed toward understanding the

basic neural structures, processes, and functions of the

circadian clock. Such efforts to elucidate the physiological mechanisms controlling normal and disordered

biological rhythms can lead to improved diagnosis and

treatment of the pathophysiological conditions associated

with circadian rhythms dysfunction. ADAMHA funded

39 extramural grants at a cost of about $4.6 million, or

about $117,000 per project.

Centers for Disease Control

National Institute for Occupational Safety and Health—

The National Institute for Occupational Safety and Health

is a component of the Centers for Disease Control. Its

mission is to conduct and support research related to

issues of occupational health and safety. Circadian

rhythm and related shift work research is presently being

conducted in one intramural laboratory, with funding of

about $100,000. Studies are being conducted on 12-hour

work schedules as well as means of promoting adaptation

to and coping with shift work (l).

National Science Foundation

The National Science Foundation (NSF) is an independent agency of the Federal Government established to

promote and advance science in the United States.

Research supported by NSF in the biological and social

sciences does not include clinical research, either in

human beings or in animal models of disease. Thus, the

research on circadian rhythms supported by the NSF is

basic research. In fiscal year 1990, NSF supported 24

grants totaling about $1.2 million of the $9.8 million

allocated to the biological, behavioral, and social sciences. These projects dealt with fundamental molecular

and cellular processes underlying biological rhythms

–217–
218 . Biological Rhythms: Implications for the Worker

across a number of species. While the results from these

studies will add to knowledge of the control of biological

and circadian rhythms, no NSF projects directly addressed biological rhythms in the workplace (13).

Department of Veterans Affairs

The Department of Veterans Affairs (VA) supports an

intramural research program related to its mission both

with its own funds and with funding from other granting

agencies. In fiscal year 1989, sleep disorders research

received about $800,000 in VA funds and $1.4 million

from other granting agencies. Within this program, four

projects related to circadian rhythms received about

$350,000. Only one of these projects focused directly on

the performance deficit associated with continuous operation and strategies for ameliorating it; the other

projects dealt primarily with the neural mechanisms of

sleep and sleep-related disorders. Total VA support of

research in fiscal year 1989 was $220 million (11).

National Transportation Safety Board

The National Transportation Safety Board (NTSB) is

an independent Federal accident investigation agency. Its

mission is to determine probable causes of transportation

accidents and to formulate recommendations to improve

transportation safety. It has investigated a number of

major transportation accidents in which fatigue, sleepiness, sleep disorders, and circadian factors were involved.

The NTSB does not have a research capability, aside from

its very important function of gathering accident data and

conducting special studies based on its investigative

experience, but it does develop agreements with other

Federal agencies when research is necessary (4).

Department of Transportation

Federal Highway Administration

The Federal Highway Administration (FHWA) supports research on highway safety in three general areas:

safety design, traffic safety research, and traffic systems.

The Traffic Systems Division is responsible for human

factors research. In fiscal year 1989 FHWA awarded a

$1.4-million contract entitled, “Fatigue and Driver Alertness Study. ” The objectives of this study are to: 1)

establish measurable relationships between commercial

motor vehicle driver activities and physiological and

psychological indicators of fatigue and reduced driver

alertness, and 2) identify and evaluate the effectiveness of

any alertness-enhancing measures that may legally be

used by commercial motor vehicle drivers. In fiscal year

1990, a companion $1.35-million contract, Physiological

Measurement of Commercial Motor Vehicle Drivers, was

awarded to the Trucking Research Institute (TRI) to

complement the project through development and implementation of additional methods for collection and

analysis of physiological data from the same group of

driver subjects. This contract is being funded jointly by

the FHWA and TRI (6).

Federal Aviation Administration

The Federal Aviation Administration’s (FAA) Civil

Aeromedical Institute conducts two kinds of research to

assess the performance of personnel in technical occupations. The first addresses individual performance, identifying factors such as workload and work schedules,

equipment design characteristics, and operational stressors that positively and negatively affect it. The second

type of research addresses system performance, evaluating the effectiveness and efficiency of agency recruitment, selection, and training programs for employees.

Specific research projects currently under way include: 1)

identification of the interactive effects of stressors such as

age, sleep loss, altitude, alcohol, and fatigue on performance, and 2) analysis of the effects of a 10-hour workday

and rotating shift schedules on measures of air traffic

controllers’ performance and attitudes (14).

The FAA is also engaged in cooperative research

efforts with the National Aeronautics and Space Administration. The FAA is providing $450,000 for three studies

in fiscal year 1991 examining alertness and controlled

napping, long-haul operations, and bunk rest for flight

crews (9).

Federal Railroad Administration

The Federal Railroad Administration (FRA) is currently sponsoring research into the effects of work-schedule-related disruptions of sleep and rest patterns on

fatigue and job performance. Most locomotive crews

work highly irregular and unpredictable schedules, resulting in sleep loss and circadian desynchronization.

The Volpe National Transportation Systems Center

(VNTSC), a part of the Department of Transportation’s

Research and Special Project Administration, has been

given tasks in two areas related to this problem. The first

task is to work with the railroad industry to develop

quantitative measures of work schedule irregularity in

various groups of workers and to explore new approaches

to scheduling in order to reduce problems. The second

task is to design and conduct experiments to quantify

degradation in train-handling performance and compliance with safety rules caused by sleep loss and circadian

desynchronization. In addition, the FRA and VNTSC

have an agreement with Transport Canada to study effects

of fatigue. Funding for FRA-sponsored projects for fiscal

1991 is approximately $400,000 (16).

U.S. Coast Guard and Maritime Administration

The Maritime Administration (MARAD) and the U.S.

Coast Guard are collaborating in sponsoring research into

a variety of issues, including scheduling of work and

sleep, related to fatigue in the merchant marine and their
Appendix B--Federal Research Activities .219

implications for safety. The VNTSC has recently completed a study of the potential impact on fatigue of

reductions in maritime crew size. Results indicate that a

major factor in fatigue is the concentration of work hours

required during port calls. Ships that make frequent port

calls, particularly those with irregular schedules, are

likely to cause sleep loss because of disruptions in

scheduling. The Coast Guard and MARAD are in the

process of planning further research into this problem.

Funding for the ship-manning programs, which sponsor

the maritime fatigue research, is on the order of $150,000

for fiscal year 1991 (16).

Department of the Interior

Bureau of Mines

For the past 6 years the Human Factors Group within

the Safety Research Division of the Bureau of Mines has

been committed to research activities on various work

schedules in the mining industry. This research has

principally been involved with factors that affect adjustment to work schedules and the effects of work schedules

on variables such as sleep quality and quantity, eating, and

physical and mental exhaustion. This project has received

approximately $150,000 per year and is funded through

fiscal year 1991 (5).

National Aeronautics and Space

Administration

Both the Life Sciences Division, Office of Space

Sciences Application, and the Information Sciences and

Human Factors Division, Office of Aeronautics, Exploration, and Technology, of the National Aeronautics and

Space Administration (NASA) support research. The Life

Sciences Division focuses on basic studies of biological

mechanisms in animal systems and on the effects that

extended time in space vehicles can have on biological

rhythms and human physiology. The Information Sciences and Human Factors Division supports research and

technology development for aeronautical problems in

cockpit crew fatigue, sleep, and circadian rhythms.

As shuttle crews engage in missions longer than a week

and planners look forward to missions lasting months,

issues of circadian rhythms have emerged as critical to

human performance. The Life Sciences Division sponsored a workshop in the summer of 1990 to develop a plan

for circadian rhythms research. Concurrently, the application of available knowledge about circadian cycles during

transmeridian flights in commercial aircraft has been the

subject of applied research and technology at NASA’s

Ames Research Center.

NASA spent some $2 million on circadian rhythm

research in fiscal year 1991. About half was for intramural

research and half for support of extramural research.

Extramural research proposals are received both as

297-935 - 91 - 8 QL 3

unsolicited applications and as responses to announcements. A recent announcement called for studies on

human sleep, fatigue, and performance for missions over

13 days long. Questions of interest include how factors in

space flight affect circadian rhythms and how to ameliorate any adverse effects. An example of this research is the

feasibility of using bright light exposure to facilitate

adaptation of astronauts to their work-rest schedules

during extended missions (15).

Over the last 8 years, the Flight Human Factors Branch

at Ames Research Center has conducted extensive field

studies to examine the issues of fatigue, sleep, and

circadian rhythms in flight crews. In some cases this

research has been part of a cooperative effort with the

FAA. The settings studied have included short and long

commercial and military operations, overnight cargo

operations, and helicopter operations. This work involved

the collection of continuous physiological data; selfassessments of fatigue and mood; and information on

sleep timing and quality, food and fluid intake, and the use

of medications, alcohol, and tobacco. Funding for aeronautical research in this domain amounted to about

$750,000 in fiscal year 1991 (8).

Department of Defense

Department of the Army

U.S. Army Research Institute for the Social and Behavioral Sciences--TheArmy Research Institute (USARI)

supports behavioral research in order to solve personnelrelated problems of substantial concern to the Army. As

part of a broad agency announcement issued in 1989 and

again in 1990, USARI solicited proposals for fundamental research in behavioral science. One area for study was

human chronopsychology--specifically, how interactions

of chronopsychological variables and characteristics of a task determine performance accuracy and

effectiveness. This program continues to be central to

USARI’s fiscal year 1991 research plans. One extramural

project has been started under this program to study

cognitive performance in relation to states of arousal and

time-of-day variables.

USARI also supports research on the effects of

continuous operations upon soldiers’ performance. (In

continuous operations, the military engagement is continuous but the demands upon the individual are not. This is

in contrast to sustained operations, in which the individual

has to perform throughout the operation.) Current research focuses upon the ability of soldiers to maintain

optimal effectiveness and endurance in chemical defense

situations for extended periods. How long can soldiers

perform effectively while wearing chemical defense suits

or being contained within tanks for up to 72 hours? What

work-rest schedules for tank crews would maintain their

ability to perform physical and cognitive tasks? Most of
220 ● Biological Rhythms: Implications for the Worker

this research is conducted as part of field exercises,

although there is some contract work, which is expected

to amount to about $175,000 in fiscal year 1991 (7).

Medical Research and Development Command—

Sleep research in the Medical Research and Development

Command is conducted through the Walter Reed Army

Institute of Research (WRAIR). Most of this research

program is intramural, with only one extramural project

now being supported, at a cost of about $1 million in fiscal

year 1989. The purpose of the program is to understand

the effects of sleep deprivation on performance in

situations of brief, fragmented sleep and extended duty

hours. Field studies as well as laboratory studies are being

conducted and have shown decrements in cognitive

functioning (i.e., ability to think, plan, and act) in persons

awake for up to 72 hours. Positron emission tomography

(PET) techniques are being used to answer questions

about brain activity during sleep. Intervention strategies,

primarily pharmacological ones, are being investigated.

For example, the use of caffeine to counter the effects of

60 hours without sleep and the use of hypnotic drugs to

enable a subject to sleep under conditions not conducive

to sleep (2,12,17).

The U.S. Army Research Institute of Environmental

Medicine (USARIEM) and the U.S. Army Aeromedical

Research Laboratory (USAARL) also examine issues

related to duty hours. The USARIEM evaluates the effects

of various environmental factors on performance and

develops appropriate strategies to reduce the adverse

effects of such conditions. In addition, USARIEM

conducts research and provides information upon which

to base Army policy and guidance on biomedical and

psychological factors limiting physical and mental performance. Since the work-rest cycle and timing of sleep

are critical factors in performance, they are often key

variables in research conducted at USARIEM. Laboratory

and field studies have examined circadian variations in

body temperature, cortisol, and spontaneous motor activity under various conditions related to military operations.

Operational models to predict and prevent occupational

stress by controlling the work-rest cycle have also been

developed and tested. Research and development on

appropriate nutritional, pharmacological, and behavioral

countermeasures are currently under way. Research in

this area was supported at a level of approximately

$400,000 for fiscal year 1990, and support for fiscal year

1991 will continue at that level (10). The USAARL

studies pilot fatigue and safety issues, including the

effects of long flights on helicopter pilots and field

assessments of work-rest cycles, activity levels, and

amounts of sleep obtained or lost by helicopter crews in

various special operations units. Sleep deprivation and

sleep stabilization and control experiments are conducted

on aircrews who fly at night, to assess pilot flight control

performance, cognitive performance, and decisionmaking, as well as the efficacy of drugs in controlling sleep

schedules during the day and slightly altering circadian

rhythms (10).

Department of the Air Force

Air Force Office of Scientific Research—The Air

Force Office of Scientific Research (AFOSR) supports

research on the basic neural mechanisms of circadian

rhythms. This research is conducted in a variety of

experimental systems, from cell cultures to invertebrates

to humans. The suprachiasmatic nucleus is of particular

interest in much of this research, with questions ranging

from the expression of gene-regulating factors and the

modulating effects of neuropeptides on these cells in

culture, to neurophysiological studies of photic (light)

entrainment of this region of the brain in rats, to the effects

of light and melatonin on the circadian rhythms of

humans. This research is supported by extramural grants

and intramural research at the U.S. Air Force’s Armstrong

Laboratory at Brooks Air Force Base; support totaled

about $1.5 million in fiscal year 1990 (3).

Department of the Navy

Office of Naval Research—The Office of Naval

Research (ONR) supports programs emphasizing the

creation and exploitation of a cumulative base of scientific knowledge from which new technologies can be

developed to improve the effectiveness of Navy and

Marine Corps personnel. There currently are no projects

relevant to sleep or circadian rhythms or their effects on

performance (18,20).

Navy Health Research Center—The Navy Health

Research Center, in San Diego, is conducting research on

sleep and circadian rhythms as they apply to activities and

performance of personnel on ships and field maneuvers.

These studies are documenting sleep profiles and circadian temperature rhythms during extended work and

rest cycles in both laboratory and field situations. They are

also investigating the use of pharmacological interventions and naps to improve performance under continuous

operations and extended duty. In fiscal year 1989, support

of these studies was about $510,000 (19).

1.

2.

3.

Appendix B References

Baker, T., Program Analyst, Office of the Director,

National Institute for Occupational Safety and

Health, Atlanta, GA, personal communication, Apr.

3, 1991.

Belenky, G., Walter Reed Army Institute of Research, testimony before the National Commission

on Sleep Disorders Research, Washington, DC, Sept.

25, 1990.

Berry, W., Directorate of Life Sciences, U.S. Air

Force Office of Scientific Research, Boiling Air
Appendix B--Federal Research Activities .221

Force Base, Washington, DC, personal communication, Feb. 7, 1991.

4. DanaheLJv National Transportation Safety Board,

testirnonybeforetheNationa.l Commission onSleep

Disorders Research, Washington, DC, Sept. 25,

1990.

5. Duchon, JvHuman Factors Research Program,U.S.

BureauofMines,Minneapolis,MN,personalcommunication, Feb. 21, 1991.

6. Eberhard, J., Federal Highway Administration, U.S.

Department of Transportation, Washington DC, personal communication, May 26, 1991.

7. Headley, D., U.S. Army Research Institute, Alexandria, VA, personal communication, Feb. 7, 1991.

8. Jenkins, J., Office of Aeronautics, Exploration, and

Technology, National Aeronautics and Space Administration, Washington, DC, personal communication,

Apr. 4, 1991.

9. Kayten, P., Deputy Scientific and Technical Advisor

for Human Factors, Federal Aviation Administration,

Washington, DC, personal communication, Mar. 28,

1991.

10. Krueger, G.P., U.S. Army Research Institute of

Environmental Medicine, Natic~ MA, personal cornmunication, March-April 1991.

11. Littner, M., Department of Veterans Affairs, Washington, DC, personal communication, Dec. 5, 1990.

12. Manning, F., Walter Reed Army Institute of Research, Washington, DC, personal communication,

Jan. 28, 1991.

13. Olsen, K., National Science Foundation, Washington, DC, personal communication, Dec. 5, 1990.

14. Shepherd, W.’ll, Manager, Biomedical and Behavioral Sciences Branch, Federal Aviation Administration, Washington, DC, personal communication,

Mar. 28, 1991.

15. Stoklosa, J., Biomedical Research Programs, National Aeronautics and Space Administration,

Washington, DC, personal communication, Feb. 7,

1991.

16. Sussman, E.D., Chief, Operator Performance and

Safety Analysis Division, Volpe National Transportation Systems Center, U.S. Department of Transportation, Cambridge, MA, personal communication,

Mar. 22, 1991.

17. U.S. Department of the Army, Walter Reed Army

Institute of Research, Annual Report (Washington,

DC: January 1990).

18. U.S. Department of the Navy, Office of Naval

Research, Cognitive and Neural Science Division

1989 Research Programs, OCNR 114289-22 (Washington, DC: July 1989).

19. Woody, J.N., National Naval Medical Center, Naval

Medical Research and Development Comman~

personnel communication, July 8, 1991.

20. Zornetzer, S., Office of NavalResearch, U.S. Department of the Navy, Washington, DC, personal communication, 1991.
Appendix C

Participants in the Workshop on

Shift Work and Extended Duty Hours

Chuck Anderson

Brotherhood of Locomotive Engineers

Cleveland, OH

John Baker

Monsanto Corp.

St. Louis, MO

Melena Barkman

United Steel Workers

Pittsburgh, PA

Mary Becker

The University of Chicago Law School

Chicago, IL

Charles Craver

George Washington University Law Center

Washington, DC

May 23, 1990

Office of Technology Assessment

U.S. Congress

Donald I. Tepas, Chairman

University of Connecticut, Storrs, CT

James Danaher

National Transportation Safety Board

Washington, DC

Curt Graeber

National Aeronautics and Space Administration

Moffet Field, CA

Vernon McDougall

International Brotherhood of Teamsters

Washington, DC

Martin Moore-Ede

Institute for Circadian Physiology

Boston, MA

Scott Nason

American Airlines

Dallas-Ft. Worth Airport, TX

Angela Presson

U.S. Department of Labor

Washington, DC

Lynn Rhinehart

Service Employees International Union

Washington, DC

Roger Rosa

National Institute of Occupational Safety and Health

Cincinnati, OH

Allene J. Scott

Navy Environmental Health Center

Norfolk, VA

Donald Sussman

U.S. Department of Transportation

Cambridge, MA

Marvin Waters

Weyerhaeuser Co.

Tacoma, WA

David Waugh

International Labor Office

Washington, DC

Frank White

Jones, Day, Reavis, and Pogue

Washington, DC

–222–
Appendix D

Acknowledgments

OTA would like to thank the members of the advisory panel who commented on drafts of this report, the contractors

who provided material for this assessment, and the many individuals and organizations that supplied information for the

study. In addition, OTA acknowledges the following individuals for their review of drafts of this report.

Chuck Anderson

Brotherhood of Locomotive Engineers

Cleveland, OH

John Baker

Monsanto Corp.

St. Louis, MO

Tom Balkin

Walter Reed Army Institute of Research

Washington, DC

Melena Barkman

United Steel Workers

Pittsburgh, PA

Bertrand M. Bell

Bronx Municipal Hospital Center

Bronx, NY

William O. Berry

Boiling Air Force Base

Washington, DC

Michael Bonnet

VA Hospital

Long Beach, CA

George C. Brainard

Jefferson Medical College

Philadelphia, PA

Robert J. Brandt

Chrysler Corp.

Highland Park, MI

Floyd J. Brinley, Jr.

National Institute of Neurological Diseases and Stroke

Bethesda, MD

Todd Brown

Association of American Railroads

Washington, DC

Kenneth Burke

Prince George’s Hospital Center

Cheverly, MD

Scott S. Campbell

New York Hospital-Cornell Medical Center

White Plains, NY

Leo Carey

Occupational Safety and Health Administration

Washington, DC

Charlotte Catz

National Institute of Child Health and

Human Development

Bethesda, MD

Benjamin Chu

Health and Hospitals Corp.

New York, NY

Carlos A. Comperatore

U.S. Army Aeromedical Research Laboratory

Fort Rucker, AL

Charles Craver

George Washington University Law Center

Washington, DC

Merle Cunningham

Health and Hospitals Corp.

New York, NY

E.C. Curtis

Westinghouse Electric Corp.

Pittsburgh, PA

James Danaher

National Transportation Safety Board

Washington, DC

Sarkis S. Derderian

Walter Reed Army Medical Center

Washington, DC

Margaret Dozark

Emerson Hospital

Needham, MA

James Duchon

Bureau of Mines

Minneapolis, MN

Charmane Eastman

Rush-Presbyterian-St. Luke’s Medical Center

Chicago, IL

Norman H. Edelman

University of Medicine and Dentistry of New Jersey

Piscataway, NJ

Jacqueline Eghrari

Children’s National Medical Center

Washington, DC

David Eisen

Newspaper Guild

Silver Spring, MD

297-935 - 91 - 9 QL 3

–223–
224 . Biological Rhythms: Implications for the Worker

Dana L. Elbein

American Hospital Association

Chicago, IL

Gary B. Ellis

Institute of Medicine

Washington, DC

Arnold Eskin

University of Houston

Houston, TX

Patrick J. Foley

DeParcq, Hunegs, Stone, Koenig& Reid, P.A.

Minneapolis, MN

Simon Folkard

University of Sheffield

United Kingdom

Clay Foushee

Federal Aviation Administration

Washington, DC

Barry Furrow

Widener University School of Law

Wilmington, DE

Philippa Gander

National Aeronautics and Space Administration

Moffet Field, CA

Alfred Gellhorn

New York State Department of Health

Albany, NY

John Gienapp

Accreditation Council for Graduate Medical Education

Chicago, IL

Andrew Gutow

Yale University Hospital

New Haven, CT

Jacqueline Hamilton

Einstein Hospital

Bronx, NY

Yolanda Hamilton-Augustus

Washington Hospital Center

Washington, DC

Janet Hammond

Office of Technology Assessment

Washington, DC

Ellen Herdman

The Washington Post

Washington, DC

Prudence Herdman

Seattle, WA

Michael Horan

National Heart, Lung, and Blood Institute

Bethesda, MD

William J.M. Hrushesky

VA Medical Center

Albany, NY

Michael P. Hudgins

U.S. Coast Guard Development

Washington, DC

Jehu C. Hunter

The Sudden Infant Death Syndrome Alliance

Washington, DC

James Jenkins

National Aeronautics and Space Administration

Washington, DC

Phyllis Kayten

Federal Aviation Administration

Washington, DC

Alonzo Keifer

Baltimore, MD

Maureen Knippen

National Center for Nursing Research

Bethesda, MD

K.H.E. Kroemer

Virginia Polytechnic Institute and State University

Blacksburg, VA

Gerald P. Krueger

U.S. Army Research Institute of Environmental Medicine

Natick, MA

Alexander C. Landsburg

Maritime Administration

Washington, DC

John Lauber

National Transportation Safety Board

Washington, DC

Lucia Lawrence

U.S. Department of Transportation

Washington, DC

Harris R. Lieberman

U.S. Army Research Institute of Environmental Medicine

Natick, MA

Michael Littner

VA Medical Center

Sepulveda, CA

Kevin Lurie

Georgetown University Hospital

Washington, DC

Thomas J. McDonagh

Exxon Corp.

Florham Park, NJ

Vernon McDougall

International Brotherhood of Teamsters

Washington, DC
Appendix D--Acknowledgments .225

K.D. McMurrain

Proctor & Gamble Co.

Cincinnati, OH

D.P. Malloy

E.I. du Pent de Nemours & Co., Inc.

Edge Moor, DE

Andrew Martin

Kenner, LA

Michael Menaker

University of Virginia

Charlottesville, VA

Russell L. Miller

Howard University

Washington, DC

Merrill M. Mitler

Scripps Clinic and Research Foundation

La Jolla, CA

Timothy Monk

University of Pittsburgh School of Medicine

Pittsburgh, PA

C. Hunter Montgomery

Exxon Corp.

Houston, TX

Robert Y. Moore

University of Pittsburgh

Pittsburgh, PA

Martin Moore-Ede

Institute for Circadian Physiology

Boston, MA

Delores Morisseau

U.S. Nuclear Regulatory Commission

Washington, DC

Debra J. Myers

St. Lukes-Roosevelt Hospital Center

New York, NY

Paul Naitoh

Naval Health Research Center

San Diego, CA

Scott Nason

American Airlines

Dallas-Ft. Worth Airport

Herbert R. Northrup

University of Pennsylvania

Haverford, PA

Janet L. Norwood

U.S. Department of Labor

Washington, DC

Phillip Olekszyk

Federal Railroad Administration

Washington, DC

J. Persensky

U.S. Nuclear Regulatory Commission

Washington, DC

Harriet Presser

University of Maryland

College Park MD

David Reeker

Office of Technology Assessment

Washington, DC

Lynn Rhinehart

Service Employees International Union

Washington, DC

Roger Rosa

National Institute of Occupational Safety and Health

Cincinnati, OH

Eduardo Ruan

District of Columbia General Hospital

Washington, DC

Barry J. Rubenstein

John Hancock Mutual Life Insurance Co.

Boston, MA

Benjamin Rusak

McMaster University

Ontario, Canada

Mark Schuster

Children’s Hospital

Boston, MA

Allene J. Scott

United States Uniformed Health Services

Rockville, MD

Thomas H. Seymour

Occupational Safety and Health Administration

Washington, DC

William T. Shepherd

Federal Aviation Administration

Washington, DC

Eugene B. Silverman

ARD Corp.

Columbia, MD

Ron Simard

Nuclear Management and Resources Council

Washington, DC

Helen Sing

Walter Reed Army Institute of Research

Washington, DC

Elizabeth Sommers

Greater New York Hospital Association

New York, NY

Everett Sparks

E.I. du Pent de Nemours & Co., Inc.

Wilmington, DE
226 . Biological Rhythms: Implications for the Worker

William F. Storm

Aerospace Medical Division

Brooks Air Force Base, TX

Frances Sundt

Georgetown University Hospital

Washington, DC

Donald Sussman

U.S. Department of Transportation

Cambridge, MA

August G. Swanson

Association of American Medical Colleges

Washington, DC

Donald I. Tepas

University of Connecticut

Storrs, CT

Michael Terman

New York State Psychiatric Institute

New York, NY

Maria Thomas

Walter Reed Army Institute of Research

Washington, DC

David R. Theme

Walter Reed Army Institute of Research

Washington, DC

Janet J. Turnage

ESSEX

Orlando, FL

Carl W. Tyler, Jr.

Centers for Disease Control

Atlanta, GA

Kirt Vener

National Institute of Allergy and Infectious Diseases

Bethesda, MD

James Walsh

Deaconess Hospital

St. Louis, MO

Marvin Waters

Weyerhaeuser Co.

Tacoma, WA

Robert M. White

Howard University Cancer Center

Washington, DC

Phyllis Windle

Office of Technology Assessment

Washington, DC

Richard J. Wurtman

Massachusetts Institute of Technology

Cambridge, MA

John Yoder

U.S. Department of Energy

Washington, DC

John z&Sky

AFL/CIO

Washington, DC
Appendix E

List of Contractor Documents

For this report, OTA commissioned six reports on various topics related to biological rhythms and shift work The

reports are available from the National Technical Information Service (NTIS) in Springfield, VA. For additional

information, call NTIS at (703) 487-4600.

. “Biological Rhythms and Human Performance,” S.S. Campbell, 1989 (NTIS No. PB 91215913).

● “Shift Work and the Worker,” T.H. Monk,1989 (NTIS No. PB 91215947).

. “Shift Work and Nursing,” C.S. Weisman, 1989 (NTIS No. PB 91215954).

● “Military Applications of Circadian Rhythm Principles,” K.S. Hull, Decision Science Consortium, Inc.,

1990 (NTIS No. PB 91215905).

● “Shift Work and Society: Demographics and Social Implications,” H.B. Presser, 1990 WS No. PB

91215939).

. “Legal and Regulatory Issues Related to Work Schedules and Hours of Work,” B.W. Mintz, 1991 (NTIS

No. PB 91215921).

–227–
Appendix F

Decade of the Brain

Public Law 101-58, 101st Congress

Joint Resolution

Whereas it is estimated that 50 million Americans are

affected each year by disorders and disabilities that

involve the brain, including the major mental illnesses;

inherited and degenerative diseases; stroke; epilepsy;

addictive disorders; injury resulting from prenatal events,

environmental neurotoxins, and trauma; and speech,

language, hearing, and other cognitive disorders;

Whereas it is estimated that treatment, rehabilitation

and related costs of disorders and disabilities that affect

the brain represents a total economic burden of $305

billion annually;

Whereas the people of the Nation should be aware of

the exciting research advances on the brain and of the

availability of effective treatment of disorders and disabilities that affect the brain;

Whereas a technological revolution occurring in the

brain sciences, resulting in such procedures as positron

emission tomography and magnetic resonance imaging,

permits clinical researchers to observe the living brain

noninvasively and in exquisite detail, to define brain

systems that are implicated in specific disorders and

disabilities, to study complex neuropeptides and behaviors as well as to begin to learn about the complex

structures underlying memory;

Whereas scientific information on the brain is amassing

at an enormous rate, and the field of computer and

information sciences has reached a level of sophistication

sufficient to handle neuroscience data in a manner that

would be maximally useful to both basic researchers and

clinicians dealing with brain function and dysfunction;

Whereas advances in mathematics, physics, computational science, and brain imaging technologies have

made possible the initiation of significant work in

imaging brain function and pathology, modeling neural

networks, and simulating their dynamic interactions;

Whereas comprehending the reality of the nervous

system is still on the frontier of technological innovation,

requiring a comprehensive effort to decipher how individual neurons, by their collective action, give rise to human

intelligence;

Whereas fundamental discoveries at the molecular and

cellular levels of the organization of the brain are

clarifyng the role of the brain in translating neurophysiologic events into behavior, thought, and emotion;

Whereas molecular biology and molecular genetics

have yielded strategies effective in preventing several

forms of severe mental retardation and are contributing to

promising breakthroughs in the study of inheritable

neurological disorders, such as Huntington’s disease, and

mental disorders, such as affective illnesses;

Whereas the capacity to map the biochemical circuitry

of neurotransmitters and neuromodulators will permit the

rational design of potent medications possessing minimal

adverse effects that will act on the discrete neurochemical

deficits associated with such disorders as Parkinson’s

disease, schizophrenia, and Alzheimer’s disease;

Whereas the incidence of necrologic, psychiatric,

psychological, and cognitive disorders and disabilities

experienced by older persons will increase in the future as

the number of older persons increases;

Whereas studies of the brain and central nervous

system will contribute not only to the relief of necrologic,

psychiatric, psychological, and cognitive disorders, but

also to the management of fertility and infertility,

cardiovascular disease, infectious and parasitic diseases,

developmental disabilities, and immunologic disorders,

as well as to an understanding of behavioral factors that

underlie the leading preventable causes of death in this

Nation;

Whereas the central nervous and immune systems are

both signaling systems which serve the entire organism,

are direct connections between the nervous and immune

system, and whereas studies of the modulatory effects of

each system on the other will enhance our understanding

of diseases as diverse as the major psychiatric disorders,

acquired immune deficiency syndrome, and autoimmune

disorders;

Whereas recent discoveries have led to fundamental

insights as to why people abuse drugs, how abused drugs

affect brain function leading to addiction, and how some

of these drugs cause permanent brain damage;

Whereas studies of the brain will contribute to the

development of new treatments that will curtail the

craving for drugs, break the addictive effects of drugs,

prevent the brain-mediated “high” caused by certain

abused drugs, and lessen the damage done to the

developing minds of babies, who are the innocent victims

of drug abuse;

Whereas treatment for persons with head injury,

developmental disabilities, speech, hearing, and other

cognitive dysfunctions is increasing in availability and

effectiveness;

–228–
Appendix F--Decade of the Brain .229

Whereas the study of the brain involves the multidisciplinary efforts of scientists from such diverse areas as

physiology, biochemistry, psychology, psychiatry, molecular biology, anatomy, medicine, genetics, and many

others working together toward the common goals of

better understanding the structure of the brain and how it

affects our development, health, and behavior;

Whereas the Nobel Prize for Medicine or Physiology

has been awarded to 15 neuroscientist within the past 25

years, an achievement that underscores the excitement

and productivity of the study of the brain and central

nervous system and its potential for contributing to the

health of humanity;

Whereas the people of the Nation should be concerned

with research into disorders and disabilities that affect the

Approved July 25,1989.

Legislative History-H.J. Res. 174 (S.J. Res. 173):

Congressional Record, vol. 135 (1989):

June 29, 1989, considered and passed House

July 13, 1989, considered and passed Senate

brain, and should recognize prevention and treatment of

such disorders and disabilities as a health priority;

Whereas the declaration of the Decade of the Brain will

focus needed government attention on research, treatment, and rehabilitation in this area: Now, therefore, be it

Resolved by the Senate and House of Representatives of

the United States of America in Congress Assembled, that

the decade beginning January 1, 1990, hereby is designated the “Decade of the Brain,” and the President of the

United States is authorized and requested to issue a

proclamation calling upon all public officials and the

people of the United States to observe such decade with

appropriate programs and activities.
Appendix G

Acronyms and Glossary of Terms

AAMC

ACGME

ADAMHA

AFOSR

BLS

CMSS

CPS

CRISP

DOT

EOWEO

EPI

FAA

FHWA

FLSA

FREIDA

FUDR

HSA

L.P.N.

MCSA

MSHA

NASA

NIOSH

NRC

NSF

NTSB

ONR

OSH Act

OSHA

OTA

PGY

POMS

PRC

QES

Acronyms

—Association of American Medical

Colleges

—Accreditation Council for Graduate

Medical Education

—Alcohol, Drug Abuse, and Mental

Health Administration

—Air Force Office of Scientific Research

—American Medical Association

—Bureau of Labor Statistics

—Council of Medical Specialty Societies

—Current Population Survey

—Computer Retrieval of Information on

Scientific Projects

—compressed workweek

—Department of Transportation

—every other weekend off

—Eysenck Personality Inventory

—Federal Aviation Administration

—Federal Highway Administration

—Fair Labor Standards Act, 128

—Federal Railroad Administration

—Fellowship in Residency Electronic

Interactive Database Access System

—5-fluoro-2deoxyuridine

—Hours of Service Act

—Labor-Management Relations Act

—licensed practical nurse

—Maritime Administration

—Motor Carrier Safety Act

—Mine Safety and Health Administration

—National Aeronautics and Space

Administration

—National Institutes of Health

—National Institute for Occupational

Safety and Health

—Nuclear Regulatory Commission

—National Science Foundation

—National Transportation Safety Board

—Office of Naval Research

—Occupational Safety and Health Act

—Occupational Safety and Health

Administration

—Office of Technology Assessment

—postgraduate year

—Profile of Mood States

—phase response curve

—Quality of Employment Survey

QUALPACS —Quality Patient Care Scale

REM —rapid eye movement

R.N.

RRC

SAD

SCN

SWS

USAARL

USARI

USARIEM

w

VA

VNTSC

—registered nurse

—Residency Review Committee

—seasonal affective disorder

—suprachiasmatic nucleus

—slow wave sleep

—U.S. Army Aeromedical Research

Laboratory

—U.S. Army Research Institute

—U.S. Army Institute of Environmental

Medicine

—ultraviolet

—Department of Veterans Affairs

—Volpe National Transportation

Systems Center

—Walter Reed Army Institute of

Research -

Glossary

Advanced sleep phase syndrome: A disorder in which

falling asleep and waking occur earlier than usual; it is

caused by diminished length and amplitude of the

circadian cycle. The syndrome is common among

elderly persons. Compare delayed sleep phase syndrome, non-24-hour sleep-wake disorder.

Amplitude: As it relates to circadian rhythms, the

difference between the maximum or minimum and

mean values of a function (e.g., body temperature)

during the circadian cycle. Amplitude provides a

measure of fluctuation within a cycle.

Attending physician: A physician who has completed all

phases of the medical education process and whose job

is teaching house staff. Compare house staff, resident.

Bargaining in good faith: Deliberation, discussion, or

conference concerning the terms of a proposed agreement in which both parties agree not to take any

unconscientious advantage of the other, even through

technicalities of law. See collective bargaining.

Benzodiazepines: A class of hypnotic drugs, including

Valium, under investigation for effects on circadian

rhythms.

Biological rhythm: Self-sustained, cyclic change in a

physiological process or behavioral function of an

organism that repeats at regular intervals. See circadian rhythm, infradian rhythm, ultradian rhythm.

Biorhythm: One of three postulated cycles that control

human behavior and performance; biorhythms have no

scientific basis.

Body clock: The internal mechanism of the body that

controls biological rhythms. See circadian pacemaker.

Bright light: As it relates to circadian rhythms, light with

an intensity of at least 2,500 lux, which is equivalent

to outdoor light at dawn. Bright light has been shown

-23&
Appendix G--Acronyms and Glossary of Terms .231

to shift circadian rhythms and has been used to treat

seasonal affective disorder, some sleep disorders, and

jet lag.

Chronobiology: The scientific study of the effect of time

on living systems, including the study of biological

rhythms.

Circadian clock: See circadian pacemaker.

Circadian cycle: The 24-hour interval between recurrences of a defined phase of a circadian rhythm. See

circadian rhythm.

Circadian pacemaker: An internal timekeeping mechanism capable of driving or coordinating circadian

rhythms. See circadian rhythm, suprachiasmatic nucleus.

Circadian rhythm: A self-sustained biological rhythm

which in an organism’s natural environment is normally synchronized to a 24-hour period. See biological

rhythm.

Circadian rhythm desynchronization: See circadian

rhythm disruption.

Circadian rhythm disruption: Disorganization among

an organism’s internal cycles or desynchrony between

self-generated rhythms and the 24-hour cycle in the

environment.

Clockwise shift rotation: A work schedule in which the

shifts move forward, from day to evening to night. See

rotating shift; compare counterclockwise shift rotation.

Collective bargaining: A procedure whereby an employer and accredited representatives of employees

bargain in good faith concerning wages, hours, and

other conditions of employment. See bargaining in

good faith.

Combat operations: Direct involvement in fighting.

Compare combat support.

Combat support: Provision of supply, communications,

or medical aid to fighting units. Compare combat

operations.

Common carrier: A transportation system that undertakes to carry all persons or goods as long as there is

room and there is no legal reason for refusal.

Compressed workweek: A schedule in which employees

work approximately 40 hours in fewer than 5 days.

Condition I Battle Readiness: The naval equivalent of

sustained operations; all systems on board a ship are

manned and operating, and no routine maintenance is

conducted. See sustained operations.

Condition II Battle Readiness: In the Navy, required

operational systems on board a ship are continuously

manned and operating, and only essential preventive

maintenance and support functions are carried out.

Continuous operations: A military situation requiring

around-the-clock manpower but not extended duty

hours for individuals. Compare sustained operations;

see extended duty hours.

Cortisol: A steroid hormone secreted by humans; cortisol

secretion exhibits a circadian rhythm and is used as a

marker for the body’s pacemaker.

Counterclockwise shift rotation: A work schedule in

which the shifts move backward, from night to evening

to day. See rotating shift; compare clockwise shift

rotation.

Current Population Survey: A survey of 55,000 to

60,000 sample households conducted monthly by the

Bureau of the Census for the Bureau of Labor

Statistics. Supplements to the survey have incorporated questions on shift work

Day shift: As defined in Current Population Surveys, a

period of work in which half or more of the hours

worked are between 8 a.m. and 4 p.m.

Delayed sleep phase syndrome: Abnormal delay of the

timing of sleep onset and waking, possibly caused by

either an abnormally long circadian cycle or a diminished responsiveness to environmental cues. The

disorder is most common among teenagers and young

adults. Compare advanced sleep phase syndrome,

non-24-hour sleep-wake disorder.

Deployment: Movement of a military unit to a strategically important location. Deployment can be routine

(planned and scheduled well in advance) or surge

(done on short notice).

Diurnal: Being active during the day.

Double shift: Two consecutive shifts worked in one

24-hour period.

Entraining agent: A factor that synchronizes an organism’s biological rhythms to the outside world; for

example, the light-dark cycle is an entraining agent for

circadian rhythms.

Environmental cue: A signal from outside an organism

that prompts it to some action.

Evening person: A general term used to describe an

individual who has difficulty waking up, is able to

sleep late in the morning, and finds it difficult to fall

asleep at night. Compare morning person.

Evening shift: As defined by the Current Population

Survey, a period of work in which half or more of the

hours worked are between 4 p.m. and midnight.

Extended duty hours: Long periods of work (usually

over 12 hours) that cause a worker to get less than usual

or no sleep.

Fatigue: Weariness caused by physical and mental

exertion.

Field study: In this report, an investigation in which a

researcher observes workers in their actual work

environment. Compare laboratory study, survey study.

Fixed shift: A work schedule in which the hours of work

remain the same from day to day. Compare rotating

shift, irregular shift.

Flextime: A system in which starting and stopping hours

of work are determined by the individual worker, with

a required number of total hours specified by the
232 . Biological Rhythms: Implications for the Worker

employer. Usually there is a daily core period when all

workers must be present.

Free-running rhythm: Circadian rhythm operating in

the absence of environmental cues; such rhythms may

be 20 to 28 hours in length. Under free-running

conditions, the human body clock has a circadian

rhythm of about 25 hours.

Full-time employment: A job consisting of 35 or more

hours of work per week. Compare part-time employment, shortened workweek.

General quarters: In the Navy, high-alert or combat

conditions at sea. See Condition I Battle Readiness.

Graduate Medical Education: Formal medical education, including substantial clinical experience, beyond the M.D. degree. See residency, resident.

House officer: See house staff.

House staff: Intern, resident physician, or fellow at a

teaching hospital. See resident.

Infradian rhythm: A biological rhythm with a cycle of

more than 24 hours; for example, the human menstrual

cycle. See biological rhythm; compare ultradian

rhythm.

Intern: A first-year resident physician. See resident.

Internal clock: See circadian pacemaker.

Internal desynchronization: Loss of synchronization

among rhythms within a single organism.

Irregular shift: A work schedule that is variable and

erratic. Compare fixed shift, rotating shift.

Jet lag: The malaise associated with travel across time

zones; it results from conflict between the traveler’s

internal clock and the external rhythms in the new time

zone.

Laboratory study: In this report, an investigation in

which the researcher attempts to simulate the

workplace in a controlled environment. Compare field

Study, SUrVey study.

Longitudinal study: Analysis of a function in the same

experimental subjects over a period of time; especially

useful in determining effects that vary widely among

individuals.

Maximum allowable flight duty period: The maximum

number of hours an Air Force crew can fly in a certain

type of aircraft in a 24-hour period.

Melatonin: A hormone produced by the pineal gland,

which is present in many animals, including humans.

Melatonin secretion is circadian, and production is

readily inhibited by light. Melatonin is being investigated as a possible circadian entraining agent in

humans. See entraining agent.

Microsleep: Brief episode of sleep experienced by a

person who is so tired that he or she cannot resist sleep.

Moonlighting: Holding more than one job.

Morning person: A general term used to describe an

individual who wakes up easily, has difficulty sleeping

late, and falls asleep quickly at night. Compare evening

person.

Neuron: A nerve cell, the basic functional unit of the

nervous system.

Neurotransmitter: Specialized chemical messenger synthesized and released by neurons to communicate with

other nerve cells.

Night float: A shift of physicians sent in at approximately

10 p.m. to relieve residents who have worked all day

and evening.

Night shift: As defined in the Current Population Survey,

a period of work in which half or more of the hours

worked are between midnight and 8 a.m.

Night shift paralysis: A rare condition marked by

short-term paralysis, usually lasting about 2 minutes,

during which individuals are aware of their surroundings but are unable to move; it is associated with

extreme sleep deprivation.

Nocturnal: Being active at night.

Nonflight support: Airfield operations, aircraft repair,

communications, and other activities in support of Air

Force flight units. Compare tactical forces, transport

forces.

Non-REM sleep: The four stages of sleep during which

the sleeper does not experience rapid eye movement

(REM) sleep. See slow wave sleep, rapid eye movement (REM) sleep.

Nonstandard work schedule: See shift work.

Non-24-hour sleep-wake disorder: The condition of

going to sleep and waking up at progressively later

times, possibly caused by the inability to perceive

light-dark cycles. The disorder appears to be prevalent

among blind persons. Compare advanced sleep phase

syndrome, delayed sleep phase syndrome.

Notice: Information, advice, or written warning intended

to notify a person of some proceeding in which his or

her interests are involved or informing him or her of

some fact that it is his or her right to know and that is

the duty of the notifying party to communicate.

Opposed landing: In the Marines, coming ashore against

armed opposition; opposed landings involve a very

intense period of sustained operations, changing to

continuous operations. See continuous operations,

sustained operations.

Overtime: Time worked at one job in excess of 40 hours

per week. Overtime may be required or voluntary.

Part-time employment: A job consisting of fewer than

35 hours of work per week. Compare full-time

employment, shortened workweek, shared time.

Per gene: A hereditary unit in the fruit fly (Drosophila

melanogaster) that appears to regulate the organism’s

circadian rhythms.

Phase response curve: Direction and amount of shifting

of an organism’s circadian rhythms plotted in response

to an environmental cue, such as light. See phase shift.

Phase shift: The resetting of an organism’s internal clock

in response to an entraining agent. The organism’s

circadian rhythms may be advanced, delayed, or not
Appendix G--Acronyms and Glossary of Terms ● 233

shifted at all, depending on the timing of exposure. See

entraining agent.

Pineal gland: A small structure in the brain that produces

the hormone melatonin. It is responsive to light and in

some species, such as birds, it is the circadian

pacemaker.

Rapid eye movement (REM) sleep: Stage of sleep

during which the eyes move rapidly, brain activity

resembles that observed during wakefulness, heart rate

and respiration increase and become erratic, and vivid

dreams are frequent. REM sleep alternates with

non-REM sleep in cycles lasting 90 to 100 minutes.

Compare slow wave sleep.

Registered nurse (R.N.): A person who has received a

baccalaureate degree in nursing.

Reinforcement: Sending more personnel and equipment

to units already deployed. See deployment.

Relocation: Transporting a military unit to another

location. Compare deployment.

Residency: Training program in a medical or surgical

specialty for postgraduate M.D.s. Residencies generally last from 3 to 7 years, depending on the specialty.

See graduate medical education.

Resident, resident physician: A postgraduate (postM.D.) medical trainee in a medical or surgical specialty.

Rotating shift: Work in which the hours change regularly, for example from a day to an evening to a night

shift. Rotation may be rapid (e.g., 3 days), mid length

(e.g., 1 week), or long (e.g., 4 weeks); it may proceed

forward, as noted above, or backward (day to night to

evening). Compare fixed shift, irregular shift.

Routine operations: See continuous operations.

Rulemaking: The procedure that allows administrative

government agencies to promulgate rules to implement, interpret, or prescribe law or policy, or to

describe the organization, procedure, or practice requirements of an agency.

Seasonal affective disorder (SAD): Recurring autumn or

winter depression that may be helped by treatment

with bright light. Although SAD has not been proved

to be a circadian rhythm disorder, it has been

hypothesized that changes in circadian rhythms cause

the disorder.

Shared time: A work schedule in which two persons

share one full-time job.

Shift maladaptation syndrome: A combination of

ailments arising from the inability of some workers to

adjust to long-term shift work.

Shift work: As used in this report, any nonstandard work

schedule (including evening or night shifts, rotating

shifts, split shifts, and extended duty hours) in which

most of the hours worked are outside the period

between 8 a.m. and 4 p.m. See day shift, evening shift,

night shift, rotating shift, split shift, extended duty

hours.

Shift worker: A person who works a nonstandard

schedule. See shift work.

Shortened workweek: A schedule of full-time employment that entails 35 or fewer hours of work per

week.

Sleep debt: The state of chronic fatigue and sleepiness

that results from the lack of sufficient sleep or

disrupted sleep. See fatigue, sleep deprivation.

Sleep deprivation: Lack of sufficient sleep. Compare

fatigue.

Slow wave sleep: The stages of sleep during which the

eyes do not move, heart rate and respiration are slow

and steady, muscles show little movement, and dreams

are infrequent. Compare rapid eye movement (REM)

sleep.

Special operations: Military operations, such as search

and rescue missions and counterterrorism activities,

which take place as the need arises, are often classified,

and often require the rapid deployment of personnel.

Split shift: A schedule of full-time work in which a period

of work is followed by a break and then another period

of work.

Standard work schedule: See day shift.

Standing watch: In the Navy, working a shift. See watch.

Strategic forces: Air Force units that man nuclear

bombers and missile silos.

Stressor: A source of stress; as used in this report,

disruption of circadian rhythms, fatigue and disruption

of sleep, and social and domestic disturbances caused

by shift work.

Subjective day: The portion of an organism’s internal

cycle that normally occurs during the day.

Subjective night: The portion of an organism’s internal

cycle that normally occurs during the night.

Suprachiasmatic nucleus: A region of the brain of

mammals that acts as an organism’s primary circadian

pacemaker, controlling or coordinating its circadian

rhythms. See circadian pacemaker.

Surge operations: Military activities carried out under

conditions requiring speed. See sustained operations.

Survey study: In this report, an investigation in which the

researcher asks the worker questions and elicits

answers, usually in one or two interviews or classroomlike sessions. Survey studies are often conducted

before and after an intervention in order to gauge its

impact. Compare field study, laboratory study.

Sustained operations: A military situation requiring

individuals to work extended duty hours, i.e., longer

than 12 hours. Combat and high-alert operations are

generally sustained. Compare continuous operations;

see extended duty “hours.

Tactical forces: Air Force units that engage in combat

and often support land warfare. Compare transport

forces.

Transmeridian flight: Travel across time zones. See jet

lag.
234 . Biological Rhythms: Implications for the Worker

Transport forces: Air Force units that fly personnel and Watch: In the Navy, a work shift. Watches are frequently

materiel from location to location. Compare tactical scheduled on a rotating basis. See rotating shift.

forces. Weekend shift: A work schedule in which a separate

Ultradian rhythm: A biological rhythm with a cycle of work force is used to work 12 hours per day, 2 days per

less that 24 hours; human sleep cycles and the release week

of some hormones are examples. See biological

rhythm; compare infradian rhythm.

Index

absenteeism, 13,81, 160

accidents

compressed workweek and, 13, 81

data sources on, 18, 100-101

employer liability for, 130-131

nuclear powerplant, 102, 143, 150

by nurses, 155

see also injuries; safety; traffic accidents

Accreditation Council for Graduate Medical Education, 21,173,

170-171, 176

activity, see physical activity

Adamson Act, 124

adenocarcinoma, 43

administrative work, 13, 81

overtime compensation, 83

shift work, 11

adriamycin, 43

afternoon shifts, 99

age/aging

and adjustment to shift work, 7, 50, 89, 95

and body temperate, 49

of children, and shift work by parents, 79

and circadian rhythms, 92

and health, 95

and hormone secretion, 49

and internal clock, 49-51,58

and physical activity, 49

and shift work, 11, 12,76,77

and sleep habits, 7,49,95

agitation, 57

Agriculture, shift work regulation in, 199,207

Air Force operations, see U.S. Air Force

air traffic controllers, 88,93, 126, 127

air transportation/travel

accident data, 101, 102

cockpit simulators, 88

direction of, 48; see also jet lag

overtime provisions, 128

see also civil air safety; flight crews

Alcohol, Drug Abuse, and Mental Health Administration,

research activities, 217

alertness, 5,47,49,50

fitness and, 112

measures of, 88, 111

nighttime, 110, 112

shift duration and, 106, 146, 161

sleep disorders and, 51

stimulant drugs and, 110

alertness-sleepiness cycles, 44

Algeria, shift work regulation in, 209,211

allergies, 43

American Board of Medical Specialties, 170, 173

American Federation of State, County and Municipal

Employees, 155

American Federation of Teachers, 155

American Hospital Association, 170

American Medical Association, 170, 173

American Nurses Association, 155

amnesia, 110

amphetamines, 110

Angola, shift work regulation in, 199,209,211

anticancer drugs, timing of administration, 43

antidepressant drugs, 52

antihistamines, 17, 110

anxiety, 57, 110, 165, 178

Area and Industry Wage Surveys, 71

Argentina, shift work regulation in, 200,207,208,209.211

Army operations, see US. Army

,

Association of American Medical Colleges, 167, 170, 173

asthma, 41,43,44, 97

astronauts, and bright light, 108

attention span, 48, 149

Australia, shift work regulation in, 200,207,209,210,211, 215

Austria, shift work regulation in, 199,200,207,208,209, 211

Automated Performance Test System, 111

Barbados, shift work regulation in, 210,211

behavior

aging and, 7

sleep and, 45

Belgium, shift work regulation in, 200,207,211

benzodiazepines, 8,56-57,58, 109-110

Berne Convention, 209

biological rhythms

adjustment of, 30

biorhythms distinguished from, 3,30

cycles, 3, 30

data collection of effects of work schedules, 33

defined, 3,29

disruption by work schedules, 3, 32; see also disruption of

circadian rhythms

entraining factors, 30

infradian, 5,44

purpose, 4,29

Ultradian, 5,44

and workplace, 31-32

see also circadian rhythms

biorhythms, distinguished from biological rhythms, 3,30

birds, circadian pacemaker, 55

bladder cancer, 43

blind persons

melatonin and sleep-wake cycles in, 56

non-24-hour sleep-wake disorder, 51

blood cell functions, 45

blood Pressure, 44

blood tests, 43

blood volume, 44

body clock, see internal clock

body temperature

adjustment after transmeridian flight, 48

aging and, 49

amplitude, 95

and circadian rhythms, 8,31,40,41,49,88

control center, 41

depression and, 52

and human performance, 6,47,98, 100

–237–
238 ● Biological Rhythms: Implications for the Worker

light and, 8, 109

night ShiftS and, 90

and rotating shifts, 14,91

and sleep, 14,38,45,46

and tolerance of shift work, 95

Bolivia, shift work regulation in, 199,200,207,209,211

brain

depression and chemical secretion in, 52

differences during stages of sleep, 45

pacemaker for circadian rhythms, 4, 40-41; see also internal

clock

Brazil, shift work regulation in, 200,207,211

bread mold, circadian rhythm in, 39

breast cancer surgery, 5,44

brotizolam, 109-110

Bulgaria, shift work regulation in, 199,201,209,211

Bureau of the Census, 69

Bureau of Labor Statistics, 18,22,33,69,71,80-81, 100

Bureau of Mines, research activities, 219

Bureau of National Affairs, 137

c-fos gene, 40, 41

caffeine, 17,97, 110

California

Agricultural Labor Relations Act, 137

residents’ work hours in, 171

Canada, shift work regulation in, 199,201,209,210,211

Cape Verde, shift work regulation in, 209,211

carbachol, 57

cardiovascular disease, 16,96-97

cardiovascular function, circadian rhythms in, 44

case studies, see military operations; nuclear powerplant control

room operators; nursing shift work; residents/residencies

catecholamines, 57

cellular clocks, 38-40

Center for Demography and Ecology, 9,70

Center for Human Resource Research, 70,71

Centers for Disease Control, research activities, 217

chemical manufacturing industries, 6, 13, 81, 101, 106

child care, shift work and, 11-12,70,76,78-79,94

child labor, regulation of, 18, 128-129, 130, 136

childbirth, 41,55

children, see married couples with children

Chile, shift work regulation in, 203,211

China, shift work regulation in, 199,201,211

chronobiology, and mood disorders, 51-53

chronopharmacology, 43

circadian rhythms, 30-31

brain pacemaker, 5,37, 40-41; see also internal clock

cellular clocks, 38-40

definition, 4-5,58

and diagnosis of medical problems, 41

in flight crews, 88

free-running, 38

genetic control of, 4,39,58

and health, 41

length of cycle, 5-6,30,37,45

meal anticipation, 41

and medical intervention, 5,41

phase response curves, 7,37-38,39,54

in physiological functions, 4-6, 31,40,42-45

properties, 37-38

in psychological functions, 4,6

research needs, 112-113

synchronized, 38,58

see also disruption of circadian rhythms; human circadian

rhythms

cisplatin, 43

civil air safety

enforcement of, 127

international flight crew problems, 48

work schedule limitations, 126-127

Civil Rights Act, 209

clerical workers, shift work by, 10-11, 13,69,74,76,81

cognitive performance, 31,48,98, 100, 111, 166, 176-177, 187

collective bargaining agreements

for government employees, 139

international, 199, 207, 210, 214

work schedule regulation, 4, 19, 124, 134, 136, 137, 155-156

Colombia, shift work regulation in, 201,207,211

Committee of Interns and Residents, 167

compensatory time, 139

compressed workweek

advantages and disadvantages, 13,81,82

effects of laws and regulations on, 13, 79

employment sectors using, 13, 81

for Federal employees, 138-139

and health, 106

and moonlighting, 13, 81

and patient satisfaction with care, 161

performance and safety concerns, 13,81,82,106

schedule, 13, 81

computer operations, 11, 81

conductors, 123

Connecticut

Labor Relations Act, 137

residents’ work hours in, 171

construction

continuous-operation projects, 32

overtime compensation, 83

prevalence of shift work in, 3, 11,74

coronary heart disease, 44

cortisol secretion

aging and, 49

purpose of, 43

and sleep, 38

Costa Rica, shift work regulation in, 209,211

Council of Medical Specialty Societies, 170, 173

criminal actions and penalties, 128

Current Population Survey

comparability of data, 71-72

definition, 69,70

job characteristics of female shift workers, 77

overtime data, 83

personal characteristics of shift workers, 76

shift work prevalence data, 8,71,73,76

Czechoslovakia, shift work regulation in, 201,207,208,209,

211

day shift, defined, 71

de Mairan, Jacques d’Ortous, 31

decisionmaking, 100, 176, 187

demographics of shift work, 69-78

Denmark, shift work regulation in, 201,209,211
Index ● 239

Department of Defense, research activities, 33, 112,219-220

Department of Health and Human Services, research activities,

217

Department of the Interior, research activities, 219

Department of Labor, regulation of working conditions, 18,32,

128, 130

Department of Transportation

data on accidents and incidents, 101

regulation of work schedules, 19, 123, 125, 126, 134, 135

research activities, 33, 218-219

safety research, 103

Department of Veterans Affairs, research activities, 218

depression, nonseasonal, 7-8,52-53,57,97, 110, 178

diabetes, 97

diet

controlling circadian rhythms in humans with, 57, 58

and jet lag, 48, 57

digestive disorders, see gastrointestinal problems

disruption of circadian rhythms

adjustment flexibility, 6,89,95

aging and, 49-51,92

compounding factors, 5, 15, 29, 87

and fatigue, 15, 92

and health, 15,49,92,95

military operations and, 21,22, 185, 187, 188, 191

and mood disorders, 51-53

nature of task and, 97-98,99-100, 102, 187, 191

and performance, 5, 15,49,92,98

and safety, 100, 101, 160

and sleep disorders, 5,7,49,51,92

work schedules and, 5, 13, 15, 87, 89-92, 107

diurnal organisms, 29

divorce, shift work and, 94, 177-178

Dominican Republic, shift work regulation in, 199,201,211

doxorubicin, 43

dual-earner couples

prevalence of shift work, 11,82

reasons for shift work, 78-79,94

work schedules of, 77-78

dreaming, 5,44,45

Drosophila melanogaster, 39

eating and drinking establishments, shift workers in, 10, 11,76,

77

eating habits, shift work and, 96,97, 162, 208

Ecuador, shift work regulation in, 201,207,211

education of workers, on effects of shift work, 18, 111-112

employment sector

shift workers by, 72-76

see also specific sectors

Energy Reorganization and Development Act, 19, 128, 135

entertainment industries, shift work in, 10, 73, 75, 76

Equal Employment Opportunity Commission, 209

errors

nursing shift work and, 160

vigilance and, 147-148

Ethiopia, shift work regulation in, 209,211

evening person, 95, 165

evening shifts, 32

defined, 71

demographic profile of workers, 11, 12,76,77

by occupation, 11-12,74-75,77

performance on, 100

prevalence, 9, 10

extended duty hours

and circadian disruption, 13, 15

defined, 3,32,87

double shifts, 147,208

effects on residents, 92, 176-178

and family and social life, 177-178

and fatigue, 17,87,89,92,101-102, 106,

and graduate medical education programs

international regulation of, 207-208

and napping, 107

and overtime, 87

and patient satisfaction with care, 161

and performance, 100, 106, 147

46,168, 87,188

166-178

regulation of, 79, 87; see also hours of service

and safety, 101-102, 106

and sleep loss, 17,21, 87, 89, 100, 101-102, 106, 155, 176,

185, 187, 188

stimulant drugs and, 110

in transportation sector, 72-73, 101-102

see also overtime

Exxon Valdez grounding, 102, 103

eye, circadian rhythm generation, 41, 50

Eysenck Personality Inventory, 165

Fair Labor Standards Act

applicability to government workers, 138-139

child labor provisions, 18, 128-129, 136, 139

equal pay for equal work, 128

exemption from requirements, 128

8-hour day, 129

40-hour workweek, 3,32,79, 129

jobs not covered by, 83

minimum wage, 18, 128, 129

overtime provisions, 18, 124, 128, 129-130, 136, 139

family attitudes and behavior, shift work and, 71

family life/responsibilities

compressed workweek and, 13, 81

employed persons with children, 71

measures of, 88

nursing shift work and, 162, 166

and psychological stress, 96

residents’ extended duty hours and, 177-178

and safety, 100

shift work and, 32,78, 82, 87, 93-94,96, 105

and sleep disruption, 93, 104, 162

of women shift workers, 94

fatigue, 32,87,97

aging and, 50

circadian disruption and, 16,92

compressed workweek and, 13,81, 82, 106

defined, 87

drugs to counteract, 109-110

environmental factors in, 149

extended duty hours and, 17, 87,89,92, 101-102, 106, 146,

168, 187, 188

fitness and, 112

and human p erformance, 48,58,98, 100, 112, 187

and injuries, 160, 166, 168

interventions, 145, 148

night Shifts and, 13, 81, 92
240 ● Biological Rhythms: Implications for the Worker

psychological state and, 165

research on, 88

rotating shifts and, 13, 81, 105, 106, 161

and safety, 101, 103

sleep disruption and, 51,92-93

sleep duration and, 94

stimulant drugs and, 110, 111

task performance time and, 187

Faverty v. McDonald’s Restaurants of Oregon, Inc., 131

Federal Aviation Act, 126, 127, 134

Federal Aviation Administration, 32

hours of service regulations, 18, 123, 126, 127, 134

research activities, 218

Federal Claims Collection Act, 124

Federal Government

employee working conditions, 11, 138-139

labor relations statutes, 136-137

preemption of State regulations, 131, 137-138

prevalence of shift work in, 75

regulation of working conditions, 4,32-33, 123-130

research activities, 217-219

see also specific departments and agencies

Federal Highway Administration, 32

enforcement of Motor Carrier Safety Act, 126, 134

Hours of Service of Drivers regulations, 18, 125

Office of Motor Carriers, 125

research activities, 218

Federal Labor Relations Authority, 139

Federal Railroad Administration

hours of service regulation, 18.123-125

research activities, 218

Federal Railroad Safety Act, 134

Federation of Nurses and Health Professionals, 155

Fellowship in Residency Electronic Interactive Database Access

System, 173

fertility

melatonin and, 55

shift work and, 70

Finland, shift work regulation in, 199,202,207,208,210, 211

firefighters

railroad, 1 2 3

see also protective services

fitness

and adjustment to shift work, 112

and sleep loss, 187

see also physical activity

fixed shifts

and body temperature, 90

characteristics of workers, 77

and circadian rhythm disruption, 90, 92, 104

defined, 87

and divorce and separations, 94

and effects of sleep loss, 93

and family and social problems, 94-95

and health, 162-164, 165

and job performance, 99, 160

occupations of workers, 77-78

panel mill example, 80

and sleep patterns, 90,92,94, 104

see also night shifts

flextime, 138

Fliess, Wilhelm, 30

flight crews

circadian rhythms in, 88,89

fatigue and performance, 187

hours of service regulations, 126-127, 134-135

international, schedules, 48,75

jet lag in, 92

napping during slack periods, 107, 110

sleep duration and fatigue in, 94

flowers, biological rhythms, 29,32

5-fluoro-2-deoxyuridine, 43

food intake, 41; see also eating habits

France

field studies of work schedules, 88

shift work regulation in, 199,202,208,210,211

frq gene, 39

fruit fly, 39

gastrointestinal problems

circadian desynchronization and, 92,96,97

jet lag and, 48

nursing shift work and, 162, 165

rotating shifts and, 208

stimulant drugs and, 110

work-related stressors and, 16

gender

and differences in regulation of shift work, 131

and shift work prevalence, 11, 12,76,77,79,82

and stress in medical residents, 177

genes, for circadian rhythms, 39-40

German

field studies of work schedules, 88

shift work regulation in, 202,207,208, 209,210,212

Ghana, shift work regulation in, 209,212

glucose, 43

Gompers, Samuel, 129

graduate medical education programs

current status of, 170

extended duty hours and, 166-178

Libby Zion case, 168-170

see also residents/residencies

graveyard shift, 29; see also night shift

Greece, shift work regulation in, 199,202.207,208,209, 212

growth hormone, 42

Guyana, shift work regulation in, 209,212

hamsters

circadian rhythms in, 39

phase-shifting effects of benzodiazepine, 56-57, 110

suprachiasmatic nucleus, 40,41

Hawaii, residents’ work hours in, 171

health

and circadian rhythms, 41,44,49,58,208

compliance with health and medication regimens, 97

diagnosis of medical problems, 41,43

duration of shift and, 106

extended duty hours, 87

nursing shift work and, 161-166

timing of medical interventions, 5, 8,41,44

timing of sleep and, 107

work-related stressors and, 32,96-97,98

health professions, see graduate medical education; nursing shift

work; residents/residencies
Index 241

health services

characteristics of workers, 78

compressed workweek, 13, 81

continuous-operation, 32

medical examination of shift workers, 208

shift work in, 3, 11,69,73,75,76,77, 82

use by shift workers, 96, 160

heart attacks, 41

heart function, 44

heart muscle function, 44

heart rate, 44

honeybees, biological rhythms, 29

Hong Kong, shift work regulation in, 202

hormone production

aging and, 49

circadian rhythms in, 5, 31,40,42-43,44

depression and, 52

light and, 53

hormones, responsiveness to, 44

hours of service/work

for drivers, 72-73, 125-126

in emergency situations, 125-126, 130

enforcement of, 123, 124, 126, 132

Federal laws, 18, 32-33; see also specific statutes

for flight crews, 126-127

for medical residents, 168, 170-176

in military services, 186

on-duty time, 124, 125, 130

penalties for violations of regulations, 124, 126, 127, 132

railroad employees, 123-124

regulation of, 4, 10,32-33, 123-124, 186

rest periods, 124, 126, 127, 129, 137

State laws, 18

survey data on, 70-71

in transportation sector, 18, 103, 123

and wages, 207-208

Hours of Service Act, 18, 123-125, 134, 135

Hours of Service of Drivers regulations, 125

human circadian rhythms, 42-45

aging and, 49-51

benzodiazepines and, 8,56-57

and body temperature, 8, 31,40,41,49,88

characterization of, 31

controlling, 8, 37,53-58

diet and, 57

eating patterns and, 96

length and amplitude, 50

light and, 8,37,53-55

marker for, 55

measures of, 88,98-99

melatonin and, 8,55-56

and performance, 47-49

physical activity and, 8,57-58

in physiological functions, 5, 31

in psychological functions, 5, 31

sleep timing, 45-47

studies of, 41-42

see also disruption of circadian rhythms

human performance

accuracy of response, 13,47,48, 81

afternoon, 99

aging and, 50

body temperature and, 6,47

circadian rhythms and, 5,47-49,58,92

duration of shift and, 106

extended duty hours and, 87, 106

fatigue and, 48, 187

and injuries and mishaps, 101

light effects, 54, 109.

measurement of, 58, 88, 99, 150

medication and drug therapies and, 109-110

monitoring, 111, 112

motivation and, 47,48, 97

napping and, 17,46, 107

nighttime, 48, 58,99

nursing schedules and, 6, 160-161

overtime and, 83

reaction time, 47-48

sleep loSS and, 6,45, 4748,58, 185, 187

speed of identification, 47

split shifts and, 106-107

stimulant drugs and, 110

transmeridian flight and, 48

work-related stressors and, 32,97-100

see also job performance

Hungary, shift work regulation in, 207,208,209,212

hunger, 44

hypnotics, 17,48,51, 109

hypothalamus, 40

Illinois, residents’ work hours in, 171

immune system

function, 45

suppression, 43

India, shift work regulation in, 207,208,212

Indonesia, shift work regulation in, 209,212

Industrial Revolution, 31,87

industries

continuous-operation, 10, 31-32, 72

paying overtime compensation, 83

using shift schedules, 9-11, 69, 72-75

injuries, shift work and, 18, 100-101, 160, 166, 168; see also

accidents; safety

insomnia, 7,48,51,55, 57, 110

Institute for Social Research, 70

insulin, 43

interleukin-2, 43

internal clock, 29-31

aging and, 49-51,58

control center in brain, 4,40-41, 58

defined, 29,58

desynchronization, 46,58

entraining agents, 5-6, 15, 37, 38, 39, 89

evaluation of, 37-38,41-42

gene expression in, 40

light-dark cycles and, 5-6,53,58

phase shifts, 6,37,44,48,53, 105

resetting, 30,40,41,54, 105

synchronization by Sun, 30

technological development and, 31

see also circadian rhythms; human circadian rhythms

International Congress for the Protection of Workers, 209

International Labor Organization

conventions, 209, 210-215
242 . Biological Rhythms: Implications for the Worker

U.S. approval of conventions, 215

international regulation of shift work

comparability of data, 215

by country, 200-207

hours and wages, 207-208

International Labor Organization conventions, 210-215

types of regulations, 210

women’s night work, 209-210

Interstate Commerce Commission, 123

interventions

clinical support, 111-112

employee education, 18, 111-112

fitness, 112

for jet lag, 48

light, 17,58, 107-109

medication and drug therapies, 17, 58, 109-1 11; see also

specific substances

monitoring systems, 17-18, 111

research needs on, 102, 113

sleeping and napping, 17, 107, 187

work schedule-related, 17, 102-107

intestinal tract, cycles in cell functions, 45

Iowa, residents’ work hours in, 171

Iraq, shift work regulation in, 208,209,212

Ireland, shift work regulation in, 199,203,207,208,210, 212

irritability, 11,97, 165

Israel, shift work regulation in, 203,207,210,212

Italy, shift work regulation in, 203,212

Jamaica, shift work regulation in, 203,212

Japan, shift work regulation in, 199,203,207,210,212, 215

jet lag, 3,5,29,47

aging and, 7

diet therapy, 48,57

in flight crews, 92

light therapy, 54

melatonin and, 56

and menstrual cycle, 5,44

in military operations, 21, 188

job performance

compressed workweek and, 13, 81

by job setting, 99

and marital problems, 177-178

measurement of, 88,99

nursing shift work and, 99, 160

Johns Hopkins Hospitals, 158

Johns Hopkins School of Medicine, 167

kidney function, 44-45

Labor-Management Relations Act, 19, 136-137, 139

latitude, and seasonal affective disorder, 51

Libby Zion case, 168-170

light

adverse effects of, 54-55

aging, and relay of, 50

and body temperature, 8, 109

controlling circadian rhythms with, 8, 17, 37, 39,40,51, 52,

53-55

fluorescent, 55

interventions in shill work, 58, 107-109

and jet lag, 48, 54

and melatonin production, 53,56

and performance, 54, 109, 149

phase-shifting properties, 7,54

therapeutic effects of, 51,52,54

light-dark cycles, synchronization of circadian rhythms with,

5-6,37,41,53,58

lithium, 57

locomotive engineers, 73,89, 123

logical reasoning, 47, 100

luteinizing hormone, 5,44

Luxembourg, shift work regulation in, 207,209,210,212

managerial jobs

overtime compensation, 83

prevalence of shift work, 11,74

manual dexterity, 5,47, 99

manufacturing industries

continuous-operation, 12, 32,99

occupations using shift workers, 3, 69

overtime compensation, 83

prevalence of shift work in, 11,74,82

reasons for shift work, 72

shift schedules in, 12, 13,79, 81

marital status

of medical residents, 177-178

of nurses, 156, 162, 165

and shift work, 11, 12,76,77, 94

see also dual-earner couples; married couples with children

Maritime Administration, research activities, 218-219

maritime safety, 127, 128

maritime transportation, 128

married couples with children

effects of shift work on, 82

reasons for shift work, 78-79

shift work prevalence, 11, 78

sleep disturbances, 162

see also single parents

Massachusetts, residents’ work hours in, 171

Mauritius, shift work regulation in, 209,212

medical education, see graduate medical education; residents/

residencies

Medical Research and Development Command, research

activities, 218-219

medication and drug therapies, 109-111; see also specific

substances

melatonin

controlling circadian rhythms in humans with, 8,55-56,58,

110

light and production of, 53,56, 108

memory, 5, 31,47,48,57, 100, 105, 187

menstrual cycle

circadian rhythms in, 3,5, 30,44

dysfunctions due to shift work, 97, 165

and jet lag, 5, 44

therapeutic implications, 5,44

mental functions

circadian rhythm disruption and, 49

circadian rhythms in, 5,47

mental illness, 52,58

merchant marines

hours of service regulation, 135

watch schedules, 92, 100, 103, 106-107, 127
Index ● 243

message decoding, 100

metabolism, cortisol secretion and, 43

metastatic adenocarcinoma, 43

meteorologists, 92

Michigan

child labor law, 130

minimum wage law, 130

residents’ work hours in, 171

microsleeps, 45

military operations

Air Force, 189-190

amphibious assault, 192-193

Army, 188-189

combat, 21, 185, 186, 188, 189, 190, 192

conditions of readiness, 191

deployment, 185, 186, 188, 189

Desert Storm, 185

drug interventions, 110

extended duty hours, 87

flight operations, 187, 188,189-190,192

24-hour marming, 188-193

hours of service regulations, 21, 186, 188, 189, 190, 192

Marine Corps, 192-193

nature of, 185-187

Navy, 21-22,93, 190-192

and night Shift paralysis, 93

reinforcement, 188

rest requirement, 21, 185, 186, 189, 190

shift work in, 3, 73

sleep discipline plans, 187

and sleep loss, 21, 185, 187

special operations, 188-189

strategic forces, 190

on submarines, 185, 191

on surface ships, 185, 191-192

tasks, 21, 187

training and operational readiness exercises, 21,185-186,188

Mine Safety and Health Act, 19, 133, 135

Mine Safety and Health Administration, 19, 133-134

mining/miners

adjustment to rotating shifts, 105

eating habits of miners, 97

injuries, 101

occupational safety and health, 133-134, 135

overtime compensation, 83

shift work, 11

sleepiness in, 107

ministeel industries, 13, 81

Minnesota, residents’ work hours in, 171

miscellaneous shifts, 11, 71,76, 77

Missouri, residents’ work hours in, 171

Mongolia, shift work regulation in, 209,212

monitoring

circadian disruption and, 92

to detect performance impairment, 17-18, 111, 149-150

motor vehicle operators, 125, 126

mood

circadian rhythms in, 47

disorders, chronobiology and, 7,51-53

drug interventions and, 110

environmental and physiological factors in, 149

measures of, 88

napping and, 46

sleep deprivation and, 177

stimulant drugs and, 110

work schedules and, 93

moonlighting, 13,81,83,93, 173

Morocco, shift work regulation in, 203,212

morning person, 95, 165

motivation

and performance, 47,48,58

work schedules and, 93

Motor Carrier Safety Act of 1984, 125-126

enforcement of, 126

hours of service regulations for drivers, 125-126

safety standards, 134

motor vehicle operators

circadian disruption in, 92

monitoring of, 125

overtime provisions, 128

performance during extended duty hours, 100

regulation of, 18, 125, 134

shift work among, 10,72

sleep detector, 111

State regulation of, 130

muscle aches, 96

napping, 17,46,47,49, 107, 187

narcolepsy, 46

National Aeronautics and Space Administration

light therapy for astronauts, 108

research activities, 33,48,88, 112,219

National Federation of Housestaff Organizations, 172

National Institute for Occupational Safety and Health

Daily Sleep and Habits Questionnaire, 111

Fatigue Test Battery, 111

research activities, 33, 160, 162, 165, 217

National Institute of Child Health and Human Development, 70

National Institutes of Health, research activities, 33,217

National Labor Relations Act, 124, 136

National Labor Relations Board, 137

National Longitudinal Survey, Youth Cohort, 70,71,78

National Science Foundation, research activities, 217-218

National Survey of Families and Households, 9,70,71

National Transportation Safety Board

data on accidents, 101, 102, 103

research activities, 218

scope of authority, 127-128

Naval operations, see U.S. Navy

nerve cells, in SCN, 50

nervousness, 11, 165

Netherlands, shift work regulation in, 203,208,210,212

Neurospora crassa, 39

Nevada, residents’ work hours in, 171

New Deal, 128

New Jersey, residents’ work hours in, 171

New York State, regulation of residents’ work schedules, 130,

169, 171

New Zealand

residents’ hours in, 172

shift work regulation in, 199-200,203, 210,212

Nigeria, shift work regulation in, 199,204,209,212

night shifts, 32

adjustment to, 90, 92, 109
244 . Biological Rhythms: Implications for the Worker

and alertness, 112

and body temperature, 90

capital investment and, 72

and circadian desynchronization, 90, 92

defined, 71, 157,214

demographic profile of workers, 11, 12,76,77

and divorce, 94

by employment sector, 11-12,74-75

and fatigue, 13, 81, 92

and health, 96

injuries and accidents during, 101, 131

international regulation of, 199-207

occupational differences in, 76, 77

paralysis, 93

part-time workers, 72

pay differentials, 199,207

performance on, 99, 100, 105

prevalence, 9, 10,72,82

reasons for, 72, 78

regulation of women’s work schedules, 131, 209-210

and sleep disturbances, 17, 104, 162

and sleep patterns, 90,93, 107

and sleepiness, 92, 104

task differences on, 99

in transportation industries, 10, 72

see also fixed shifts

nocturnal animals, 29

norepinephrine, 96-97

Norway, shift work regulation in, 199-200,204,208,209, 212

nuclear powerplant control room operators

characteristics of, 143

fitness-for-duty regulations, 20, 135, 150

8-hour schedules, 144, 145, 146-147

12-hour schedules, 106, 144, 145-147

hours-of-work regulation, 128

job characteristics and effects, 106, 143, 147-149

licensed reactor operators, 143, 147

monitoring performance of, 20, 149-150

overtime schedules, 128, 144, 147, 147

senior reactor operators, 143, 147

sleepiness in, 107, 143

training, 143

vigilance of, 148, 149

nuclear powerplants

accidents/incidents, 102

control room configuration, 148

control room simulators, 88

outages, schedules during, 147

Peach Bottom atomic power station, 143, 150

regulation of, 128, 144-147

Shift staffing, 128, 144-147

technical specifications, 18, 145

Three Mile Island, 102, 143,150

Nuclear Regulatory Commission, 32

cooperation with OSHA, 144

data on accidents and incidents, 101

examination of control room trainees, 143

fitness-for-duty regulations, 20, 135, 150

guidance on shift scheduling and working hours, 18,20,144,

150

jurisdiction, 144

oversight of nuclear powerplants, 144

research activities, 33

resident inspectors, 144, 149

scope of authority, 18, 128, 135, 143, 144, 149-150

and shift schedules, 144-147

Systematic Assessment of Licensee Performance, 146

nursing shift work, 6

and accidents, 155

and collective bargaining by unions, 155-156, 157

compressed workweek, 13, 81

consequences, 159-166

and digestive disorders, 162, 165

extended duty hours, 155, 156

and family and social life, 20, 156, 166

and fitness, 112

full-time, 156

and health, 20, 160, 161-166

and injuries, 166

and job dissatisfaction, 20, 158-159

job performance ratings, 99, 160

licensed practical nurses, 159

and marital status, 156

and menstrual dysfunction, 165

and night Shift paralysis, 93

overtime, 156, 162

part-time, 156, 162

patterns, 156, 157-158

and performance of workers, 160-161

prevalence, 11,20,77,82, 156

and psychological and nervous disorders, 20, 165

and quality of patient cam, 20, 160-161

registered nurses, 155-156

research needs, 20-21

sick days and use of health services, 20, 160

and sleep disturbances, 20, 162

stress, 20, 159

and substance use and abuse, 165-166

occupations

continuous-operation, 31-32

with extended duty hours, 87

fatigue during night work, 92

of female shift workers, 11, 77

receiving overtime compensation, 83

using of nonstandard work schedules, 3-4,6,9-11, 13,69,

72-75,81,82

Occupational Safety and Health Act

applicability to government workers, 138, 139

employer obligations under, 132

enforcement of, 33, 132

general duty clause, 19,33, 132-133

jurisdictional overlap with other laws, 133, 135-136

purpose, 131-132, 136

State plan provisions, 133

Occupational Safety and Health Administration

burden in general duty proceedings, 132

cooperation with NRC, 144

data on workplace accidents, 101

research on biological rhythms, 4, 33

rulemaking by, 132

scope of authority, 4, 32-33, 132

standards for work scheduling, 132

Occupational Safety and Health Review Commission, 132-133
Index .245

offshore oil rigs, 13, 81

Ogle, William, 31

ovarian cancer, 43

overtime

basis for calculating pay, 124

and extended duty hours, 87

at nuclear powerplants, 144, 145, 147

by nurses, 156

and performance, 83

prevalence of, 83

regulation of, 79, 129-130, 137, 147

and rotating shifts, 87

and safety, 83

for State employees, 139

see also extended duty hours

Panama, shift work regulation in, 204,208,212

paper industry, 13,80,81,94

Papua New Guinea, shift work regulation in, 204,212

Paraguay, shift work regulation in, 208,212

Pennsylvania, residents’ work hours in, 171

peptic ulcer disease, 96

per gene, 39

perceptual-motor tasks, 100

performance, see human performance; job performance

personality, and adjustment to work schedules, 95

Peru, shift work regulation in, 209,212

petroleum industry, 13,81,89,98

pharmacokinetics, 43

phenobarbital, 57

Philippines, shift work regulation in, 204,207,209,212

physical activity

aging and, 49

and circadian rhythm adjustment, 8,57,58, 109, 187

and jet lag, 48

see also fitness

physiological functions

aging and, 7

circadian rhythms in, 5,31,47, 88

depression and, 52

effects of work-related stressors on, 89

light and, 108

measures of, 88

monitoring of, 112

see also specific functions

pineal gland, 55,56

plants, circadian rhythms in, 31

Poland, shift work regulation in, 204,209,212

policy issues and options

data collection on workplace safety statistics, 23-24

research effort on effects of work schedules, 22-23

well-being of shift workers, 24-25

polysomnography, 45

Portugal, shift work regulation in, 207,208,212

pregnancy

outcomes, shift work and, 16,97, 178

restrictions on work during, 209-210,214, 215

printers, 93

professional jobs, overtime compensation, 83

Profile of Mood States, 165

prolactin, 42

protective services

characteristics of workers, 78

continuous-operation, 10, 32

fatigue during night work, 92

four-platoon schedule, 104

health of workers, %

Philadelphia police work schedules, 104

prevalence of shift workers, 3, 10, 11,73,76

protein synthesis, 38

proto-oncogene, 41

psychological functions

circadian rhythms in, 5, 31,47

extended duty hours and, 106

light and, 108

measurement of, 165

in medical residents, 178

monitoring of, 112

of nurses on shifts, 165

and performance, 100

psychomotor tests, 111

puberty, melatonin, 55

quality control, circadian disruption and, 92

Quality of Employment Survey, 70-71

quality of patient care

nursing shift work and, 160-161

resident work schedules and, 168

Quality Patient Care Scale, 161

race/ethnicity, and shift work, 11, 12,76,77

Rail Safety Improvement Act of 1988, 124

railroad engineers, 92

Railroad Safety Act of 1970, 19, 125, 135

railroads, hours-of-work regulations, 18, 123, 128, 131, 134

Railway Labor Act, 124, 136-137

rats, circadian rhythm synchronization in, 55-56

reaction time, 5,47, 97, 100, 161, 176

recognition, 47

registered nurses, 155-156; see also nursing shift work

regulation of working conditions

compressed workweek, 13, 81

costs of implementation for residents, 169-170

current areas of action, 18, 123-130

by Federal Government, 18-19,32-33, 123-130

Federal preemption of State laws, 131, 137-138

gender differences in, 131

hours of service, 32

labor relations statutes, 136-138

for medical residents, 170-176

occupational safety and health laws, 131-133

penalties for violations of, 124, 126, 127

potential areas of action, 18-19, 130-138

by States, 18-19, 130

see also international regulation of shift work; nuclear

powerplants; transportation; and specific agencies and

statutes

research activities

data collection by Federal Government, 22,33

Department of Defense, 33, 112,219-220

Department of Health and Human Services, 33,217

Department of the Interior, 219

Department of Transportation, 33,218-219

Department of Veterans Affairs, 218
246 ● Biological Rhythms: Implications for the Worker

National Aeronautics and Space Administration, 33,88,112,

219

National Science Foundation, 217-218

National Transportation Safety Board, 218

research methodologies

and comparability of data, 71, 215

design needs, 112

field studies, 88

human circadian rhythms, 41-42

human performance and work schedules, 98-99

laboratory studies, 88

physiological measures, 88

placebo effects, 88

problems in studying seasonal affective disorder, 52

self-selection process, 96

survey studies, 88

on work schedules, 88,96

research needs

on circadian rhythms and shift work, 18, 82, 112-113

on interventions, 17, 102, 113

nursing shift work, 20-21

performance effects of work schedules, 98

safety and work schedules, 18, 113

transportation safety, 103

Residency Review Committee guidelines, 21, 173-175

residents/residencies, 87

characteristics, 167

classifications of, 167

continuity of care by, 21, 167, 168, 169, 173

defined, 155

effects of extended duty hours on, 21,92, 155, 168, 176-178

family and personal life, 177-178

marital status, 177-178

medical mistakes by, 168-169, 170, 177

in New Zealand, 172

night floats, 176

pregnancy outcomes of students, 178

regulation of hours, 21, 130, 168, 169, 170-176

sleeping patterns, 168

specialty-related standards, 21, 173-176

State regulation of work hours, 171

substance abuse by, 178

training programs, 166-167, 173

unions, 167

work schedules, 155, 167

workload, 168

see also graduate medical education

respiratory infections, 96

respiratory system, circadian rhythms in, 44

rest-activity cycles, 44, 97

rest periods, 124

retail industries, shift work in, 10, 11, 73,75

Romania, shift work regulation in, 204,213

Roosevelt, Franklin D., 129

rotating shifts

4 to 40, 158,161

adjustment to, 17,50,89-90,95

aging and, 50,95

Baylor plan, 158

and body temperature, 14, 91

circadian disruption, 13, 15, 89

4 days on, 4 days off, 147

defined, 3,32,87

demographic profile of workers, 11, 12,76,77,78

direction of rotation, 12-13, 17,79, 105, 145

every other weekend off, 146

and family responsibilities, 79, 166

and fatigue, 13, 81, 105, 146

and health, 96, 160, 162-165

8-hour schedules, 80, 106, 145, 146, 157

12-hour schedule, 80, 106, 145-146, 157, 161

and injuries, 166

light therapy, 109

at nuclear powerplants, 20, 145

by occupation, 11-12,74-75,77

and overtime, 87

part-time, 78

patterns of, 157-158

performance on, 99, 100

prevalence of, 9,71,72,82,156

in pulp/paper mills, 80

reasons for, 145

and sleep disruption, 14, 15, 17,92,93, 105, 107, 162

and social life, 166

speed of rotation, 12-13, 17,79, 89,91, 105, 107, 145,208

and substance use and abuse, 165-166

survey data on, 70, 71

2-2-2 system, 91

and task characteristics, 105

in transportation industries, 10, 72

safety

compressed workweek and, 13, 81

emergency authority of FRA, 124-125

extended duty hours and, 106

overtime and, 83

research needs on, 17, 113

shift work and, 17, 18, 131

of women, 209

work-related stressors and, 32,97-100

Safety Appliance Act, 123

Saudi Arabia, shift work regulation in, 209,213

search performance, 99

seasonal affective disorder, 7,51-52,53,54,55

semen production, melatonin and, 55

serotonin, 57

Service Employees International Union, 155

service industries

continuous-operation occupations, 10, 32, 73-76

dual-earner couples in, 78

prevalence of shift work in, 3, 10,11,74,75,76,82

sex hormones, 42

sexual excitement, 44

shift changes, 13, 81, 82

shift work, 29

adjustment to, 15,89,95, 112

age and, 7, 76, 95

body temperate and tolerance of, 95

capital investment and, 10, 72

data sources on, 8,9, 13,69-71,80-81

definition, 3,32,87

demographics of, 69-78

by employment sector, 9-11,72-76,82

and family life, 32,78,82,87,93-94,96, 105
Index ● 247

health and, 32,87,96-98, 106, 161-166

8-hour schedules, 80, 145

12-hour schedules, 80, 145-147

motivations for, 10, 11-12,69,72,76,78-79, 87

at nuclear powerplants, 144-147

and occupational exposure limits, 13, 81

pay differentials, 158

and performance, 6,97-100

physiological effects of, 6,32

prevalence, estimates of, 8-13,32,69,70,71-72, 87, 199

and safety, 17, 18, 131

schedule determinants, 79-80

and sleep loss, 14,32,58,87,92,97, 107, 112, 162

social effects of, 3$29,32,87,94-95,96, 105, 166, 176-177

types, 12-13,69,79,80

see also extended duty hours; fried shifts; international

regulation of shift work; night shifts; regulation of work

schedules; rotating shifts; split shifts

shift workers

characteristics, 11-12, 76-78,79, 82

defining, 69

full-time, 9,72,73,76

part-time, 72,73

problems of, 58, 208-209; see also family life/

responsibilities; health; safety; sleep disruption/loss;

social life

surveys of, 69

sick days, shift work and, 96, 160

signal detection, 97

Singapore, shift work regulation in, 203,213

single parents, shift work by, 11

sleep

accommodations for, 124, 130

aging and, 49,95

and body temperature, 14, 38,45,46

brain activity during, 99

compressed workweek and, 13, 81

and cortisol secretion, 38

daytime, 95, 110,208

debt, 15,93, 105,107,208

depression and, 52-53

detectors, 111

diaries and questionnaires, 88

dreams, 5,44,45

duration, 15,92,93, 112, 162

employee education on, 111-112

falling asleep, 46,95

habits, 93,95

and hormone secretion, 42

latency test, 46

measurement of, 45, 88

microsleeps, 45

napping, 17,46,47,49, 107

quality, 16,38,45,58,88, 104

regulation under FLSA, 129-130

REM, 45,46,52

research, 88

slow wave, 45

social and domestic disturbances and, 93

stages, 5, 44

stimulant drugs and, 110

timing, 7,38,45-47,51, 52,58,88, 105, 107, 111

total time, 46

wrist activity monitors, 88

sleep disorders

advanced sleep phase syndrome, 50,51

age and, 50, 58

circadian rhythm disruption and, 49, 51

clinics, 112

delayed sleep phase syndrome, 51

insomnia, 7,48,51,55,57

jet lag and, 48

light therapy, 54

night Shifts and, 104

non-24-hour sleep-wake disorder, 51

sleep disruption/loss, 3, 29

adjustment to, 95, 176

and behavior, 45

causes, 92-93

circadian rhythm disruption and, 5, 16,49,92

detection, 111

and employer liability for accidents, 130

extended duty hours and, 17, 21,87,89, 100, 101-102, 106,

155, 176, 185, 187, 188

and fatigue, 92-93

and night Shift paralysis, 93

nursing shift work and, 162

and performance, 6,45,4748,58,98, 100, 162, 176, 185

and safety, 101, 112, 178

shift work and, 14,32,58,87,92,97, 107, 112, 162

sleep-wake cycles

adjustment after transmeridian flight, 48

of blind persons, 56

body temperature and, 46

circadian rhythms, 31, 37

depression and, 52

and napping, 107

and shift work, 6,58

sleepiness

aging and, 49

control of, 40

daytime, 47

defined, 87

drugs to counteract, 109-110

jet lag and, 48

interventions for, 148, 149

and napping, 107

and night Shift paralysis, 93

night shifts and, 15, 92

and performance, 6, 100, 187

and safety, 100

social life

disruption by work schedules, 3,29,32,87,94-95,96, 105

measures of, 88

nursing shift work and, 166

residents’ extended duty hours and, 176-177

sleep disorders and, 51, 104, 162

and synchronization of circadian rhythms, 53

South Africa, shift work regulation in, 205

South Korea, shift work regulation in, 205

Spain, shift work regulation in, 199,205,207

split shifts

defined, 3,32,71

effects of, 106-107, 131, 147
248 ● Biological Rhythms: Implications for the Worker

prevalence, 9

restrictions on, 137

women on, 77

see also merchant marines

Sri Lanka, shift work regulation in, 210,213

Stanford Research Institute, 160

States

employee working conditions, 11, 139

Federal preemption of regulations, 131, 137-138

labor relations legislation, 137-138

mine safety and health standards, 133

occupational safety and health enforcement, 133

prevalence of shift workers in public sector, 11,75

regulation of working conditions, 4, 32, 130, 131

resident work hours regulation, 171

steel workers, 92

Stimulant drugs, 110

stomach, cycles in cell functions, 45

stress

and cortisol secretion, 43

and health, 97

on-the-job monitoring and, 111

among nurses, 159

stressors, see work-related stressors

substance use and abuse

detection of, 111

by medical residents, 178

regulation of, 134, 135

shift work and, 96,97, 102, 165-166

suicide, 52

suprachiasmatic nucleus, 5,4041,50,58

Surinam, shift work regulation in, 210,213

Swaziland, shift work regulation in, 209,213

Sweden

divorce rate in shift workers, 94

field studies of work schedules, 88

shift work regulation in, 199,205,207,209,213

switch operators, 123

Switzerland, shift work regulation in, 199,205,207,209,210,

213

technical jobs

overtime compensation, 83

shift work in, 11

technical maintenance, 13, 81

technological development

and circadian rhythms, 31-32

and shift work prevalence, 10-11,76

teenagers

insomnia in, 51

work restrictions, 128-129, 136,207

temperature, see body temperature

Thailand, shift work regulation in, 209,213

theophylline, 57

tides, 29

traffic accidents

drug use and, 102

factors contributing to, 17, 101-102, 104, 178

fatigue-related, 102, 178

shift duration and, 106

timing of, 46,99

train operators, 123

transmeridian flight, effects of, 5,7,44,48,58, 89;

see also jet lag

transportation problems of shift workers, 208,209

transportation sector

civil air safety, 126-127

continuous-operation occupations, 32

extended duty hours, 87, 100

fatigue in workers, 92

hours of service regulations, 10,32,72-73, 103, 123-126

industries using shift workers, 3

international regulation of, 199, 207

maritime safety, 127

motor carrier safety, 125-126

occupational safety and health regulation in, 134-135

overtime compensation, 83

prevalence of shift work, 10, 11,72,75,82

railway, 92,123,124,125,128,131, 134,135, 136-137

safety concerns, 18

shift schedules in, 79

State regulation of work schedules, 130

work history of locomotive engineer, 73

work schedule limitations, 126-127

see also air transportation/travel; civil air safety

tranquilizer use, 97

triazolam, 56-57, 109-110

tryptophan, 17, 110

tumor necrosis factor, 43

Tunisia, shift work regulation in, 199,205,213

Turkey, shift work regulation in, 199,206,207,208,209, 213

ultraviolet radiation, 55

United Kingdom

field studies of work schedules, 88

nursing shift work in, 158

residents’ hours in, 171

shift work regulation in, 199,206,209,210,213

United States

approval of International Labor Organization conventions,

215

shift work regulation in, 199,206,207, 209, 213

Uruguay, shift work regulation in, 206,213

U.S. Air Force

Office of Scientific Research, 33,220

research activities, 33, 220

strategic forces, 190

tactical and transport forces, 189-190

Us. Army

Aeromedical Research Laboratory, 220

biological rhythm research activities, 219-220

combat operations, 189

deployment operations, 188

flight operations, 189

reinforcement operations, 188

research activities, 219-220

Research Institute of Environmental Medicine, 220

Research Institute for the Social and Behavioral Sciences,

219-220

Safety Management Information System, 101

special operations, 188-189

U.S. Coast Guard

authority over work scheduling, 18, 103, 127, 135

research activities, 218-219
Index .249

U.S. Congress, Subcommittee on Investigation and Oversight,

33

U.S. Constitution

commerce clause, 130

equal protection clause, 131

U.S. Marine Corps, amphibious assault operations, 192-193

U.S. Navy

flight operations, 192

Navy Health and Research Center, 220

Office of Naval Research, 220

research activities, 220

submarine operations, 191

surface ship operations, 191-192

U.S.S.R., shift work regulation in, 206,207,208

urine production, 44-45

utilities

overtime compensation, 83

using shift workers, 3, 10,72

work schedules, 13, 81

see also nuclear powerplants

Valium, 56

Venezuela, shift work regulation in, 206,208,213

verbal reasoning, 47

vigilance

circadian disruption and, 92

environmental and physiological factors affecting, 149

and human error, 147-148

in military operations, 191

napping and, 187

and performance, 100, 149

sleep loSS and, 187

and sleepiness and fatigue, 147

stimulant drugs and, 110

tests of, 88,99

Walter Reed Army Institute of Research

Performance Assessment Battery, 111

research activities, 218-219

women shift workers

with children, 13, 78, 81

compressed workweek, 13,81

family responsibilities of, 16,94

international restrictions on, 207

job characteristics, 11,77,78

medical residents, 176, 177

moonlighting by, 83

night work regulation, 131,209-210

prevalence, 76

safety of, 209

stress in, 16,94

surveys of, 70

Women’s Health Equity Act of 1991, 161

work schedules, 87

characteristics that can be varied, 87, 103-104

compressed workweek, 79

and disruption of circadian rhythms, 3,5, 89-92

economic incentives for limiting, 124

and fatigue, 92-93

4-hours-on, 8-hours-off, 100

8-hour day, 79, 129

12-hour, 82, see also compressed workweek

40-hour workweek, 3,32,79

interventions related to, 17, 102-107

methodology for studying effects of, 88

research needs, 112-113

and safety, 103

and sleep disruption, 92-93

and social and domestic disturbances, 93-95

stressors caused by, 89-95

see also shift work

work-related stressors

circadian rhythm disruption, 15, 87,89-92

consequences of, 16,.89,95-102

and health, 16,96-97

and performance, 97-100

and safety, 100-102

sleepiness and fatigue, 92-93

social and domestic disturbances, 93-95

sources, 15-16,89

worker satisfaction, work schedule and, 13, 81, 82, 96, 104,

158-159

working conditions, Federal Government oversight, 32-33

workplace

biological rhythms and, 31-32

simulators, 88

Yugoslavia, shift work regulation in, 206,207,213

Zaire, shift work regulation in, 209,213