PubSications

NBSIR 76-1132

AlllOl 75t5Sl

Personnel Guardrails for the

Prevention of Occupational

Accidents

S. G. Fattal, L. E. Cattaneo

G. E. Turner, S. N. Robinson

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

July 1976

Final Report

Prepared for Hrcupational Safety and Health Administration — ^artment of Labor QC • 100

.U56

shington, D. C. 20210

76-1132

1976

National Bureau of Standards

Libfary, E-01 Admin. BIdg,

OCT t 5 1982

PERSONNEL GUARDRAILS FOR THE

PREVENTION OF OCCUPATIONAL

ACCIDENTS

NBSIR 76-1132

l9 7^

S. G. Fattal, L. E. Cattaneo

G. E. Turner, S. N. Robinson

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

July 1976

Final Report

Prepared for Occupational Safety and Health Administration

Department of Labor

Washington, D. C. 20210

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Acting Director

TABLE OF CONTENTS

Page

Abstract 1

1. Introduction—Objectives and Scope 2

2. Review of Existing Standards and Technical Literature 4

3. Anthropometric Data 12

4. Field Survey of Guardrail Installations 25

5. A Conceptual Model of Safety 53

6. An Analysis of Guardrail Accidents 60

7. Summary 76

ii

PERSONNEL GUARDRAILS FOR THE PREVENTION OF OCCUPATIONAL ACCIDENTS

S. G. Fattal, L. E. Cattaneo,

G. E. Turner and S. N. Robinson

Existing information is compiled which would assist in determining structural and

non-structural safety requirements for guardrails used for the protection of employees

against occupational hazards. Critical aspects of guardrail safety are identifed through

exploratory studies consisting of field surveys of prototypical installations, reviews of

existing standards and industrial accident records, and compilation of relevant anthropometric data. These exploratory studies will be utilized to design an experimental program

which will consist of structural tests to determine design loads and non-structural tests

to determine geometric requirements for guardrail safety.

Key Words : Anthropometric measurements; guardrails; industrial accidents; non-structural

safety; occupational hazards; performance standard; personnel railings; personnel safety;

structural safety.

1
1. Introduction - Objectives and Scope

This report documents the first phase of research studies conducted at the National

Bureau of Standards (NBS) in response to a request by the Occupational Safety and Health

Administration (OSHA) for technical assistance in developing performance standards and

design guidelines for guardrails which will be used to protect employees against occupational

hazards. Under the Occupational Safety and Health Act of 1970, OSHA exercises a mandate

over employee safety regulations including prescriptive requirements for all guardrails that are installed in areas where employees conduct work-related activities. The

general lack of technical literature to support the existing OSHA guardrail regulations,

and, for that matter, guardrail provisions of other mandatory or voluntary standards, has

been one of the principal motivating factors behind the research program. The two principal

objectives of the project were the development of basic technical information through

research and the utilization of this information to prepare performance-oriented recommendations for the design, construction and evaluation of guardrail systems which come under the

jurisdiction of OSHA.

The scope of this project was established by mutual agreement between OSHA and NBS

participants. It was agreed that NBS research should apply to temporary and permanent

guardrails used for the protection of employees against occupational hazards, and therefore,

should only consider factors associated with guardrail use by adult personnel during

the conduct of their assigned tasks. It was further stipulated that NBS research should

exclude consideration of guardrail loading situations arising through flagrant abuse or through the impact of power-driven vehicles or other heavy mobile objects propelled by

people. In addition, it was agreed that NBS research need not be concerned with investigations of whether or where the installation of guardrails will be required.

The types of guardrail installations given high research priority by OSHA included

the following, listed in the order of decreasing priority: (1) elevated walkways (2) erected

and swinging scaffolds, (3) balconies and mezzanines, (4) hot-dip galvanizing operations,

(5) roofing operations, (6) cast-in-place concrete construction, (7) petro-chemical towers,

(8) mobile equipment, (9) elevated work or storage areas, and (10) marine dry docks. It was understood that as many of these installations as possible should be examined within

the specified project resources without diluting the credibility of the end product. NBS

researchers examined eight of these installations, the excluded ones were chemical towers

and mobile equipment

At the beginning of this project It was reasoned that if the principal factors con- tributing to the safe functioning of guardrails could be identified in some systematic

fashion, the task of developing an effective approach to meet the specified project

objectives would be simplified. Accordingly, one of the earlier tasks was to devise a

2
conceptual model which considers both human and environmental factors and their interactions

with respect to safety and to proceed to study guardrails within the framework of this

model. (See Section 5).

Using the guidelines of the safety model, a two-phase approach compatible with the stated

project objectives was formulated. The first phase was exploratory in nature and was necessitated by almost a total lack of rational basis behind existing guardrail design provisions. It was aimed towards such studies as the prevailing modes of guardrail use in service,

the adequacy of present design and construction practices, factors influencing human-guardrail

interaction, and the principal agents of potential hazards. Specifically, the scope of the

first phase included the following disciplinary studies which are documented in this report for

the benefit of researchers and analysts concerned with guardrail safety.

(1) A literature search of available technical information and a study of the provisions

of existing guardrail design standards (Section 2)

(2) A compilation of existing statistical data on the anthropometric and kinematic

characteristics of the human body relevant to guardrail analysis (Section 3).

(3) A field survey of prototypical guardrail installations (the eight types mentioned

above), to become familiar with current practices and, if possible, to identify safe and

unsafe employee activities and environmental characteristics (Section 4)

(4) An analysis of employee accident records compiled by various agencies to determine

the frequency and nature of those accidents which appear to be guardrail-related (Sections 5 and 6)

In phase two, the results presented herein will be used in the preparation and subsequent conduct of an experimental-analytical program. It is expected that these exploratory studies will prove valuable in designing experiments to measure the static and dynamic

loads induced on guardrails during simulated accident situations, and in developing a data base from which the essential safety features of guardrails can be established. On

the basis of information acquired from the above, performance-oriented recommendations and

a guide for the design and evaluation of guardrails will be prepared.

The implementation of this project was carried out through the cooperative efforts of

NBS research investigators from the structural, architectural and psychological disciplines.

For convenience in recovering the original sources and data, a reference list for each of

the four tasks Identified above is appended to the end of the appropriate section.*

Citations of references are Indicated by numbers in brackets.
2. Review of Existing Standards and Technical Literature

This section presents a summary of existing guardrail provisions of some of the major

codes and standards that are widely used througout the United States and Canada. For ease

of reference, these provisions are presented in tabular form (table 2.1) consisting of

entries of prescribed horizontal and vertical design loads, required height of guardrail,

and notes related to these entries. The first entry gives the code references and the

pertinent sections from which the listed data have been excerpted. The references from

which table 2.1 has been prepared and the sequence in which they have been listed, (which

is arbitrary) are as follows:

(1) Uniform Building Code [2.10]

(2) The BOCA Basic Building Code [2.11]

(3) Building Code of the City of New York [2.12]

(4) Southern Standard Building Code [2.13]

(5) The National Building Code [2.14]

(6) National Building Code of Canada [2.5]

(7) Canadian Construction Safety Code [2.16]

(8) Occupational Safety and Health Standard, Part 1910 [2.2]

(9) Construction Safety and Health Regulations, Part 1926 [2.1]

An examination of the information compiled in table 2.1 reveals a general lack of

consistency and uniformity between load and height requirements. Some base their load

requirements on the number of occupants while others specify loads according to guardrail

location. In cases where two or three different loadings are specified, it is not always

clear whether these loads are intended to be applied simultaneously or individually in

design. Quite often, certain critical decisions are left to the designers with such

terms as "substantial guardrails shall be provided. . ."or "openings should restrict

climbing." The requirements of some of the codes are much more stringent than others.

Certain codes and regulations give standard member sizes and dimensions. Sometimes there

are ambiguities with regard to whether the specified loads are factored or unfactored

(ultimate strength design vs working stress design)

The wide diversity of guardrail practices as evidenced by the foregoing study is

principally attributed to the paucity of technical information needed to develop a rational

k
and unified engineering approach to guardrail analysis and design. Specifically, it

points out the need for experimental research to establish criteria for guardrail loads

induced by human subjects either accidentally or through normal usage, and for guardrail

geometry to inhibit accidental falls resulting from geometric inadequacies such as insufficient height and/or width, or excessively large openings.

In an attempt to utilize available technical knowledge and at the same time avoid the

possibility of research duplication, a computerized research of published literature on

the general subject of guardrails was carried out using the Engineering Index and the

Government Reports Index (NTIS) . This search identified more than 100 publications on experimental and analytical research investigations of highway guardrails and other

vehicular crash barriers; however, no document related directly to personnel guardrails

could be located. Subsequently, a selected number of these publications were acquired and

examined for technical content for possible application to the analysis of personnel

guardrails. However, some of these documents proved to be of little utility because they

dealt with investigations of the response of guardrails under vehicular impact, which is

fundamentally different from that produced by the human body. A number of other publications

dealt with the evaluation of automotive safety devices through tests using human subjects

and anthropomorphic dummies. Some of these publications, [2.3, 2.4, 2.22] provide information on the energy absorption characteristics of the simulated human body. A number of

other publications compiled anthropometric and engineering data on the human body

[2.5-2.9, 2.23-2.28].

5
Table 2.1 Summary of Guardrail Provisions of Existing Building Codes and Safety Standards

Ref. Sect.

Horiz

Load

Vert.

Load

Height

in

Notes

i ) UdL / 1 / lO

/3305(i)

/Table 23-C

Guardrails & stair railings

Interm. rail req'd.

Max. opening = 9 in.

30-34 Stair handrails

50 plf

20 plf

Occupancy > 50

Occupancy < 50

2) BOCA/417.5.5

/615.2

/616.5.1

/616.5.2

/870.5

23-36

JU- J J Railings - public assembly

Handrails on ramps

200 lb any pt. & dire. 30-34 Handrails - stairways

Guards - floors, mezzs. , landings

Balusters: 6 in max. spa. Interm. rails: 10 in max. spa. Other: mesh, grill, walls

50 plf 20 plf Railings - other than public assembly

or 200 lb any pt. & dir. 50 plf & 20 plf not concurrent

50 plf 100 plf Railings - publ. assembly

50 plf * & 100 plf ^ concurrent

Engineering Design Guardrails - Fl. & wall openings

Toeboard req'd.

3) NYC/503.4

/503.8

/604

/604.13

/709.5

/710.6

/MDL Sec. 62

/902.3

/iy03.2

/ 1 Qn7 Q

42 Guard: rails, fence or parapet

Guards — roof recreation

36 Railings - skylight

Handrails - stairs

32 1 Handrails - fire escapes

36 Guards - landings

Max. opening = o m.

Guards & parapets - roof

vehicular parking areas —

Guards - vehicle wheels

Guards & railings - perimeter of

interior fir. openings. 42-^ Guard railings & parapets: wire

(mult . dweii .

40 plf 50 plf 42 Railings - non-publ. assembly;

H & V simultaneous

50 plf 100 plf / o 4/ Railings - public assembly

20 plf 20 plf 4/ Railings - 1 & 2-family dwellings

or 200 lb any pt. & dir.

40 plf 50 plf Rails: intermediate & bottom; H & V simult. (not for post and anchor

design)

20 psf Solid panels of railings

300 plf or 2500 lb

(the >)

Vehicular, applied at 20-in ht.

42 Guardrails & solid

enclosures - perim. of excavations

jtD — HZ Guardrails (standard) — construction

toprail: 2x4

midrail: 1x4

posts: 2 X 4 at 8 ft. altern: 1 1/4-in Std pipe;

2 X 2 X 1/4 angles

6
Table 2.1 (cont.)

Horiz.

Load

Vert.

Load

Height

in

Notes

4) Southern/512.9 26-36 Railings - public assembly

/1108 36-42 Guardrails - exterior balconies

Max. opening = 8 in

Max. opening at floor = 2 in

/1115.f 20 plf

50 plf —

Railings - stairways

Railings - balconies

D) wacxonai/ jio .

ZD— JO Railings - public assembly

/604.8 30-34 Handrails - stairs

/902.4

/1201.2

50 plf --

36 Railings - stairs & balconiesGuardrails + 6-in toeboard - construction.

/1207. 48 Railings + 6-in toeboard - construction

fir. openings.

6) Canadian

/ J . J . 1 . iZ /tz9 Guard railings — balconies, roofs,

mezzanines; Max. opening = 4 in. ZD- JO Guards - public assembly

/. 9 Guards: bleachers; (msd. abv. ft.

rest); Max. opening = 12 in.

36 Guards: bleachers; (msd. abv. seat

board); Max opening = 12 in. ~ 33 Guards: front bleachers; (msd. abv.

ft. rest); Max. opening = 12 in.

/3.4.8.5 32-36 Handrails - stairs

/. 9 HZ Barriers - stairway windows.

/ 'i /. Q A JO Guards - stairways, ramps, passageways;

Max. open. = 6 in. 42 Guards - around landings; Max opening =

0 in.

/4. 1.10.1 40 plf plus

ZUU ID cone. Rails - exterior bale, of Individ,residences

100 plf Railings - exits and stairs

ijU pit Railings - public assembly

ZjU pit Guards - grandstands & stadia including

ramps

ZjOU lb or

jOO plf

Guards: vehicular applied at 21-in ht.;

2500 lb over widths of vehic. space.

125 lb — Guards - industr. catwalks (e.g.)

where not crowded.

20 psf Solid panels

/ ^ . 1 . lU . i lUU pit Guards - acting separately from req'd

horiz. Ids.

/9.8.7.4 32-36 Handrails - houses & small buildings.

/ 9 42 Guards - small buildings & houses

except

79.8.8.4

36

42

u a L ^ u d1. vl o , Landings; except:

/9.8.8.5 32 Stairguards - dwelling units

79.8.8.6 42 Guards - garage floor openings + 6-in

high board

79.8.8.7 Max. opening. = 4 in

79.8.8.8 Openings size should restrict climbing.

7
Table 2.1 (cont.)

Ref. Sect.

Horiz

Load

Vert

Load

Height

in

1 Notes

7) Canadian

Construction

Safety /3.5.22

/3.11.5

42 Guardrails + toeboards - shaft openings

36-42 |<>JUcl.LUl.clJ.Xo« _l Xil UIXLL* IIL.* UOdJiJctLU. w/

! 2 X 4 on 2 X 4 at 8-ft. spacing; midrail

3-in wide on inside of posts

or

1 X CtLt U -L / C XLL WXi.C k^dU-LC ^ XLl WXLlC vert, separators at 8 ft spacing

48

or Snow fencing: 4-ft vert, wood strips

(1 1/2 in wide x 3/8 in thick at 3 1/2-in

spac.) tied with specif, taut strands.

8) OSHA

(Occupational

Safety)

/1910.23

/1910.23

/1910.28

49 XVaXXXilgo • ^ A. H dLiU UIXLL y KJvX. Z. A H at 6-ft spac; or 2 perp. 1 x 4's top on 2 X 4 at 8 ft spac. (2x4 mid)

1 1/2-in pipe top and mid. on posts at 8-ft spac.

or

9 V 9 V / ft flnolpQ tTiD pnH nriH on nrml"'^ at 8-ft. spac.

200 lb any pt. & dir.

30-34 Handrails: 2-in diam. wood;

X1 X/Z. 1 — nn T^TT^o moiint'ca/^ at* ft—"Ft" CT^ar* 200 lb any pt. & dir. XLL ^Xpc LUULlLlLcLL du O J. L o ^di_ • except up 36-42 Guardrails - scaffold: 2x4 top;

1x4 mid; supported at 10 ft. (or

equiv.) (1x6 mid. for single pt.

suspens.)

9) OSHA

(Constr. Safety)

/1926.500 200 lb any pt. & dir.

except up.

42 "Standard railing:

2x4 top; 1x6 mid;

2x4 posts at 8-ft spac.

or

± J./ z—pipe Lup , inxa , pobub

or

2 X 2 X 3/8 top, mid, posts

or Equivalent

30-34 Stair railing (plus standard rail req.)

Jl\J J Ll\JU lit O / HU^ O

/ 601-7

42 Ranlnnoc LVdXXXLlgo — Vialr* UdX^a Fvu t* oo "F rlcir»l^G i.\J\Jl. Max. opening = 5 in.

50 plf 100 plf Railings

Not clear if H & V concurrent.

Anchors: should not fail under twice

specified loads.

8
References

2.1 Construction Safety and Health Regulations, (Federal Register Part 1926), Occupational

Safety and Health Administration, U.S. Department of Labor, Washington, D.C., June 24, 1974.

2.2 Occupational Safety and Health Standards, (Federal Register Part 1910), Occupational

Safety and Health Administration, U.S. Department of Labor, Washington, D.C., October 8, 1972.

2.3 Walunas, J. B., and Miller, J. S., An Evaluation of Dynamic Performance Characteristics

of Anthropometric Test Devices, Volume 3, DOT HS-800 863, National Highway Traffic

Safety Administration, U. S. Department of Transportation, Washington, D. C. 20590,

May, 1973.

2.4 Ross, H. E., Jr., White, M. S., Young, R. D., and Lammert, W. F. , Vehicle Exteriors

and Pedestrian Injury Prevention, Volume IV-Drop Test of Dummies on a Mock Vehicle

Exterior, DOT HS-801-544, National Highway Traffic Safety Administration, U. S. Department of Transportation, Washington, D. C. 20590, May 1975.

2.5 Weight, Height, and Selected Body Dimensions of Adults, United States 1960-1962,

U.S. Department of Health, Education and Welfare, Washington, D. C. , June 1965.

2.6 Diffrient, N., Tilley, A. R. , and Bardagjy, J. C, Humanscale 1/2/3, MIT Press,

Massachusetts Institute of Technology, Cambridge, Massachusetts, 1974.

2.7 Roebuck, J. A., Jr., Kroemer, K. H. E., and Thomson, W. G. , Engineering Anthropometry

Methods, John Wiley & Sons, New York, N. Y.

2.8 McCormick, E. J., Human Factors Engineering, McGraw-Hill Book Company, New York, N. Y., 1970.

2.9 Handbook of Human Engineering Data, Tufts College Institute for Applied Experimental

Psychology, 1951.

2.10 Uniform Building Code, International Conference of Building Officials, 1973.

2.11 The BOCA Basic Building Code, Building Officials and Code Administrators International,

Inc., Chicago, 111., 1975.

2.12 Building Code of the City of New York, Volumes 1, 2, 1972.

2.13 Southern Standard Building Code, Southern Building Code Congress, Birmingham, Alabama,

1973.

9
2.14 The National Building Code, American Insurance Association, New York, N. Y. 1967.

2.15 National Building Code of Canada, National Research Council of Canada, Ottawa, Canada,

1975.

2.16 Canadian Construction Safety Code, National Research Council of Canada, Ottawa,

Canada, 1975.

2.17 Minimum Property Standards, U.S. Department of Housing and Urban Development, Washington,

D.C., 1973.

2.18 Building Construction and Facilities, Volume 4, National Fire Codes, National Fire

Protection Association, Boston, Massachusetts, 1973-1974.

2.19 Floor and Wall Openings, Railways, and Toeboards, American Standards Association,

New York, N. Y. , May, 1932.

2.20 American Standard Safety Code for Building Construction, American Institute of

Architects, National Safety Council, New York, N. Y., June 1944.

2.21 Safety Requirements for Floor and Wall Openings, Railings, and Toeboards, ANSI A12.1-

1973; Safety Requirements for Personnel Hoists, ANSI AlO. 4-1973; Safety Requirements

for Dredging, ANSI AlO. 15-1974; Safety Requirements for Concrete Construction and

Masonry Work, ANSI AlO. 9-1970; Safety Requirements for Scaffolds, ANSI AlO. 8-1969,

American National Standards Institute, New York, N. Y.

2.22 LeFevre, R. L. and Silver, J. N. Dummies - Their Features and Use, Proceedings,

Automotive Safety Seminar, General Motors Training Center, Warren, Michigan, June 1973.

2.23 Swearingen, J., Determination of Centers of Gravity of Man, Project 62-14, Civil

Aeromedical Research Institute, Oklahoma City, Oklahoma, 1962.

2.24 Kromer, K. , Push Forces Exerted in Sixty-Five Common Working Positions, AMRL - TR - 68 -

143, Aerospace Medical Research Lab, Wright-Patterson Air Force Base, Daytona, Ohio, 1969.

2.25 Croney, J., Anthropometrics for Designers, Van Nostrand Reinhold Co., New York, New York,

1971.

2.26 Van Cott, H. P., Human Engineering Guide to Equipment Design, American Institute for

Research, Washington, D. C, 1972.

10
2.27 Singleton, W. T., Fox, J. G., and Whitfield, D. , Measurement of Man at Work: An

Appraisal of Physiological and Psychological Criteria in Man-Machine Systems, Van

Nostrand Reinhold Co., New York, New York, 1971.

2.28 Woodson, W. E. and Conover, D., Human Engineering Guide for Equipment Designers,

University of California Press, Berkeley, California, 1973.

11
3. Anthropometric Data

3.1 Introduction

The objective of this section is to compile general anthropometric data on human

subjects for application in the formulation of design requirements for guardrails. For instance, the kinematic aspects of the human body could be utilized to estimate the nature

and intensity of human-induced loads on guardrails. Body measurements might be relevant

in specifying certain geometric aspects of guardrails such as the maximum size of openings

to prevent passage of people into hazardous areas. Anthropometric studies could also assist

in establishing relevant hypotheses requiring experimental verification such as the relationship between the height of the guardrail and the centroidal height of the human subject to the inhibit accidental falls.

The anthropometric information presented herein consists of four categories of data

broken down according to sex and percentile levels. The first category compiles various

height measurements where the subject is in a standing or sitting posture. The second

category consists of dimensions and weights of the human body and the heights of convenient

reference points on the body for locating other measurements such as the whole-body centroid.

The third category specifies the displacement bounds of the body centroid when the subject assumes various postures with and without a 20-lb (89-N) backpack. The fourth category

of data provides information on the maximum intensitites of forces human subjects are capable

of exerting on the guardrail. Measurements reported herein are categorized for the 97.5,

50, and 2.5 percentile levels. Percentiles are values representing the percentage of people

at or below a certain measurement. They can delineate an upper or lower bound for a specific

characteristic. With regard to body height, for example, the 98th percentile designates

the height at which 98 percent of the sample are shorter and 2 percent of the sample are

taller.

The 50th percentile in a group of measures is called the median. It is the score that

divides the ranked measures such that one half of the measures are larger than the median,

and the other half are smaller. Similarly, the 97.5 percentile can represent the larger

body measurements and the 2.5 percentile can refer to the smaller body measurements.

Although the median value for either male or female, does not exactly represent the arithmetic average or mean, it is a close enough approximation for the purposes of this report.

The average adult is the arithmetical mean between the median male and median female. All

data are for U. S. adults.

The anthropometric data presented herein have been excerpted primarily from three

different publications [3.1, 3.2, 3.3]. In addition, four other sources were consulted for

general background information [3.4 through 3.7].

12
3.2 Anthropometrics Relatable to Guardrail Height

Criteria upon which proper guardrail height may be determined focus on the necessity

of guardrails to be easily seen and to be capable of keeping an individual from a hazardous

area. The following heights may influence the determination of proper guardrail heights:

(1) Standing height : distance from floor to vertex of head, measured from either front

or back when subject is standing erect with heels together.

(2) Eye height : distance from floor to inner corner of eye when subject is standing

erect with heels together.

(3) Shoulder height : distance from floor to uppermost point on the lateral edge of

shoulder when subject is standing erect with heels together.

(4) Elbow height : distance from floor to the depression at elbow formed where bones of

the upperarm and forearem meet, when subject is in standing erect with heels together.

(5) Crotch height : distance from floor to crotch when subject is standing erect

with heels together.

(6) Seat height ; distance from floor to horizontal seat reference plane measured

when subject is in sitting posture.

(7) Kneecap height : distance from floor to top of kneecap when subject is standing

erect vrLth heels togehter.

Figure 3.1 gives a schematic illustration of the heights defined above and table

3.1 compiles their magnitudes for the 97.5, 50 and 2.5 percentile U. S. male and female

adults. These data were prepared from various recent civilian and military samples [3.1].

Guardrails could serve as a visual as well as physical barrier for most situations.

In cases where visual barriers are of primary importance, guardrail heights could be related

to eye height. In instances where a guardrail need not serve as a visual barrier but as a physical barrier and where there is little threat of individuals climbing the rail, a top

rail height just above the body centroid might prove to be sufficient. Guardrails of

elbow height are easy to lean on and could serve as work counters. Guardrails of lower

heights would not present a barrier too high to cross, but could still adequately isolate

individuals by defining hazardous areas.

13
3.3 Anthropometrics Relatable to Guardrail Height and Strength

The centroid of a body may be visualized as the point at which the resultant of

the distributed gravitational body forces acts. Other factors being equal, the stability

of an object is dependent on the location of its centroids above the ground. Stability

generally decreases as the height of the centroid relative to the ground increases and vice

versa. Consequently, it may be conjectured that a person coming in contact with a guardrail either by leaning on it or inadvertently walking into it might be less likely to go over it if the top of the rail is close to his centroid. In this case, the anthropometric

value relevant to guardrail height would be the centroidal height of the human subject.

Certain guardrail strength requirements, may be established on the basis of static

loads transmitted by human subjects in any one of a variety of stationary body postures

such as leaning or sitting, as well as dynamic loads generated by the impact of moving

human subjects. Anthropometric data relevant to estimating such body forces would be

quantitative information on the weights of the body and individual body segments. In addition, anthropometric data on shoulder and hip width, for instance, can help in

establishing lengths or areas over which body forces may be distributed.

The following anthropometric measurements excerpted from ref. [3.1] are sketched in

Figure 3.2 and compiled in table 3.2 for the 97.5, 50 and 2.5 percentile U. S. male

and female adult

(1) Whole-body centroidal height : distance from floor to the centroid of the body when

the subject is standing erect with heels together.

(2) Ischium height : distance from floor to the top of the lowermost of the three sections

of the hip bone when the subject is standing erect with his heels together. The ischium

is used as a reference point for location of other points in the body such as the centroid.

(3) Shoulder width : maximum horizontal distance across the shoulder muscles when subject

is in erect sitting posture with upper arms touching his sides.

(4) Standing hip width : maximum horizontal distance across the hips when subject is

in erect standing posture with heels together.

(5) Sitting hip width : maximum horizontal distance across the hips when subject is

in erect sitting posture.

(6) Body weight : total body weight of the subject without clothing.

It should be pointed out that data on the centroidal height of the U. S. adult female

is not available. However, Swearingen [3.2] notes that in spite of the wide variety of

Ik
Figure 3.1 Body measurements related to guardrail height (cf. table 3.1),

Figure 3.2 Body measurements related to guardrail height (cf. table 3.2).

15
Table 3.1 Height measurements from the floor level with

human subjects in standing or sitting posture.

——

Type of Percenti le Male Femal

e

'Average Adul t Measurement Level

°l'o

i nches (cm) inches (cm) i nches (cm)

Standing 97.5 74.0 ( 188.0) 68 c;J (174.0)

Height

50 68.8 ( 174.8) 63 6 (161 .5) '6.2 (168.1)

2.5 63 .

6

161 .5) 58 7 (149 11

Eye 97.5 69.3 ( 176) fid 1

1 (162.8)

Height

50 64.4 ( 163.6) 59 6 (151 .4) '2.0 (157.5)

2 .

5

59.6 1 51 .4) 54 7

Shoul der 97.5 61 .4 ( 156.0) DO Od (142.7)

Height

50 56.6 ( 143.8) 51 9 (131 .8) 'A . 2 ( 1 37 7)'

C . J 1 J 1 . o y 47 8 \ \ L \ )

El bow 97.5 45.3 ( 115.1 ) A ^ 4 1 00 (106.2)

Height

50 42.0 ( 106.7) 38 6 ( 98.0) 40.3 (1 02 4)

C , 0 JO . D 35 2

{ PQ A \

Crotch 97.5 35.1 ( 89.7) JO L ( 91.9)

Height

50 32.5 ( 82.6) 33 3 ( 84.6) '2.9 ( 33.6)

2 .

5

29.6 ( 75.2) 30 4

( 77 ?)

Seat 97.5 18.5 ( 47.0) 16 9 ( 42.9)

Height

50 17.0 ( -13.2) 15 6 ( 3q.6) ( 41.4)

2.5 15.6 ( 39. C) 14

-1 ( 36.3)

Kneecap 97.5 21 .a

( 54.4) 19 6 ( 49. C)

Height

50 19.7 ( 50.0) 18 n 1 -5.7) Ib.'^ ( 47.8;

2.5 18.0 ( 45.7) 16 ( ^1 .9)
Table 3,2 Measurement of heights, widths and weight

of human subject in standing or sitting

posture.

Type of Percenti 1

e

•a 1 e Femal

e

Average Adult

Measurement Level T nches (cm) i nches 1 ncnes ^ cin j

Who 1 e Body 07 C y / . 0 4 1 . ^: Centroid

Height 50 37.9 ( 96.3)

2.5 34.6 ( 87.9)

Ischium 9/ . b on c 39 . b ( 1 00 . 3

)

35 .£ (91 .9) Height

50 36.4 ( 92.5) 33.3 (84.6) 34.9 (88.6)

2.5 33.3 ( 84.6) 30.4 (77.2)

bhou 1 der 9/ . b 19.4 (49 . 3 j T "7 "71 / . / (4b . 0

)

Width

50 17.7 (45.0) 16.0 (40.6) 16.9 (42.9)

2.5 16.0 (40.6) 14.4 (36.6)

^t"anHi •J LOi lU 1 nn11^ 10./

Hip

Width 50 13.1 (33.3) 13.8 (35.1) 13.5 (34.3)

2.5 11.7 (29.7) 11 .5 (29.2)

Si tt i nQ y / . 0 ICQ 17 7 1 / . / Hip

Width 50 13.9 (35.3) 14.6 (37.1) 14.3 (36.3)

2.5 12.4 (31 .5) 12.3 (31 .2)

Body* 97.5 192 (854) 157 (699)

1 Weight

50 172 (765) 145 (645) 159 (708)

2.5 151 (672) 133 (592)

*lb or (N)

17
body sizes and mass distributions there is surprisingly little variation in the location

of the whole body centroid of U. S. men for any given posture when measured from a reference

point on the pelvis (i.e.: ischium), with the centroid of at least 90 percent of the adult

male population falling within a sphere of 2 in (5.08 cm) in diameter. Based on the premise

that this will more or less be true in the case of U. S. females, the differences between

the centroidal and ischium heights of the U. S. males may be added to the ischium heights

of the corresponding percentile levels of female population to arrive at generally con- servative (high side) but sufficiently accurate estimates of the centroidal heights of U. S. females. This procedure together with the appropriate data in table 3.2 yields centroidal

heights of 37.9 in (96.3 cm), 34.8 in (88.4 cm) and 31.7 in (80.5 cm) for the 97.5, 50 and

2.5 percentile female population, respectively.

3.4 Location of Centroid for Selected Body Postures

The heights, weights, and widths of body components are of limited value in

calculating static force vectors if the direction of those vectors cannot be determined.

The whole-body centroid can serve as a reference point for these static force vectors.

Since the centroid varies with the positions of the body and its extremities, it is

necessary to identify the various locations of the whole-body centroid with respect to those body postures that approximate guardrail use. Swearingen has measured centroid

variation relative to body position in subjects chosen to represent a wide range of body

sizes and weights [3.2]. Data which appear to be of relevance to guardrail use and design

are excerpted from this reference and presented in tables 3.3 through 3.6. A further

discussion is presented in reference 3.2.

3 . 5 Peak Forces Exerted by People on Guardrails

If an individual has proper auxiliary support and can push against a guardrail thereby

causing it to collapse, then a possible anthropometric criterion of maximum guardrail

strength might be the maximum strength of an individual. Strength in this sense refers

to the muscular capacity to exert force under static, conditions. Kroemer [3.3] has

measured the strength of 45 male college students. Subjects pushed against a force plate

as shown in Figure 3.3. For those infrequent instances where this loading condition is

felt to govern guardrail design, reference 3.3 should be consulted to obtain the required

load magnitudes.

3.6 Analysis of the Anthropometric Data

The intent of the anthropometric survey was to incorporate within the body of this

report a condensed and expedient source of information to assist in the evaluation of the

possible effect of human body characteristics on guardrail design rather than provide an exhaustive study on the subject. Although human body characteristics alter with time, the

rate of change is so slow as to be insignificant, design-wise over relatively long periods.

18
Table 3,3 Displacement of body e.g. by anterior movements.

Body Position Location of Av. C. G.

Horizontal &

Vertical Hange

l''or Subjects A. Body standing straight B. Head forward

C. Both arms extended forward D. J lead and trunk forward

E. Both logs straight forward

F. All body parts in maximum

anterior position

(•1. 5Th) (4%. 5S)

(5!i, 7)

(5li, 4)

(9, 11)

(12, lOS)

± Tu" ± %" ±%"

± ir

± v,r ± iH"

Table 3.4 Displacement of body e.g. by posterior movements.

Body Position Location of Av. C. G,

Horizontal &

VcTtical Hange

For Subjects

A. Standing, bodv straight (5!i, 6) i Ui"

B. Head back (5)4, 5K) ± 1" C. Arms back (SS, 6)i) ± 1" D. Head & trunk back (7!^, 5);) ± Vi"

E. Legs back (dr.. ir,) ± 1"

F. All body parts in maximum (9x, evn) posterior position

Table 3.5 Displacement of body e.g. by lateral movements.

Body Position Location of Av. C. G.

Horizontal ii Vertical Range

Kor Subjects A. Standing, body straight (0, 5X) ± j;" B. Head flexed to side ( a. 5%) ± X"

C. One arm extended laterall) ( !«. 6?;) ±

D. One arm extended across chest ( %. ay,) ± %"

E. Head and trunk in lateral (IK, 5ii) ± 3."" flexion

F. One leg abducted (la, («) ± %"

G. Maximum lateral movement of (IK. es) ± V

both legs H. All body parts moved laterall)' (4«, 7)i) ± 1«"

Table 3.6 Displacement of e.g. by 20-lb back pack

In sitting and standing positions

(e.g. of pack 18 5/8 In above Ischium, 6 In back).

Body Position Location of Av. C. C.

Horizontal &

Vertical Range

For Subjects

A. Sitting without pack

B. Sitting with pack

C. Standing without pack

D. Standing with pack

(87;, 951) (7«, 10)4) (5, 5S)

(33;, 7ii)

± 1)4" ± 1)4" ± S" ± S"

19

Percentiles can be used in design to delineate the bounds for a particular characteristic

measurement. The design of equipment or structures normally accommodates 95 percent of the

sample population by specifying an upperbound, a lower bound or both. In the latter case,

the data can be utilized directly to include 95 percent of a group having a particular body

characteristic falling within the 2.5th and 97.5th percentile values shown. In guardrail

design, however, the value of interest is more likely to be a maximum or a minimum. For

instance, if the guardrail height were to safely accommodate 95 percent of the population

(i.e., inhibit people from accidentally falling over it), then the measurement of interest

would be the centroidal height of the 95th percentile subject. Similarly, to impede the

accidental passage through the guardrail, the size of openings would probably have to relate

to the head, shoulder or chest dimension of the 5th percentile subject.

The statistical data compiled in tables 3.1 and 3.2 exclude measurements for the 5th

and 95th percentile subject required in guardrail analysis. Intermediate percentiles of

body characteristics may be retrieved by making use of the fact that anthropometric measurements generally tend to adhere to the normal probability law. Figures 3.4 and 3.5 were

developed from the measurements listed in tables 3.1 and 3.2. The ordinates in these charts

represent the magnitudes of the given measurements and the abscissa represents the percentage

of population whose corresponding measurements are less than the specified values. The

scale of the abscissa is such that the plot of a normally distributed function would

appear as a straight line. Note that in most instances the points representing the 97.5th,

50th and 2.5th percentile levels of a particular measurement are collinear. This indicates

that the distribution is symmetric but not necessarily normal. Connecting these points with

a straight line for the purpose of interpolation indicates that a normal distribution is

being assumed to describe the variable in question.

Figures 3.4 and 3.5 provide an expedient means of extracting the 5th and 95th percentile

body characteristics of both male and female subjects. The percentile characteristics of

a mixed sample may be estimated with a reasonable degree of accuracy by averaging the cor- responding measurements of the male and female subjects. With regard to the interpretation

of body weights, however, a word of caution is in order. Curves A in figure 3.4 give the

average body weights of male and female subjects corresponding to respective standing

height percentiles specified by curves A in figure 3.5. The average weight of a man having

the 95th percentile height, (see curve A of figure 3.4), for instance, is less than that of

a man having the 95th percentile weight.

21
22
INI) d'3'a S3AlinD HOJ aiVDS

(Nil p sgAanp aod giVps

CN O 00 CN o 00

in •o

(Nil g QNv V S3AanD aod aivDS

23
References

3.1 Diffrient, N. Tilley, A., and Bardagjy, J. Humanscale 1/2/3, MIT Press, Massachusetts

Institute of Technology, Cambridge, Massachusetts, 1974.

3.2 Swearingen, J., Determination of Centers of Gravity of Man, Project 62-14, Civil

Aeromedical Research Institute, Oklahoma City, Oklahoma, 1962.

3.3 Kromer, K. , Push Forces Exerted in Sixty-Five Common Working Positions, AMRL - TR - 68 -

143, Aerospace Medical Research Lab, VJright-Patterson Air Force Base, Dayton , Ohio, 1969.

3.4 Croney, J., Anthropometrics for Designers, Van Nostrand Reinhold Co., New York, New York,

1971.

3.5 Van Cott, H. P., Human Engineering Guide to Equipment Design, American Institute for

Research, Washington, D. C, 1972.

3.6 Singleton, W. T., Fox, J. G., and Whitfield, D., Measurement of Man at Work: An

Appraisal of Physiological and Psychological Criteria in Man-Machine Systems, Van

Nostrand Reinhold Co., New York, New York, 1971.

3.7 Woodson, W. E. and Conover, D. , Human Engineering Guide for Equipment Designers,

University of California Press, Berkeley, California, 1973.

2k
A. Field Survey of Guardrail Installations

4.1 General

This section presents a general overview of the types and locations of guardrails in

the work environment based on information acquired through a field survey.

The objective of the site visits was to gain familiarity with current practices of

prototypical guardrail installations and their use. Field examination of the various

guardrail types helped identify safe as well as unsafe situations due to inadequacies in

design and construction, exposure to corrosive agents and other detrimental environmental

conditions, and, in some instances, the inadequacy of the physical environment to permit

the installation of appropriate safety barriers.

Prior to the field survey, ten different types of guardrail installations in public

and industrial settings were identified by OSHA to be of primary concern. These installations

are listed in the approximate order of decreasing priority as follows:

(1) Elevated walkways

(2) Scaffolds and staging platforms

(3) Balconies and mezzanines

(4) Hot-dip galvanizing operations '

(5) Roofing operations

(6) Cast-in-place concrete construction

(7) Petro-chemical towers

(8) Mobile equipment

(9) Elevated work and storage areas

(10) Marine dry docks

Eight of these installations were included within the scope of the field survey. The

excluded ones were petro-chemical towers and mobile equipment. In addition, in a series

of "by chance" encounters, other miscellaneous types of guardrail installations were

observed to be used for the purpose of restricting human movement in a variety of extremely

hazardous to slightly hazardous areas. In all but one of the locations visited during

this survey the purpose of the guardrail was to prevent falls from a higher elevation to a lower elevation. The one location which differed was a hot-dip galvanizing plant where

the "guardrail" was used to prevent movement or falls into the hot-dip kettle containing

molten zinc at a level above the working surface. Because the barrier has considerable

width in addition to height, both of these geometric features contribute to the prevention

of workers from accidentally coming into contact with the zinc.

Visits occurred during working hours on week days. A member of the staff of the

facility being visited served as a guide for the team of NBS observers. Observations

25
during each visit were recorded on a checklist supplemented by photographs. The majority

of the visits to both public and private organizations were prearranged.

The checklist was categorized to include observations not only of guardrails, but

also other aspects of their environment. This method provided an ordered and overall view

of accident safety and a basis for developing the second phase tasks of the project. The sources of the data were: (1) comments supplied by the guide, (2) impressions of the NBS

observers, and (3) dimensional measurements and material descriptions of the guardrails.

The information gathered consisted of: (1) the general location and function of the

guardrail within the installation, (2) types of employee activities near the guardrail,

(3) environmental characteristics of the area in the immediate vicinity of the guardrail

as well as the general topography of the background, and (4) a physical description of the

guardrail.

4.2 Elevated Walkways

4.2.1 Shopping Center, First Site

The first guardrail installation examined was located on the second level of an enclosed shopping center. The area was an elevated walkway which provided access to a variety of retail stores. The guardrail functioned as a barrier resticting movement or accidental falls into a series of large wells opening to the ground level (figure 4.1).

Several types of employee activities were observed in the vicinity of the guardrail.

Human traffic to and from various locations typically occurred during the hours that the

center was open. Surveillance and monitoring of the ground floor by security employees

occurred intermittently during which time the guardrail was used for casual leaning and

watching events at the lower level. Maintenance activities near the guardrail involved

cleaning of carpets, benches and ashtrays and emptying waste receptacles.

The guardrail was well defined relative to the background and highly visible from all

points of entry into the region aided by uniform electric and natural lighting through

skylight openings in the roof. The surfaces adjacent to the guardrail were carpeted

floors with rubber tile in areas around benches.

The top rail was made of aluminum tubing material and was located 41.75 in (106 cm)

above the tread. The steel posts of tubular section were spaced at 5 ft (152.4 cm) on centers and the tubular steel toeboard was approximately 2 in (5.08 cm) high. There were

no intermediate rails but rather 0.5-in (1.27cm) round steel balusters placed 5 in (12.7 cm) on centers. As indicated in figure 4.1, several of these bannisters were bent out of

shape creating a potentially hazardous situation for accidental passage of children through

guardrail openings. However, consideration of such a concern Is not within the scope of these

studies which are addressed to the guardrail needs of adult personnel.

26
4.2.2 Shopping Center, Second Site

The second guardrail installation examined was located at the edge of an elevated

walkway at the exterior of the same shopping center (figure 4.2). The walkway was used

for delivery of merchandise to the stores and removal of trash. The guardrail served as a barrier to prevent falls into a sodded area one story below.

Three types of employee activities were observed occurring on the walkway: (1) routine

use of the walkway to gain access to either the stores or the parking area, (2) pulling or pushing hand trucks filled with merchandise, and (3) carrying boxes, packages, and other

miscellaneous discarded objects.

No extreme environmental characteristics were observed. The temperature and lighting

were natural, the sound level was produced by light vehicular traffic. The walkway was

5.9 ft (1.8 m) wide and consisted of a cast concrete slab supported by steel framing

cantilevered from the building.

The guardrail was a solid wall made of 8--in nominal concrete masonry units (7.5 in or 19 cm in actual thickness) and precast concrete capping. The top of the guardrail was

43 in (109.2 cm) above the tread surface.

4 . 3 Scaffolds and Staging Platforms

4.3.1 Library Structure

The guardrails examined at this site were located around scaffolds erected on two sides of a seven-story library building (figure 4.3). The scaffold was being used for the

purpose of applying masonry facing to this building. The function of these temporary

construction guardrails was to prevent accidental falls to a concrete plaza one to seven

stories below.

Work-related employee activities near the guardrail involved bending, stooping,

crouching and standing to perform the masonry work necessary in the marble-facing operation.

Other activities such as walking towards exit points and delivery of materials to locations

along the scaffold occurred periodically.

Visibility of the guardrails was generally good. The flooring of the scaffolds

consisted of aluminum planks. The two adverse environmental conditions observed were the

presence of materials and equipment stored along walking and working surfaces and the occurrence of intermittent wind gusts particularly at the higher elevations.

The top and intermediate rails were aluminum angles or pipe sections located at a height of 39 in (99.1 cm) and 21 in (53.3 cm) from the tread surface, respectively,

27
Guardrail location within enclosed

shopping center.
(a)

Figure 4 . 3 Temporary guardrails used during

construction of a multi-story

library building.

29
Toeboards were frequently absent. When used, they were made of 1-in by 4-in (2.54-cm by

10.16-cin), nominal, wood board. Guardrail elements were connected by bolts or miscellaneous

clamping devices.

4.3.2 Pharmaceutical Supply Co .

At this location, the guardrail was attached to a suspended scaffold being used in

the application of fascia materials to the building (figure 4.4). The intended function

of the guardrail was to prevent inadvertent falls to the ground three stories below.

The employee task near the guardrail was the application of bolts to the concrete

facade. The activity involved bending and standing. The workmen were wearing safety

belts with rope lanyards attached to the wood top rail which was being used to serve as a lifeline as well as a safety barrier.

The work was being performed on the exterior of the building and there were no unusual

characterisitcs observed with respect to lighting or temperature. The floor of the scaffold was made of aluminum planks. A potentially hazardous characteristic observed was the

presence of power tools and extension cord attachments on the floor of the scaffold.

The top rail was a 2 -in by 6-in (5.08-cm by 15. 24 -cm), nominal wood board, about 42

in (106.7 cm) above the tread. Although this rail was intended to serve as a lifeline as well as a barrier, it appeared to be structurally quite inadequate to support the impact

load of a falling human subject transmitted through the lanyard. The wood toeboard was 1 in by 4 in (2.54 cm by 10.16 cm), nominal. There were no intermediate rails. Suspended

from the roof by a counterweight device mounted on wheels (figure 4,4 b), the scaffold

could be moved easily along the building perimeter. Roofers were working at the same time

as the men on the scaffold and the perimeter guarding system for the roofers was either

removed or being laid down to allow the mobile scaffold support system to move along the

building edge. This was the first observation of a conflict between a safety requirement

for one trade and the construction method of another.

4.3.3 Miscellaneous Suspended Scaffolds

Two sites of suspended scaffolds were examined while passing buildings where construction

activity was occurring (figure 4.5). For one instance, the scaffold was being used by

bricklayers (figures 4.5 a). It was constructed entirely of wood. The guardrail consisted

of plywood boards attached to vertical wood posts joined by horizontal members at the top.

The second scaffold was located at the site of a building being remodelled (figure 4.5 b)

It appeared to have a metal plank floor and no guardrails at the ends or at the side

nearest the building. At the far side, the wood guardrail consisted of top and intermediate

rails and a toeboard, all supported by two end posts estimated to be at least 20 ft (6.1 m)

apart. This spacing was judged to be excessive in relation to the apparent size of the

30
(b)

Figure 4.4 Temporary guardrails on scaffolds or staging platforms used during con- struction of pharmaceutical building.

31
(a)

Figure 4 . 5 Examples of temporary guardrails on

suspended scaffolds used In construction, maintenance or renovation

of buildings.

32
top rail to prevent a structural failure in the event of an accidental fall of the em- ployee against the guardrail.

4 . 4 Balconies and Mezzanines

4.4.1 Hotel Structure, First Site

The first guardrail installation examined was located at the edges of the balconies

of the guest rooms of a hotel. The guardrail served as a barrier to prevent falls from

heights of one to six stories above grade (figure 4.6).

Cleaning the sliding glass doors and windows from the balcony was the principal

employee activity identified at this site.

The temperature and lighting were natural. The balcony slab was cast-in-place concrete.

The walls were either glass panels or brick, veneer. The balcony was about 31 in (78.74

cm) wide.

All guardrail components appeared to be made of aluminum. The top rail was a 2-in

wide by 4- in deep (5.08-cm by 10.16-cm) rectangular tube, the top of which was 42 in

(106.7 cm) above the tread. There were no toeboards or intermediate rails but rather,

0.75-in (1.9-cm) square tubular balusters 6 in (15.2 cm) on centers between the top rail

and a 1-in. (2.54-cm) square tubular bottom rail 6.5 in above the tread. The posts were

2-in (5.08 cm) square tubular sections at 52-in (132 cm) intervals. Each post was fitted

into the sleeve of a base plate and attached to it by two screws driven from opposite

sides. The rail components were connected by welds and screws. The square base plate was attached to the concrete slab with four anchor bolts and nuts which were not galvanized.

As a result, evidence of severe corrosion was observed at several locations. In addition,

many of the nuts had become loose or completely detached.

4.4.2 Hotel Structure, Second Site

The second guardrail installation examined was located within the lobby of the same

building. The lobby served as an access to various hotel service areas and as a sitting

lounge. On each side of an open stairway, a guardrail served as a barrier to prevent

falls to the ground level one story below (figure 4.7).

The employee activities occurring near the guardrail were routine walks from one location to another and cleaning operations of floors.

The light level was high because of a nearby window wall. In additon, the window

wall produced a significant amount of reflected glare in the location adjacent to the

guardrail.

33
(a)

Figure ^.6 Permanent guardrail Installations on

balconies of multi-story hotel

structure

3U
(a)

Figure 4.7 Permanent guardrails used in lobby

of hotel structure.

35
The guardrails were quite similar in materials, layout and sectional configuration to those installed at the balconies (section 4.4.1) except the top rail was a 2-in wide by 4-

in deep (5.08-cm by 10.16-cm) finished wood board. Since these guardrails were located

indoors, no evidence of corrosion at the anchorages was anticipated and none was observed.

4 . 5 Hot-Dip Galvanizing Operations

4.5.1 Galvanizing Plant, First Site

The first location examined was a galvanizing kettle containing molten zinc

equipped with an overhead conveyor system (figure 4.8). In this case the walls of the

kettle above the work surface served as a barrier (guardrail) to keep the employees from

accidentally coming in contact with the zinc. The top shelf of the wall sefved as a support for hand tools used by the employees working at the kettle.

Routine work-related employee movements included walking, standing next to and leaning

over the barrier to skim the zinc surface with a wooden paddle and tapping the galvanized

objects with long implements as they were retreived from the kettle.

The lighting around the work area was generally much dimmer than in a typical office.

The concrete floor surfaces adjacent to the kettle were generally cluttered with debris.

The top of the wall barrier was 31 in (78.7 cm) above a 7-in high by 34-in wide

(17.8-cm by 86.4-cm) platform (tread surface) located on the working side of the kettle.

The width of the wall was 28 in (71.1 cm) at the top. This surface was made of welded

steel plates. A typical sectional configuration of the barrier is shown in Figure 4.8 b.

4.5.2 Galvanizing Plant, Second Site

The galvanizing kettle examined at this location was similar to the first one except

the kettle walls were shallower and there were no raised work platforms (figure 4.9). As

before, both the height and width of the kettle walls served as barriers to restrict employees

from coming in contact with the molten zinc. The top of the wall was used as a shelf for

various tools and as a means to gain leverage in maneuvering the galvanized objects with

metal implements.

In addition to the work activities observed at the first site, the employees were

engaged in manipulating and aligning a large suspended appliance. This involved pulling

cords, pushing and tapping the appliance with hand implements, and jacking it with long

rods using the shelf of the wall as pivot.

The environmental charactertistics were similar to those observed earlier. The

accumulation of substantial debris on the floor adjacent to the exit side of the kettle

36
ten"*'' wm:'

(a)

First example of wall barrier

around molten zinc kettle used in

galvanizing operations.

37
(the foreground area shown in Figure 4.9 b) caused a reduction in the wall height at that

location and consequently in its effectiveness to function as a safety barrier.

The sectional configuration of the wall barrier was rectangular as shown in figure

4.9(c), the height and width being 26 in (66cm) and 24 in (60.1 cm), respectively. The

walls consisted of an assembly of welded steel plates.

4.5.3 Galvanizing Plant, Third Site

At this location the galvanizing was carried out by using manually controlled

chain and pulley equipment (figure 4.10) as opposed to the use of conveyor systems observed

at the first two locations (figures 4.8 and 4.9). As before, the walls of the kettle

functioned as barriers to prevent accidental body exposure to molten zinc and as support

for the hand tools used by the employees working at the kettle.

Besides the activities noted earlier, this operation required manipulation of the

chain-pulley assembly to lower or raise the objects being galvanized. The kettle was equipped with a ledge which provided a bearing surface for the foot to facilitate pulling

the object out of the vat. However, the ledge reduced the effective height of the barrier

and encouraged hazardous postures, for the putpose of gaining reach advantage, such as shown in Figure 4.10 c.

Visibility and other environmental factors were similar to those observed at the

other two locations. The concrete tread surfaces near the kettle were likewise littered

with various objects and debris.

The barrier was 25 in (63.5 cm) high on all four sides and had an 11-in high by 10-in

wide (27,9-cm by 25.4-cm) ledge or projecting shelf on the working side, thereby reducing

the effective height of the barrier above it to 15 in (38.1 cm). The 31-in (78.7-cm)

width of the barrier was in excess of those at the other two locations. The surfaces were made from welded steel plates. The line drawing in figure 4.1 (d) shows the cross sectional

configurations of the kettle.

4 . 6 Roofing Operations (Retail Merchandise Distribution Center)

The purpose of this visit was to examine the perimeter-guarding installations used

during a large built-up roofing operation on a warehouse having approximately 46 acres of

(18.63 ha) storage area. The roof was approximately 30 ft (9.1 m) above grade and the

roofing operations were at various stages of completion (figure 4.11 and 4.12). The

guardrails at this site were symbolic rather than physical barriers, placed at a distance

from the edge of the roof to alert workers of the potential hazards of the region beyond

the demarcation line. These rails were not in compliance with the existing perimeter

38
(b)

Figure 4.9 Second example of wall barrier

around molten zinc kettle used in

galvanizing operations.

39
Figure A .10 Third example of wall barrier around

molten zinc kettle used In galvanizing

operations

UO
guarding regulations of OSHA. However, because of an absence of construction provisions,

prior to the roofing operations, for the attachment of compliant guardrail systems, the

roofing contractor had been given a variance by OSHA to use the portable symbolic guardrails

shown, subject to specific restrictions governing the movement of workers within defined

hazard zones at the periphery of the roof.

The primary activities for installing the roofing were pushing and pulling machines

while applying layers of felt or tar, bending to place installation, or standing and

shovelling gravel. At one time or another, the application of each layer required the

employees to get close to the edges. Operations and application of roofing to the edge

required the joint effort of 2 to 3 workers whose movements included standing, walking

leaning and crouching.

Extension of the facade beyond the top of the roof provided about a 12-in (30.5-cm)

high ledge at its periphery. This served the (unintended) function of a toeboard and

provided some measure of safety for employees when conducting their work tasks in a crouched

posture. The roofing consisted of a corrugated steel deck on open web steel joists, and

layers of rigid insulation boards, tar-coated roofing felts and gravel. At times the 1/4-

in (0.6-cm) wire rope warning rails were not readily discernible against the background

terrain (figure 4.11 a) and in some instances the light brown gravel surface merged with

the clay-colored terrain 30 ft (9.1 m) below making it difficult to visually discriminate

the drop beyond the roof edge. The presence of equipment and various materials on the walking

surfaces near the edges required a certain level of alertness on the part of the observers

to avoid tripping. Also very hazardous, was the slippery corrugated metal deck surface when wet.

The symbolic guardrail consisted of two 1/4-in (0.64-cm) wire ropes clamped to steel

posts attached to 40-lb (178-N) cast concrete blocks at the base. Trials were being

made to increase the lateral stability of the posts through adhesion of stick clips with

the tar surface (figure 4.12 b) . Without such adhesion, a 6 lb. (26. 7N) horizontal force

applied to the top of the post would cause it to overturn.

4. 7 Cast-In-Place Concrete Construction

Two types of guardrails which were used in cast-in-place concrete construction work were

examined while passing sites where construction was occurring. At the first site, the guardrail was being used to prevent falls from a walkway work platform adjacent to the concrete

forms around the buildings (figure 4.13 a). The walkway appeared to be used by

carpenters during the preparation of the wood formwork, by workers placing the steel

reinforcement inside of the forms, and by workers casting and curing the concrete.

The guardrails were assembled in a manner to permit quick dismantling and reassembly

for use in construction of additional floors of the building. They consisted of 2-in

kl
Figure A. 11 Symbolic guardrails used in built-up

roofing operations.

U2
Figure 4,12 Additional exhibits of built-up

roofing operations.

U3
by 4-in (5.08-cm by 10.16-cm), nominal, wood, top and intermediate rails and vertical

supports spaced approximately 8 ft (2.44 m) on centers. The rails were fitted into the

slots of plywood gusset plates nailed to the posts. The platform guardrail assembly was supported by equally-spaced 4-in (10.16-cm) square, nominal, wood beams wedged between the

exterior concrete floor beam and 4-in (10.16-cm) square, nominal, spliced wood shoring

posts below, and by diagonal members fastened to the same shoring posts. No guardrail

toeboards were observed at this site.

At the second site visited (figure 4 . 13 b and c) , the concrete had already been cast

and the forms removed. The guardrails were placed at the edge of the concrete slabs to prevent accidental falls of workers engaged in concrete curing and finishing operations.

The guardrails consisted of modular steel pipe framing units Joined together by a wood top

rail. The assembly was seated on the concrete slab but not attached to it.

4 . 8 Elevated Work or Storage Areas

4.8,1 Library Building, First Site

The guardrails examined at this site were located in construction work areas around

large central openings inside the building (figure 4.14) to prevent accidental falls of

workers from 12-ft to 72-ft (3.66-m to 21.95-m) high elevations.

The only employee activity observed was the routine movement of walking past the

guardrails. Other construction-related activities are likely to occur near the rails

where the interior finishes are applied and permanent guardrails are installed at the same location before the building is put in service.

The lighting around the guardrail area was generally dim. As a result, the. cable

rails and sometimes the wood rails as well, tended to merge with the background and were

not always readily visible. Another hazardous situation was the presence of miscellaneous

construction materials and debris on the concrete floor adjacent to the rails.

There were two types of guardrails installed around the opening. One was constructed

of wood (figure 14. a) with a 42-in (106.7-cm) high top rail and 24-in (61-cm) high intermediate rail. The spacing of the vertical posts varied from 5 ft to 7 ft (1.5 m to 2.1 m) on centers and the toeboard height varied from 4 in to 10 in (10.16 cm to 25.4 cm). The

wood members were typically 2 in by 4 in (5.08 cm by 10.16 cm), nominal, and were fastened

together with nails. The second type (figure 14. b) used 1/2-in (1.27-cm) wire rope top

and intermediate rails, 43 in (109.2 cm) and 22 in (558 cm) from the tread, respectively.

The vertical wood supports were spaced between 5 ft to 7 ft (1.5 to 2.1 m) on centers.

The wood toeboard was 6 in (15-2 cm) high. The wire ropes were looped around and tied to concrete columns located along the periphery of the openings. They were kept taut by means

of turnbuckles.

kk
Figure 4.13 Miscellaneous types of temporary

guardrails used in cast-in-place

concrete building construction.

U5
Figure 4.14 Temporary guardrails installed around

openings during construction of

raulti-story buildings.

U6
4.8.2 Library Building, Second Site

The second location observed was a materials storage area adjacent to a large opening

in the exterior wall of the building (figure 4.15). The location served as a storage area

for bricks and as an access point to the exterior scaffolding. The guardrail was symbolic

and served the purpose of alerting workers to the opening approximately 10 ft (3 m) away.

The only employee activity observed was the routine movement of walking past the

guardrail. It was assumed that the use of hand and motorized vehicles for carrying brick

occurred near the rail.

The concrete floor surface adjacent to the rail was littered with wood remnants and

other miscellaneous debris.

The guardrail consisted of two wire ropes loosely attached to two of the building

columns approximately 30 ft (1.4 m) apart. The top rail was 35 in (89 cm) high and the

intermediate rail was 14 in (35.6 cm) high. There were no toeboards.

4.8.3 Post Office Building

The guardrails examined were located in the mail sorting and routing areas of a large

post offfice. They were installed around platforms used for the maintenance of conveyor

belts and other machinery (figure 4.16). The platforms were approximately 12 ft (3.66 m)

high and the rails served as barriers to prevent falls (figure 4.16).

While no employee activities were observed during the visit, the guide noted that

cleaning, repair and maintenance work of motors and other pieces of equipment were the

primary type activities on the work platforms.

The lighting on the platforms was adequate to distinguish between small objects. The

working surface was made of steel grating .

The top rail on the first type of platform was 41 in (104.1 cm) high with a 20-in

(50.8-cm) high rail and a 3-in (7.62-cm) high toeboard. Vertical supports were located at 5.25-ft (1.6-m) intervals. The top rail, intermediate rail, and toeboard were made of

steel angles connected with bolts, and welds. On the second type of platform, the top

rail was 41 in (104.1 cm) high, the intermediate rail was 21 in (53.3 cm) high, and the

toeboard was 3 in (7,62 cm) high. Vertical supports were spaced at approximately 3 ft

(91.4 cm) on centers. The rails were steel pipe sections and the toeboard was a steel

angle. All connections were welded joints. On the third type of platform the top rail was 36 in (91.4 m) high, intermediate rail was 18 in (45.7 cm) high, and the toeboard

was 4 in. (10.16 cm) high. Vertical supports were spaced at approximately 5.75 ft (1.75 m) on centers. The rails were steel pipe sections and the toeboard was a steel angle.

All connections were welded joints.

UT
Figure 4.15 Temporary guardrails around storage area used during construction of

multi-story building.

Figure 4.16 Guardrails installed around platform

used for maintenance of machinery.

1^8
4 . 9 Marine Dry Docks

4.9.1 Ship Yard, First Site

The guardrails examined at this site were located around a dry dock for the maintenance

and repair of ships (figure 4.17). Judging from a posted sign warning people not to lean

against them, these guardrails were intended to be symbolic rather than physical barriers

to prevent falls to a concrete surface approximately 50 ft (15.2 m) below.

The warning signs were not always effective in discouraging employees from leaning

against the guardrail to observe activities in the dry dock area (figure 4.17 b) . There were no other activities observed except employees walking past the guardrail.

The guardrail was visible at all locations visited. There was evidence of corrosion

which is probably aggrevated by the proximity of a large body of water as well as by rain

and humidity. Another potentially hazardous condition experienced was the occurrence of

high wind gusts in the general vicinity of the guardrail.

The guardrail consisted of cast steel posts spaced at 7.25 ft (2.2 m) on centers, a set of 2 or 3 steel chain rails passing through slots in the posts and occasionally, a 7- in (17. 8-cm) high concrete curb or metal toeboard (figure 4.17), Despite the warning

sign, at first glance the guardrail could convey the false (and dangerous) impression of

being structurally sturdier than it actually is. This is partly due to the fact that the

chains are installed with a built-in slack and are not constrained from sliding through

the slots. Consequently, a force applied to the rail will cause it to sag excessively by

taking up the slack from the adjacent spans as in figure 4.17(b), It also appeared that some of the post anchorages would not be capable of transmitting lateral forces to the

foundation because of either loose fittings, or insufficient edge distance.

4.9.2 Ship Yard, Second Site

At this site the guardrail was located around a marine railway catwalk (figure 4.18).

The marine railway is used for the maintenance and repair of submarines. The guardrail

functioned as a barrier to prevent falls into water or onto a wood deck or concrete surface

approximately 50 ft (15.2 m) below.

While no employee activities were observed during the visit, the guide noted that the

catwalk was used only as a walkway.

The surface around the guardrail was a wood plank floor. The catwalk was 42 in

(106.7 cm) wide. The characteristics considered potentially hazardous were excessive

projections of the anchoring devices into the walkway and the occassional gusts of wind.

h9
(b)

Figure 4.17 Permanent symbolic guardrails installed at marine dry dock facility.

50
There were different guardrails on each side of the walkway. On the outside (the

side away from the ship being worked on), the top rail was 37.5 in (95.2 cm) high with

vertical supports at 5 ft (1.5 m) on centers (figure 4.18 a). There was no intermediate

rail or toeboard. The top rail and vertical supports were made of steel pipe connected by

bolts and welded joints. On the side adjacent to the ship, the guardrail was a series of

sections of steel pipe 17.5 in (44.4 cm) high by approximately 6 ft (1.83 m) long (figure

4.18 b) . The sections were spaced approximately 4 ft (1.22 m) apart. Connections were

made by bolts and welded joints. The size and design of the rail appeared to provide

little protection from falls.

51
Figure A . 18 Permanent guardrails on elevated catwalks.

52
5. A Conceptual Model of Safety

5.1 Introduction

Safety research attempts to identify methods by which accidents and their consequences

can be eliminated or mitigated to insure an acceptably low level of risk of injury or death. Since gtiardrails are intended to prevent people from entering or falling into

hazardous areas, they may be treated as units within a broader framework of a safety system

consisting of human and environmental factors. This framework can then serve as a qualitative guide in the preparation of safety requirements for guardrails.

A number of conceptual models have been developed which attempt to identify causes of

accidents [5.2, 5.3]. Although most of these descriptions have assisted in further

exploration and understanding of accidents and the accident development process, their

practical usefulness in designing safe environments or determining safe behavior are

limited. This is largely due to the fact that accident research, in general, attempts to identify the causes of accidents post hoc, based on accident data which is seldom adequate.

On the other hand, safety research is focused on the prevention and control of accidents

through the specification of the requirements for safe environments and procedures. Another

deficiency of accident research models is that they emphasize either human causes of accidents

or environmental causes of accidents. Safety is a result of complex interactions between

both sets of variables, however, and can best be developed and maintained through a simultaneous treatment of both.

The safety model presented in this section attempts to systematize a decision-making

process that has heretofore been subjective and often incomplete. Since it is based on fundamental notions of safety originally formulated by Gibson [5.1], a brief introduction

to Gibson's ideas is presented first. This is followed by a detailed description of the

safety model.

5.2 Gibson's Margin of Safety Concept

Gibson proposes that a margin of safety exists between an individual and an accident.

By behaving recklessly an individual overextends his margin of safety and increases the

likelihood of an accident; conversely, he may behave very cautiously and decrease the likelihood of an accident. Safe behavior is that which falls within an individual's margin of

safety.

According to Gibson, Individuals overextend their margin of safety in two ways. The

first is by misperceiving danger in the environment (i.e., perceptual failures), the second

is by reacting inappropriately to a perceived danger (i.e., behavioral failures). In short,

"an individual may suffer harm from a failure to perceive or a failure to act." Perceptual

53
and behavioral failures are often due to the absence of the environmental characteristics

which indicate danger (as in a dark surrounding) , or due to unreliable environmental

characteristics (such as seats that look sturdy but are not) . Perception may fail even when environmental characteristics are present and reliable. This may occur because of

(a) defects in the sensory apparatus; (b) immaturity of the sensory apparatus; (c) temporary

incapacity from drugs or illness; (d) untrained discrimination; (e) inattention. Behavior

may likewise fail even though the environment provides cues to safety performance. This

may occur because of defective, inadequate untrained, or temporary incapacities of behavior.

As with perceptual failures the solutions to these performance failures most often involve

training and education.

5 . 3 A Conceptual Framework of Safety

The conceptual safety model displayed in figure 5.1 extends Gibson's- fundamental

notions of safety by taking into account additional human and environmental factors and

their interrelationships. First, accidents occur in social as well as physical environments.

Safety is often a function of interpersonal activities or cultural attitudes. Safe individual behavior may do little to prevent an accident if others are behaving carelessly. Similarly, in many settings safety is a matter of management policy or the social norms of a community.

Second, safe physical environments as well as social environments can be considered

in more detail. ' In addition to failures in the most immediate (proximal) environment,

accidents may be caused by failures in the distal environment. The extent of fire damage

to a building, for example, is often related to the inaccessability of firefighting

equipment or units. To be complete in specifying safety requirements then, any conceptualization must include characteristics of distal as well as proximal environments.

Third, Gibson's approach appears to account only for perceptual and behavioral failures

as it does not specifically address individual characteristics and abilities. Accidents,

however, are often caused by structures or equipment whose design does not incorporate the

body measurements (anthropometric) of their users, or by the lack of physical or mental

ability of an individual to perform the proper activity, as in the case of the elderly.

Fourth, by focusing on the prevention of accidents, Gibson considers only part of the

total accident sequence. A more complete analysis might apply Gibson's principles not only

to the human (behaviors, abilities, and anthropometrics) and environmental (social and

physical, proximal and distal) factors preceeding an accident, but also to those factors

which contribute to the continuation of the accident and factors which prevent or impair

I recovery from an accident. By including such factors, safety practitioners can identify the

safety requirements for the control of and recovery from accidents, as well as for accident

prevention.

5h
Finally, by suggesting that the margin of safety concept is focused on behavior,

Gibson precludes many of the factors that originate in the environment. Not only do

individuals cause accidents by perceptual failures, behavioral failures, etc., but environments cause accidents by failing to provide proper or adequate information which supports

behavior.

The model shown in figure 5.1 incorporates the foregoing factors and provides a schematic illustration of the interactive process. As indicated in the figure, human

factors that contribute to accidents may be related to an individual's physical characteristics, abilities, or activities. Physical characteristics include body measurements (anthropometric data) and body structure (mechanical properties) ; abilities include physical and

mental abilities; and activities include perceptual and motor behaviors. Environmental

characteristics can originate from either the social or the physical environment. Physical

environmental factors are found in either the proximal or distal environments. In particular,

guardrails can be considered as physical factors located in the proximal environment, as shown by the shaded elements in figure 5.1.

Table 5.1 summarizes the analysis step of the safety model. In this step, each human

and environmental factor is analyzed to identify how they may contribute to an accident.

Human factors may contribute to accidents by being defective, inadequate, temporarily

incapacitated, or untrained (or underdeveloped). Environmental factors can contribute to accidents by being absent or unreliable. In addition, the safety model reveals that human

factors may conflict with environmental factors to cause accidents, as when an elderly

individual attempts to climb a set of stairs that are dimly lit or do not have a handrail.

In other instances, anthropometric characteristics may conflict with proximal environmental

characteristics, as when guardrails with toprails set below the human body centroid height

make it physically easier for an individual to fall over them. Also, individual activities

may be in conflict with proximal environmental characteristics as in the case -of welders

working on skyscrapers. The model, then, provides a framework for the qualitative statement

of safety requirements. Table 5.2 illustrates how this may be achieved. For example,

besides training, developing, educating or selecting abilities, the safety practitioner

might accommodate or incorporate the physical characteristics or activities of the user

into the design of the environment.

55
SICAL

TERISTIC BODY MEASUREMENT

PHY!

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ACTIVITIES PERCEPTUAL BEHAVIOR

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SICAL

TERISTIC DISTAL

PHYJ

IAriAl> PROXIMAL

OTHER THAN

GUARDRAILS

u GUARDRAILS

ENVIRONMEKTk

FACTORS <^

INTERACTIONS

Figure 5.1 The conceptual model of safety.

56
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References

5.1 Gibson, James J., The Contribution of Experimental Psychology to the Formulation of

the Problem of Safety, a Brief for Basic Research, Behaviorial Approaches to Accident

Research, Association for the Aid of Crippled Children, New York, New York, 1961.

5.2 Johnson, W. G., Sequences in Accident Causation, Journal of Safety Research, National

Safety Council, Chicago, Illinois, June 1973.

5.3 Surry, Jean, Industrial Accident Research, A Human Engineering Appraisal, Labor

Safety Council, Ontario Ministry of Labour, Toronto, Ontario, 1974.

59
6. An Analysis of Guardrail Accidents

6.1 Introduction

Industrial accident reports are analyzed within a conceptual framework which considers

guardrails as units within a safety system (section 5), Included is information on the

location of guardrail accidents, the work tasks and activities of the employee at the time

of the guardrail accident, the injuries resulting from the guardrail accident, and the

sequence of events that led to the guardrail accident. A clear understanding of effective

as well as ineffective guardrail performance is important. The analysis of guardrail

accidents reported herein attempts to identify activities associated with guardrail misuse

or failure.

This section consists of three main sub-sections. The first describes the approach

used in the analysis of guardrail accidents in industrial settings based on the conceptual

safety model. The second presents an analysis of industrial accident investigations collected

from a major source of accident reports: the National Safety Council (NSC). The third

section presents a statistical analysis of causes of industrial accidents collected from

two sources of industrial accident statistics: the New York Department of Labor and the

United States Bureau of Labor Statistics.

6.2 Systems Approach to Guardrail Safety

The interaction between guardrail factors and guardrail user (employee) factors that

contribute to guardrail accidents are shown in table 6.1. Each employee/guardrail interaction creates one of four work situations (i.e., accident, incompetence, victimization or emergency) each of which varies in the degree of safety present. Incompetence situations

arise from an employee exhibiting unsafe behavior near a safe guardrail, such as sitting

or standing on the top rail. An employee working near the edge of an unguarded, elevated

surface represents a victimization situation. Accident situations occur "for no apparent

reason," that is, when an employee is apparently exhibiting safe behavior near a safe

guardrail. Emergency situations occur when an employee is acting carelessly near an unsafe

guardrail.

Each work situation suggests guidelines which may rectify the unsafe conditions.

These are shown in table 6.2 Incompetence situations suggest the specification of human

performance guidelines to promote safe conditions. Victimization situations suggest the

specification of design and construction guidelines to promote safe conditions. Emergency

situations suggest the adherence to design and construction guidelines previously specified

by the incompetent and vicimization situations. Accident situations suggest the specification of new or improved design, construction or user performance criteria. In addition,

each unsafe situation suggests the need to implement prevention, control, and recovery

60
Table 6.1 Employee/guardrail interactions and the four

levels of safety situations that they create.

HUMAN/ENVIRONMENT

INTERACTIONS

FOR

GUARDRAILS

GUARDR/!\ll FACTORS

Safe guardrail

factors

Unsafe guardrail

factors

EMPLOYEE

ACTIVITIES

Safe

employee

activities

ACCIDENT

SITUATIONS

VICTIMIZATION

SITUATIONS

Unsafe

employee

activities

INCOMPETENCE

SITUATIONS

EMERGENCY

SITUATIONS

Table 6.2 Safety guidelines and safety countermeasures

suggested by work situations

WORK

SITUATION

SAFETY

GUIDELINES

SAFETY

COUNTERMEASURES

ACCIDENT

SITUATION

New design guidelines

New construction guidelines

New human performance

guide! ines

INCOMPETENCE

SITUATION

Human performance

guidelines

Prevention countermeasures

Control countermeasures

Recovery countermeasures

VICTIMIZATION

SITUATION

Design guidelines

Counstruction guidelines

EMERGENCY

SITUATION

Adherence to: Design guidelines

Construction quidelines

Human performance guidelines

61
countermeasures . Prevention counterraeasures decrease the probability of occurrence of

unsafe situations. Control countermeasures either control the unsafe condition or mitigate

the severity of the consequences. Recovery countermeasures alleviate the nature, extent,

or severity of personal injury or property damage. Table 6.2 indicates that prevention,

control and recovery countermeasures all may interact with design, construction, and user performance guidelines.

6 . 3 Analysis of Guardrail Accident Reports

The National Safety Council (NSC) volunteered 5,467 reports on accidents of various types

for analysis. These data were originally collected in 1974 by the NSC for the American Society

for Testing and Materials (ASTM) during a project which was focused on identifying areas of need

for occupational safety and health standards [6.1, 6.2]. Since the companies were assured that

they would remain anonymous, no names will be reported in this review.

The sample represents 80 establishments employing a total of about 40,000 workers in

the following eight, industries: automotive, steel, mining, building materials, construction,

meat packing and leather, retail, and chemical.

The NSC revision of the OSHA Form 101 titled "Supplementary Record of Occupational

Injuries and Illnesses," was used in the project. It combines the standard narrative

reporting along with a precoded feature helpful in computer analysis. The narrative

statements proved to be most useful in identifying major types of guardrail accidents, and

these were analyzed following documented procedures [6.3, 6.4].

The analysis of the accident reports revealed six major types of guardrail-related

accidents, (1) guardrail failure, (2) guardrail misuse, (3) guardrail as cause of injury

(guardrail absent), {h) walking surface accident (guardrail absent), (5) platform accident

(guardrail absent), (6) fall from high elevation. A composite of each accident type is

described below. Included in each description is information as to where the accident

occurred (Location), the task that the employee was performing at the time of the accident

(Task), the activity that the task necessitated (Activity), the injury that resulted from

the accident (Injury), and a brief description of the sequence of events of the accident

(Sequence of events). Following the third and sixth accident types, guidelines and countermeasures are suggested that might rectify the unsafe situations.

6.3.1 Accident Type #1, Guardrail Failure

Location: Within a specified work area.

Task: Performing specific work tasks.

62
Activity : Walking, bending, reaching, pulling, pushing, etc.

Injury : Broken bones and concussions.

Sequence of events : Many times objects would fall from one elevation and injure an employee

working below. Other times, an employee would trip on debris or a rough or slippery floor

surface, fall toward a guarded edge, and over a low guardrail.

User-environment interaction : A common demoninator of these accidents is that they could

have been controlled or prevented through safe guardrail design or construction practice.

With respect to the above examples, toeboards would prevent objects from sliding under

guardrails and higher guardrails would prevent individuals from falling over them.

Similarly, individuals would be prevented from falling through guardrail openings if the

space between the rails was minimized. Since the employees appear to exhibit safe behavior

in these instances, the accidents may be mostly attributed to unsafe guardrail factors

and as such would fall under "victimization" work situations (table 6.1). It was noted,

however, that with respect to other accident types, these accidents seemed to occur somewhat less frequently.

6.3.2 Accident Type #2, Guardrail Misuse

Location : On the job, in the plant or work area.

Task : Operating equipment or handling materials.

Activity : Reaching, climbing, or jumping.

Injury : Sprained ankle, leg, arm or back.

Sequence of events : Employee misuses guardrail to climb upon, or over, and often to circumvent a more time consuming or difficult action. As a result, the guardrail fails to protect the employee from a hazardous area or dangerous fall.

User-environment interaction : This type of accident represents an "Incompetence" situation

in which the user of the guardrail does not exhibit safe behavior (see table 6.1). The

only difference between this type and Accident Type #1 is that the guardrail structure does

not fail under misuse, although , they both involve static forces applied by the employee.

6.3.3 Accident Type //3, Guardrails as Causes of Injury

Location : On the job, in the plant or work area.

Task : Operating or servicing equipment.

63
Activity : Walking from one location to another in a work area while performing task.

Injury : Bruise or fracture of leg, arm, or hand.

Sequence of events : Employee often falls upon or impacts against the guardrail. The cause of the fall is often not related to the guardrail; however, the guardrail is usually

the cause of the injury. In some cases, proper placement of the guardrail could have

averted the accident.

User-environment interaction ; Since guardrail factors are safe and the employee usually

exhibits safe behavior, this accident type is categorized as an "accident" situation

(table 6.1).

6.3.4 Suggested Guidelines and Countermeasures for Unsafe Situations in Which Guardrails

Were Present but Were Either Misused or Caused Injury

Accident types //2 and #3 could have been mitigated had the employees not misused the

guardrails and if the guardrails were designed properly. Improved design, construction

and behavioral guidelines, though, could better control the accident situation and to some extent even the incompetence situation. First, guardrails may be designed and constructed

to withstand a limited amount of misuse. Studies by Kromer (see Section 3.5) identified

maximum forces that an individual can exert against a guardrail-type barrier. These

accident data provide some support for using push-force information in designing and

constructing guardrails that are strong enough to withstand forces exerted by employees

using them as supports. A second set of guidelines might focus on dynamic forces that

falling people could transmit to guardrails. Furthermore, many accident situations indicate

that guardrails which are more noticeable than others are less likely to cause injury.

These accident data suggest countermeasures that would make guardrails more noticeable and

less likely to be bumped into or fallen upon. Such measures might involve new construction

materials as well as height or placement guidelines. Finally, type #1 accident situations

could be controlled and/or prevented by guardrail designs which complement employee activities.

6.3.5 Accident Type #4, Guardrail Absent: Walking Surface

Location : In the plant but not on the job. Often in a public area or hallway.

Task: Employee is usually not performing a work task at the time of the accident.

Activity : Walking or standing.

Inj ury ; Bruise or strained back or leg. Lacerations of the hand, leg or arm are also

common.

6h
Sequence of events ; Employee slips or trips and falls on walking surface while walking

from point A to point B on company property. Common accident agents are slippery floors,

holes or cracks in the sidewalk, protruding equipment or stock. In many instances the

victim does not fall but strains himself while restoring his balance. Other times, the

employee hits his head on overhanging equipment or cuts his hand or leg on protruding

stock or machinery.

User-environment interaction : This type of accident can be categorized as a "victimization"

situation since the employee is exhibiting safe behavior in the environment but an unsafe

guardrail factor (unguarded area) causes the accident (table 6.1).

6.3.6 Accident Type #5, Guardrail Absent: Fall from an elevation

Location : On the job, in the plant or work area.

Task: Maintenance and materials handling.

Activity : Walking, standing, climbing, or reaching.

Injury : Back and head injuries.

Sequence of events : Employee is often working around an unguarded area, loses his balance

and falls from one elevation to another. He is often performing a maintenance task of some kind in which he subjects himself to some degree of risk.

User-environment interaction : Due to the absence of guardrails, the environment must be

considered unsafe in most cases. As long as the employee is not engaged in reckless behavior

the unsafe situation can be considered one of "victimization."

6.3.7 Accident Type #6, Guardrails Absent: Platforms

Location : On the job, in the plant or work area.

Task : A variety of job tasks ranging from operating equipment and hand tools, to clerical

work in an office or stock area.

Activity : These accidents predominantly occur while the employee is stepping down, stepping

off or stepping onto a raised platform of some sort.

Inj ury : Twisted ankles or knees.

Sequence of events : Employee twists his/her ankle while stepping off an unguarded platform.

65
User-environment interaction : Inasmuch as a guardrail, properly placed, might have

prevented the individual from leaving or entering th platform at the hazardous area (an area on which a twist is more likely than not^ , this situation is categorized as "victimization." Obviously, this does not apply to cases in which the platform was merely a stool

or a bench. This categorization does apply to low platforms where guardrails would

designate safe areas to enter or exit.

6.3.8 Suggested Guidelines and Countermeasures From Unsafe Situations in Which

Guardrails Were Absent and Employees Were Injured as a Result of Falls on Walking Surfaces, From Platforms, or From One Elevation to Another

All the accident types relevant to the guardrail-related falls reported above represent

"victimization" situations in which the lack of guardrails led to an injury. This implies

that the presence of guardrails might have prevented the fall or at least controlled it well

enough to minimize injury. Guidelines for the proper placement of guardrails might prevent

death resulting from a fall into an open pit as well as a twisted ankle resulting from a fall off a low platform. These data emphasize that the placement and function, as well as the design and construction of guardrails, are components in a complex building safety

system in which guardrails contribute to the prevention and control of accidents.

6 . 4 Statistical Analysis of Guardrail Accidents

6.4.1 New York Department of Labor Data

The predominance of guardrail-related falls revealed in the accident analysis suggested

that an assessment of fall-related accidents in industry might identify those industries

most affected by the lack of guardrails or inadequate guardrails. The New York report,

"Characteristics and costs of work injuries in New York State, 1966-70" was obtained from

the New York State Department of Labor and was analyzed with respect to work-surface

accidents [6.5] involving scaffolds and stagings, platforms and ramps, and roofs, since the

previous accident analysis suggested that these might be guardrail-related settings. Data

from the thirteen industries with the highest percentages of injuries from guardrail-related,

work-surface falls to a different elevation are summarized in table 6.3. Also shown for each

industry are the total number of injuries, total number of injuries due to unsafe work-surface,

the total number of injuries involving falls to a different elevation, and the amount of

compensation for injuries involving falls to a different elevation (Rows 7-10).

It is of importance to note in table 6.3 that at least 13 of the industries in New York

State had injury rates of 48% or greater for injuries involving falls to a different elevation

due to unsafe work-surfaces and that the total compensation for just fall injuries in

these industries was over 50.8 million dollars.

66
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67
In these industries injuries due to unsafe work-surfaces ranged from 15% to 48% and

injuries involving falls to a different elevation ra'-ged from 1% to 38% of the total.

A significant portion of work-surface injurie- (8%-43%) were due to scaffolds and stagings,

platforms, and ramps, or roofs (i.e., guardrail-related). Of these guardrail-related,

work-surface injuries, 79%-96% involved falls to a different elevation. Although a good

portion, 4%-21%, of the guardrail-related, work-surface injuries did not involve falls to a different elevation, these data suggest that proper placement and construction of guardrails

on scaffolds and stagings might have prevented or controlled many of those injuries that did.

Similarly 48%-78% of injuries involving falls to a different elevation were due to unsafe

work-surfaces and of these ll%-57% were due to scaffolds and stagings, platforms and ramps,

or roofs. Since many injuries (at least 43%) involved falls to a different elevation that were not due to scaffolds and stagings, platforms and ramps, or roofs, there remains a sizeable number of accidents from falls that might have been prevented or controlled through

the proper placement of guardrails.

To summarize these results, about 25% of work-surface accidents seem to be guardrailrelated with 87% of these involving falls to a different level. About 60% of the injuries

involving falls to a different level are due to unsafe work-surfaces and at least 30% of

these seem to be guardrail-related. One conclusion that is suggested by these data is

that most guardrail-related accidents involve inadequate protection from falls to a different elevation, and thus, guardrails might most effectively prevent and control accidents

through proper placement, design and construction.

6.4.2 Bureau of Labor Statistics Data

The analysis of industrial accidents suggested that placement and function of guardrails were of critical importance to their effectiveness in preventing and controlling falls

in industrial settings. A statistical analysis of industrial accidents was conducted to find evidence to further support or reject this implication. Data were obtained from sixteen

independent reports on work injuries and accident causes gathered by the Bureau of Labor Statistics

for different intervals during 1941-1966 [6.6 to 6.21]. Industries represented are listed below:

Water-Supply Utilities

School Lunchrooms

Fabrication of Structural Steel and Architectural Metalwork

Concrete Brick and Block

Hotel

Hospital

Longshore

Shipyard

Textile Dyeing and Finishing

Clay Construction Products

68
Plumbing Operations

Carpentry Operations

Paperboard Containers

Warehousing Operations

Boilershop Products

Data from selected industries regarding work Injuries due to inadequate guarding

and/or lack of guardrails are summarized in tables 6.4 thru 6.6. Work Injury frequencies were converted to percentages of all work injuries to allow across-lndustry comparisons.

Weighted mean percentages were calculated from frequencies and percentages as general

indicators of trends. Conclusions as to the relative importance of one major category

(column) to another should be made with caution since no tests of significant differences

have been performed. There is little reason to believe, however, that when large differences

are evident, they do not represent "real" differences in trends and can therefore serve as general, though rough, indicators. Weighted mean percentages of the data suggest that

injuries due to Improperly guarded agencies occur with moderate frequency in relation to those injuries due to other hazardous conditions. Also, the category "inadequate guarding"

may include machine mechanism guards as well as guardrails and should be interpreted in

that light. Finally, industries that were "selected" for each table, were selected solely

on the basis of availability of data.

Table 6.4 This table shows work injuries due to lack of guardrails and inadequate guarding

(includes machine-mechanism guards) by type of accidents for selected industries. Although

a variety of accident types are Indicated with respect to inadequate guarding, only falls

are consistently Important with respect to lack of guardrails. Also indicated is a preponderance of falls to a different level.

Table 6.5 This table identifies various activities recorded previous to accidents due to inadequate guarding and lack of guardrails. Consistent weighted mean percentages Indicate

manxial handling, walking and using hand tools as most common. The high average for operating power equipment under "Inadequate guarding" is inconsistent with the low average under

"lack of guardrails" and is therefore probably due to inadequate machine guards as opposed

to a lack of guardrails.

Table 6.6 This table specifies the causes of guardrail-related accidents. Inconsistencies

in magnitude and direction of weighted mean percentages suggest that most accidents due

to the lack of guardrails involve machines or work surfaces.

The accident analysis of Bureau of Labor Statistics data suggests that when guardrails

are absent work injuries occur from falls to a different level onto work surfaces or machinery while the employee is walking. Falls through or over guardrails (guardrail

failures) are not indicated as a significant cause of work injuries due to inadequate

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71
Table 6.6

Work Injuries due to the lack of guardrails and inadequate

guarding by agency of accluents for selected Industries.

(ref. 6.6 - 6.21)

INDUSTRY

Total

Cases

//(%)

Stock & Materials

//(%)

HandtooIs

it(%)

Machines

(%)

Work

Assemblies

Working

Surfaces

#(%)

Vehicles

#(%)

Other

#(%) LACK OF GUARDRAILS

Structural 24 1 — 12 6 5 steel & metal (1.7) (__) (—

)

(1) (~) (50) (25) (21)

Carpentry 382 — 333 49 operations (4.2) (~) (~) (~) (~) (87) (~) (13) Concrete 10 1 4 5 0 brick & block (0.8) (~) ( —

)

(10) ( —

)

(40) (50) (0) Paperboard 29 4 17 1 7 containers (2.0) (~) (—

)

(14) (—

)

(59) (3) (24)

Clay construc- 65 3 31 30 tion products (1.1) (~) (—

)

(5) (2) (48) (~) (46)

Water-supply 27 4 7 2 14 utilities (1.5) (--) (15) (26) (—

)

(~) (7) (52)

Warehousing 59 13 1 19 11 11 operations (4.4) (22) (~) (2) (6) (32) (19) (19)

Hospitals 438 — 397 — 3 3 35 (1.4) (~) (~) (91) (--) (.5) (.5) (8) WEIGHTED MEAN

PERCENTAGES (2.6) (22) (15) (87.89) (5.2) (78) (14.37) (23.32)

INADEQUATE GUARDING

Structural 214 27 16 60 11 13 13 74 steel & metal (14.8) (13) (7) (28) (5) (6) (6) (35) Concrete brick 119 — 6 62 15 4 26 6

& block (10) (~) (5) (52) (13) (3) (22) (5) Carpentry 1350 379 446 333 192 operations (14.9) (—

)

(28) (33) (~) (25) (—

)

(14)

Paperboard 356 296 18 10 32 containers (24.4) (~) (~) (83) (~) (5) (3) (9) Clay construc- 388 21 19 148 32 38 47 83 tion products (6.8) (6) (5) (38) (8) (10) (12) (21)

Water-supply 196 20 14 82 13 67 utilities (11.4) (—

)

(10) (7) (~) (42) (7) (34)

Warehousing 165 13 8 32 15 29 36 32 (12.4) (8) (5) (19) (9) (17) (22) (20)

Hospitals 766 — 512 — 3 49 202

(2.5) (~) (~) (67) (~) (1) (6) (26)

Boilershop 294 2 41 110 15 2 122 products (14.6) (1.5) (14) (37) (1.5) (5) (1.5) (41)

Plumbing 162 — 3 — — 43 — 116 operations (6.0) (—

)

(1) (--) (~) (27) (~) (72)

Shipyards 106 5 70 1 30

(16.2) (—

)

(~) (5) (~) (66) (1) (28)

Textile dyeing 711 166 10 419 29 1 86

& finishing (9.6) (23) (1) (59) (~) (5) (0) (12)

Hotels 129 91 7 31 (3.3) (~) (~) (70) (~) (6) (~) (24)

School 140 127 5 8 lunchrooms (7.8) (-) (-) (90) (~) (4) (6) WEIGHTED MEAN

PERCENTAGES (11.25) (19.22) (23.26) (56.6) (8.95) (27.41) (12.25) (29.16)

72
guarding. This would imply that placement of guardrails is at least just as significant a factor in preventing or controlling accidents as guardrail design.

6 . 5 Conclusions

The results of the accident analysis suggest that guardrail accidents could be better

prevented and controlled by the proper placement of guardrails, by making guardrails more

noticeable, and by determining guardrail design criteria with respect to how guardrails

are used and who uses them. Many of the accidents resulting from structural inadequacies

of guardrails can be prevented by determining guardrail strength criteria with respect to guardrail use. Similarly, accidents resulting from non-structural inadequacies could be

prevented through proper height, size of openings and placement of guardrails and by

environmental cues to alert an employee to the presence of a hazardous area sooner and thereby

decrease the severity of the guardrail accident.

73
References

6.1 Kelley, Doug, Joint NCS/ASTM Project Points Way to More Effective Standards Development,

National Safety News, National Safety Council, Chicago, Illinois, 1975.

6.2 Kelley, Doug, A New National Safety Council Member Service. . .Computerized OSHA

Reporting and Analysis Service, National Safety News, National Safety Council,

Chicago, Illinois, 197A.

6.3 Festinger, L. and D. Katz, Research Methods in the Behavioral Sciences, Holt,

Rinehart and Winston, New York, New York, 1966.

6.4 Selltiz, C, Johoda, M. , Deutsch, H., and Cook, S. Research Methods in Social

Relations, Holt, Rinehart, and Winston, New York, New York, 1959.

6.5 Characteristics and Costs of Work Injuries in New York State, Special Bulletin

No. 243, New York State Department of Labor, New York, New York, December 1972.

6.6 Injuries and Accident Causes in Water-Supply Utilities, BLS Report No. 166.,

Bureau of Labor Statistics, Washington, D.C., 1953.

6.7 Injuries and Accident Causes in the Fabrication of Structural Steel and Architectural

Metalwork, BLS Report No. 266., Bureau of Labor Statistics, Washington, D.C., 1962.

6.8 Work Injuries and Accident Causes in School Lunchrooms, BLS Report No. 316.,

Bureau of Labor Statistics, Washington, D.C., 1967.

6.9 Work Injuries and Accident Causes in the Concrete Brick and Block Industry, BLS

Report No. 317., Bureau of Labor Statistics, Washington, D.C., 1967.

6.10 Work Injuries and Accident Causes in Hotels, BLS Report No. 329., Bureau of Labor

Statistics, Washington, D.C., 1967.

6.11 Work Injuries and Accident Causes in Hospitals, BLS Report No. 341., Bureau of Labor

Statistics, Washington, D.C., 1968.

6.12 Injuries and Accident Causes in the Longshore Industry, 1942, Bulletin No. 764.,

Bureau of Labor Statistics, Washington, D.C., 1944.
6.13 Fatal Work Injuries in Shipyards 1943 and 1944, Bulletin No. 839., Bureau of Labor

Statistics, Washington, D.C., 1945.

6.14 Injuries and Accident Causes in Textile Dyeing and Finishing, Bulletin No. 962.,

Bureau of Labor Statistics, Washington, D.C., 1949.

6.15 Injuries and Accident Causes in the Manufacture of Clay Construction Products,

Bulletin No. 1023., Bureau of Labor Statistics, Washington, D.C., 1951.

6.16 Injuries and Accident Causes in Plumbing Operations, Bulletin No. 1079., Bureau No. 1079., Bureau of Labor Statistics, Washington, D.C., 1952.

6.17 Injuries and Accident Causes in Carpentry Operations, Bulletin No. 1118., Bureau of

Labor Statistics, Washington, D.C., 1953.

6.18 Injuries and Accident Causes in the Manufacture of Paperboard Containers, Bulletin

No. 1139., Bureau of Labor Statistics, Washington, D.C., 1953.

6.19 Injuries and Accident Causes in Warehousing Operations, Bulletin No. 1174., Bureau

of Labor Statistics, Washington, D.C., 1955.

6.20 Injuries and Accident Causes in the Boilershop-Products Industry, Bulletin No. 1237.

Bureau of Labor Statistics, Washington, D.C., 1958.

6.21 Shipyard Injuries and Their Causes, 1941, Bulletin No. 722., Bureau of Labor

Statistics, Washington, D.C., 1943.

75
7 . Summary

This report presents results of the phase one study at the National Bureau of Standards

consisting of existing information compiled in order to assist in determining structural

and non-structural safety requirements for personnel guardrails. The literature search and

study of existing guardrail design provisions revealed a general lack of consistency between

load, height and strength requirements, and a paucity of quantitative test data and analysis

procedures upon which such requirements could be based. The anthropometric data indicate

those body measurements which might be significant to human-guardrail interaction. This

is of value not only in determining non-structural requirements such as minimum guardrail

openings, toeboard heights, etc., but also in establishing the range of guardrail sizes over which load testing should be planned for the phase two effort to follow. The field

survey provided a valuable perspective by showing the broad range of usage of guardrails

in service, while the analysis of guardrail-related accidents revealed that the placement

of the guardrail may be as significant a factor in accident prevention as the actual design

of the guardrail.

It is apparent from this study that a lack of knowledge of realistic gervice loads is a major obstacle to the ability to develop rational guardrail design criteria. In addition,

a quantitative description of the relations between certain anthropometric data and guardrail measurements remains obscure. Accordingly, the phase two effort will consist of an experimental-analytical program which will seek to measure, among other things, static and

dynamic loads on guardrails resulting from simulated accident situations. On the basis

of the above information, phase two will conclude with a performance-oriented guide and

criteria for the design and evaluation of personnel guardrails.

8. Acknowledgements

The contributions made by Drs . Robert A. Crist and Bruce R. Elllngwood in critically

reviewing this report are gratefully acknowledged.

The authors also express their appreciation to the many organizations which made

available their records and facilitated field observations of guardrails in service

to provide the necessary information for this report.

76
NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. mini. (CATION OR RI-;PORT NO. NBSIR 76-1132

2. Gov't Accession

No.

3. Recipient's Acces.sion No.

4. TITLF. AND SUBTITLK

Personnel Guardrails for the Prevention of Occupational

Accidents

5. Public ation Dafr November 1976

6. Performing Organization Code

^Sf^5"°M^1:tal, L.E. Cattaneo, G.E. Turner, S. N. Robinson

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4612471

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Occupational Safety and Health Administration

Department of Labor

Washington, D. C. 20210

13. Type of Report & Period Covered

Final Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less (actual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.) Existing information is compiled which would assist in determining structural and

non- structural safety requirements for guardrails used for the protection of employees

against occupational hazards. Critical aspects of guardrail safety are identified

through exploratory studies consisting of field surveys of prototypical installations,

reviews of existing standards and industrial accident records, and compilation of

relevant anthropometric data. These exploratory studies will be utilized to design

an experimental program which will consist of structural tests to determine design

loads and non- structural tests to determine geometric requirements for guardrail

safety.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons ) a.i.1 ^- -i • Anthropometric measurements ; guardrails ; industrial accidents

non- structural safety; occupational hazards; performance standard; personnel railings;

personnel safety; structural safety.

18. AVAILABILITY [^Unlimited

1 ! For Official Distribution. Do Not Release to NTIS

1 1 Order From Sup. of Doc, U.S. Government Printing Office Washington. D.C. 20402. SD Cat. No. C13

1 >t Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

79

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

$5.00 1 USCOMM-DC 29042-P74