NBSIR 76-1092

Consumer Product Portability

as Related to Warranty

Rulemaking

Joel J. Kramer

Patrick G. Meguire

Human Factors Section

Product Systems Analysis Division

Center for Consumer Product Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

Final Report

June 1 976

Issued August 1 976

Prepared for Division of Special Statutes

U. S. Federal Trade Commission

Washington, D. C.

NBSIR 76-1092

CONSUMER PRODUCT PORTABILITY

AS RELATED TO WARRANTY

RULEMAKING

Joel J. Kramer

Patrick G. Meguire

Human Factors Section

Product Systems Analysis Division

Center for Consumer Product Technology

Institute for Applied Technology

National Burau of Standards

Washington, D. C. 20234

Final Report

June 1 976

Issued August 1 976

Prepared for Division of Special Statutes

U. S. Federal Trade Commission

Washington, D. C.

°*eau o*

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

ABSTRACT

The Federal Trade Corrmission (FTC) has the responsibility for

determining what may be reasonably expected of consumers in their fulfillment of the terms of a consumer product warranty. Such determination

necessitates, in part, providing an empirical basis for defining and

quantifying various factors influencing product portability. This

report discusses the problem of defining consumer product portability

within the context of a consumer product return activity, offers a

working definition of product portability within this context, summarizes

and discusses the results and utility of previous portability related

studies, and describes the results of a controlled experiment which more

directly relates to the task of establishing maximum reasonable product

weight for a consumer product return activity. Statistically significant

differences in maximum reasonable product weight were found for the

variables of method of product carry and sex of customer. No statistically

significant differences were found for the variables of consumer age and

product size (at least for the sizes chosen for study) . Distributions

of maximum reasonable weight for product return are presented and

recommendations for warranty rulemaking are given.

Key words: Anthropometry; biomechanics; carrying; consumer product

portability; ergonomics; human factors; lifting; manual

materials handling? physiology; psychophysics; safety;

warranty

-li-

ACmMLEDGEMENTS

Several individuals deserve recognition for their valuable contributions

to the success and completion of this project:

The perseverance, dedication and creativity of Mrs. Mary Abbott in

typing the text and preparing the figures and tables for the original

manuscript and its several revisions are greatly appreciated.

Special thanks to Mr. John Donaldson for his interest, enthusiasm,

support, encouragement, and, most of all, his constructive criticism and

suggestions throughout all phases of this project.

Dr. Charles Fried for his helpful suggestions in the areas of

statistics and data analysis.

Last, but certainly not least, to Dr. Melvin Meyerson. Chief, Product

Systems Analysis Division (NBS) , Mr. Gary Laden and Mr. Christian White

(FTC) for providing the dollars to do the research and recognizing the need

in the first place.
Table of Contents

Page

Abstract ii

Acknowledgements iii

List of Figures v

List of Tables . vi

1 . 0 Introduction 1

2.0 Problem Analysis 1

2.1 Human Variables 2

2.2 Task Variables 6

2.3 Product Variables ..... 7

2.4 Environmental Variables 7

2.5 Definition of Consumer Product Portability 8

3.0 Literature Review 9

3 . 1 Approach 9

3.2 Findings 10

3.3 Summary and Conclusions 13

4.0 Experimental Approach 16

4.1 Method 17

4.2 Subjects 17

4.3 Apparatus 18

4.4 Design 18

4.5 Procedures 20

4.6 Safety and Ethical Considerations 22

5.0 Results 23

5.1 Product Weight . 23

5.2 Product Size 31

5.3 Product Handles 31

6.0 Conclusions and Recommendations 33

7.0 Selected Bibliography 35

APPENDIX A - Details of Studies References in Tables 3, 4, and 5 . . 44

APPENDIX B - Instructions to Subjects 76

APPENDIX C - Research Participant Agreement 77

APPENDIX D - Semantic Differential Scale Used to Evaluate

Subjects' Opinions Concerning the Weights and

Sizes of the Simulated Products Carried 78

APPENDIX E - Basic Descriptive Statistics 79

APPENDIX E - Statistical Hypothesis Testina ............ 83

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LIST OF FIGURES

Figure Number Page

1 Simulated Products 19

E-l The Normal Distribution 80

E-2 Positively Skewed Distribution 81

E-3 Negatively Skewed Distribution 81

E-4 Leptokurtic Distribution . . . . * 81

E-5 Platykurtic Distribution 81

-v-
LIST OF TABLES

Table Number Page

1 Variables Kncwn to Influence Portability 3

2 Variables Chosen for Consideration in Phase II . . . 4

3 Summary of Research Related to Maximum Acceptable

Weight of Lift and Carry for Males and Females ... 12

4 Summary of Research Related to Maximum Acceptable

Weights of Lift and Carry for 50% of Male and

Female Population by Age Group 14

5 Summary of Research Concerning the Effects of Size

Upon Maximum Acceptable Weight of Lift and Carry . . 15

6 Counterbalancing of Treatment Conditions 21

7 Descriptive Statistics for "Maximum Reasonable

Weight" for Each of 24 Experimental Treatments and

Subject Characteristics 25

8 Mean Maximum Reasonable Product Weight for the Four

Main Treatment Effects 26

9 Analysis of Variance: Male Data 27

10 Analysis of Variance: Female Data 28

11 Maximum Reasonable Product Weights for a Consumer

Product Return Activity for Various Percentages of

the Consumer Population 30

12 Results of Semantic Differential Evaluation of

Simulate! Product Size 32

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1 . Introduction

The Magnuson-Moss Warranty-Federal Trade Commission Improvement Act

of 1975 is aimed at improving the adequacy of consumer product warranty

information, preventing deception in the sale of products, and improving

competition in the market place. To this end, the Federal Trade Commission

(FTC) is required to promulgate rules for the warranting of consumer products

based upon substantive evidence. Included as a rule-making item is a statement of what consumers must do and expenses they must bear relative to full

and limited product warranties in the event of a product defect or malfunction.

Related to the requirements to be imposed upon consumers is the determination

of what may be reasonably expected of consumers in their fulfillment of the

terms of a warranty. Determining what a consumer may reasonably be expected

to do necessitates, in part, considering and defining the portability of

consumer products , since a product return requirement presumes that the

product is, in fact, portable.

The objective of the National Bureau of Standards' (NBS) support to

FTC was to contribute to the empirical basis for defining and quantifying

the various factors influencing product portability. This objective was

Implemented in two phases. Phase I consisted of a review of the portabilityrelated literature, and the preparation of a study design suitable for FTC's

developing quantitative portability guidelines to be used in consumer product

warranty rule-rnaking. Phase II consisted of operational testing, data

analysis, and formulating portability recommendations for FTC based upon

testing results.

The first three sections of this report summarize the activities

undertaken during Phase I and, as such, are essentially identical to the

corresponding sections of an earlier report (Center for Consumer Product

Technology Memorandum Report, April, 1976) . Sections 4, 5 and 6 of this

report detail the methodology, results, conclusions and recommendations

of Phase II experimentation. These sections thus represent the principal

difference between the earlier Phase I report and the present final report.

2. Problem Analysis

PIC's goal in the development of reasonable consumer product portability

requirements, as related to product warranty provisions, is to ensure a reasonable degree of ease and safety for consumers in the manual handling

of consumer products. A major problem in achieving this goal is the

development of a meaningful definition and quantification of product

portability.

-1-
Nurrerous variables are known to influence the ease and safety with

which products can be manually handled. These variables may be classified

into four major types: (1) human characteristics, e.g. motivation and

strength; (2) task characteristics, e.g. method and duration of manual

handling; (3) product characteristics, e.g. size, shape and weight; and

(4) environmental characteristics, e.g. temperature and humidity. Furthermore, many of these variables are known to interact in complex ways, making

generalizations concerning product portability a difficult undertaking re- quiring extensive multi-variate experimentation and analysis. Table 1

provides a listing of the variables most frequently cited in the

portability literature and gives illustrative references.

Table 2 lists the variables chosen for study during Phase II experimentation. Comparing Tables 1 and 2, it is evident that many potentially

significant variables were excluded from formal consideration in the present

investigation. These exclusions were dictated for the following reasons:

(1) project schedule and funding limitations did not permit systematic

investigaton of all variables, (2) seme variables appeared to have little

practical utility in terms of FTC's rule-making responsibilities, and

(3) the results of the Phase I literature review (highlighted in Section 3)

suggested that several variables were of only marginal significance in

the determination of overall level of portability.

2 . 1 Human Variables

Of all the human characteristics of potential significance in the

determination of product portability, those of age and sex were felt to

be of most potential utility for FTC's rule-making objectives. Information

concerning the lifting and carrying capabilities of males and females

of various ages would provide FTC with greater flexibility in the

development of rules for warrantors and manufacturers whose products

are used by identifiable sub-populations of consumers. Information

concerning the makeup of product user populations is frequently

available to manufacturers through detailed marketing analyses.

The significance of age and sex as determinants of product portability

has been supported by numerous earlier studies (see Section 3) . For

example, it is widely accepted that, on the average, the lifting strengths

of vonen (and their perceived estimates of "maximum reasonable weight of

lift") are approximately 60 to 70 percent of those of men. Whether this

relationship holds true within the context of a consumer product return

activity had not previously been investigated. Previous research dealing

with the possible effects of age on product portability are equivocal.

Thrussel (96) has shown that a general decrease in overall work capacity

occurs with increasing age, beginning at about age 28. However, Snook (85)

found no significant differences between the maximum acceptable weights of

lift and carry for young versus middle aged men. Snook suggests that older

people may be able to lift and carry as much as younger people because they

utilize more efficient manual handling techniques, e.g. by using slower

rates of work, taking more frequent rests, etc. It should be noted that

Snook's results were based upon a task in which subjects were allowed to

-2-
Table 1,

Variables Known to Influence Portability

Variable Type Gammon Variables Reference

Sex (87)

Age (85)

Human

Body Measurements (7)

Strength (83)

Motivation (55)

Skill & Experience (15)

Lifting Action

Method (77)

Frequency (52)

Height

:

(56)

beginning St end

Task

Carrying Action

Method (28)

Frequency/rate (85)

Distance/Duration (18)

Size (104)

Weight (91)

Product/Obj ect Shape (57)

Weight distribution (45)

Location of handles (50)

Temperature , humidity (53)

air movement

Environment Lighting, noise,

chemical environment

(45)

Discrete hazards (30)

(stairs, doorways, etc.)

-3 -
Table 2

Variables Chosen for Consideration in Phase II

Variable Type Variables Studied in Phase II

Human

Sex

Age

Body Measurements

Task

LIFTING ACTION

Method

CARRYING ACTION

Method

Distance

Product/Object Size

Weight

Environment Discrete hazards

-4 -
pace themselves, whereas Thrussell was concerned with tasks of a forcedpace nature. While it may be appropriate to assume that a consumer

product return activity is essentially a self-paced activity, Snook's

findings with respect to age needed further substantiation.

Many investigators have reported significant relationships between

anthropcrnetric characteristics (body dimensions) and the manual handling

capacities of human subjects. Ayoub (7) has developed several psychophysical models capable of predicting with a fair degree of accuracy the

lifting capacities of industrial workers based upon their anthropometric

characteristics. While the merits of such predictive modeling techniques

are many, they do not appear to be of any direct relevance to FTC's

rulemaking responsibility, i.e. separate portability limitations for

individual consumers based upon their anthropcrnetric characteristics is

certainly well beyond the scope of FTC's intentions.

For the purposes of Phase II experimentation, subjects were selected

to be representative of the general consumer population in terms of

height, weight, and various body dimensions. Thus, the results obtained

should reflect the manual handling capacities of persons distributed

over a wide range of human body types.

Related to the method of representative subject sampling, and the

considerable amount of variability which is typically found among subjects

in measurement of human characteristics and capacities, is the concept

of population percentiles. Within the context of defining reasonable

warranty portability requirements, the question becomes: what percentage

of the consumer population should be accommodated by product warranty

size and weight limitations? The answer to this question involves a

trade-off between the desire to accommodate as large a percentage of the

consumer population as possible and the necessity to maintain reasonable

standards for engineering quality, while avoiding severe economic impacts.

For example, setting warranty limitations on the sizes and weights of

products based upon the judgments of the "average consumer" (50th percentile)

could result in unreasonable requirements being imposed on the remaining

50% of the consumer population, while limitations based upon the "95th

percentile consumer" could result in undesirable engineering and economic

impacts. While military systems and equipment are generally designed to

be acceptable to at least 90% of the military population (46, 70), it is

difficult to ascertain whether this value would provide a satisfactory

trade-off for the definition of product-warranty portability requirements.

Hence, for the purposes of this report, 95th, 90th, 75th, and 50th

percentile values have been provided wherever possible to ensure adequate

information for anticipated trade-off evaluations.

Consumer strength, motivation, skill and experience were not propose!

for study in Phase II. As was the case for consumer anthropometric

characteristics, the physical strength characteristics of individual

consumers did not seem germane to FTC's informational needs. Furthermore,

physical strength is more related to the determination of maximum capability

-5-
than to judgments of maximum reasonable . Clearly, consumers capable of

lifting a product weighing 45.4 kg (100 lbs) with a maximum peak physical

exertion would probably not judge the requirement for returning such a product to a retailer as being reasonable. The return activity involves

components including both strength and endurance , two aspects which tend

to be mutually exclusive in a given individual.

Description and evaluation of consumer motivational factors were felt

to be beyond the scope of the present investigation, requiring extensive

consumer surveys and extended operational testing. Furthermore, it vrould

not have been possible to study all of the potentially significant motivational factors (and combinations of factors) related to the willingness of

consumers to return products. For example, given the option of paying a

service call charge for product pickup and delivery, what would consumers

decide to do? How might this cost alter consumers ' judgments of portability?

To what lengths would consumers go to avoid the payment of service charges?

Certainly many consumers would prefer to seek the assistance of friends

or relatives or employ readily available external aids in the return of

unusually heavy or bulky products. Obviously, such economic and motivational factors contribute to the difficulty involved in defining and

quantifying consumer product portability.

Skill and experience in manual handling were judged to be of only

minor significance in the determination of warranty portability requirements,

since consumers generally receive little or no specific instruction in

the use of proper lifting and carrying techniques.

2.2 Task Variables

Numerous manual handling task characteristics are known to influence

product/object portability. Perhaps the most important of these characteristics are: (1) the frequency with which the task is performed, (2) the

rate at which the task is performed, (3) the method of lift and carry

used in completing the task, (4) the height of lift involved, and (5)

the distance of carry involved.

Since the product return activity is presumably a relatively infrequent

event in the life of a consumer and the rate at which the activity is

accomplished is entirely at the discretion of the consumer, these variables

were felt to be irrelevant to the determination of warranty portability

requirements. The method of lift and carry used in the handling of a

product, however, was felt to be of possible significance, as certain

product design configurations may influence the method by which a product

is handled. For example, products having a top-mounted, single handle or

recessed hand hold may be lifted and carried more easily by means of a "one-handed" method, while products lacking a top-mounted handle and/or

of moderately bulky dimensions may be lifted and carried more easily by

means of a "two-handed" method. For this reason, one-handed vs. twohanded methods of lift and carry were included in Phase II experimentation.

While the use of other manual handling techniques, e.g. use of shoulders,

backs, external aids, etc. are undoubtedly employed by consumers in the

-6-
movement of bulky products, these methods were judged to occur far less

frequently in actual product return activities.

/

The distances of carry and heights of lift associated with product

return activities probably vary considerably from one situation to

another. Since data concerning the influence of these variables on

product portability was felt to be of little practical value for FTC

purposes, these variables were not selected for detailed investigation.

It was necessary, however , to select specific values for these variables

to be used during Phase II experimentation. The distance of carry

selected was 122m (400 ft) , while the height of lift at the beginning of

the experimental task was 43.2 an (17 in) . The simulated product had to

be lowered to floor level at the end of the experimental task. The

rationale behind the selection of these values is found in Section 4.5.

2 . 3 Product Variables

Consumer products may be characterized by a wide variety of physical

attributes relevant to the determination of ease of manual handling.

These attributes include weight, shape, size, distribution of internal

weight load and number and type of built-in handling aids (e.g. wheels,

handles , straps , etc . ) . As a result of time and funding constraints

,

detailed analyses of each of these attributes could not be undertaken in

the present investigation. More specifically, this study was aimed

primarily at consumer products of a relatively compact size and shape,

such as television sets, air conditioners, sewing machines, vacuum

cleaners, and the like.

Since weight and size are the attributes most frequently cited in

the literature as being of prime importance in the determination of ease

of manual handling, these attributes were selected for more detailed

investigation during Phase II experimentation. Product weight, or more

properly "perceived maximum reasonable weight" was actually the dependent

variable of Phase II, while product size was an independent variable.

The rationale behind the selection of weight as the dependent variable and

the selection of two specific sizes are found in Section 4.3.

2.4 Environmental Variables

Under the assumption that most consumers return products under

relatively favorable environmental conditions, it was felt that environmental variables (stressors) play comparatively minor roles in the

determination of ease of manual handling. Hence, all Phase II experimentation was conducted under relatively ideal environmental conditions:

level, non-slippery walking surfaces; cool, still, dry air; adequate

illumination levels, etc. In an attempt to maintain realism with respect

to common discrete hazards associated with manual handling activities,

however, impediments were incorporated into the Phase II experimental task.

These included a flight of stairs (with landing) and a doorway (with

unopened door)

.

-7-
2.5 Definition of Consumer Product Portability

In view of the number and conplexity of variables known to influence

product portability, it was extremely difficult to arrive at a ccrnpletely

satisfactory quantitative definition of consumer product portability.

However, based upon the problem analysis presented in the preceding

sections and a review of the pertinent literature (Section 3.0) , the

following non-quantitative definition was derived for the purposes of

the present report:

"A consumer product is portable within the context of a typical warranty product return activity if it can be

lifted and carried by most consumers a distance of

at least one city block without excessive strain or

exhaustion and without the use of external aids."

The selection of a specific percentage value associated with

most consumers involves a trade-off between consumer interests and

manufacturer interests. That is, a value judgment is required concerning

the percentage of consumers which should be acccmmodated by warranty

portability legislation, the percentage of manufacturers which should

be acconrnodated by warranty portability legislation, and the percentage

of manufacturers which should be required to alter their existing

warranty policies. Nevertheless, the most ccomonly accepted values

found today in the literature of the human engineering profession are in

the range of 90 to 100 percent.

Variables which may significantly alter product warranty weight

and size limitations in accordance with the above definition of consumer

product portability are (1) the sex of the consumer, (2) the age of the

consumer, (3) the method by which the product is handled (which in turn

is influenced by the location of product handles) , and (4) the size of

the product. These variables were studied in Phase II of the present

investigation

.

-8-
3. Literature Review

3 . 1 Approach

Sane 600 to 700 references of possible relevance were identified

during the Phase I literature search. These references were obtained

through a variety of sources, including (1) computerized searches of

American Psychological Association abstracts, National Technical Information Service abstracts, Defense Documentation Center abstracts, and

Consumer Product Safety Carmission abstracts; (2) manual searches of

Ergonomic Abstracts and many other technical journals; and (3) personal

corinunications with several of the leading authorities in the field of

portability including:

(1) Dr. M. M. Ayoub

Professor of Industrial Engineering and

Biomechanical Engineering

Texas Technical University

Lubbock, Texas

(2) Dr. Donald B. Chaffin

Professor of Industrial and

Operations Engineering

University of Michigan

Ann Arbor, Michigan

(3) Dr. Colin G. Drury

Assistant Professor of Industrial Engineering

State University of Nov York

Buffalo, New York

(4) Dr. Stover H. Snook

Director, Ergonomics Research

Liberty Mutual Research Center

Hopkinton, Massachusetts

As a result of project schedule and funding constraints it was not

possible to review all of the reference articles identified. Therefore,

priority was given to reviewing only those articles which were (1) written

by recognized authorities in the field, (21 non-medical in nature, and

(3) provided specific, quantitative data. In this manner, 104 articles

were selected and reviewed. The complete references for these articles

are listed alphabetically in the bibliography.

-9 -
3.2 Findings

Of the 104 articles reviewed, none dealt specifically with the problem

of consumer product portability as related to a product return activity.

The great majority of the articles were oriented toward industrial

manual materials handling, '-lore specifically, these studies emphasized

object portability requirements from the viewpoint of young, healthy, male,

industrial workers who repeatedly handle heavy objects as part of their

day-to-day job requirements. While the latter situation is considerably

different than that of the typical consumer involved in the return of a

defective product, the results of approximately 30 of the articles

reviewed were thought to be of some general relevance to the determination of product portability guidelines. The results of these studies are

highlighted briefly belcw, while specific details concerning the methodological approaches used in these studies are provided in Appendix A.

It was evident from the studies reviewed that a great number of

empirical approaches have been utilized in the study of product/object

portability. These approaches have generally been of three basic types:

medical, physiological, and behavioral.

Medical studies tend to emphasize the type, severity and frequency

of manual handling injuries, and as such are primarily safety oriented.

The usefulness of such studies for defining warranty portability requirements

is extremely limited, however, primarily as a result of the inadequate

diagnostic and statistical techniques characteristic of these studies (45)

.

While the size, shape, and weight of products/objects are identified in

these studies as the the attributes of greatest significance in the

determination of manual handling injuries, recommendations for reducing

these injuries vary considerably and place a strong emphasis upon improved

worker selection and training techniques. In view of their inconclusive

results and poor statistical controls, medically oriented studies were

excluded from further consideration in the present literature review.

Physiological studies tend to emphasize the physiologically optimum

conditions for manual handling, and thus are primarily efficiency oriented.

The results of these studies are generally stated in terms of amount of

physiological stress (circulatory, metabolic, biomechanical, or neuromuscular) per unit of manual work accomplished. Studies of this type

usually employ long duration, repetitive, manual handling tasks, which allow

sufficient time for physiological indices to stabilize. Problems associated

with this approach include: (1) the lack of agreement amoung authorities on

what constitutes "Maximum acceptable physiological stress" and (2) the complexity of procedures and techniques employed in the measurement of physiological stress.

-10-
Behavioral (psychophysical) studies tend to emphasize the preferences

and judgments of people regarding the reasonableness of manual handling

tasks. Measurements are nade of what people are willing and capable

of doing in the movement of heavy objects. Advantages of this approach

include simple procedural techniques and high reliability. The main disadvantage is that they are based upon highly subjective data and hence

appear to have lew face validity.

In reviewing the portability literature, emphasis was placed on those

studies which provided specific, quantitive data of possible relevance to

the development of product warranty portability requirements. To simplify

inter-study comparisons, the results of these studies are presented in

tabular form (Tables 3, 4 and 5*) and categorized in accordance with the

portability variables identified in the preceding sections (_see Table 2)

.

In view of the diversity of experimental approaches used and the possibility

that these approaches may lead to substantially different conclusions, study

results were also categorized in terms of "study approach." The results

of studies for which appropriate percentage values could not be determined

have generally been assumed to be acceptable to 90 percent of the population

studied, as this is a commonly accepted percentage value for product design

for military and some industrial users (46, 70) . In seme cases the

results have been assumed appropriate for 50 percent of the population,

as the authors have made reference to the "average man" or some similar

statement.

Table 3 summarizes the effects of sex and task characteristics

(method and frequency) on maximum acceptable weights of lift and carry.

The "Two-handed" method refers to objects grasped with both hands in

front of the body, while the "One-handed" method refers to objects

grasped using a handle centrally located on top of the object and held

at the side of the body. "Repeated lifts" implies insufficient time

between "single lifts" for fatigue effects to dissipate.

Based upon the data shewn in Table 3, the following observations

appear to be worth noting:

(1) Mean maximum acceptable weights of lift and carry for women

tend to cluster around 50 to 70 percent of the weights for men. These

values are in good agreement with the value of 60 percent which is generally

recognized by authorities in the field of portability (45, 87).

*Further details concerning the studies referenced in Tables 3, 4, and 5 are presented in Appendix A. The order of presentation of the Appendix A

studies is identical to that of the table references.

-11-

(2) In 25 of 31 studies, maximum acceptable weights of lift and

carry for 90 percent of the male (industrial worker) population were found

to be between 13 and 30 kg (29 and 65 lbs). For women, 13 of 14 studies

showed these weights to be between 6 and 24 kg (13 and 52 lbs)

.

(3) Maximum acceptable weights for single lift tend to be considerably

greater than those for repeated lift.

(4) Maximum acceptable weights for two-handed repeated lift tend

to be of similar magnitude to those for two-handed carry.

(5) Maximum acceptable weights for two-handed lift tend to be

slightly higher than those for one-handed lift and carry.

Table 4 summarizes the effects of age on maximum acceptable weights

of lift and carry for males and females. These data suggest that, with

the possible exception of persons under 20 or over 50 years, age generally

is not an important variable in the determination of object portability.

However, it should be noted that in most of these studies subjects were

required to maintain a constant rate of lift or carry, a situation probably

not found in most consumer product return activities. Snook (85) found

the age of male industrial workers to be unrelated to maximum acceptable

weight of lift in an unpaced task situation.

Table 5 sumrarizes the effects of object size (widths) on maximum

acceptable weights of lift and carry for 50 percent of the male (industrial

worker) population. Two study types are represented: (1) those which

suggest or imply a maximum acceptable size for lift or carry (70, 22 and

47) , and (2) those which suggest a carpensatory reduction in weight for

increases in object size (66, 5, 67 and 98). The former suggest maximum

acceptable objects sizes of 38, 51, 63.5 an (15, 20 and 25 in), respectively/

while the latter suggest weight reductions of .45 - .91 kg (1-2 lbs)

for each additional 2.54 an (1 in) of object size. No studies were

found which provided useful information on acceptable object shapes.

3.3 Sumrrary and Conclusions

In reviewing the literature no references aimed directly at the

quantification of consumer product portability requirements were found.

Most of the studies reviewed were concerned with portability requirements

for healthy, male, industrial workers in the context of performing their

jobs.

Because of the complexity of the variables involved, the variety of

experimental approaches used, and the unrepresentativeness of the subject

samples studied, no definitive recommendations concerning absolute product

weight and size limitations for consumer product return activities can be

made based upon the Phase I literature review . VJhile maximum acceptable

weights of lift and carry for 90% of the industrial worker population

(13-30 kg for males; 6-24 kg for females! may be considered suggestive of

-13-
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90%

male

and

female

values.
Table 5

Summary of Research Concerning the Effects of Size

Upon Maximum Acceptable Weight (kg ) of Lift and Carry*

Method of

Lift/Carry

Study

Approach

Width of Product/Obj ect

Reference

25 am 38 cm 51 cm 64 cm

Two-handed

single lifts

Behavioral Approximately 2.3 kg for each additional

13 cm of width - base value not cited

(66)

Unspecified 30 30 - - (70)

Two-handed

repeated

lifts

Behavioral

r

‘ '

32 30 27 25 (5)

|_. i One-handed

single

lift

Behavioral 31 29 27 25 (67)

(22)

Unspecified j - 16 16 : - - 9 (47)

Two-handed

1 Behavioral/ 2.3 - 4.6 kg for each additional

(98) Carry Biomechanical 13 am of width - base value not cited

*Table entries represent maximum acceptable weights for 50% of the

male populations studied. Lifting is from floor to table top height.

Carrying involves holding the object with two hands in front of the body.

-15 -
appropriate product weight limitations, these values can not be assumed

adequate for warranty rule-making purposes. The development of such

rules requires controlled experimentation with subjects more representative of the consumer population, performing tasks more closely related to

those actually involved in consumer product return activities. Such study

was undertaken during Phase II of the present investigation.

Sore general observations concerning relative limits for maximum

acceptable weights of lift and carry did emerge from the literature

review. Specifically, maximum acceptable weights of lift and carry are

(1) less for women (60%) than for men, (2) less for persons under 20 or

over 55 years of age, (3) less for objects designed to be carried with

one hand than with two, and (4) likely to be reduced by 2-5 kg (4.4-11.0 lbs)

for each additional 13 cm (5 in) of product/object width within the range of

25 to 65 cm. The utility of these observations is largely dependent on

the specific nature of the portability rule contemplated by FTC. Should

a multi-variate approach to the ruling be undertaken (e.g. by setting

different weight and size limitations for products returned by predominantly

men or women) , these observations may be helpful. If no such multivariate approach is attempted, they may serve little directly useful

purpose.

4 . Experimental Approach

Numerous approaches were available to NBS researchers during Phase II

experimentation. These approaches included: (1) the analysis of manual

materials handling injury data, (2) the measurement of physiological

stress and strain, (3) the measurement of human energy expenditure, and

(4) the measurement of subjectively perceived stress and strain utilizing

psychophysical/behavioral techniques

.

An analysis of manual materials handling injury data was not undertaken because Herrin, Chaffin, et al. (45) have indicated that the diagnostic categories associated with these data are often so non-specific that the

resulting injury and illness statistics are totally inadequate. Furthermore, data from statistical "control groups" are unavailable. Measurements

of physiological stress and strain and human energy expenditure were also

not undertaken as the same authors have noted a lack of agreement between

authorities with respect to the criteria to be used in the evaluation of

these physiological and energy expenditure measures. These same problems

were noted in the Phase I literature review.

Numerous studies have demonstrated that subjectively perceived stress

and strain is positively correlated with physiological stress and strain

(11, 12, 14 and 35). This correlation is in the range of .70 to .85, and

these studies have typically been aimed at demonstrating that the perception

of muscular effort and force obeys the psychophysical power law (i.e., the

perceived amount of muscular effort or force is directly related to the

amount of weight lifted by means of a mathematical power function) . Several of these authorities have noted that with adequate repetition and

experimental control, psychophysical techniques may be just as reliable as

- 16-
their corresponding physiological techniques (35, 62 and 85) . Numerous

authorities have utilized psychophysical techniques for the specific

purpose of establishing weight and size limitations for safe manual

handling (7, 20, 32, 33, 85, 86, 88, 89, 90, 91). The methodological

ard procedural simplicity of the psychophysical/behavioral approach coupled

with the merits of previous research utilizing this approach, provided

the rationale for selecting this approach for Phase II experimentation.

4.1 Method

The approach used was a variation of the psychophysical method

of "magnitude production." In magnitude production, the experimenter

states or indicates a series of sensory magnitudes, and the subject attempts

to adjust a stimulus to produce them. This experiment did not deal with

a series of weight magnitudes, but rather with only one — the maximum

reasonable weight of lift and carry. More specifically, subjects were

required to adjust the weight of simulated products to final values

which they believed to be the maximum reasonable weight that they would

be willing to handle in a real-life, product-return activity. Reasonable

was defined as meaning without excessive strain or exhaustion. The

adjustment was accomplished by adding and/or removing lead shot to/fram

the simulated products.

4.2 Subjects

A total of 96 subjects participated in the Phase II experimentation

as follows:

Age

Number of Subjects

16 - 29 30 - 44 45 - 60+

Male 16 16 16

Fenale 16 16 16

Subjects were NBS atployees who volunteered to participate and were

selected to be representative of the U.S. population in terms of age,

sex, height and weight based on 1970 Bureau of Census and 1960-62 HEW

National Health Survey data (94) . Each subject was required to attend

two, 30-minute experimental sessions, each session occurring on a different day.

- 17-
4.3 Apparatus

Two simulated consumer products were used, one being a 38.1 cm

(15 in) cubical wooden box, the other a 30.5 cm (12 in) cubical wooden

box. These box sizes were chosen to reflect acceptable and unacceptable

sizes for one-handed and two-handed lifting and carrying activities based

upon related anthropometric data for the general population (25) . The

sizes were also chosen to be representative of many of the compact

consumer products found in the Sears and J. C. Penney 1975 spring and

summer catalogs, i.e. , portable television sets, sewing machines and

microwave ovens. Available catalog models of these products were found

to range in volume from .016 - .18 m

3 (.56-6.3 ft 3

)

.

The volumes of

the simulated consumer products chosen for experimentation were within

this range, and at least one mode^. of each product had dimensions

approximately equivalent (within - 5 an) to one of the chosen sizes.

Project schedule and funding constraints did not permit more systemtic

and extensive investigation of the size variable or, for that matter,

product load characteristics (e.g. , top-heavy and bottom-heavy products)

.

However, the larger simulated product was nearly twice the volume of the

smaller simulated product and reflected a size which was judged by most

participants as being awkward.

Smaller wooden inner boxes were located at the physical centers of

the two simulated products to enable the addition and/or removal of lead

shot to/from the products, yet maintaining the center of gravity at or

near the physical centers of each box. False bottoms below the inner

boxes were present to enable setting the initial weight of the products

in a manner such that subjects could not use visual clues to bias their

judgments. A hinged top with a central handle (for one-handed lifting

and carrying task) was located on each box. The simulated products are

shewn in Figure 1.

4 . 4 Experimental Design

A 3x2x2x2 repeated measures, mixed-model design was employed . The

major independent variables were: (1) Age of Consumers (3 levels: 16-29,

30-44, 45-60+, (2) Sex of Consumers (2 levels: male, female) , (3) Method

of Carry (2 levels: one-handed, with handle; two-handed, without handle)

arid (4) Size of Product (2 levels; 38.1 cm cube; 30.5 cm cube). The

between-subjects variables were Age and Sex, while the within-subjects

variables were Method and Size. The dependent variable was the subject’s

judgment of maximum reasonable weight. The design did not include a check on repeatability because pilot study results showed a within-subject,

by condition standard deviation of only - 2.3 kg (5 lbs) . For the purpbses

of this study, this level of variability was thought to be acceptable,

and resulted in not having to take repeated measurements within subjects

for each condition.

-18-
Figure 1

:

Simulated Products

-19-
4.5 Procedures

Each subject was required to adjust the weight of each of the

two simulated consumer products under both one and two-handed handling

conditions to a value which he or she believed to be the maximum reasonable

weight which he or she would be willing to carry in a real-life product

return situation. "Reasonable" was defined for subjects as meaning

without excessive strain or exhaustion . This weight adjustment was

accomplished through the addition and/or removal of lead shot from the

simulated products. The initial (pre-adjustment) weights of the

simulated products were different for each of the four within-subj ects

treatment conditions, and for each of two same-day trials. These weights

were either 10% or 40% of the subject's ideal body weight (based on height

and body frame) and were selected in an effort to force subjects to

arrive at their judgments of maximum reasonable weight by both adding

(10% initial weight) and subtracting (40% initial weight) to/from the

simulated products. The results of a pilot study indicated that the

10% value was generally perceived as being "too light", while the

40% value was generally perceived as being "too heavy."

The order of presentation of the various within-subj ects treatment

conditions was counterbalanced across subjects with the following

restrictions: (a) subjects experienced only one level of size on any

given day, (b) subjects never experienced two successive trials using

the same carrying method, and (c) subjects never experienced two successive

trials using the same initial simulated product weight. Table 6 depicts the

counterbalanced condition orders and the number of subjects assigned to each

of these conditions.

Upon completion of each of the four weight adjustment tasks, each

subject was required to lift and carry the simulated product through a

simulated product return activity to verify his/her judgment of maximum

reasonable weight. This activity included carrying the simulated product

a distance approximating one city block (122 m (400 ft) )

,

through a

closed door, and up a flight of stairs. This distance was selected to

represent a worst-case condition distance-wise. Due to project schedule

and funding constraints it was not possible to formally survey the actual

distances consumers carry products in return activities. Furthermore,

considering the many consumers who return products to facilities located

in shopping centers, the distance selected was thought to be representative

of the carrying distances ccmmonly encountered when close-in parking is not

available.

Subjects were permitted to stop and rest as often as desired during

the carrying activity and were allowed a single opportunity at about the

half-way point for one final weight adjustment to the simulated product.

Subjects were allowed to walk at their own preferred pace. Subjects were

given instructions concerning the experiment via a standard portable

tape-recorder. The instructions given are presented in Appendix B.

-20-
Table

6.

Counterbalancing

of

Treatment

Conditions

to to i—I i—

bococo ro m ro ro

•9^0 W 0) )-j •H tj & w

ft

—{NJ fO i j i—I i—I lO LO

-J • • • • 72m

00 00 o o ro ro ro ro £ ‘, dP dP dP dP • 1 o c o o 4J r-4 '<? *H

(NH (NH ^ H (N n ^ 8

rH• i—LO• LO• w 00 00 o o

ro ro ro ro

dP dP df> dP o o o o 4J «H ^3* fH *’3* •Hc

CM rH CM fH

5C

z*= 3•H

ft8

•H

to

H CM

O

M1

LO LO rH rH O O 00 00 n ro ro ro

p

•Hc

oc op up df> O © O O i-l •fl' r-l

in ”3

fl

H (N ro

•H

ftg rH rH lO lO

CO 00 00

-CO ro o o

<ZL <ZL

4J3 c*P dP • o o 4J H $

ft

H (N ro ^ H

H (N ro ^ It) •H

ft ^ ^ ^ _

w

LO uo rH rH <D rH 5—

LO LO • • • • N • • e • o o 00 00 •H CO 00 o o

ro ro ro ro

•9-t! ro ro ro ro • o>P dP cfO <#> 4J O O O O

•HH TTH ^r

HMHfN

§£85

31s

in o N S' MM 10

4J2£

-U *a

dP dP O O rH ^ a

ft

h (N

n ^ 3•H

ft ! I

CM

>* I I

21-
Upon completion of each of the four carrying activities, subjects

were asked to fill out a five-point semantic differential questionnaire

to further verify the maximum reasonable weight selected. If, at this time,

a subject indicated that the weight carried was unreasonably too heavy or

too light, the subject was asked to return at a later date to repeat

the experimental task. A copy of the semantic differential questionnaire

used is presented in Appendix D.

4.6 Safety and Ethical Considerations

The Phase II experimentation plans discussed in the preceding

sections were submitted to the NBS Human Research Ethics ODirmittee for

review. The Director of NBS approved conducting the experiment on

December 9, 1975. The major safety concerns raised during the approval

process were (1) the maximum weight a subject would be allowed to ex- perience in the study, and (2) determining the medical history of subject

volunteers.

Based upon the opinion of the NBS Medical Officer, to ensure safety

of subjects and experimenters, the maximum weight a subject was allowed

to experience during the course of Phase II experimentation was 50%

of his ideal body weight (based upon height and body frame) or 34 kg

(75 lbs), whichever was less . If any subject reached this limit during

the course of the weight adjustment process, he or she was to be terminated

before beginning the verification carrying activity. The impact of this

safety limitation on the experimental procedures employed was negligible,

however, as no subjects attempted to make a weight adjustment at or in

excess of the safety limits set. It should be noted that subjects had no

knowledge of these restrictions at any time during their participation.

NBS experimenters were required to ascertain the medical history of

each volunteer subject. Volunteers indicating any of the following ailments

were not permitted to participate in the Phase II experimentation: (1)

dizziness, fainting spells or loss of balance, (2) hernias, (3) heart

trouble, (4) back trouble, (5) recent operations or (6) "any other

medical problems which the volunteer felt might disqualify him or her

from participating in the study." The experimenters were also required

to obtain approval from the NBS Medical Officer in the event of the

slightest doubt concerning the physical soundness of a subject. Thus,

all generalizations based upon the results of the present investigation

must be limited to essentially healthy persons.

-22-
5. Results

As described in Section 2, two fundamentally different product

characteristics are of prime importance in the determination of product

portability for consumer product return activities, product weight and

product size. As these characteristics are qualitatively dissimilar,

the results concerning each are discussed separately below.

5.1 Product Weight

The dependent variable of the experiment was maximum reasonable

weight of lift and carry, where subjects were free to adjust the weight

of the simulated products to their subjective limit of reasonableness.

Upon completion of each experimental task, subjects were given a final

opportunity to indicate their satisfaction with the weight they had

handled. Their opinion was obtained through the use of a forced-choice

semantic differential-type questionnaire (See Appendix D) . On this

questionnaire "slightly" less or more than the maximum reasonable weight

was defined for the subjects as being within 2.3 kg (5 lbs) of what they

thought might be their actual maximum reasonable weight. While on most

(60%) of the 384 total experimental trials the subjects indicated that

the weight they had carried was maximum reasonable, seme trials did in

fact result in opinions of "slightly less than maximum reasonable" (21%)

or "slightly more than naximum reasonable" (19%) . Only 4 trials resulted

in opinions of either "unreasonable-too light" or "unreasonable-too

heavy," and the subjects offering these opinions were asked to return at

a later date to repeat the trials. After repeating these trials, each

subject changed his/her opinion to ''maximum reasonable weight" with a corresponding change in the weight actually selected.

In an effort to improve the validity of subjects' selected weight

values, all weights identified as being "slightly less than maximum

reasonable" were increased in magnitude by 10% for the purpose of

statistical analysis, while all weights identified as "slightly more

than maximum reasonable" were decreased by 10%. This 10% correction

factor was selected based upon the results of an earlier pilot study,

and typically resulted in weight adjustments of between .9 and 2.3 kg (2

and 5 lbs) for 9 and 23 kg (20 and 50 lb) original product weights,

respectively. Product weights identified as being "the maximum reasonable

weight" were left unaltered. It should be noted that the net effect of

applying this correction factor to mean maximum reasonable weight values

is minor, as an approximately equal number of subjects rated their

weights as either "slightly less than maximum reasonable" or "slightly

more than maximum reasonable."

Before conducting statistical analyses of a more sophisticated

nature, elementary descriptive statistics were compiled to characterize

the frequency distribution of "maximum reasonable weight" for each

treatment condition. These statistics included the arithmetic mean

(X) , the standard deviation (s) , the moment coefficient of kurtosis (m^)

-23-
and the moment coefficient of skewness (m ) . These statistics are presented

in Table 7 along with some descriptive characteristics concerning the 96

subjects who participated in the study. Appendix E reviews the interpretation of these basic descriptive statistics.

A cursory examination of Table 7 reveals considerable information

relevant to maximum reasonable product weight for product return. Thus, a comparison of the 24 treatment means suggests that the sex of the

consumer and the method of product carry play far more important roles

in the determination of maximum reasonable product weights than do the

age of the consumer and the size - within the range of (30.5-38.1 cm3

)

( (12-15 in) 3

) . These cursory observations are made even more apparent

when the means of the appropriate treatment cells are "pooled" together,

as in Table 8 .

Of more theoretical than practical significance are the intercell

differences between s, m , m. statistics. These values provide some insight into to the shapessof the various treatment frequency distributions

of product weight. Briefly, these values indicate that there is less

variability among females (mean s = 3.6 kg) than among males (mean s =

5.1 kg) in judgments of maximum reasonable weight, probably as a result

of the more marked positive skewness in the female distributions (mean

m =0.5) than in the male distributions (mean m = 0.1) . Both female

and male distributions are characterized by rougRly equivalent amounts

of kurtosis (mean m, = 2.7) , both distributions being slightly platykurtic.

In other words, themale frequency distributions may be considered more

nearly normal in nature than the female distributions, primarily with

respect to the amount of skewness present. This conclusion was further

substantiated by the results of a series of (x

2

) "goodness-of-fit" tests,

which revealed the male distributions to be statistically normal, while

the female distributions differed significantly from normal

.

Sample frequency distributions more accurately reflect their corresponding population distributions the greater the number of sample

observations. One way of increasing the number of sample observations is

to "pool" the observations of these treatment conditions which can be

shown to be statistically nonsignificantly different from each other

(i.e. the observations can be thought of as coming from identical frequency

distributions) . Clearly, in the present investigation two of the treatment

conditions studied appear to meet this criterion: consumer age and product

size . Before proceeding with the pooling of the age and size distributions,

however, it is necessary to demonstrate statistically that these distributions, do not, in fact, differ from each other significantly. To do this, a statistical technique known as Analysis of Variance (ANOVA) was required

(see Appendix F) . One of the assumptions underlying ANOVA is that treatment standard deviations be homogenous. Since male and female standard

deviations are not homogeneous, it is clear that separate ANOVA ' s are required for the male and female data. The results of these ANOVA's are presented in Tables 9 and 10.

-24-
Table

7.

Descriptive

Statistics

for

"Maximum

Reasonable

Weight"

for

each

of

24

Experimented

Treatments

and

Subject

Characteristics.

_ ^ in rH oo O O rH rH CO CN in '3- c *c o> CO Ov CN O CN CO CO CO CN ^ CN -H -r-i ID D ^ r- — VD ' ' VD — VD ^

-p

,c in ON CO rH CC rH CO o CO VD 00 rH

-H ID r- d r- in O o in CO VD o r- r*** ID VD VD

r—

1

rH rH rH rH rH

f5 II II II II II II ii ii ll ll II ll lx CO X s X s lx co X s X s d co CO rH id rH s> rH CO C0 rH C .Q

•rH r— CN O' in cn O rH ID VD ao rr rH CO

ID N VD CN CC CO CO rH ro co <3* CN

C/3 -P rH rH ' rH ' r-H r-H "*—

a -C — — '—1 '— • M

Eh -H ID CO o o ao co r- r- D CO co in

C/3 .S> -I in o

r- rH

r-H d

• • CN LO d

- 2

SI

U'- rH 5 rH ID VD rH VD rH j*

H II II II n ii ii ii ll ll n ll lx CO X s X s lx co X s X s

03 6 <30 r- r rH rH rH rH ID in co *=3- G>

F-. X in CN r- in CO id CO co VD cn in E c CN CO in CN CO in 3 ii II II II n n ii ii II II ii ii 03 0

CT <

lx CO X s X s lx CO X s X s

U ID VD ID ID VD VD

rH rH rH rH rH g ii II ll ll ii ii z C c c G C C

3

r- co d cr CN 00 CN O co d VD P

T) c^ o CO CN 00 OC ^ 00 co rH VD § §

rH rH co —

co ^ CO

32 rH in h ^ o CO CN ID O C CN in id CO rH C0 D rH o co o cn 8 Cl ^ (N c o“\ in co o rH r-H LD CO CN C in co cn o ^ CO CO o £5 C CNl rH CN | •p ii 1 II II II II II II n ii ii ii ii n ii ii II II II II ii ii n ir lx to Ef’S;

0’ lx co E^e05 lx to EV X s yms

IX to E^e"

5 X s yms

G

ID in S r- ao vd cn r- on in rH

r—

i

O O' o o CN 00 CO D rH C^ VD D

1

rH CN ^ CO ^ CN ^

6 la)c ^ in ^ in cn in CO 00 ^ rH O rH CO 00 CO H Is* VD CN O ^ (Ti rH CD Tf f\ O CO CN O on n co o CO CO CO o f ^ c\ o CN CO CO O • O CT rH rH rH | rH rH

CD X

1 II II U II m ii n n ii ii II II II II ll ll II II ii ii ii ii n ii lx to EV ix to e^e

01 ix to eV Ix to eV X s yms

IX to E^V

rH in co rH r- vd r- co VD in ^

X 3 CN Csl r- co o o in oo in co rH r- 5 'S “ in rH rH in rH co ^ co ^ co ^

t—

l

K

C3 ID D rH O in O VD "T C' on cc n rH a> o o O OUD CN co ^ vd in U Q

• •H jS co in cn o rH ID CN O

CN

CN ^ CN O VD CO CN d VD CO rH o ^ CO CN o

'S Cr x II 1 II II n n n ii II II II II II II II II II II II II H ii ii n c

lx co EE lx to E*e" lx to EfV Ix to eV Ix to E^ s X s Xui

CM 3

1 CN ^ in r- in cn CN r- vd VD rH 3 •O O rH o co CO rH ON D CTV rH r-

<3 X

rH rH C1 rH CN ^ CN rH CN 0

in

CN CN m (N CN 00 ^ r- rH <T\ rH CN ON 00 rH in co h* in CN O (N £ oo in cn o 00 ID rH O o m h o CO CN CN O co in cn o CN CO ^ rH o O cr rH rH rH 1 CO -X

II II II II 11 II II n II II II II ii ii II II ii ii n ii II ll II II !x 0 E*E° ix to ErV5 lx to E*E

W

lx to \m

s

lx to Ix to

0

N 5 S' ON 4 4

03 g y

CN vD CN VD *

u> 1 1

1 1

i 1 1 L flj ID o in VD o in

CO M S' rH co rH co 3

<

fa -25'
o

<p

-P•&

00

I

enable

Product

Weight

in

lbs

44.9 31.4 00

• 00

ro

37.9 37.7

<x>

9 00

co

37.7 35.1 41.2

co

rtf &

I CM <x> CM r—1 LO rH cr> t"-

• 9 e 9 9 e 9 9 9 Cn o ^r r- f'- O' r~- LO CO X CM r—1 l—1 i~

1

1 1 t—1 i—1 1

1 1—

1

CO CO

^

•P CO CTi 4

C

•H c•H -j £ co 0 CM <£> c a

SI rH 0 i—

1

(N) LD 3 r3 £ 9) i—

1

« i I

S 1 f—

I

as

-P rg £ N—• ! i i rtf Qj s q3 CD o to CO CO 0

<D M ip f—

1

cn c £ 0 0 o

in 00

9 9 O 1

1 ro cn

>—

<4-1 ft o

-P <4-1 0 <p m ip P v

o o 1 0 R 0 O <0 H 0 Lj 3 3 o H <4-1 >< CO 0 5 0 T5 £ 3 p 0 c c N 0 -P o w co Q <c 0 •H ft 0 O o CO CP S

<

26'
Table

9.

Analysis

of

Variance:

Male

Data s

CO(D

>-i S S

CO<D

>-i § o in in OC o rH o o in r- CN o rH o • • • • • • • r—1 o rH CO rH VO rH V ro V V

ro r- o rH CO CM co rH CO CO

in ro CM ID r- o CO o> CD CM o • t • • • • • • t • in CO 00 rH o in CM i—1

in o

f" CO 00 o ro CO rH rH

*fa ro *3* rH fa

CM

fa

CN LT) VO rH o CN r-~ CN ro CO O' CO in ro co o in r* CM c CTC o ro o CO in CO

CO r- VO rH CO ro in in CO in o CN 4H r- in CN r- CO CO ro o ro 00 CN ro o ro ro o CO *3* CN CO rH <3* CO up CO t"- r- CO CN ro rH 3

CN rH rH eu

fa

fa!0

COu

Os

r-" <n in

*3* cn in CN in CN in §

+1

<o •HI

faoa 5a

fa

CO fao

cu •ro •B

CO

0)

fa

fa0 a &

S' CO 1£ s u

fa

fafa0 c c <D < \ \ N \ g g

fa

H

g

g

g

mm

fa U) < fa

m < co

27-
Table

10.

Analysis

of

Variance:

Fenale

Data

co CD 0 0 0 CO CD 0 00 0 0 0 CO in

Cm

® • • • • 0 r- •H1 f—1

rH 1—1

rH

(N

V

V

V

0) Oc in co r- r- 0 CN "S’ CN Si ! 1 O cn -s* r- 0 0 •^r in 1 1

ta in cn •'S* <N rH rH rH 00 CTi CD 0 m in rH rH rH

CN f—1

rH

cn

<D § § § §

ca

CD rH in 1—1 —1

CN r- CO 1

1 CN r* 'S' rH N* CN CN r- "S* CJ\ in r» iH <Ti 'S’ 0 in • • • • • • • • • • • • • • rH oc O oc 0 in rH CN OC 00 Ch in

r- CD ! 1 in 0 LO CN CD CN CN 1—1

r~

CO CO CT> 0 rH CD CD CN v

CO cn 00 rH rH

CXi r- CN LD

•'S' 'S* n1 CM in CN in

-s' CN

m S

•H

•HI

14-I o

Q)O

eg

caB8

-m

•B

ca

CQ f—1 § < O —

n3

4-> 3 (D O p S' \ H m <c ca

U) 4-> o

<D •ro •8

cacH

'4 CQca

u

+j 1

M—I o

d)N

*H

ca

a ca

a

a

ca • 28-
For males, the ANOVA showed that two treatment effects were statistically significant at the .05 level of probability*: Method of Carry (B)

and the interaction between Method of Carry and Size of Product (BC)

.

All other effects were nonsignificant. The significant BC interaction

for males may be interpreted to mean that maximum reasonable product

weights were significantly greater for the 30.5 cm (12 in) cubical box

than for the 38.1 an (15 in) cubical box, but only in the two handed

method of carry .

For females, the ANDVA shewed that only one treatment effect was

statistically significant at the .05 level of probability: Method of

Carry (B) . All other effects were again nonsignificant.

Finally, a series of separate "t-tests" revealed that male-female

differences in the judgment of maximum reasonable product weight were

also significant at the .05 probability level. This was true not only

for the overall sex effect (t = 7.7) , but also for the sex effect

associated with the 30.5 an (12 in) cubical box (t = 7.8) , the 38.1 cm

(15 in) cubical box (t = 7.4) , the one-hand carry method (t = 9.8) , and

the twe-hand carry method (t = 6.6)

.

In summary, only the main effects of Method of Carry and Sex of

Consumer were found to be statistically significant at the .05 level

(i.e. the frequency distributions associated with males and females, and

one-handed and two-handed carries were significantly different) , while

the other effects were statistically nonsignificant. This does not

imply that the Consumer Age and Product Size effects were trivial under

all circumstances, but that these effects were trivial under the range

of conditions studied in the present investigation. Hence for FTC's

purposes, the various frequency distributions associated with Consumer

Age and Product Size effects may be pooled together, resulting in larger

overall distributions for the Consumer Sex and Method of Carry treatment

conditions

.

Table 11 presents the maximum reasonable product weights acceptable

to various percentages of the consumer population. Separate distributions

are presented for males and females, and for one-handed and two-handed

methods of carry. In addition, an "overall" distribution is provided

which represents pooling of data over all conditions. The latter distribution while being the most general, is also the least flexible in

dealing with differential capabilities of men and vomen using different

product carrying methods.

*Results which would be expected to occur by chance only 5% of the time.

-29-
Table

11.

Maximum

Reasonable

Product

Weights

fora

Consumer

Product

Return

Activity

for

Various

Percentages

of

the

Consumer

Population.

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weights

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under

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present

investigation.
5.2 Product Size

The data of the present investigation are equivocal with respect to

the determination of maximum reasonable product size for a consumer product

return activity. While no significant differences were found to exist

between the maximum reasonable weight distributions for the 30.5 cm (12 in)

and 38.1 cm (15 in) cubical boxes (except for males using the two-handed

carrying method) , the post experimental opinions of subjects expressed by

means of the semantic differential scale (Appendix D) indicate that

volume changes of this magnitude may contribute significantly to the

difficulty involved in the manual handling of consumer products.

Table 12 shows the percentage of subjects who agreed with each of

the five semantic differential scale values and indicates a strong difference

in opinion concerning the reasonableness of the two simulated product sizes.

Thus approximately 97% of the male subjects (averaged over method of carry)

felt the smaller box ((30.5 cm) 3 (12 in) 3

) was at or belcw their criterion

for maximum reasonable size, while approximately 78% felt this to be true

about the larger box ((38.1 cm) 3 (15 in) 3 ). For females, the corresponding

percentages were approximately 97% and 54%.

It should be noted, however, that a more detailed review of the raw

data surrmarized in Table 12 indicates that, of the total of 384 size opinions

given by the subjects using the semantic differential scale, approximately

18% (70) of the responses reflected seme degree of within subject inconsistency.

For example, 75% of the male subjects (one-handed condition) found the larger

box to be at or belcw their criterion for maximum reasonable size, while only

68.8% found the smaller box to be belew their criterion for maximum reasonable

size, thus resulting in an inconsistency of 6.3%. Examination of the raw data

reveals that 94% of the 70 inconsistent opinions concerning maximum reasonable

size were of the same type, i.e. the same subject using the same method of

carry rated both the smaller and larger box as being "maximum reasonable."

When the data are reanalyzed after elimination of all inconsistent opinions,

the difference in opinion concerning the reasonableness of the two simulated

product sizes becomes more pronounced; then , averaged over method of carry, 97%

of the males found the smaller box to be at or belcw their criterion for

maximum reasonable size, while only 73% found the larger box to be at or belcw this criterion. The corresponding values for females were 96% and 46%.

Subjects apparently were not compensating for their judgment of increased

awkwardness of the larger box by reducing the weight selected (as reflected

by ANOVA results) . This suggests that there is little relationship between

maximum reasonable product size and weight.

5.3 Product Handles

Although the present investigation was not intended to study the relationship

between product handle placement and product portability, the data collected for

the one and two-handed methods of carry indicate that subjects, for a given

product size, consistently selected greater maximum reasonable product weights

in the two-handed (no handle available) than in the one-handed (a single central

handle on the top of the box available) carrying method. This would seem to

irrply that the availability of handles on the top of consumer products adds

little to the amount of weight which the consumer can comfortably handle, but

rather is more of a convenience in that it precludes the necessity of stooping

to get the product into a comfortable, two-handed carrying position.

-31-
Table

12.

Results

of

Semantic

Differential

Evaluation

of

Simulated

Product

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- 32-
6. Conclusions and Recommendations

The results of the present investigation are in agreement with the

findings of the Phase I literature review. The variables of greatest

significance to the determination of product portability for a product

return activity appear to be (1) the sex of the consumer, (2) the method

of carry used in handling the product, and to a lesser extent (3) the

size of the consumer product, at least over the range of sizes studied

here. The age of the consumer appears to have little effect in the

determination of what weight he/she judges to be maximum reasonable. The

latter conclusion is, of course, limited to persons of 16 to 60 years of

age who are in good health. The lack of a significant age effect is

presumably the result of the willingness of older persons to walk more

slowly and take more rests than younger persons in carrying objects of

roughly similar weight.*

The selection of the most appropriate population percentage value

to be used in the promulgation of consumer product portability rules is a complex problem. While a value of at least 90% is most frequently en- countered in the human engineering literature dealing with military

equipment and systems design, many other factors should be considered by

FTC before reaching a final decision. Thus, the behavioral data of this

study would be viewed as providing just one of the many pieces of information on which to base a ruling. Other factors which should be considered

are the influence of the ruling on (1) product cost, (2) competition

among manufacturers, (3) the cost and duration of product repairs, and

(4) the willingness of consumers to use other inconvenient, but safe,

means of returning consumer products (e.g. the use of external aids or

rental vehicles , the assistance of friends and neighbors , etc . ) . Furthermore, it should be stressed that the generalization of results obtained

from this investigation is limited to situations where the tasks and

product characteristics are similar to those employed in this study.

The results are based on laboratory conditions and may be of limited

applicability to conditions substantially different from those represented herein. Hence, products with unstable loads, handles placed at

locations other than over the center of gravity, having slippery surfaces,

etc. may be expected to have smaller values of maximum reasonable weight

and size. Inclement weather conditions, unusually long carrying distances,

lifting activities associated with trunk, roof, back and front seats of

cars, numerous flights of stairs, and the like may have similar effects.

*In the present study differences were found between the three age

groups studied in terms of both the mean duration and the total number

of rests taken. The mean durations of carry for the 16-29, 30-44, 45-60+

age groups were 137, 139, and 155 seconds respectively. The total number

of rests taken by these same groups were 67, 81 and 119.

- 33-
Nevertheless, with the above limitations in mind, the present

investigation fully supports all of the previous observations concerning

relative limits for maximum acceptable weights of lift and carry (pages

12-13) , and, in addition, suggests that for behavioral purposes absolute

limits for product weight should be on the order of 9.0 kg (19.9 lbs) to

15.6 kg (34.4 lbs) (depending upon the specific sub-population under

consideration) to satisfy 90% of the consumer population. The limit

for maximum acceptable size of lift and carry should be within the

range of (30.5 cm) 3 ((12 in) 3

) to (38.1 cm) 3 ((15 in) 3) for compact

products of roughly cubical dimensions, again to satisfy approximately

90% of the consumer population. While the presence of handles on

products may contribute to handling convenience (e.g. provide a choice

of one-handed versus two-handed method of carry) , they should not

influence the maximum acceptable weight of lift and carry associated

with product-warranty rulemaking.

- 34-
1 .

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,

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.

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86. Snook, S. G. and Ciriello, M. "Low Back Pain in Industry."

Amer. Soc. Safety Eng. Journal 17(4), (1972), 17-23.

87. Snook, S. G. and Ciriello, M. "Maximum Weights and Work Loads

Acceptable to Female Workers." J. Occup. Med. 16(8),

(1974), 527-534.

88. Snook. S. G. , and Irvine, C. G. "Maximum Acceptable Weight of Lift."

Amer. Ind. Hyg. Assoc. J . 28, (1967), 322-329.

89. Snook, S. H. and Irvine, C. H. "Maximum Frequency of Lift Acceptable

to Male Industrial Workers." Amer. Ind. Hyg. Assoc. J. 29(6)

(1968), 531-536.

90. Snook, S. H. and Irvine, C. G. "Psychological Studies of Physiological

Fatigue Criteria." Human Factors 11 (3)

,

(1969), 291-299.

-41-
91 . Snook, S. G., Irvine, C. G. and Bass, S. F. "Maximum Weights and

Work Loads Acceptable to Male Industrial Workers."

Amer. Ind. Hyg. Assoc. J. 31, (1970), 579-586.

92. Srivastave, S. S. "Load Carriage by Infantry Soldier: Criteria for

Assessment of Physiological and Psychological Fatigue."

Defense Science Journal 18(2), (1968), 53-60.

93. Stoudt, H. W. "Muscle Strength." In Human Eng. Guide to Equipment

Design edited by Morgan et. al. New York: McGraw-Hill, 1963.

94. Stoudt, H. , Damon, A. and McFarland, R. Weight, Height and Selected

Body Dimensions of Adults, United States, 1960-1962 . Public Health Survey Publication Number 1000 - Series 11, No. 8,

1965, Washington, D. C.

95. Switzer, S. K. Weight-Lifting Capacities of a Selected Sample of

Human Males . Technical Report No. MRL-TDR-62-57,

Behavioral Sciences Lab . , Wright-Patterson Air Force Base

,

Ohio (1962)

.

96. Thrussell, M. R. "The Mechanics of Lifting and Carrying by Manual

Means." J. Junior Institution of Engineers 80(9),

(September 1970), 265-272.

97. Tichauer, E. R. "A Pilot Study of the Biomechanics of Lifting in

Simulated Industrial Work Situations." J. Safety Research 3(3),

(September 1971) , 98-115.

98. Tichauer, E. R. Ergonomic Aspects of Biomechanics . (Chapter 32 in

The Industrial Environment - Its Evaluation and Control )

,

Government Printing Office, Stock Number: 1701-00396.

99. Tichauer, E. R. , Miller, M. and Nathan, I. M. "Lordosimetry:

A New Technique for the Measurement of Postural Response to

Materials Handling." Amer. Ind. Hyg. Assoc. J. 34,

(January 1973) , 1-12.

100. Tichauer, E. R. , Yagoda, H. P. , Weinstein, J. M. and Wall, R. A.

Design Criteria for Packages and Containers . National Institute

of Occupational Safety and Health, Cincinnati, Ohio (October 1972)

.

101. Troup, J. D. G. and Chapman, A. E. "The Strength of the Flexor and

Extensor Muscles of the Trunk." J. Biomechanics 2, (1969), 49-62.

ifl?

-42-
102. Wald, A. and Harrison, L. B. "Oxygen Consumption and Heart Rate:

Changes and Relationship in Static Work." Ergonomics 18(3),

(1975) 299-309.

/ 103. Whitney, R. "The Strength of Lifting Action in Man,"

Ergonomics 1, (1958) 101-128.

104. Woodson, W. E. and Conover, D. W. , Human Engineering Guide for

Equipment Designers, Second Edition . Berkeley: University

of California Press, (1964).

- 43-
APPENDIX A - Details of Studies Referenced in Tables 3, 4 and 5

The details concerning each of the 35 references cited in the

Section 3.0 literature review (Tables 3, 4 and 5) are presented here.

Each study is detailed on a separate page using a standardized summar- ization format. The studies are grouped according to type and frequency

of task, and methodological technique employed. The results shown in

many cases had to be derived from data provided in the actual studies

through such techniques as interpolation and extrapolation and inferences

concerning the standard normal distribution. Thus, in many cases the

specific values presented in the "results summary" should be considered

only approximate. The conditions selected as being most relevant to the

typical consumer product handling task generally include: (1) lifts to

"table top height" (3 to 4 ft; or approximately 1 m) and (2) carrying

distance of as long a value as possible.

-44-
Reference (37) Task: Two-Handed, Single Lift Study Approach: Behavioral

Enmanuel, I., Chaffee, J. W. , and Wing, J. A Study of Human Weight

Lifting Capabilities for Loading Ammunition into the F-86H Aircraft.

Task Summary

Method: Two-handed, straight back

lift, but backs not

necessarily vertical

Frequency : Not stated

*Distance/Height/Duration: 5 heights

studied

Criterion: Psychophysical adjustment

procedure to avoid feeling

of possible injury

Product/Object Surtmary

Type: Box

Size: 27.3 cm x 6418 cm x 17.1 an

(10 3/4" x 25 1/2" x 6 3/4")

Load Distribution: Not stated; however 4.5 kg (10 lb ) bags of shot used to adjust weight

Presence of Handles & Location: Not stated

Results Sunmary

Subject Sunnvary

Number: 19

Sex: Male

Age: 17 to 28

Occupation: Soldiers and

college students

Physical Condition: "Good"

Task Training: None

Maximum Acceptable Weights of Lift (in kg ) for Five Heights of Lift

and for Various Population Percentiles

Height of Lift Percent of Population to Which Acceptable

95% 75% 50% 25% 5%

0 to 1 foot (0-30.5 cm ^ 65 91 105 121 137

i 0 to 2 feet (0-61.0 cm ) 63 75 86 97 118

0 to 3 feet -(0-91.4 cm

)*

** 35 44 52 62 78

0 to 4 feet (0-121.9 cm ) 25 31 37 44 51

0 to 5 feet (0-152.4 cm ) 17 21 26 32 38

j

*Independent variable

**Condition selected as being most relevant to a consumer product lifting task

-45-
Reference (21) Task : Two Handed, Single Lift Study Approach : Behavioral

Chaffin, D. B. Human Strength Capability and Low Back Pain.

Task Summary

Method: Two-handed lift, object 51 cm

off floor and 51 an (20") in

front of subject

Frequency: Once

Distance/Height/Duration: 4 second

duration

Criterion: Maximum capable lift

that could be sustained

for 4 seconds

Product/Object Sunmary

Type: Platform attached to

"lifting force meter"

Size: 46 cm (18") across

Load Distribution: Not applicable

Presence of Handles & Location: 2 handles,

one on each

side of platform

Subject Sunmary

Number: Approximately 400

*Sex: Approximately 250 male;

150 female

Age: "Wide range"

Occupation: Industrial workers

Physical Condition: "Good"

Task Training: Not stated

Results Summary

Maximum Capable Lifting Weight (in kg ) for Various Percentages

of the Male and Female Populations

SEX % of Population Which is Capable

90% 75% 50% 25% 10%

Male 13 17 23 31 41

Female 6 9 13 18 24

Note: Chaffin’s data show that lifting strength is

positively skewed.

* Independent variable

( 20 ")

46-
Reference (83) Task; Two Handed/ Single Lift Study Approach: Physiological

Poulsen, E. and Jorgenson, K. Back Muscle, Strength, Lifting, and Stooped

Working Positions.

Subject Summary

Number: 50

*Sex: Male and Female

*Age: 4 age groups investigated

Occupation: "Various"

Physical Condition: Not stated

Task Training: Not stated

Product/Object Summary

Type: Not

Size: Not

Load Distribution : Not

Presence of Handles

and Location: Not

Results Summary

Maximum Capable and Permissible Weights for Single and Repeated

Lifts for Males and Females by Age (in kg ) LIFTING

CONDITIONS

Sex: Average Male Average Female

Age: 15 25 45 55 15 25 45 55

Maximum

Capable for

Single Lift

77 95 98 93 43 49 47 39

Maximum ** Permissible

for Single

Lift***

54 66 69 65 31 35 33 27

Maximum ** Permissible

for Repeated

Lifts

39 47 49 47 21 24 23 20

stated

stated

stated

stated

Task Summary

Method: Two-handed lift

*Frequency : Single and repeated lifts

Distance/Height/Duration: Table height

Criterion: Maximum capable for

single lift only

* Independent variables

** Table values not based on data, but represent these authors' judgment.

This rationale for maximum permissible, single lift being 70% of

maximum capable, single lift and maximum permissible, repeated lifts

being 50% of maximum capable, single lift is not specified in reference.

***Condition selected as being most relevant to a consumer product lifting task

-47-
Reference (70) Task: Two Handed, Single Lift Study Approach : Unspecified

MIL-STD-1472A: Human Engineering Design Criteria for Military Systems,

Equipment and Facilities (pg. 141)

.

For objects "of convenient configuration

(not more than 15" long, or 12" high)".

Height of Lift Maximum Acceptable Weight of Lift (in kg )

1 ft. (30.5 err* ) 39

2 ft. (61.0 cm ) 36

3 ft. (91.4 cm )* 29

4 ft. (121.9 cm ) 23

5 ft. (152.4 cm ) 16

Condition selected as being most relevant to a consumer

product lifting task.

-48-
Reference (80) Task: Two Handed, Single Lift Study Approach : Unspecified

Peres, N. Human Factors in Industrial Strain (textbook not retrieved)

" recommended maximum load for male adults in the

United Kingdom as 130 lbs., but then recommended 100 lbs.

for Australian males" (Quote is from reference no. 61,

pg. 237)

-49-
Reference (56) Task; Two Handed, Repeated Lift Study Approach : Behavioral

Kassab, S. J. and Drury, C. G. The Effects of Working Height on a Manual Task. Personal Ganmunication.

Subject Suninary Task Summary

Number: 11

*Sex: 5 male, 6 female

Age: 19-24

Occupation: Industrial workers,

professionals, and

students

Physical condition : "Good"

Task Training: None, but industrial

workers had experience

in lifting as part of

job.

Method: Two-handed, improper lifting

techniques used as a result

of large container size.

Frequency: "Frequent lifting"

*Distance/Height/Duration: 6 heights

studied

Criterion: Psychophysical adjustment

procedure to avoid

excessive strain

Product/Object Summary

Type : Cubic box

Size: 50.8 cm (20") per side

Load Distribution: Not stated

Presence of Handles

and Location: Not stated

Results Summary

Mean Acceptable Weights (in kg ) of Repeated Lift for Six

Heights of Lift for Males and Females.

HEIGHT OF LIFT

Males Females

From To

0" 23.4"(59.4 cm ) 27 16

0" 47 2

" (-U9. 9cm J

1** 24 13

0" 70.9"(180.1 err ) 18 9

23.4"(59.4cm ) 47.2"(119.9 cm ) 29 15

. 23.4"(59.4cm ) 70.9"(180.1 cm ) T9 13

47.2"(119.9cm ) 70.9TL80.1 cm ) 20 10

Note: Acceptable weights for females range from 50% to 59% of

acceptable weights for males.

independent variables

**Condition selected as most relevant to a consumer product lifting task.

-50-
Reference (7) Task: Two Handed, Repeated Lift Study Approach: Behavioral

Ayoub, M. M. , Dryden, R. D., McDaniel, J. W. , and Knipfer, R. E.

Psychophysical Based Models for the Prediction of Lifting Capability of

Industrial Workers.

Subject Sumrary Task Sumnary

Number: 135

*Sex: 68 males; 67 females

Age: 25-50

Occupation : Industrial workers

and students

Physical Condition: "Good"

Task Training: Brief instruction

on proper lifting

method

Method: Two handed, using proper

lifting technique

Frequency: Frequent lifting as part of job

*Distance/Height/Duration: 3 heights

studied

Criterion : Psychophysical adjustment

procedure to avoid

excessive strain

Product/Obj ect Sunmary

Type: Industrial tote box

Size: 34.3 an x48.3 cm xl4.0 cm (13 1/2"x19"x5 1/2")

Load Distribution: Not stated

Presence of Handles

and Location: Two handles, one on

each side of box

Results Sumnary

Maximum Acceptable Weights of Repeated Lift (in kg ) for Three

Heights of Lift and for Various Population Percentiles

Percent of Population to Which Acceptable

HEIGHT OF LIFT Sex 90% 75% 50% 25% 10%

Floor to Knuckle Height**

M 16 19 24 30 35

J F 9 10 15 18 21

Knuckle Height to

Shoulder Height

M 18 21 25 28 31

F

10 11 12 13 14

Shoulder Height to

Extended Arm Reach

M

16 19 22 26 ~irn

F

8 10 12 14 JJ

independent variables

**Condition selected as being most relevant to a consumer product

lifting task.

-51-
Reference (85) Task: Two Handed, Repeated Lift Study Approach: Behavioral

Snook , S . H . The Effects of Age and Physique on Continuous-Work Capacity

.

Subject Sunroary

Number: 28

Sex Male

rAge: 14 subjects 25-35,

14 subjects 45-65

Occupation: Industrial workers

Physical Condition: "Good"

Task Training: Brief instructions

on proper lifting

method, also exercized

for one week prior to

experiment

Task Summary

Method: Two handed using proper

lifting technique

*Frequency: frequent lifting as part

of job; slow and fast

lifting rates studied.

*Distance/Height/Duration: 3 heights

studied

Criterion: Psychophysical adjustment

procedure to avoid

excessive strain

Product/Object Suimvary

Type: Industrial tote box

Size: 34.3cm x48.3cm xl4.0cm (13-l/2"xl9"x5-l/2 ) Load Distribution: Evenly distributed with

lead shot

Presence of Handles

and Location: Two handles, one on each end

of box

Results Surrmary

Mean Maximum Acceptable Weights of Repeated Lift (in kg ) for Three

Heights of Lift at Slow and Fast Lifting Rates

HEIGHT OF LIFT

Frequency

,

once every

25-35 yr.

males

45-60 yr.

males Mean

Floor to Knuckle Height** 60 sec.** 23 26 24.5***

14 sec. 19 22 20.5

Knuckle Height to Shoulder 60 sec. 23 25 7T~

Height 11 sec. 20 21 20.5

Shoulder Height to Extended 60 sec. 23 21 22

I Arm Reach 10 sec. 17 17 17

independent variables

**Condition selected as being most relevant to a consumer product lifting task

***Percentile values in Table 3 are based upon a standard deviation of

5.7 kg (12.50 lbs )

.

-52-
Reference (87) Task: Two Handed, Repeated Lift Study Approach: Behavioral

Snook, S. H. Circello, M. Maximum Weights and Work Loads Acceptable

to Female Workers.

Subject Summary

Number: 31

Sex : Female

Age: Mean age industrial

workers = 38.5

Mean age housewives = 35.6

Occupation: 15 industrial workers

16 housewives

Physical Condition: "Good Health"

Task Training: Brief instructions

on proper lifting

method, also exercised

for one week prior to

experiment

Task Surrraary

Method: Two handed using proper

lifting technique

Frequency: Frequent lifting as part of job

*Distance/Height/Duration : 3 heights

studied

Criterion: Psychophysical adjustment

procedure to avoid

execessive strain

Product/Qbj ect Sum-nary

Type: Industrial tote box

Size: 34.3cm x48.3cm xl4.0cm (13-l/2"xl9"x5-l/2")

Load Distribution: Evenly distributed

with lead shot.

Presence of Handles and Location: Two handles,

one on each

end of box

Results Summary

Maximum Aceptable Weights of Li

Twc Occupations, and Various Po]

ft (in kg ) for Three Heights of Lift,

oulation Percentiles

Percent of Population to Which Acceptable | HEIGHT OF LEFT Occup- ation 90% 75% 50% 25% 10%

Height* Floor to Knuckle ** Ind.

women

13 15 17 19 21

House- W1 VPS** 6 8 10 11 12

Knuckle Height to Shoulder

Height

Ind.

women 11 13 15 17 19

House- wives 7 8 10 11 12

Shoulder Height to Extended

Ana Reach

Ind.

women

11 12 13 15 16

| Housewives

6 7 8 10

""

1 11

*Independent variables

**Conditions selected as being most relevant to a consumer product lifting task

-53-
Reference (88) Task: TWo Handed, Repeated Lift Study Approach: Behavioral

Snook, S. H. and Irvine, C. M. ffaxirrum Acceptable Weight of Lift.

Subject Suntnary Task Summary

Number: 9

Sex: Male

Age: 25 - 37, mean =30.1

Occupation: Industrial workers

Physical Condition: "Good health"

Task Training: Brief instruction on

proper lifting method,

also exercized for one

week prior to experiment.

Method: Two handed using proper

lifing technique

Frequency: Frequent lifting as part of job

*Distance/Height/Duration : 3 heights

studied

Criterion: Psychophysical adjustment

procedure to avoid

excessive strain

Product/Object Surrcnary

Type: Industrial tote box

Size: 34.3cm x48.3cm xl4cm (13-l/2"xl9"x5-l/2")

Load Distribution: Evenly distributed

with lead shot

Presence of Handles and Location: Two handles,

one at each

end of box

Results Summary

Maximum Acceptable Weights of Repeated Lifts (in kg ) for Three

Heights of Lift and for Various Population Percentiles

Percent of Population to Which Acceptable

HEIGHT OF LIFT 90% 75% 50% 25% 10% Height* Floor to Knuckle ** 24 27 30 33 36

Knuckle Height to Shoulder Height 23 26 28 31 33

Shoulder Height to Extended Arm

Reach

22 24 27 31 33

Note: Snook reconmends 23 kg (50 lbs ) as the maximum acceptable weight of lift

for unselected male industrial workers.

* Independent variable

**Condition selected as being most relevant to a consumer product lifting

task

-54-
Reference (91) Task: Two-Handed , Repeated Lift Study Approach: Behavioral

Snook, S. H., Irvine, C. M. and Bass, S. F. Maximum Weights and Work Loads

Acceptable to Male Industrial Workers.

Subject Summary

Number: 28

Sex : Male

Age: Mean age = 39.9

Occupation : Industrial workers

Physical Condition: "Good"

Task Training: Brief instructions

on proper lifting

methods, also

exercised for one week prior to

experiment

Task Summary

Method: Two-handed, using proper

lifting technique

Frequency: Frequent lifting as part of job

*Distance/Height/Duration : 3 heights

studied

Criterion: Psychophysical adjustment

procedure to avoid

excessive strain

Product/Object Summary

Type: Industrial tote box

Size: 34.3cm x48.3cm xl4.0an ( 13-1/2 Mxl9"x5-l/2")

Load Distribution: Evenly distributed

with lead shot

Presence of Handles and Location: Two handles,

one at each end

of box

Results Summary

Maximum Acceptable Weights of Repeated Lifts (in kg ) for Three

Heights of Lift and for Various Population Percentiles

HEIGHT of LIFT

Percent of Population to Which Acceptable

90% 75% 501

"

) 5% 10%

Floor to Knuckle Height** 17 21 25 29 32

Knuckle Height to

Shoulder Height

16 20 24 28 32

Shoulder Height to

Extended Arm Reach

13 —18

fa22 27 31

!

independent variable

**Condition selected as being most relevant to a consumer product

lifting task

-55-
Reference (95) Task : Two-Handed , Repeated Lift Study Approach : Behavioral

Switzer, S. A. Weight Lifting Capabilities of a Selected Sample of

Human Males.

Subject Summary

Number: 75

Sex: Males; three stature groups*

Age: Mean age = 19.5

Occupation : College students

Physical condition: "Good"

Task Training: Brief instruction on

proper lifting methods

Task Suntnary

Method : Two-handed

,

"proper lift methods"

Frequency: "Work to be carried

out for seme time"

*Distance/Height/Duration : 3 heights

studied

Criterion: Psychophysical adjustment

procedure to avoid

excessive strain

Product/Qbject Surrmary

Type: Sheet metal box

Size: 15 .2cm x30 . 5cm x30 . 5cm (6"xl2"xl2")

Load Distribution: not stated, but bags of

lead shot added to box

Presence of Handles and Location: Two, 11.4 cm. (4-1/2 " ) handles ; one

on each side of box

Results Summary

ffean Maximum Acceptable Weights of Repeated Lifts (in kg ) for

Three Male Stature Groups

HEIGHT of LIFT

Short

Male

Subjects

(1-15%)

Medium

Male

Subjects

(45-60%)

Tall

Male

Subjects

(85-99%)

0 to 18 inches (0 to 45.7 cm ) 56 63 66

•k*k 0 to 42 inches (0 to 106.7cm ) 33 42 44

0 to 62.5 inches (0 to 158.8cm) 24 30 31

*Xndependent variables

**Condition selected as being most relevant to a consumer

product lifting task

-56-
Reference (6) Task : Two-Handed , Repeated Lift Study Approach: Physiological

Asmussen, E. , Poulsen, E. , and Rasmussen, B. Quantitative Evaluation of

the Activity of the Back Muscles in Lifting.

Subject Summary Task Sunmary

Number: 610 Method: Two-handed, "straight back

*Sex: 360 males, 25 females

(10th percentile body heights)

*Age: 8 age groups studied

Occupation: Not stated, but

"residents of urban

area"

Physical Condition: Not stated

Task Training: Brief training on

proper lifting

methods

inclined 45°

Frequency: Repeated lifting required;

"few rest intervals"

Distance/Height/Duration: Table height

Criterion : Physiological measures

(electromyograms)

.

Recommended weights based

on 40-55% of maximum

capable isometric back

strength.

Product/Object Sunmary

Type: Box

Size: "15.7 inches across" (39.9 cm ) Load Distribution: Not stated

Presence of Handles and Location: Two handles,

one on each

end of box

Results Summary

Maximum Acceptable Weights of Repeated Lift for Males and

Females of Various Ages (in kg )

SEX AGE 15 20 25 35 45 50 55 65 Mean**

Male 25 29 31 32 32 - 30 27 30

Female 18 19 19 20 19 18 16 19

.1

independent variables

**Data selected as being most relevant to a consumer product

lifting task.

- 57-
Reference (83) Task : Two-Handed, Repeated Lift Study Approach : Physiological

Poulsen, E. and Jorgenson, K. Back Muscle Strength, Lifting, and Stooped

Working Positions.

Subject Summary

Number: 50

*Sex: Male and Female

*Age: 4 age groups investigated

Occupation: "Various"

Physical Condition: Not stated

Task Training: Not stated

Task Summary

Method: Two-handed lift

*Frequency: Single and repeated lifts

Distance/Height/Duration: Table height

Criterion: Maximum capable for

single lift only

Product/Container Variables

Type : Not stated

Size: Not stated

Load Distribution: Not stated

Presence of Handles and Location: Not stated

Results Summary

Maximum Capable and Permissible Weights for Single and Repeated

Lifts for Males and Females by Age (in kg ) LIFTING

j CONDITIONS

Maximum

Capable for

Single Lift

Sex: Average Male Averaae Female

Acre: 15 25 45 55 15 25 45 55

77 95 98 93 43 49 47 39

Maximum **

j Permissable

j for Single

Lift

54 66 69 65 31 35 33 27

Maximum ** Permissible

for Repeated

Lifts***

39 47 49 47 21 24 23 20

* Independent variables

Table values not based on data, but represent these authors' judgment.

Their rationale for maximum permissible, single lift being 70% of maximum

capable, single lift and maximum permissible, repeated lifts being 50%

of maximum capable, single lift is not specified in reference.

""Condition selected as being most relevant to a consumer product lifting task

- 58-
Reference (72) Task : Two-Handed, Repeated Lift Study Approach : Unspecified

Munchunger, R. Manual Lifting and Carrying

Reconmendations for Maximum Weight for Repeated Two-handed Lifts (in kg ) of Compact Objects (International Occupational Safety and Health Information Center)

SEX AGE 14-16 16-18 18-20 20-35 35-50 Over 50

Male 11 15 17 19 16 12

Female 8 9 11 11 10 8

-59-
Reference (104) Task : Two-Handed, Repeated Lift Study Approach : Unspecified

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

Design (2nd Edition)

Recommendations for Maximum Weight* of Repeated, Two-Handed Lift (in kg ) for Three Box Sizes and Three Heights of Lift

Size of Object in Inches

| HEIGHT of LIFT 30.5cm x30.5cm x30.5cm 30 . 5cmx30 . 5cmX4 5 . 7cm 15 . 2cmx20 . 3cmx91 . 4an

(12"xl2"xl2") (12"xl2"xl8") (6

,, x8 ,, x36")

0 to 3 feet

(0 to 91.4cm) ** 34 43 50

0 to 4 feet

|l (0 to 121.9cm ) 25 34 43

0 to 6 feet

| (0 to 182.9cm ) 18 23 23

*50th percentile - male

**Condition selected as being most relevant to a consumer product

lifint task.

-60-
Reference (67) Task: One-Handed, Single Lift Study Approach: Behavioral

McConville, J. T., and Hertzberg, H.T.E. A Study of One-Handed Lifting.

Subject Summary Task Suirmary

Number: 30

Sex : Male

Age: 18-39; mean =26.4

Occupation: military & civilian employees

college students

Physical Condition: "Average"

Task Training: Subjects told to use

proper lifting method

Method: One-handed lift

Frequency : Not stated

Distance/Height/Duration: Table top

height

Criterion: Psychophysical adjustment

procedure to avoid ex- cessive exhaustion.

Product/Object Summary

Type : Boxes

*Size: Various widths

Load Distribution: Evenly distributed;

lead shot used

Presence of Handles and location: One handle at

top of box

Results Summary

Maximum Acceptable Weight of Repeated One-Handed Lift (in kg ) for Seven Box Sizes and for Various Population Percentiles

Width of Percentage of Population to which Acceptable

Box

95% 75% 50% 25% 5%

8 in (20.3cm ) 22 29 34 37 44

12in (30.5cm ) 22 28 31 35 40

** 16in (40.6cm ) 19 26 30 33 37

20in (50.8an ) 19 25 27 29 34

24in (60.9cm ) 17 24 26 28 33

28in (71.1cm ) 15 20 23 26 31

32in (81.3cm ) 12 18 22 25 29

Note: According to these authors, the best equation for predicting

maximum acceptable weight of one-hand lift is: Weight = (60-width)

independent variable

**Condition selected as being most relevant to a consumer product lifting task

-61-
Reference (85) Task : Two-Handed Carry Study Approach : Behavioral

Snook, S. H. The Effects of Age and Physique on Continuous-Work Capacity

Subject Sunmary Task Summary

Number: 28

Sex : Male

*Age: 14 subjects 25-35,

14 subjects 45-65

Occupation: Industrial workers

Physical Condition: "Good"

Task Training: Brief instructions

given on proper lifting

method, also exercized for

*Method: Two-handed, "straight-arm" and

"bent am" carrying methods

studied

*Frequency: 3 rates of carry studied

*Distance/Height/Duration : 3 distances

studied

Criterion: Psychophysical adjustment

procedure to avoid

excessive strain

one week prior to experiment

Product/Object Sunmary

Type: Industrial tote box

Size: 34.3cm x48.3cm xl4.0an ( 13-1/2 "xl9"x5-1/2")

Load Distribution: Evenly distributed with lead shot

Presence of Handles and Location: Two handles, one on

„ , , each end of box Results Surrmary

Maximum Acceptable Weights of Carry (in kg ) for Two Distances,

Three Rates, and Twd Age Groups.

METHOD of CARRY Distance

Carried

Rate,

Once Every

Age,

25-35

Age,

40-60

Mean

| Knuckle Height** 2.13m (7ft ) 60 seconds 30 35 32

(Straight Am) 2.13m (7ft ) 12 seconds 24 29 26

8. 5m (28ft )** 60 seconds** 26 28 27***

8.5m (28ft ) 18 seconds 20 20 20

Elbow Height 2.13m (7ft ) 60 seconds 24 28 26

(Bent Am) 2.13m (7ft ) 12 seconds 21 22 21

8.5m (28ft ) 60 seconds 19 22 21

8.5m (28ft ) 18 seconds 15 15 15

independent variables

**Condition selected as being most relevant to a consumer product

carrying task

***Percentile values presented in Table 3 are based upon a standard

deviation of 5.7kg (12.50 lbs ).

-62-
Reference (87) Task : Two-Handed Carry Study Approach : Behavioral

Snook, S.H., and Ciriello, M.S. Maximum Weights and Work Loads Acceptable

to Female Workers

Subject Summary

Number: 31

Sex : Female

Age: Mean age: industrial workers = 38.5;

housewives = 35.6

*Occupation: 15 industrial workders

16 housewives

Physical Condition: "Good health"

Task Training: Brief instructions given

on proper lifting methods,

also exercized for one

week prior to experiment.

Product/Object Sunmary

Type: Industrial tote box

Size: 34.3an x48.3cm xl4.0crr (13-l/2"xl9"x5-l/2")

Load Distribution: Evenly distributed with

lead shot

Presence of Handles and Location: Two handles, one on

each end of box

Results Sunmary

Task Summary

Method: Two-handed,

"straight-arm" carry

Frequency: "As part of job"

*Distance/Height/Duration

:

3 distances studied

Criterion : Psychophysical

adjustment procedure

to avoid excessive

strain.

Maximum Acceptable Weights of Carry (in kg ) for Three Distances, Two

Occupations, and Various Population Percentiles

Percent of Population to Which Acceptable

Distance

Carried Occupation 90% 75% 50% 25% 10%

2.13 m

(7 ft )

Industrial Women 13 15 17 20 21

Housewives 8 10 11 13 15

4.3 m

(14 ft )

Industrial Women 13 15 17 19 21

Housewives 7 9 10 12 14

8.5 m.

(28 ft )**

Industrial Women 11 13 15 18 20

Housewives** 6 8 10 11 12

1

independent variables

**Conditions selected as being most relevant to a consumer product carrying task.

-63-
Reference (91) Task : Two-Handed Carry Study Approach : Behavioral

Snook, S.H., Irvine, C.H., and Bass, S.F. Maximum Weights and Work

Loads Acceptable to Male Industrial Workers.

Subject Summary Task Summary

Number: 28

Sex: Male

Age: Mean age = 39.9

Occupation : Industrial workers

Physical Condition: "Good"

Task Training: Brief instructions

given on proper lifting methods,

also exercised for one week prior

to experiment.

*Method: Two-handed, "straight-arm"

and "bent-arm" carrying

methods studied

Frequency: "As part of job"

*Distance/Height/Duration: 3 distances

studied

Criterion : Psychophysical adjustment

procedure to avoid

excessive strain.

Product/Object Summary

Type: Industrial tote box

Size: 34.3cm x48.3cm xl4.0an ( 1 3-1/2 "xl9"x5-1/2")

Load Distribution: Evenly distributed with lead shot

Presence of Handles and Location: Two handles, one on

each end of box

Maximum Acceptable Weights of Carry (in kg ) for Two Methods, Three

Distances and Various Population Percentiles

j METHOD of CARRY

Distance

Carried

Percent of Population to Which Acceptable

90% 75% 50% 25% 10%

Carry* Knuckle Height **

I (Straight-Arm Carry)

2.13 m

(7 ft ) 22 27 32 38 43

4.3 m

(14 ft ) 20 24 29 33 37

8.5 m

(28 ft )** 19 23 27 31 35

Elbow Height Carry

(Bent-Arm Carry)

2.13 m

(7 ft ) 18 22 26 30 34

4.3 m

(14 ft ) 16 20 23 27 30

8.5 m

(28 ft ) 15 17 20 24 26

* Independent variables

**Conditions selected as being most relevant to a consumer product carrying task.

-64 -
Reference (20) Task : Two-Handed Carry Study Approach : Physiological

it Chaffin, D. B. Some Effects of Physical Exertion

Subject Summary Task Summary

Number : Not stated

*Sex: Male and female

Age : Not stated

Occupation: Not stated

Physical Condition: "Good"

Training : Not stated

Method: Two carrying methods studied

(see Table below)

Frequency:Walking rate of 4.8kph (3 mph)

Distance/Height/Duration : 4 minutes

Criterion: Physiological, based upon

maximum acceptable average

metabolic rates (Kcal/min)

Product/Object Sunrnary

Type: Industrial tote box

Size: 34. 3cm x48.3cm xl4.0cm ( 13-1/2 "xl9"x5-l/2")

Load Distribution: Balanced

Presence of Handles and Location: Two handles, one

on each end

Results Summary

METHOD Of CARRY

Maximum Acceptable Weight of Carry

(in kg ) Males Females

Two-handed , load held

waist high

24 19

Two-handed, load held

at arms length thigh)* (against **

30 24

* Independent variables

Condition selected as being most relevant to a consumer product

carrying task

-65-
Reference (53) Task: Two Handed Carry Study Approach: Physiological

Kamon , E. and Belding, H. The Physiological Cost of Carrying

Loads in Temperate and Hot Environments.

Subject Summary Task Summary

Number: 3

Sex: Male (assumed)

Age : 20,21,24

Occupation: Not stated

Physical Condition: Not stated

Task Training: "Some"

Method: Two-handed carry

Frequency: Continuous carrying,

without rest

Distance/Height/Duration: 5 minute

carry at normal walking

speed

Criterion: Physiological (heart rate),

with emphasis on "efficiency of carry."

Product/Object Summary

Type: Corrigated fiberboard

Size: 40.6cm x30. 5cm x30. 5cm (16"xl2"xl2")

Load Distribution: Not stated

Presence of Handles

and Location: None

Results Summary

"In terms of cardiac cost, approximately 15 kg (33 lbs ) is the

upper limit for repetitive handling of bulky loads in

front of the body."

-66-
Reference (57) Task: Two-Handed Carry Study Approach: Physiological

Kellerman, F. T. and Van Wely, P. A, The Optimum Size and

Shape of Container for Use of the Flower Bulb Industry

Subject Summary Task Summary

Number: 18

Sex: Male

Age: Mean = 41.5

Occupation: Various (proprofessionals , students and

clerks

)

Physical Condition: "Good

health"

Task Training: None

Method: Two-handed carry

Frequency: 3 frequencies**

(6, 12, & 24 carries)

Distance/Height/Duration :12 .19m (40 ft ) Criterion: Physiological with

emphasis on "efficiency

of carry" in terms of

"minimum use of energy

per meter-kilogram (foot-pound)

of work"

Product/Container Variables

Type: Flower bulb carrying boxes (wood)

*Size: 3 sizes studied***

*Load Distribution: Three weights 9,18,&35kg (19,39 & 77 lbs ) each evenly distributed,

with little load shifting

Presence of Handles

and Location: Not stated

Results Summary

"18 kg (39 lbs )is carried slightly more efficiently than

35 kg (77 lbs ) and both are carried more efficiently than

9 kg (19 lbs )"

independent variables

**35 kg box carried 6 times; 18 kg box carried 12 times;

9 kg box carried 24 times

***50.8cmx35.6cm x25. 4cm* 99.1cm x30.5cmx20.3cm; 66.0cmx45.7cm x20.3cm

recommendation for ootimum size not based on physiological

data, but rather on what could best fit on a pallet.

-67-
Reference (74) Task : Two-Handed Carry Study Approach: Physiological

Muller, E. A., Vetter, K. , and Blumel , E. Transport of Muscle

Power Over Short Distances

S ubject Summary Task Summary

Number

:

Sex

:

Occupation: * Physical Condition:

Task Training: \

Method: Tw

Frequency

:

Unknown

Distance/He

Criterion

i-handed carry

Continuous without

rest

ght/Duration : Unknown

Physiological with

emphasis on "efficiency

of carrying"

Product/Object Summary

Type : Size

:

Load Distribution:

Presence of Handles

and Location:

f

Unknown

V. Results Summary

"It was much more efficient to transport the same total

load in units of 15 to 28 kg (33 to 62 lbs ) instead of in units of 4.1 kg

(9 lbs )" (Actual reference not yet retrieved; quote and Task Summary

information obtained from Ergonomics Abstracts)

-68-
Reference (9) Task; Two-Handed Carry Study Approach : Unspecified

Bedale, E. M. Comparison of the Energy Expenditure of a Woman Carrying Loads in Eight Different Postions

"A weight is heavy when it reaches 35% of body

weight." While this recommendation translates

to 21 kg , 22 kg , and 23 kg , for the 95th,

90th, and 50th percentile woman respectively,

the recommendation is based on only one female

subject

.

Reference (22) Task: Two-Handed Carry Study Approach : Unspecified

Chaffin, D. B. and Ayoub, M. M. The Problem of Manual Material

Handling

"Hence, [for male industrial workers] objects of

greater that 50.8 cm (20") breadth and/or which

require the hands to be more than 40.6 cm (16")

in front of the hips when in a carrying position

should be handled by two persons when the load

exceeds 16 kg (35 lbs )"

-69-
Reference (42) Task; Two-Handed Carry Study Approach: Unspecified

Grand jean, E. Fitting the Task to the Man: An Ergonomic

Approach

Maximum Weights (in kg ) "to avoid accidents"

CONDITIONS

Adults Youths

Male Female Male Female

Occasional Lifts 50 20 20 15

Continuous work

(carry) 18 12 11-16 7-11

Reference (51) Task: Two-Handed Carry Study Approach: Unspecified

International Laborer Office. Maximum Permissible Weight to

be Carried by One Worker

Maximum Permissible Weiaht (in kg ) to be _ P^rri pH hv One Worker

AGE Male Female

Adult 40 15-20

16-18 yrs. 16-20 12-15

70-
Reference (70) Task: Two-Handed Carry Study Approach : Unspecified

MIL- STD- 14 7 2A : Human Engineering Design Criteria for Military

System, Equipment and Facilities Cpg. 151)

"Individual portions of equipment may weigh up

to 16kg (35 lbs ) if the load is balanced and is

distributed over many muscle ,groups , and it is not

necessary for the system to maintain the pace of

an infantry movement."

-71-
Reference (20) Task: One-Handed Carry Study Approach: Physiological

Chaffin, D. B. Some Effects of Physical Exertion

Task Summary

*Method: Two carrying methods

studied (see table below)

Frequency talking rate of4.8kph (3mph)

Distance/Height/Duration: 4 minutes

Criterion: Physiological, based

upon maximum acceptable

average metabolic

rates (cal/min)

,

Product/Object Summary

Type : Not stated

Size: Not stated

Weight Distribution: Not stated

Presence of Handles

and Location: Not stated, but

"good grip available"

Subject Summary

Number: Not stated

*Sex: Male and female

Age: Not stated

Occupation: Not stated

Physical Condition: "Good"

Task Training: Not stated

Results Summary

METHOD OF CARRY

Maximum Acceptable Weight of Carry

(in kg ) Males Females

One-handed

,

load held waist

high

12 10

One-handed

,

load held at

arm length***

(against thigh)

14 12

independent variables

**Condition selected as being most relevant to a consumer

product carrying task

-72-
Reference (29) Task: One-Handed Carry Study Approach : Unspecified

Daman, A. The Human Body in Equipment Design

"For men the maximum load carried in one hand

should be 27 kg (60 lbs ) for short distances

and 16 kg (35 lbs ) for longer distances."

-73-
Reference (66) Task: Two-handed / Single Lift Study Approach : Behavioral

Martin, J. B. and Chaffin, D. B. Biomechanical Computerized Simulation of

Human Strength in Sagittal-Plane Activities.

Subject Summary Task Summary

Number: 89

*Sex: 41 Male and 48 Female

Age: (18-52) mean males = 31

mean females =29

Occupation: "production workers"

Physical Condition: Not stated

Task Training: Not stated

Method: Two-handed Lift

Frequency: Single Lift capability

Distance/Duration/Height: Lifting force from

30.5,91.4, & 152. 4on

( 12, 36 & 60 in ) vertical heights

Criterion: Maximum Capable Single Lift

Product/Object Summary

Type: Platform attached to "lifting force meter"

*Size:45.7 am (18 inches) across, hand holds at different horizontal displacements from body.

Load Distribution: Not applicable

Presence of Handles

and Location: 2 handles, one on each side of

platform

Results Summary

HORIZONTAL DISPLACEMENTANKLE JOINT TO HANDS (INCHES) HORIZONTAL DISPLACEMENTANKLE JOINT TO HANDS (INCHES) -74-
Reference 15) Task : Two-Handed y Single Lift Study Approach : Behavioral

American Industrial Hygiene Association: Ergoncmic Guide to Manual Lifting.*

« The maximum number of pounds that 50 percent of the healthy,

male industrial worker population can be expected to lift, is:

HEIGHT of LIFT

Object Width (inches away from the body)

10 15 20 25 30

Floor Level to 32 30 27 25 23

Knuckle Height**

Knuckle Height to 30 27 25 23 21

Shoulder Height

Shoulder Height to 30 27 25 23 21

Extended Arm Reach

* Recommendations of AIHA are based upon the results of studies (88) , (72) , and (67)

.

**Condition selected as being most relevant to a consumer product lifting task.

Reference (47 ) Task : Two-Handed Carry Study Approach : Unspecified

Hertzberg, H.T.E. Handbook of Instructions for Aircraft Ground Support

Equipment Design (2nd Edition)

.

The weight of bulky articles, around 76.2 an. (30 inches) to a side

should not exceed 9 kg (20 lbs )

.

- 75 -
APPENDIX B

Instructions for Subjects

We want you to assume that you are returning a product in need of

service from your home to a service facility. More specifically, assume

that you must (1) lift and carry the product, by yourself , and without

the use of any external aids (carts , wheels , etc . ) , from your home to your

car, (2) drive your car to the repair facility, and (3) lift and carry the

product from your car to the repair facility, (assume the latter distance

to be approximately one city block) . At seme point during these return

activities, assume that you must carry the product either up or down a single flight of stairs .

With the above assumptions in mind, your job will be to adjust the

weight of a simulated product to a level which you believe to be the

maximum reasonable weight which you would be willing to handle in a reallife situation . By reasonable , we mean without excessive strain or

exhaustion .

Your weight adjustment of the simulated product will be accomplished

through the addition and/or removal of lead shot. You have to make enough

adjustments so that you get a good feeling for what is too heavy and what

is too light. You can never make too many adjustments - but you can make

too few. You will be required to perform this adjustment procedure twice

today and twice at a later date. After each adjustment procedure you will

be asked to actually lift and carry the simulated product the entire length

of a hallway and up a single flight of stairs. You will be allowed to

rest as frequently as you like during this task, but you should not plan

on resting more often than you would normally in a real-life situation.

Remember:

This is not a contest !

We want your judgment of how much weight you feel is reasonable

for you to lift and carry when returning a product for repair.

Keep in mind that this is a task which would ordinarily be required

of you only once or twice a year.

-76-
y

APPENDIX C - RCSCARCII PARTICIPANT AGRCEMCNT % 1 A V* . W

i'-' 1 i«wcm , ii."«h Informed Consent Form

Joel J. Kramer

2» OiviMim/bu lion 441.04

4. LOCtlflOM

• ^X] G.'Xllinf stxrt 0

N.mfl Code L| Other (iitrcify)

Portnhilitv Guidelines for Federal Trade Commission

liris experiment is designed to obtain data (information) related to the maximum reasonable

nzc and weight limits for products that are to be returned' by consumers tor servicing,

repair, etc. The participant will be required to adjust the weight of two simulated consumer

products (by the addition and/or removal of lead shot) to a level which is believed to be

:he maximum reasonable weight which he/she would be willing to handle in a real-life

;ituation. The -participant will then be required fo actually lift the product and carry it

1 distance of approximately 400 ft. and up a single flight of stairs.

t . Risk*; lo Participant Potential risks to the participant include all forms of accidental injury normally associated

:ith the lifting and carrying of heavy objects (slips and falls, ‘dropping objects on feet,

mscle strain, over- exertion, etc.). The likelihood of such injuries occuring is

jxtremely small, if the participant follows all of the instructions' given..

it. Responsibilities of ?ar ticipont "he participant will:

(1) Attend two, 30-ninute experimental sessions, each session taking place on a different day.

7) Wear flat-bottomed shoes and suitable clothing.

'3) Follow instructions of experimenter (s)

[4) Permit photographs to be taken.

'5) Permit measurements of (a) height, (b) weight, (c) arm reach, (d) shoulder- elbow length,

(f) elbow breadth, (g) maximum body breadth, (h) distance from floor to knuckles (i)

' distance from body vertical center- line to product center- line for one-handed activity,

and m distance from buttocks to fingers for two-handed activity

» Besponsihil ili'es of Invcsuooioi is). he investi gator (s) will:

'!) Ensure the safety of participants at all times.

Z) Schedule the experimental sessions at times convenient for the participants

’3) Provide participants w-ith knowledge of results upon completion of the experiment.

’4) Ensure that no data reported for the participants will be identifiable in any

publication and that participant data will not be disclosed for any other

purpose exccnt as required bv law.

O. IT is iiNOtr.stOOO that HTiicn the principal investigator, the participant, or the participant's parent or guardian mat

Terminate the participants involvement in the research at any time without incurring legal liability for Such

TERMINATION.

t. I Ih!H-I»v cci lily iii.-ii my |i,iiii<*iiK,iiiin is volunl.ivy .mil iA.il I fwivc ic.id ond occctil |iic Icinis ol tins dgfeorncrtl.

Partiriiont. o> Parent or Gu.irdi.in tSw**lure/

• Or le

I'niK ilMl lnvi*>liiMlt*( (

•

i. liiilv 1 u (i-i'iwi 1

on liy / .S11//1.1I uifl

#

V U.ilu

* use OMU-NIIN-I ••

- 77-
APPENDIX D - Semantic Differential Scale used to Evaluate Subjects

Opinions Concerning the Weights and Sizes of the

Simulated Products Carried.

Instructions : Complete each of the following two statements so that

they most accurately express your opinion concerning the (A) weight and

(B) size of the simulated product which you have just handled. In

completing these statements, keep in mind the specific task requirements

which were imposed upon you by the experimenters (e.g. the 400 ft.

distance of carry, the stairs, the method of carry used, etc.)

.

A. The weight of the simulated product was:

1. unreasonable - too light

2. slightly less than the maximum reasonable weight

3. maximum reasonable weight

4. slightly more than the maximum reasonable weight

5. unreasonable - too heavy

B. The size of the simulated product was:

1. unreasonable - too snail

2. slightly less than the maximum reasonable size

3. maximum reasonable size.

4. slightly more than the maximum reasonable size

5. unreasonable - too big

-78-
APPENDIX E - Basic Descriptive Statistics

In an attempt to maintain both simplicity and technical accuracy.

the following discussion is presented in terms of "population statistics"

rather than "sample statistics," thus resulting in a discrepancy between

the symbols used in the text of this report and those of this Appendix.

Sample statistics are often used as estimates of population statistics,

and the general concepts are the same for both types. The sample

statistic symbols used in the text are X, sample mean; s, sample standard

deviation; n, number of observations in sample; m

g

, sample skewness;

and m^, sample kurtosis.

The frequency of occurrence of many human traits (both physical

and psychological) within the human population may often be characterized

by the so-called "normal distribution," the shape of which is completely

determined by its mean, y,and standard deviation a. The mean, y, is

a measure of central tendency and in the normal distribution represents

(1) the most frequently occurring observation, (2) the midpoint of the

range of observations, and (3) that value in the distribution around

which all deviations sum to zero. The standard deviation, a, is a measure

of dispersion around the mean and for a finite population of N observations

is estimated by the formula

range of observations ( 1 through N) and x^ indicates the value of each

of the specific observations. In a normal distribution, the percentage

of observations falling within plus or minus one, two or three standard

deviations of the mean is a constant, these percentages being 68.3%,

N

where I indicates summation over the entire

i=l

-79-
95.5% and 99.7%, respectively (see Figure E-l) . The percentage of

observations occurring between the mean and any given may be found

through the use of the formula 3 = (X^ - u)/a, where 3 represents a

"standard normal score" which can be used with any standard "3 table"

to obtain the corresponding percentage of observations.

Figure E-l. The Normal Distribution

Some human traits are better characterized by skewed or flattened

variations of the normal distribution. In such cases the amount of

skewness, m

g

, present in the distribution can be estimated

by the formula N

m = Z (x. - y)

3/N)/a 3 r S i=l

while the amount of flatness

(kurtosis) , m^, present can be estimated by the formula

N

m^ = E (x^ - y)

4/N)/a 4

. The expected value of m^ is zero in the

i=l s

normal distribution, while positive and negative values of m

s indicate distributions which are positively and negatively skewed, respectively (See Figures E-2

and E-3)

.

- 80-
4-1o

4-1o

Figure E-2. Positively Skewed

Distribution

Figure E-3. Negatively Skewed

Distribution

The expected value of is three (3) in the normal

distribution. Larger values indicate distributions which are peaked or

" leptokurtic" in nature (See Figure E-4) , while smaller values represent

distributions which are flattened or "platykurtic" in nature

(See Figure E-5)

.

Figure E-4 . Leptokurtic

Distribution

Figure E-5. Platykurtic

Distribution

- 81-
When distributions differ significantly from "normal," population

percentiles can no longer be directly derived through the use of the

standard 3 tables, thus necessitating other statistical techniques to

obtain the desired percentile values.

- 82-
APPENDIX F - Statistical Hypothesis Testing (ANOVA)

Hypotheses concerning the differences between sets of scores

collected under various experimental conditions are frequently tested

through the use of statistical techniques involving a comparative

analysis of between set score variances versus within set score variances. To the extent that these sets of scores are identical (i.e.,

when the experimental conditions have no significant effects) , the ratio

(F) of variance between set scores divided by variance within set scores

should approximate a value of 1. The larger the difference between sets

(i.e. the greater the effects of the experimental conditions), the

greater should be the value of F. The level of statistical significance

associated with F depends upon both the number of sets of scores, and

the number of scores within each set (these numbers are roughly equivalent to the number of "degrees of freedom") . If more than two sets of

scores are involved in the analysis of variance, the determination of

statistical significance is called an "F-test," or Analysis of Variance

(ANOVA) , if only two sets of scores are involved, it is called a "ttest." A detailed discussion of the assumptions and computational

procedures underlying these tests may be found in any standard statistical textbook. Of importance to the analysis conducted in the present

investigation, however, is the requirement that all treatment variances

involved in an ANOVA be roughly equivalent (homogeneous) . Since the

variances associated with male and female data were quite different, it

necessitated the computation of separate ANOVA 'a for the male and female

data sets.

- 83-
MBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 76-1092

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

Consumer Product Portability as Related to Warranty Rulemaking

5. Publication Date June 1976

6. Performing Organization Code

7. author(S) Joel J. Kramer, Patrick G. Meguire 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.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Federal Trade Commission

Division of Special Statutes, Room 520

633 Indiana Avenue, N. W.

Washington, D. C. 20580

13. Type of Report & Period Covered

Final Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less lactual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

The Federal Trade Commission (FTC) has the responsibility for determining what

may be reasonably expected of consumers in their fulfillment of the terms of a consumer product warranty. Such determination necessitates, in part, providing

an empirical basis for defining and quantifying various factors influencing

product portability. This report discusses the problem of defining consumer

product portability within the context of a consumer product return activity,

offers a working definition of product portability within this context, summarizes

and discusses the results and utility of previous portability related studies, and

describes the results of a controlled experiment which more directly relates to

the task of establishing maximum reasonable product weight for a consumer product

return activity. Statistically significant differences in maximum reasonable product

weight were found for the variables of method of product carry and sex of customer.

No statistically significant differences were found for the variables of consumer

age and product size (at least for the sizes chosen for study). Distributions

of maximum reasonable weight for product return are presented and recommendations

for warranty rulemaking are given.

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)

Anthropometry; biomechanics; carrying; consumer product portability; ergonomics;

human factors; lifting; manual materials handling; physiology; psychophysics;

safety; warranty

19. SECURITY CLASS 21. NO. OF PAGES

(THIS REPORT)

is 83

UNCL ASSIFIED

20. SECURITY CLASS 22. Price (THIS PAGE)

is

UNCLASSIFIED

18. AVAILABILITY Uni imited c For Official Distribution. Do Not Release to NTIS

[ Order From Sup. of Doc., U.S. Government Printing Office Washington, D.C. 20402, Sp_Cats_N_oi_CJ^____________

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