NBSIR 76-1146

A Study of Personal Fall-Safety

Equipment

Harold L. Steinberg

Product Systems Analysis Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

June 1977

Final

Prepared for OSHA

NBSIR 76-1146

A STUDY OF PERSONAL FALL-SAFETY

EQUIPMENT

Harold L. Steinberg

Product Systems Analysis Division

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

June 1977

Final

Prepared for OSHA

U S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director
- .

, ,

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TABLE OF CONTENTS

Page

1.0 Introduction 1

1.1 Purpose 1

1.2 Project Approach 1

1.3 General Background 3

1.4 Terminology and Symbols 4

1.5 Units of Measure 7

2.0 Physiological Aspects of Fall Injuries 9

2.1 Human Body Reactions 10

2.2 Tolerable Limits 13

2.3 Information from Accidents Involving Fall- 20

Arrest Systems

3.0 Fall-Safety Systems 23

3.1 The Physics of Fall-Arrest 23

3.2 Anthropometric Basis 32

3.3 Behavior of a Fall-Safety System During Fall- 35

Arrest

3.3.1 Containment 37

3.3.2 Energy Absorption 40

3.3.3 Limited Fall Distance 41

3.3.4 Rescue 4 3

3.4 Classification and Description of Systems 43

3.4.1 Class I Systems 45

3.4.2 Class II Systems 46

3.4.2.

1

Class Ila Systems (Ascent./ 46

Rescue)

3. 4. 2.

2

Class lib Systems (Descent/ 47

Rescue

)

i
Page

3.4.3 Class III Systems 48

3.4.4 Class IV Systems 50

3.4.5 Class V Systems 52

3.4.6 Class VI Systems 55

3.5

Descriptions and Functions of Components 56

3.5.1 Containment Devices 56

3.5.2 Lanyards 57

3.5.3 Lifelines 58

3.5.4 Rope Grabs and Shock Absorbers 58

3.5.5 Ascent and Controlled Descent Devices 58

3.5.6 Anchorage 59

3.5.7 Other Components 59

3.o Components, Requirements, and Limitations 59

3.6.1 Mechanical Requirements 60

3.6.2 Electrical Requirements 62

3.6.3 Environmental 63

3.6.4 Deterioration in Use 70

3.6.5 Other Use Factors 72

3.7 Test Procedures 73

3.7.1 Static Strength Tests 77

3.7.2 Elongation (Extensibility) Tests 78

3.7.3 Dynamic (Drop) Tests 82

3.7.4 Electrical Tests 88

3.7.5 Other Tests 88

3.8 Prototype, Production Line, and Field Testing 90

3.8.1 Prototype Testing 91
3.8.2 Production Line Testing

3.8.3 Field Testing

Page

91

4.0 92

Recommendations 96

4.1 General Considerations 96

4.2 Design and Fabrication 97

4.3 Performance 102

4.4 Use 108

4 . 5 Testing H3

4.6 Information To Be Furnished 116

4.7 Suggested Areas for Additional Work 119

Bibliography 122

Appendix A - Experimental Program A-1

A. 1 Introduction

A. 1.1 Purpose A_1

A. 1 .

2

Scope A_1

A. 2 Rationale A_2

A. 2.1 Rationale for Testing Components A~2

Separately

A. 2.

2

Rationale for Using Static Test Results A-4

to Predict Impact Parameters

A. 3 Experimental Procedures A-6

A. 3.1 Test Specimens A-6

A. 3.1.1 Lanyards A-6

A. 3. 1.2 Body Belts A-8

A. 3.

2

Testing Apparatus A-8

A. 3.

3

Lanyard Tests A-14

A. 3.

4

Body Belt Tests A-18

iii
Page

A. 4 Data Analysis A-25

A. 4.1 Reduction of Experimental Data A~25

A. 4.

2

Computations Using Analytical Model A-32

A. 4.

3

Model Validation and Comparison with A -41

Other Results

A. 5 Computation of1 Load vs. Elongation Functions A-72

for Various Length Lanyards

IV
Tables

Page

1. Factors for Converting from U.S. Customary to 8

SI Units of Measure

2. Body Centered Geometry System Used to Describe 11

Accelerations

3. Peak Force on Lap Belt and/or Torso 12

4. Acceleration Levels Accepted by the Naval Aerospace 17

Medical Research Laboratory

5. Ratio of Tension in Lifeline to Tension in Lanyard 30

6. Weights for Selected Percentiles of Males by Age for 33

the United States

7. Estimated Weights of Construction Workers when 34

Clothed and Equipped

8. Waist Depths of Various Segments of the Population 36

9. Proposed Classification for Active, Personal 44

Fall-Safety Systems

10. CSAO ' s Conclusions and Recommendations Regarding 53

Fall-Safety Equipment with Rope Grabs

11. Criteria for Determining Performance Requirements 61

for Fall-Safety Equipment

12. Recommended Working Load as a Percentage of Breaking 62

Strength for Various Fiber Ropes

13. Effects of Environments on Rope Strength 67

14. NPTR Knot Test Data 74

15. Anchorages and Anchor Linkages to be Used when 79

Strength Testing Lanyards

16. Performance Criteria for Fall-Safety Equipment 104

17. Recommended Maximum Permissible Drop Line 106

Extensibilities

18. Fall Parameter Limits above which Impacted Lanyards 111

should be Replaced

v
I

A1

A2

A- 3 (a-c)

A-4 (a, b)

A5

A6

A- 7 (a-d)

A- 8 (a-d)

A9

A- 10

A- 1

1

A-12

Calibration of Rope Testing Machine

Typical Data for Manually Obtained Lanyard

Central-Section L/E Measurements

Typical Output from a Third Degree Polynomial

Fit of L/E Data

Example of Output of Main Computer Program

Summary of Calculated Peak Impact Forces

for Selected Fall Parameters

Page

A-9

A-17

A-27

thru A-29

A-3 5 & 36

A-37 & 38

Summary of Calculated Peak Impact Decelerations A-39&40

for Selected Fall Parameters

Calculated Peak Impact Forces for Selected A-42

Fall Parameters

Calculated Peak Impact Accelerations for A-46

Selected Fall Parameters

Comparison of Absorbed Energy as Measured with A-65

a Planimeter and Calculated Using a Computerized Model

Comparison of Calculated and Actual Forces for A-66

a Test Spring Obeying Hooke's Law

Comparison of Given Breaking Strengths (BS) A-67

with Average Values for Various Lanyards

Comparison of Calculated Peak Impact Forces A-69

with Comparable Values as Experimentally

Determined by Equipment Manufacturers

A-13 Comparison of Calculated Peak Impact Durations with A-70

Comparable Values as Determined by

Equipment Manufacturers

A-l 4 Coefficients of the Polynomial

1.8 m (6 ft) Lanyards

Equations for A-7 3

A- 15 Coefficients of the Polynomial

Pure Rope Sections of Lanyards

Equations for A-74

A- 16 Elongation of 9/16 inch New Spun Nylon Lanyard

Computed from Test Data

A- 7 5

vi
Figures

page

1. Acceleration tolerance along the z axis 15

2. Damped spring mass system 24

3. Assumed force-elongation relationship for 26

damped spring

4. Computed acceleration imparted to a rigid mass 29

as a function of the ratio of free fall distance,

h, to spring length, L, when k/Mg = 70

n

5. Simulated horizontal lifeline 30

6. Commonly used types of body containment devices 38

7. Equal energy absorption by two idealized 42

fall-safety systems

8. Comparative sunlight and weather resistance 64

commercial ropes

9. Impact strength vs. temperature curves for 69

a carbon and an alloy steel

10. A possible setup for tensile testing of 80

linemen's pole straps

11. A possible setup for tensile testing of 80

linemen's body belts

12. Schematic diagram of a drop test 84

13. A possible test weight configuration 86

14. A possible setup for dynamic testing of 87

linemen's body belts

15. A possible setup for dynamic testing of 87

linemen's pole straps

16. Electric contact configuration for dielectric 89

testing of ropes

17. Correlation between lanyard extensibility at 95

two loads

Vll
Page

A-l Flow diagram of experimental procedures A7

A2

Initial experimental setup used to measure

the extension of lanyard center (pure rope)

sections

A-ll

A3

The step-interval extensometer developed at

NBS for use in load-extension testing

or ropes

A-12

A4

Load-elongation curve for lanyard using

step-interval extensometer

A-l 3

A5Record sheet for lanyard test A-15

A6Load-elongation curve for 9/16 inch new

spun nylon lanyard

A-19

A7Length-measurement configuration for

body belts

A-2 0

A8

Tensile test configuration for body belts A- 21

A9Load elongation curve for a tongue buckle

belt

A-2 3

A-l 0 Load elongation curve for a friction

buckle belt

A- 2 4

A- 1

1

Load/relative extension curves obtained

for 13 lanyard types

A- 30

A- 12 Load/relative extension curves obtained for

13 lanyard types; center rope sections

A- 31

A- 1 3 Load/relative extension curves obtained for

1/2 inch filament nylon lanyards

A- 3 3

A-14 Load/relative extension curves obtained for

1/2 inch gold filament nylon lanyards

A- 3 4

A-15 a-m Calculated peak impact acceleration as a function of the ration of free fall distance,

h, to lanyard length, L

A- 5 0

thru

A- 6 2

A-l 6 Comparison of test results with Cordage

Institute L/E data

A-6 3

viii
Acknowledgments

Richard Yates was responsible for much of the modeling

of fall-arrest systems and both Mr. Yates and Michael Vogt

share credit for transformation of the model into a computer program and for related computations. Martin

Cordes and Ron Rehm of the Mathemetical Analysis Section,

Applied Mathematics Division, National Bureau of Standards,

gave invaluable assistance in several different mathematical

aspects of the physics required for our model development.

The author wishes to extend his appreciation to

John Michalak of the Engineering Mechanics Section,

National Bureau of Standards, who performed our tensile

tests and whose careful and conscientious work and frequent

suggestions were much appreciated.

Recognition should be extended to the NBS Instruments

Shops Division for assistance in the design and fabrication

of the special device used to measure lanyard extensions.

Thanks are also in order for William Beine of my section

who assisted the project at an early stage. Sincere

thanks are also in order for the safety equipment manufacturers who so willingly gave of their time and who

contributed test samples and test data. A similar note of

thanks must go to the users of these equipments who so

graciously allowed project team members to visit job sites

to gain a working knowledge of worker/fall-safety-system

interactions

.

Finally, the author wishes to express a special

acknowledgment to Roscoe L. Bloss for his extensive

editorial organization and textual revision of this report.

His contributions as editor were to emphasize the essential

experimental results of the study, to focus on the

findings that are particularly relevant to the development of safety criteria, and to summarize safety equipment

data for use by manufacturers of fall-safety equipment,

construction workers, and standard setting groups.

IX
\

' .. •-•r:, }
A STUDY OF PERSONAL FALL-SAFETY EQUIPMENT

1.0

1.1 Introduction

Purpose

Each year falls injure, maim, or kill many thousands of

United States citizens, and a significant fraction of these

accidents occur in an occupational setting. Some of these

injuries are the result of falls experienced by workers

whose jobs require that they perform tasks many feet above

the ground. The Occupational Safety and Health

Administration (OSHA) recognizes the need for performance

standards for fall-safety systems to protect such workers

and also recognizes that current standards are inadequate.

Therefore, OSHA is drafting a performance standard for

worker restraint systems, with primary focus on the

construction industry. It is anticipated that this will lay

the groundwork for related standards to protect linemen,

tree pruners, window washers, etc.

The work covered by this report was directed towards

providing a valid basis for a comprehensive OSHA performance

standard for fall-safety systems and their components, in

particular safety belts, harnesses, lanyards, and lifelines.

The major effort was devoted to fall-arrest systems in

contrast to fall-restraint systems.

1.2

Project Approach

The project approach involved a literature search,

written and telephone inquiries, work site visits, visits to

safety equipment manufacturers, the conduct of laboratory

tests, analyzing and correlating data from laboratory tests

and from the literature, examining all of the information

obtained in terms of requirements for fall-safety systems,

and formulating recommendations pertaining to a performance

standard for fall-arrest systems and their components.

The review phase of the project covered:

(1) Data on falls from heights, in particular those

where fall-safety equipment was involved;

- 1 -
(2) Relevant injury threshold limits and their

physiological foundations;

(3) Test data for fall-arrest systems and components;

and

(4) Relevant voluntary and mandatory standards.

The visits to work sites were planned to provide an

opportunity to observe various types of fall-arrest

equipment in use and the worker/work environment/safety

system interactions that result. These observations were

used to estimate the degree of worker acceptance and

utilization of fall-safety equipment and to determine the

factors that influence such acceptance.

Visits were made to manufacturers of fall-safety

equipment to observe the fabrication facilities and

procedures as well as the testing carried out as part of the

development and quality control process. These visits

served to assure that recommendations would not make

unreasonable demands on the producers.

A limited experimental program was used to generate

more comprehensive data on strength and energy absorbing

characteristics of some components than was available in the

literature. This data, though limited in scope, provide the

basis for a test procedure that may be simpler and more

definitive than current methods.

Information gathered in the NBS experimental program

was compared with data taken from the literature to

determine the variability of the component products and to

compare results obtained using static and dynamic test

me thods

.

The analysis and distilling of the information gathered

was aimed at providing recommendations that would be

realistic in terms worker safety and production considering

the current state-of-the-art. In addition, areas were noted

beyond the scope of this study where more information is

needed

.

- 2 -
1.3 General Background

Falls are a major cause of accidental injury and death

in this country. The National Safety Council recorded over

15 000 deaths due to falls in 1975 (7.4 fall-related deaths

per 100 000 people) . The construction industry has one of

the highest occupational disability and death rates, and it

has been estimated that one of five workers faces the

prospect of being injured or killed at a construction site.

Falls from walking or working surfaces are a major cause of

these accidents.

The existing Code of Federal Regulation [CFR] standards

covering fall-safety equipment for industrial and

construction workers [CF-3, CF-6, CF-8]* is generally

accepted as being unsatisfactory. The part of this document

dealing with fall-safety equipment is based on insufficient

and antiquated data, and it contains internal and

interrelational inconsistencies. The test methods and

procedures prescribed by this standard are poorly devised

and inadequately described.

Because of the deficiencies in the CFR standards,

industia.al interests have developed and adopted a consensus

regulation, ANSI A10.14 [AN-1]. Unfortunately this

regulation suffers from many of the weaknesses of the

previous regulations. The greatest drawback comes from a lack of sufficient, relevant, and accurate data upon which

to base its requirements. In order to overcome these

deficiencies and provide an adequate background for a comprehensive standard for fall-safety systems, the study

covered by this report was conducted at the National Bureau

of Standards (NBS) under the sponsorship of the Occupational

Safety and Health Administration (OSHA)

.

Three basic modes for protecting workers from fallrelated injuries are guardrails, safety nets, and personal

fall-safety equipment. Each of these have a proper role

and, in many cases, more than one may be used concurrently.

All three types were observed during this study, but only

active, personal fall-safety equipment was evaluated. Such

systems, which require that the worker secure himself to a suitable anchorage, consist of components such as body

belts, body and chest harnesses, lanyards, rope grabs, shock

absorbers, lifelines, pole straps, safety straps, ascent and

controlled-descent devices, anchorages, and other relevant

hardware. The study did not include window cleaners' and

tree trimmers' belts, ladder safety systems, and bosuns'

chairs, and only marginally covered fall

‘References to items in the Bibliography section of this

report are shown in brackets.

- 3 -
I

restraint systems designed to prevent a worker from

maneuvering into a potential fall position.

A study of guardrails [FA-1, FA-2, FA-3] was carried

out at NBS by the Center for Building Technology during the

same time that this study was being made.

1.4 Terminology and Symbols

Every attempt has been made to use terms that are

generally used by the producers and users of fall-safety

equipment. However, since such usage is not entirely

uniform, the following terms are defined as they are used in

this report and other sources [AN-1, BE-2 , IS-1, OS-1]:

(1) Anchorage . A secure point of attachment to which

is secured a lifeline or lanyard.

(2) Arrest Force . The force imposed on the worker or

test weight at the time the fall-arrest system stops

the fall. This is usually the peak force experienced

during the fall.

(3) Body Belt . A simple or compound strap with means

for securing it about the waist and with means for

securing a lanyard or snaphook to it. It is the part

that secures the worker to each fall-safety system.

(4) Body-Restraint System . A simple or compound strap

that is secured about the wearer and attached to a load-bearing anchorage. Body belts and chest- and

body-harnesses are the usual body-restraint systems.

(5) Buckle . A device for fastening two loose ends of

a belt or strap usually attached to one end and

grasping the other end by friction or by a tongue

passing through a hole.

(6) Drop Line . A vertical lifeline.

(7) Effective Worker Weight . Effective worker weight

is taken as the gross weight of a worker including his

clothes, tools, and personal protective gear.

(8) Fall-Arrest System . Any active device designed to

arrest a fall m such a way as to minimize the length

of fall and the potential for fall-related injury.

- 4 -
(9) Fall Distance . The "free fall distance,"

exclusive of lanyard elongation.

(10) Fall-Restraint System . Any active device designed

to prevent a worker from maneuvering into a potential

fall situation.

(11) Fall-Safety System . Personal equipment designed

to provide a worker at heights with protection from

falls from a working or walking surface or, should he

fall, to minimize the length of the fall and the

potential for fall-related injury. Fall-restraint,

emergency-retrieval and fall-arrest systems are all

considered to be fall- safety systems.

(12) Lanyard . A short length of flexible line or strap

webbing which is used to secure a safety belt or body

harness to a lifeline or to a fixed anchorage.

(13) Lifeline . A line from a fixed anchorage or

between two fixed anchorages, independent of walking

and working surfaces, to which a lanyard is secured.

(j.4) Lineman's Body Belt . A belt which consists of a

cushion section, a body belt, a tool saddle, and deering (s) which are secured to the strength member of the

belt

.

(15) Lineman's Pole (Safety) Strap . A strap used for

support while working on poles, towers, or platforms.

Snaphooks provide for attachment to the lineman's body

belt.

(16) Restraint Line . A line used to secure a worker to

a fixed anchorage

,

x thus allowing limited mobility while

preventing maneuvering into a position to fall from the

working surface.

(17) Rollout . A physical process whereby one coupling

device can inadvertently disengage from a mating unit

when a torque is applied to the pair.

(18) Rope Grab (Safety Clamp) . A device, used to

couple a body belt or lanyard to a dropline, which,

upon impaction, will actuate to arrest a fall within a short distance.

- 5 -
(19) Safety Belt . Conventionally used in a generic

sense to describe all fall-arrest restraint systems

and/or their components. This term is not used in this

report

.

(20) Safety (Design) Factor . The ratio of the computed

strength (or deceleration) of a load bearing member or

material to the maximum load (or deceleration) the

component is expected to sustain in use. ,

(21) Safety Line . A horizontal lifeline.

(22) Snaphook . A self-closing hook with a keeper latch

or similar arrangement which will automatically close

and remain closed until manually opened.

(23) Strength Member . Any component of a fall-arrest

system, including anchorages, that could be subject to

loading in the event of a fall.

(24) Total Fall Distance . Fall distance plus maximum

lanyard extension during impact and/or the distance

along a dropline that a rope grab travelled before

locking and/or any additional fall distance due to a shock absorber activating.

The following symbols are used throughout this report:

a = acceleration

f = degradation factor to account for possible

reduction in strength due to tie-off conditions

h = free fall distance

BS = breaking strength

D = contingency, or safety factor

F - force

L = length under unloaded conditions

M = mass of a fall victim or test weight

subscript a = pertaining to acceleration

subscript max = maximum value

- 6 -
subscript min = minimum value

subscript obs = observed or measured value

subscript x, y, z = direction referred to orthogonal

axes or body centered geometry system (Table 2).

1.5 Units of Measure

In general, quantities in this report are presented in

botn the International System of Units (SI) and in U.S.

Customary Units. This dual presentation is made in order to

facilitate communication with users of the SI system adopted

by the 1960 General Conference of Weights and Measures while

avoiding confusion in the user area that is more familiar

with U.S. Customary Units. In some cases, particularly in

tabulations, where dual units would be awkward, U.S.

Customary units have been chosen as being less confusing for

the primary users of this report. Conversion factors for

these cases are given in Table 1. A more complete listing

of conversion factors can be found in the literature [AS-5]

.

An exception is the extensive use of the acceleration of

free-fall, g^, (9.80665 m.s~2 or 32.174 ft.s“2) as the unit

of acceleration. This unit is widely recognized and

accepted in both technical and popular usage.

7 -
Table

1.

Factors

for

Converting

from

U.S.

Customary

to

SI

Units

of

Measure

00

00

CN00

oo

<rocn

oi

QJ

U)

4-1 c3

ooo

•H33

;>>

>-4 to6o

4-J cn3O

CO6O

J-i

TJ

CU

C/D 3

S-i o

4Jo

CO

0/ J3H
2.0 Physiological Aspects of Fall Injuries

Injuries can result from a fall involving a fall-safety

system in several ways, including:

(1) Through breaking of a component so that the fall

is not safely arrested;

(2) By forces from the containment system (belt or

harness) crushing, twisting, or abrading the body of

the victim;

(3) By excessive acceleration which can cause severe

internal injuries, such as tearing away of organs and

rupturing of blood vessels, and skeletal injuries due

to flailing, twisting, and jackknifing;

(4) From colliding with parts of a structure or other

objects due to excessive fall distance, swinging, etc.;

(5) Through elongation of the containment system

allowing the victims to be released.

A satisfactory fall-safety system must be designed,

constructed, and used so as to avoid such injuries or at

least to reduce their severity so that substantial disabling

does not result. Whereas (1) , (4)

,

and (5) above relate to

the physical characteristics of the system only, (2) and (3)

require that the tolerance of the human body to external and

inertial forces be considered.

By far the largest portion of data relevant to arrested

fall injuries is presented in terms of acceleration, almost

always given in units of "g ." This information is also

based upon limited tests generally carried out with young,

healthy, male volunteers. Most tests have been made with

the subject restrained in an optimal position and

anticipating the impact from the test. The acceleration

levels have, of course, been deliberately kept well below

the serious injury level with the effects of higher

accelerations being estimated. In short, we have an

inadequate basis for estimating the maximum acceptable

acceleration for a frightened person of questionable

physical condition, falling in a unconstrained position,

with the fall being arrested through a belt or harness. It

is also unknown whether the tolerance levels are the same

for females and for males.

- 9 -
2.1 Human Body Reactions

Since the acceleration tolerance of the human body is

dependent upon the direction of the acceleration, a simple

geometric system for identifying the direction is useful.

Such a body centered system is shown in Table 2.

Since for arrested falls we are generally concerned

with a retarded motion, the acceleration is usually in the

direction opposite to the motion. For example, a person

falling feet first would, when the fall is being arrested,

be subjected to a +a z acceleration.

In addition to being sensitive to the direction of the

acceleration, it has been reported [BO-1] that human

tolerance to acceleration is conditioned by factors such as:

(1) magnitude of the acceleration,

(2) duration of the acceleration,

(3) rate of change of acceleration (jerk), and

i A ) the distribution of restraining forces over the

body

.

These factors, like body orientation during a fall, are

highly variable and not readily controlled or predicted.

The human body is a very complex, articulated, viscoelastic

structure that will almost certainly undergo twisting,

tumbling, flailing and/or jackknifing during a fall. The

effects of all of the above factors can be expected to vary

with time and body location, and local accelerations may be

expected that are considerably higher than an average value

computed from measurements of total force or acceleration of

the center of gravity.

The human body in a real impact will absorb a significant amount of the kinetic energy that must be

dissipated. Flail, rotational, and jackknifing motions,

compression of the body, redistribution of body fluids and

organs, internal friction and abrasion of straps against

clothes and skin torso all contribute to this energy

absorption process. This effect can be seen in data from

tests of lap belts using a variety of test objects ranging

from a rigid mass to a human subject. Such data are shown

in Table 3 [AR-3] . Such force measurements relate to an

average acceleration and may not reflect the peak

- 10 -
Table 2. Body Centered Geometry System Used to Describe

Impact Accelerations

Type Acceleration Symbol

Equivalent

"Eyeball" System Terminology

Towards the Front +a

X Eyeballs in

Towards the Rear -a

X Eyeballs out

Towards the Right +a

y

Eyeballs left

Towards the Left -a

y

Eyeballs right

Upwards +a

z Eyeballs down

Downwards -a

z Eyeballs up

- 11 -
Table 3. Peak Force on Lap Belt and/or Torso [AR-3]

Peak Force Recorded

Test Subject kN lbf

Wooden body block (no moving parts) 43.4 9760

79.4 kg (175 lb) articulated wooden

dummy (ARL F-50)

37 .

2

8370

73.5 kg (162 lb) sandbag 33.5 7530

73.5 kg (162 lb) highly articulated

wooden dummy (ARL VI-50)

29.2 6570

73.5 kg (162 lb) highly articulated

dummy with pliable thorax and some

incernal structures simulating

human anatomy (Sierra Engineering

Co. 292-850)

25.0 5630

Human (extrapolated from lower 18.9 4250

acceleration levels)

- 12 -
accelerations encountered by the non-rigid test objects.

However, it is evident that peak forces with a rigid test

object are about twice what would be expected with a human

subject. This factor, which is important in determining

strength requirements for safety systems, is corroborated by

results of drop tests by Boeing Safety Engineers [BO-1]

using rigid objects and an articulated dummy and by the

Construction Safety Association of Ontario (CSAO) [CS-3]

using rigid objects and sandbags. Although the factor of

two between the force generated by a rigid mass and a human

under the same fall conditions is accepted for use in this

report, additional verification with a variety of fallsafety systems and fall conditions is needed.

The human body has a resonant frequency for

displacement of internal organs of about 50 to 60 Hz.

Motion of these organs could be excited by forces having a pulse width approaching a half period of this resonance.

Sucn short pulses, about 0.01 second duration, are not

likely to occur in fall-arrest situations.

It must be noted that the majority of available data

relating to human subjects undergoing arrested motion is

based upon lap or shoulder belt seat belt tests. Under

these conditions, the forces are applied to skeletal

structures rather than the soft abdominal region that would

be acted upon by a body belt. Conversations with

physiologists invariably indicated that much larger forces

can be sustained by the pelvic girdle than by the abdominal

region without resulting in injury.

2.2 Tolerable Limits

The level of force or acceleration that can be

tolerated by the human body without severe injury is

dependent upon several factors. In particular, for the case

of a person having a fall arrested by a personal fall-safety

system, the chance of severe injury will depend upon the way

in which the force is transmitted to the body by the

containment device, the location of the attachment point and

the orientation of the body at the time of impact as well as

upon the levels of force and acceleration that are

encountered. Unfortunately, the information that is

available on the force and acceleration levels that can be

tolerated is meager and has come from tests on young,

nealthy, male volunteers, carefully restrained in an optimal

position and anticipating the impact. Such tests have

- 13 -
generally been concerned with ejection seats, lap belts, and

shoulder harnesses for automative and airplane use or

parachutes with body harnesses. Using such data to

establish limits for accidental falls, especially where body

belts and chest-waist harnesses are used, must be done with

extreme caution.

In discussing injuries in crashes of aircraft, H. G.

Armstrong [AR-5] states:

"The forces transmitted to occupants of the

aircraft are determined by: (1) their attenuation and

absorption by structures intervening between the

occupant and areas of the aircraft impinging against

the ground; (2) distance and direction of displacement

of the occupant; (3) area, configuration, and

resistance of objects against which the occupant is

decelerated; (4) attenuation and absorption of force by

the body of the occupant; (5) rate of application of

the forces; (6) frequency characteristics; and (7)

duration

.

"The problem of evaluating the effect of these

factors requires controlled experimental exposure of

human, animal, and anthropomorphic dummy subjects to

crash type decelerations. Progressively augmented

combinations of these variables will determine

tolerance and survival limits. Simultaneously, the

efficacy of various restraint configurations and

development of basic principles of crash protection can

be explored.

"Progress in the field has been limited by the

formidable mechanical problems, the difficulties of

developing, maintaining and operating experimental

apparatus subjected to high impact forces, and the

hazardous nature of the experiments for human

subjects .

Since the duration of an impact has an effect on its

tolerance by the human body, it is convenient to show injury

potential in the form of "Eiband" curves where injury levels

are shown as a function of acceleration level and duration.

Such a plot using data from [BI-1 and SN-1] is shown in

Figure 1. This curve shows that, for accelerations in the a

z direction, acceleration up to 10 g n are acceptable to

volunteers while accelerations over 30 g n can be expected to

result in severe injuries. Ejection seats, where use may

- 14 -
200

cn

o

z

o

o

yj

(/)

<

£TUi

_1LUO

o

<

cro

U.z

ID

Li. o

<

QC3Q

(Sll N n &) NOI1VU31300V WdOdlNO

- 15 -

Figure

1.

Acceleration

Tolerance

along

the

Z-axis.
acceptably result in some injury, are designed for impacts

of 18 to 20 gn . It should be noted that all of the data in

Figure 1 were taken with maximum body support.

In their chapter on Aviation Medicine [GL-1], A. P.

Gagge and R. S. Shaw state:

"In exposure to accelerations lasting about 1/10

sec, the time is too short for development of anoxic

neurologic symptoms of long-term positive acceleration

and for moving sufficient volumes of blood to cause the

vascular effects of long-term negative acceleration.

Tolerance limits to acceleration of this duration are

defined by stress limits of the supporting structures

of the body, such as the bones, ligaments, and organ

attachments

.

"Acceleration tolerance increases as exposure time

decreases to hundredths and thousandths of seconds,

because in these brief periods, high forces will result

in only small displacements of the portions of the body

to which the force is applied relative to the rest of

the body. Small displacements may be absorbed by

elastic compression of the body without damage. When

forces of this duration are excessive, the resultant

d^iury is apt to be localized to the point of

application of the force and characteristic of a blow.

Here it is not the magnitude of the force per se which

is important in causing injury, but rather the

magnitude of the pressure to which tissues are

subjected. Thus, the area over which the force is

applied is of great importance and will be discussed

under crash injury."

The Naval Aerospace Medical Research Laboratory

presently accepts the acceleration levels shown in Table 4

as design criteria for military personnel equipment such as

ejection seats and parachutes.

Physiologists and others concerned with the causes of

impact injuries were found to agree that significantly

higher levels of impact can be tolerated with a restraining

belt around the pelvic girdle rather than the abdominal

region. These authorities estimate the injury threshold at

less than 10 gn for restraint about the abdominal region and

at 15 to 20 gn for belts around the pelvic girdle.

- 16 -
Table 4

Acceleration Levels

Naval Aerospace Medical

Accepted by the

Research Laboratory

Direction (a) Magnitude (gn ) +a

z 25

-a

z 20

+a- y

15

+a

X

15

-a

X

38.7

(a) Referred to body centered geometry system.

Table 2

.

- 17 -
Best's Safety Directory 1976 [BE-2] points out that the

level of shock loading in the body in a fall involving an

industrial body belt will depend upon the location of the

dee-ring. Since the back and ribcage will be subjected to

pressure as the belt is loaded, a shock load below 8900

newtons (2000 lbf) is suggested. It is therefore

recommended that, with a body belt, the shock load be

limited to 8900 N (2000 lbf) or 8 gn with a maximum free

fall of 0.6 meters (2 ft). With a body harness a maximum

free fall of 1.8 m (6 ft) is recommended.

Several organizations, including the American National

Standards Institute (ANSI) [AN-1] , the Canadian Standards

Association (CSA) [CS-1] , and the Construction Safety

Association of Ontario (CSAO) [CS-3] have adopted a 10 gn acceleration limit in the +az direction. Although the

limited available injury data does not appear to contradict

this value, it may be higher than should be allowed when

body orientation cannot be controlled and especially with

the use of body belts.

The British Standards Institute [BS-4] limits the free

fall distance to 0.6 m (2 ft) and 1.8 m (6 ft) for use of

body belts and body harnesses, respectively. This is based

upon the use of a lanyard 1.8 m (6 ft) long.

In evaluating ejection seats and the acceleration

environments experienced after separation from the aircraft,

the U.S. Navy [AS-2] limits +az to 17 gn for an' expected

rate of spinal injury of 5% or less.

C. T. Morgan comments [MO-1] that the limiting factor

in human tolerance to headward acceleration (+az ) in the

normal seated posture is spinal fracture in the upper lumbar

portion. With optimum alignment up to 35 gn can be

tolerated at less than 500 gn per second onset. However,

with the back bent forward to the limit of motion, this

limit diminishes to less than 15 gn .

In the use of parachutes, injuries may occur as often

as once in 20 uses, where accelerations exceed 20 gn . Again

C. T. Morgan [MO-1] reports that parachutes opening shocks

are greatest at high altitudes and that impact accelerations

below 20 gn are considered safe, 20 to 30 gn are borderline

and over 30 gn are dangerous for man, parachute and harness.

Somewhat in contrast, a French medical team that

watched drop tests with an articulated mannequin concluded

- 18 -
that it would be an exceptional person that could withstand

accelerations greater than 6 to 8 gn [AR-1, AR-2], This

same study reports that a heavily clothed stuntman jumped

about 0.67 m (2.2 ft) with a belt in the thoracic position

resulting in an impact force of about 4700 N (1058 lbf) . The pain from this impact was so intense that the experiment

was terminated at the subject's request. Although the mass

of the subject was not reported, an estimate of 80 kg (175

lb) would indicate an acceleration of about 6 gn .

In another study [NS-3] performed by the General Motors

Research Laboratory, a 75 year old man jumped in the prone

position (belly whopped) from 10.7 m (35 ft) into a shallow

pool of water. Accelerometers attached to the man recorded

an acceleration of 70 gn , leading to the conclusion that the

human chest can withstand substantial stress without injury.

However, other reports from the same laboratory [KR-2, KR-3,

NE-2, NE-3] show poor correlation between thoracic impact

forces and injuries, but indicate that serious injuries to

cadavers occurred at force levels below 4450 N (1000 lbf)

.

The German Alpine Club has published the results of

tests from which it concluded that waist tie-ins can result

in death when forces exceed 3750 N (840 lbf) . In

mountaineering a rope is usually tied around the waist to

form a body restraint system. Such a narrow belt would

result in a higher pressure (stress) than the usual body

belt.

The effect of age and physical condition on

acceleration tolerance is pointed out by UIAA tests which

showed that climbers under 34 years of age can normally

withstand two to three times the acceleration that older

climbers can accommodate.

In the use of a lineman's belt, there is a high

probability that a fall would result in a +ax acceleration

and backbend or reverse jackknife. Because of the large

chance of vertebral damage, the acceptable level of average

body acceleration is probably only 4 to 5 g n . Military specification MIL-S-18471 for airplane

ejection seats calls for a maximum impact velocity for

parachutists with a vertical component not exceeding 7.3 m/s

(24 ft/s)

.

This would be equivalent to a free fall of 2.7 m

(9 ft) and would accept a moderate level of injury since the

concern is to save the life of the ejector. Experienced

jumpers and physiologists suggest that the impact speed

- 19 -
4 should not exceed 4.6 m/s (15 ft/s), equivalent to a free

fall of 1.1 m (3.6 ft)

,

if a moderate injury rate is not

acceptable

.

From the above discussion, it can be seen that there is

limited information available on the acceleration and force

levels that would be acceptable for construction and

industrial workers using personal fall-safety systems.

Since even this limited information has been obtained under

optimal test conditions, both in terms of the subject and

the fall parameter, levels significantly lower should

probably be specified. Certainly additional information

should be sought to provide a better basis for specifying

maximum acceptable levels.

Efforts are now being made to model the response of the

human body to impact loads using mathematical modeling

techniques, for example see [SA-1] . Although much of this

effort is now being directed at automobile crash situations,

the technique being developed may be applicable to the study

of fall-arrest.

2.3 information from Accidents Involving Fall-Arrest Systems

In the course of this study more than one hundred

possible sources of fall-related injury data were contacted.

These included military and other Government agencies,

industrial organizations, safety associations, mountain

climbing and skydiving clubs, workmen's compensation

organizations, and foreign groups. Little pertinent

information was obtained because the reports generally did

not contain sufficient details to be of use or the pertinent

cases could not be readily extracted from the mass of

information on file.

At least half of the fall data obtained involved fallsafety devices that were not correctly secured to an

anchorage, i.e. the falling worker did not remain linked to

the anchorage under the impact of the fall. These falls

generally resulted in fatalities and serve more to

illustrate the misuse of these devices than the

effectiveness when properly secured.

Only about 35 cases involving falls into correctly

secured fall-arrest systems were located, and in two of

these the lanyards failed upon impact, probably due to sharp

edges on the structural members they were tied around. In

- 20 -
the remaining cases, the falls were successfully arrested

with no significant injuries. Most falls were reported to

have involved free falls of from 1.2 to 2.4 m (4 to 8 ft),

and presumably involved fall-safety systems using body

belts. The few injuries that were received came from

contacts with other surfaces during the fall.

The interest in fall-safety equipment that is generated

by an accident is shown in the work of the Safety

Engineering Department of the Boeing Company [BO-1] . To

quote from this work:

"During a modification program at Wing II, an airman,

wearing a safety belt, lanyard, and shock absorber,

fell when an elevator work platform from which he was

working failed because of improper assembly. The

airman's safety devices arrested his fall and saved his

life. Because similar safety equipment is used by

Boeing personnel, this accident aroused much interest

about shock absorption characteristics of various

safety devices used and the degree of attenuation of

the shock load."

The study instigated by this accident found

considerable information relating to catapult and seat

ejection situations, but found no literature or data about

shock absorption properties of commonly used personnel

protective devices. With a few modest exceptions, the

situation is essentially the same today.

Another study by the Construction Safety Association of

Ontario [CS-3] was, in part, instigated by the deaths noted

above of two Canadian contraction workers in unrelated

accidents due to failure of their fall-arrest systems. Both

failures were attributed to lanyard severing by sharp edges

of beams. As a result, tests were made to determine system

strength as a function of anchorage type and tie-off method.

In contrast to the relatively good history of

industrial use of fall-safety equipment, an article in a mountaineering magazine "Summit" [KI-2] discussing the

swami-belt reports:

"Of 20 swami-belted climbers who fell and were rescued

after hanging in their ropes, three died immediately

after rescue; two others developed kidney failure; and

one could be saved. Three others died within 1 to 11

- 21 -
days after rescue, despite intensive care to restore

circulation .

The swami-belt is essentially a rope tied around the waist

to form a body restraint device.

The relatively few documented case histories of

accidents involving the proper use of current industrial

type fall-safety systems indicate that radical modifications

of these systems are not required. Small changes, a better

understanding of the various components and their

interactions to improve system selection, and more education

on the proper use and limitations of the systems may be

adequate. However, more adequate data based upon the use of

such systems are needed and could result in future

modification of a regulation controlling the production and

use of these systems.

/

- 22 -
3.0 Fall-Safety Systems

For the purpose of this report, fall-safety systems

consist of personal equipment designed to provide a t worker

with protection from falls from a working or walking surface

or, should he fall, to arrest his motion with a minimum

chance of injury and to provide for his rescue. These

include fall-restraint systems designed to prevent a worker

from maneuvering into a potential fall situation, fallarrest systems designed to limit the fall distance and

minimize possible injuries, and emergency retrieval systems

intended to allow a fall victim or a co-worker to bring the

victim to a safe location. In this report, the emphasis is

on fall-arrest systems.

The functions of any requirements for a fall-arrest

system can be related to the simplified, lumped parameter,

damped spring mass system shown in Figure 2. In this

figure, the damped spring corresponds to the fall-arrest

system, in particular the lanyard; the mass, M, corresponds

to the fall victim, and the pan, P, simulates the constraint

system (belt, harness, etc.). For simplicity, it is assumed

all parts except the mass are negligibly light and that the

damping is negligible. It is also noted that previous

discussions have shown concern for injuries resulting from

force, acceleration, and velocity at impact.

Mass, M, falls freely, under the influence of gravity,

a distance, h, before contacting the pan, P, which is

rigidly attached to the damped spring, k. As a result of

this impact, the spring will elongate a distance, AL, before

the downward motion is arrested by the tension, T, of the

spring. Depending upon the damping, there may be subsequent

oscillations, but these will not be considered here since

the highest values of the parameters of concern will occur

during this first downward motion.

During the free fall, potential energy of the mass, PE

= Mg n

h, will be converted to kinetic energy, KE = Mv^/2

.

Since these quantities are equal, the velocity at impact

will be

3.1 The Physics of Fall-Arrest

v . (i

)

impact v ; where gn is the acceleration due to gravity.

( 1 )

- 23 -
Figure 2. Damped Spring Mass System

- 24 -
At any point during the fall, the change of potential

energy of the mass must be equal to the kinetic energy (KE)

of the mass plus the energy stored by the spring (SE) . In

particular, at the point of arrested motion, the spring will

have extended a distance, AL, the kinetic energy will be

zero, and

SE = Mgn

(h + A L) (2)

The energy of the spring, SE, can also be computed from

the force to elongation relationship of the spring, which

might be of the form shown in Figure 3. This energy is

given by the area under the curve over the elongation 0 to

AL (the shaded area) . For given values of M, h, and forceelongation relationship, an iterative procedure can be used

to find the maximum tension, I^na

x

, and the elongation, AL.

This is best done by computer techniques.

In Figure 2, the total force acting on Mass, M, in the

upward direction is

F = T - Mg (3)

XI Using the familiar relationship, F = ma, the upward

acceleration of mass, M, due to tension, T, in the spring

(lanyard) is given by

a

x = F/M = T/M - g^ (4)

However, it is probably the total acceleration imposed upon

the body in a short increment of time that is a major factor

in causing injury. In a fall accident situation, this

quantity is more properly given by

a = (a

x + gn

) = T/M (5)

This quantity, a, is also the one that would correlate with

the results of arrested sled tests where the effect of

gravity is perpendicular to the acceleration generated in

the test.

In this report the acceleration is considered to be

that defined by Equation 5 unless otherwise stated, and the

tension in a lanyard for a given acceleration is

T = M(a

x + g ) = Ma (6)

- 25 -
H

30dOJ

,>mo

M-l

Qj •Hwco

•H4-> fO I-1 Q) OCCOH4-1 RJ

tr> C0

rHw1 a>o5-1 O

Cm

(D

r

O E <1) 3 a w g w ec < Q

ro

0)

5-1 3

tn •H

Cm - 26 -

Spring
The relationship between the peak force or acceleration

imposed upon the falling object, the free fall distance and

the spring (lanyard) characteristics can be put in a readily

usable form if the spring can be assumed to obey Hooke's

law. This is a linear relationship and is given by

F = kAL/L or AL = FL/k (7)

But the energy absorbed by the spring (lanyard) is

SE = Mg (h + AL) (2)

n

and, assuming a linear relationship, is also given by

SE = F ( AL)/2 (8)

Substituting for AL and equating these expressions gives

F

2 /2Mg - F - kh/L =0 (9)

n

Solving for the force and noting that F jq 0

F = [1 + (1 + 2kh/Mg

nL)^]Mgn

(10)

or the acceleration in units of g„J is

n

a = F/Mg

n =[!+(! + 2kh/Mgn Lp] (11)

Letting the ratio of the spring stiffness, k, to the weight

of the falling object, Mg

n

, equal k^ , gives

a = [1 + (1 + 2k

1

h/L)^2

] (12)

Several things can be seen from this last equation.

These include:

(1) The imparted acceleration becomes greater as kq

increases, i.e. with a stiffer spring or a lighter object.

(2) The force or acceleration is a function of the ratio of

free fall distance to spring length, h/L, i.e. greater fall

distances can be tolerated if longer lanyards can be used

without introducing other problems.

(3) The minimum acceleration when no free fall occurs, h =

0, is 2 gn . The lowest peak force that a lanyard will be subjected to in arresting a fall is therefore 2 Mgn .

- 27 -
Figure 4 shows computed values, assuming Hookian

behavior, of acceleration for h/L values from 0 to 2 (the

maximum value possible), and a k/Mgn value of 70. A

straight line fitted to the points for h/L values from 0.3

to 2.0 is also shown. Although the function is not linear,

it is suggested that the linear approximation could give

realistic guidance for the design, selection, and use of

fall-safety equipment. The assumptions of rigid mass and

ideal fall conditions should also be noted.

A more detailed discussion of this concept, in

particular Equation 10, as applied to safety in

mountaineering can be found in [WE-1]

.

Another situation of interest involves the use of a horizontal lifeline to permit a worker freedom of horizontal

motion while protecting him from a vertical fall. This

situation corresponds to Figure 5 where the lifeline

corresponds to ABC, the lanyard to BD, and the fall victim

to the mass, M. To be conservative and for simplicity, it

is again assumed that all energy is absorbed in the lanyard

and the maximum tension in the lanyard can be found as

described above. Using the principles of statics, the

tension in the two ends of the lifeline are found to be:

T

T = - (13)

1 cos a tan 8 + sin a

T

T = (14)

2 cos a tan 8 + sin a

The greatest lifeline tensions occur when a and 8 are small,

and the worst case is when a = 8 . Some values of the ratio

of lifeline tension, T^ , to the lanyard tension, T, when a = 8

are shown in Table 5. From this table, it is seen that

lifeline loads can become quite large when only a small sag

is permitted.

All of the above have ignored any energy absorption or

dissipation within the falling body or by rotational or

swinging motions of the body. As was discussed earlier, the

human body is a complex, highly articulated, non-rigid

structure, and will absorb significant energy during an

arrested fall. In fact, it was suggested that the peak

force in an actual fall accident would be about one-half of

that computed using the rigid body assumptions of the model

used here. It should be noted, however, that this value is

empirical and based on very limited data.

- 28 -
ACCELERATION,

g

n

Figure 4. Computed Accelerations Imparted to a Rigid Mass as

a Function of the Ratio of Free Fall Distance, h / to

Spring Length, L, when k/Mg

n

= 70.

- 29 -
////////

4444

4

4

- 30 -

Figure

5.

Simulated

Horizontal

Lifeline
Table 5

Ratio of Tension in Lifeline to

Tension in Lanyard (Figure 5)

Angel a = B Ratio T^/T

2 degree 14.33

5 5.74

10 2.87

15 1.93

30 1.00

45 0.71

60 0.58

75 0.52

80 0.51

85 0.50

- 31 -
The model also assumes that no energy is absorbed by

any part of the fall-safety system except the lanyard.

Since this will not be strictly true, the actual forces and

accelerations will be less than predicted by the model.

3.2 Anthropometric Basis

The design, performance requirements and testing

procedures for fall-safety equipment depends upon an

anthropometric knowledge of the workers who are to be

protected. In particular, with regard to performance

requirements and testing procedures, the range of worker

weight and waist dimensions are of concern.

A survey conducted in 1962-63 by the National Center

for Health Statistics (NC1IS) [NC-2] provides the weight data

shown in Table 6. It should be noted that these data are

for partially-clothed subjects (1 kg or 2 lb estimated) , and

that similar data for 1977 might be expected to be slightly

higher, perhaps 0.5 kg (1 lb). Nude weights would therefore

be estimated at 0.5 kg (1 lb) less than shown in Table 6.

These data are in reasonable agreement with estimated

industrial worker weight, taken from a pre-1946 survey [MC1] , after corrections are again made for clothing weight and

increase in average weight since 1946.

In order to obtain the effective weight of the worker,

an estimate of the weight of clothing and other items is

needed. For construction workers these might include:

(1) shirt, trousers, belt, socks, and undergarments;

(2) watch, wallet, keys, etc.;

(3) safety shoes;

(4 ) safety hat

;

(5) tools and tool pouches;

(6) jacket and gloves; and

(7) body containment device of the fall safety system.

Military studies [DA-2] indicate that the standard Army

uniform (underwear, shirt, trousers, shoes, socks, steel

helmet, and helmet liner) adds 5.4 kg (11.8 lb) to the nude

weight of a soldier and an overcoat adds an additional 3.1

kg (6.8 lb). It is therefore estimated that the clothing

and equipment of a construction worker will add about 7.3 kg

(16 lb) to his nude weight. Making these modifications to

Table 6 gives the values given in Table 7 as estimated

weights of equipped construction workers.

- 32 -
Table

6.

Weights

for

Selected

Percentiles

of

Males

by

Age

for

the

United

States

- 33 -
fd

X in 00 o 00 r~

— rH •'3* CM 00 CO CM

•^r 0 CM CM rH rH rH

X VO

G 0 l fd Qj LO 0 in

m in UO

a in >1 iJV • • • • X rH co rH CM r-' G rH o 00 VO in

cr i—1

rH

wXG VO ^r VO VO rH

rd

X in CO 00 CO

pH CM CM 1—1

rH 1—1

Td 0 0 LO G X i fd in uo X in 0 • • 0 Cn VO VO VO av

rH

X i—1 o 00 VO

m oG

rH 1—1 0Xs <Ti *r vo CTV vo X in CO 00 vr CO

0) rH CM CM rH rH rH G w 0 G X l fd G in 0 in in in in 0 co >1 Cn • • • • £ X VO r" rH

rH

O 00 VO VO

C pH rH 0XoG X co 00 -cr av G rH VO CO 00 CM X rr cn CM CM rH rH f 1 w co G C » <d 0 in 0 in in in UO u CM >i Cn • • • • X CTv 00 CO uo CO X iH o 00 VO UO 0

CO

rH rH

XX VO cn CM av o

CnX CM C- CO CO

•H rH CM CM rH rH pH 0 cn 3£ CM G 1 fd TD 00 0 in 0 1—1 >i Cn X X rH 00 CO CTv <d i—1 o VO in e rH pH •HX0w 0

rH•H • X

c- c0 CTV in o in rH 0 o av <n in rH G X 0

<d Eh

G

•HXG0B

(U i—I 00>

•Hxo0am0Gxo

fd0O

4-> W

XI

UO

tGG

•H

T3

<d

>1 X

X!0G

•H

fd +J Xo0g

fdw0X0e

•HXW • 0 VO 0 0

CO rH 0 X X 0

Eh Eh

rd

34 -
From Table 7, it is seen that a weight range of 59 to

113 kg (130 to 250 lb) would include workers in the first to

98th percentile. However, it should be noted that this does

not allow for any predisposition for ethnic or age groups to

enter the construction trades, nor does it consider the

possibility of female workers.

Data compiled by Dr. Van Cott [VA-1] on the waist depth

of various segments of the population is shown in Table 8.

A 1962 study by NCHS [NC-1] showed that the average waist

girth in the general population was 890 mm (35.0 in). This

has probably increased at this time to 915 to 940 mm (36 to

37 in). Based upon Table 8, it is estimated that the waist

depth of the current construction worker is about 255 mm (10

in) . Based upon these values and assuming that waist has an

elliptical shape, the average worker's waist breadth is

estimated to be about 330 mm (13 in). To summarize, the

average construction worker is estimated to have waist

dimensions of

circumference = 925 mm (36.5 in)

depth = 255 mm (10 in)

breadth = 330 mm (13 in)

The fully dressed worker might be 13 mm (0.5 in) larger

than this in depth and breadth and about 40 mm (1.5 in)

larger in girth. Mandrels and torso dummies of this

approximate size and shape would be appropriate for testing

body belts.

3.3 Behavior of a Fall-Safety System During Fall-Arrest

For a fall-safety system to have successfully arrested

a fall, it must have:

(1) contained the body of the victim without causing

injury or undue discomfort;

(2) absorbed the kinetic energy of the falling body so

that force and acceleration levels remain

tolerable

;

(3) limited the fall distance so that injuries are not

caused by contact with other objects; and

(4) provided a means for delivering the victim to a safe location.

- 35 -
Table.

8.

Waist

Depths

of

Various

Segments

of

the

Population ^ «—« LT) in uj o

CTl rH

i—I o>

—

00

in

CTi

4-> 0)

tnu

Q) XN

4-> U

(L) X

n3

-P

CD

fO T3C

fO X

4-> oc

(13 i"Hu

(0

fcl us O V CD - 36 -

Gifford

et

al.

(1965)
3.3.1 Containment

The containment device is the body belt, chest-waist

harness, body harness (parachute type) , or other components

designed to contain the body of a falling worker and to

distribute the forces resulting from an arrested fall so as

to minimize the possibility of injury. The three types of

containment devices most commonly used are shown in Figure

6. These devices are generally attached to a lanyard. They

are not expected to absorb an appreciable amount of energy.

The observed actions of body belts during drop tests

with articulated and anthropomorphic dummies was reported by

Boeing safety engineers [BO-1] as follows:

"Arresting force is transmitted to the area in contact

with the belts. A portion of the kinetic energy is

absorbed in decreasing the linear velocity by

translational and rotational acceleration imparted to

the body the the arresting lanyard. The hinge points

around which these forces act depend on the body

attitude at the time of the application of the force.

Maximum force on the body would be experienced when the

Kody mass is moving in a downward direction and the

restraining device is moving in the upward direction.

If a body is falling in a feet-first attitude, the

unrestrained parts of the body are rotated around the

belt as the lanyard tightens. The rate and direction

of rotation depend on the relationship of the body

center of gravity to the point of the arresting force.

If the body CG is below the D-ring of the belt, the

belt will have tendency to pull up toward the head. If

the belt is loose, there is danger of the individual

slipping out, or of the body area in contact with the

belt being severely abraded. As the force increases,

the head and upper parts of the body are given an

angular acceleration as the dee-ring of the belt is

pulled normal to the axis of the belt. The portion of

the body below the support area acts as a counterbalance. Therefore, the unbalance force depends

on the ratio of the center of gravity of the mass above

and the center of gravity of the mass below the point

of application of the arresting force. Note then, that

a waist belt acts as a fulcrum around which the

unrestrained parts of the body rotate. Direction of

rotation depends on the location of the dee-ring.

Should the dee-ring be located at the front of the

person, the arresting force would be in the negative

- 37 -
xr=-

I. BODY BELT

3. PARACHUTE TYPE HARNESS

Figure 6. Commonly Used Types 'of Body-Containment Devices

\

- 38 -
chest-to-back direction. Arrest from even a three foot

fall with the arresting force applied in the negative

direction could result in serious (if not fatal)

injury. Also, the impact force is applied over a small

area of the body. Internal injuries such as tearing of

arteries, spleen, and intestines, and rupture of the

kidney have been caused by waist belts during impact.*

Should this belt be used to arrest a fall in a confined

area, there is danger of head injury as a result of the

jackknifing of the body around the belt. Results of

this test show that, when a safety belt is used with a rope-grab shock absorber, the shock load is in the 3 g

range. However, from the above observations, the use

of this type device for protection against an

accidental fall is not recommended."

The Boeing report [BO-1] also included the evaluation

of chest-waist harnesses with the following conclusions:

"The chest- waist harness distributes the shock load

over a larger area of the body than a waist belt.

Arrest with this type of harness is less severe and the

arrested attitude is more nearly in an erect position.

If is believed that there would be considerable

discomfort caused by this harness from severely pulling

up under the arms. It was found that, to prevent this

harness from severely pulling up under the arms, the

waist belt had to be excessively tight. If this

harness is used for protection against a free fall, the

waist belt must be fastened uncomfortably tightly."

A body harness is quite similar to a parachute harness

except for being coupled to a lanyard and anchor rather than

to a parachute. If the victim falls feet first,

an impact akin to a "parachute opening shock" will be

experienced

.

The standard parachute has four riser straps coming up

from the harness and linking up with the chute above the

wearer. The standard Class VI body harness, however,

secures to a lanyard by means of one of several dee-rings

usually present on these harnesses. Except for -a z acceleration (which can cause brain hemorrhages) , man is

most susceptible to + ay accelerations. For impact

acceleration durations of about 0.1 to 0.2 s, the limiting

+ay values above which it is probable that disablements will

occur, are about 12 to 13 g n [AS-2]

.

Thus, were a worker to

fall into a harness secured to a lanyard through a dee-ring

*The reference alluded to here is a report on seat belt

protection in automobile crashes.

- 39 -
at the 3 to 9 o'clock position (where the buckle corresponds

to 12 noon) and were he to suffer, say a 20 g n deceleration,

a disabling injury would probably occur. It is therefore

imperative that a Class VI harness only be securable from a dee-ring high up on the back (between the shoulder blades)

or from riser straps coupled to a dee-ring above the

worker's head.

The action of the body harness is further described in

Air Standard 61/1 [AS-2] as follows:

"Another important factor is the placement of the

fixation point of lanyard on the belt (harness). This

must be on the back and not the chest in order to avoid

the quick movement of the head towards the back. It is

important to place it as high as possible, so that the

body is vertically suspended after a fall, this means

that the fixation point should be at the point where

the shoulder straps cross in the back at level of the

shoulder bone in an eye provided for this purpose. The

dynamic strain is thereby divided between the two

shoulder straps, transmitted to the safety belt in 4

different places, which assures a good distribution of

t^ Q pressure points on the thorax."

Although an impact into a body harness is not likely to

produce a force profile identical to that for a flyer

ejected from an aircraft, nevertheless, both produce

basically +a z accelerations and, in both cases vertebral

injuries are possible. The flyer, besides possible age and

physical condition advantages, has a basic advantage of

being accelerated in an optimal configuration into which he

is, essentially, locked. It is most unlikely that a construction worker falling into a body harness-lanyard

system (even one with riser straps off each shoulder) will

impact in an optimal configuration.

In the Boeing study [BO-1] a tested body harness pulled

up severely in the crotch region of an impacted dummy. Such

potential action, although not necessarily engendering

serious or irreversible injuries, could generate antipathy

in workers with regard to body harness utilization.

3.3.2 Energy Absorption

In arresting a fall, the kinetic energy of the falling

body must be absorbed (stored or dissipated) . For most

- 40 -
fall-safety systems, it is assumed that the lanyard is the

primary, if not sole, component to absorb this energy.

Exceptions would be where shock absorbers or rope grab

systems that can reliably absorb appreciable energy are

used. The energy absorption comes from the action of the

force in elongating the lanyard and, as shown in Section

3.1, can be calculated as the area under the forceelongation curve. In absorbing this energy, it is also

necessary to keep the maximum force (tension) below the

value that will cause injury to the victim and also below

the breaking strength of the lanyard and other components of

the safety systems. The system must also function so as to

prevent the victim from being subjected to accelerations

large enough to cause injury. A consideration of Figure 7

will show that the peak force and hence the peak

acceleration will be significantly less for the system that

elongates to d-2 than for the stiffer system that only

elongates to dj . The areas under the two curves are the

same. Of course, other factors must also be considered

since a greater elongation will provide more chance for

striking other objects and will also impose a longer

acceleration pulse which may be more likely to cause injury.

3.3.3 Limited Fall Distance

The total fall distance is significant because, as

shown in Section 3.1, it is this parameter combined with the

mass of the falling body that determines the energy that

must be absorbed, and hence the force and acceleration

levels that must be sustained. The fall distance takes on

further significance since all injuries found involving

properly secured fall-safety systems (about 35 cases)

resulted from contact with other objects during the fall.

The fall distance is limited by controlling the length

of the lanyard and method of anchoring so that the free

fall, before taking up the slack in the lanyard, cannot

exceed a predetermined limit. The total fall distance also

includes the elongation of the lanyard (and other parts of

the fall-safety system) and can be limited by making these

systems stiff. As discussed in the previous sections, a compromise is necessary to avoid excessive fall distance and

also keep force and acceleration levels to tolerable values.

- 41 -
ELONGATION

Figure 7. Equal Energy Absorption by Two Idealized

Fall Safety Systems

- 42 -
3.3.4 Rescue

Little is accomplished if a fall is arrested only to

nave the victim suspended to suffer injury or death from

exposure or impact due to swinging into other objects.

There are also situations where a worker may descend or

ascend into relatively inaccessible areas where assistance

from a co-worker, or possibly a self-controlled ascentdescent device, will be needed to insure his safe return.

If the worker is descending through a narrow opening and may

become injured or unconscious and have to be extracted by a co-worker, it is essential that the safety system maintain

him in an upright position so he can pass through the

opening

.

In a controlled descent situation, if the worker is

immobilized, the device should lower him at a controlled,

slow rate to the level below, either automatically or with

the assistance of a co-worker on an independent surface.

The device should also be adjustable so that the worker, if

uninjured, can control his rate of descent as he finds

desirable. In all events, the device must permit reaching a lower safe surface and control the speed at arrival to a safe level; perhaps 4.5 m/s (15 ft/s) is a reasonable

maximum.

3.4 Classification and Description of Systems

In order to provide for fall-safety systems that meet a

variety of operational requirements, a scheme for dividing

these systems into six classifications has been devised.

This proposed method of classification is an extension and

modification of the four-class scheme presented in ANSI

A10.14 [AN-1]. The six classes are shown in Table 9 with

proposed maximum acceptable free fall distances and examples

of significant features of each class.

A principal reason for developing the six-class scheme

for fall-safety equipment (see Table 9) was to accommodate

those rope-grab and shock-absorbing devices not readily

classified in ANSI's four-class system [AN-1]. Performance

and test criteria for our Class IV systems can be unique

and, thereby, cover the special characteristics that

distinguish these devices. That is by expanding the

classification scheme established by ANSI, we permit the

development of more specific performance criteria which, in

turn, may enhance the viability of these Class IV systems

- 43 -
Table

9.

Proposed

Classification

for

Active,

Personal

Fall-Safety

Systems

M TO M QJ

coP

a) jp

toC

cfl“ TO rO QJ M C

bO

•H

•> co CO QJ I—I XI M

CO rH

QJ rH

co co co cx

CO -rHCJCHX

cx

C_)

coB

QJ XI

XI o

co

C

CO QJX

Oh CO XI

QJ CO

<4H E

CO 0) CO xl I

cO

COrH

CO

0)

CO

CO QJ

CO .c

XI TO

0) *> •H • CXI Q)

•rH • CO -H

CO '

CO rH CO o o

•H

QJ XI X -H

CO fP •H

QJ cm > QJ O TO

co co

•rH i—I JP i—I XI

CO XI JP -H

bO cm PO

JP ' I XI QJ

CO •HU

QJX

cx

co

co jp o

QJ

C

OO Z TO

TOe

01 co x - 44 -

to

prevent

or

arrest

falls).

Nevertheless,

for

the

want

ofa

better

generic

terminology

all

above

are

referred

to

as

"Fall-Safety

Systems"

throughout

the

text

of

this

report.

Laddersafety

devices

have

been

excluded

since

they

were

outside

the

purview

of

this

study.

They a

usually

active,

personal,

fall-safety

devices

and

would

readily

fit,

say,

between

Classes

II

III.
systems which frequently offer worthwhile modifications of

standard Class V and VI fall-arrest systems. Although it is

true that the buyer must pay a premium for a Class IV system

or device, this premium is frequently more than compensated

for by enhanced worker acceptance, efficiency, and safety.

3.4.1 Class I Systems

The principal purpose of a Class I fall-safety system

is to prevent vertical falls by preventing the worker from

maneuvering into a potential fall position. These systems

generally consist of a tether line attached to a minimal

body belt or similar arrangement. By intent and design,

they are generally not suited to arrest any significant

vertical fall. The chance of injury due to the functioning

of the system is minimal.

The following criteria should be considered in the

design of Class I systems:

(1) A tether line cannot have enough stretch nor be

sufficiently adjustable to permit the user to

inadvertently maneuver into an area where a serious

fall hazard exists (assuming the device was correctly

installed to begin with)

.

(2) Should a worker in performing his duties forget

that he is tethered and impact into a Class I system,

he must not be caused to fall or otherwise be

significantly injured. Thus if a body belt is used in

conjunction with a tether line, the belt should secure

the worker above his center-of-gravity

.

(3) The system cannot accidentally become disengaged

from its anchorage nor lose its integrity upon the

application of maximum anticipated forces or torques.

(4) The system should have sufficient strength to

absorb anticipated impacts and pressures without

failing. For example, a fall on a horizontal surface

could deliver a significant impact to the system.

Class I component breaking strengths in excess of 2000

lbf would appear to be reasonable.

- 45 -
3.4.2 Class II Systems

The Class II systems are primarily intended for

emergency egress and rescue operations and not for arresting

a significant vertical fall. Although they may utilize a body containment device (harness) designed to permit

accelerations up to 15 gn , it must be considered that the

user may be unconscious or otherwise disabled. A maximum

acceleration of 4 gn is therefore proposed. For the worst

case of a 113 kg (250 lb) worker, and allowing a safety

factor of 2.5, the minimum strength of the system

components, calculated using equation 6, should be 11.1

kilonewtons (2500 lbf )

.

3.4. 2.1 Class Ila Systems (Ascent/Rescue)

In certain industrial situations a worker must descend

through a narrow opening or orifice and into an enclosed

area (pit, mine, tank, bin, sewer). The worker may descend

under his own power or he may be lowered into a confined

area by means of a hand-operated or motorized winch. If

noxious fumes may be present or if the possibility of the

worker's becoming disabled within the confines exists, then

an assistant on the outside must be in a position to rescue

his disabled partner —and preferably without having to also

descend into the confines. Thus the first worker should be

secured to the ascent/rescue system at the time he makes the

descent

.

The partner may not have the benefit of additional

assistance when performing this rescue. Therefore, the

system should be designed so that one man can readily

extract a worker from a confined area without further

harming the disabled worker. The critical point is usually

at the opening. If it is sufficiently narrow the disabled

worker may only fit through if his head and upper torso

remain upright. To this end a Class Ila system should

confine the user so that:

(1) He cannot accidentally slip (i.e., "submarine")

out of the body restraint except by specific efforts

towards this end.

(2) His upper torso must be maintained in an erect

posture so as to present a minimum area in the

horizontal plane when suspended by the system.

- 46 -
The confining space a worker finds himself in may be

such that any substantial free fall would probably result in

injuries due to contact with protuberances along his descent

path. Therefore, a Class Ila system, if mechanized, should

be so designed as to rule out the possibility of accidental

rapid and/or extensive free fall descent.

For worker acceptance the confining part of the Class

Ila system should be reasonably comfortable to wear and

should permit the worker to perform his job when so

confined.

A chest-waist harness with thigh straps, a whole body

harness or a bosun's chair or sling with integrated shoulder

and thigh straps are, therefore, candidate Class Ila

systems

.

3. 4. 2. 2 Class lib Systems (Descent/Rescue)

There are many industrial and construction work-atheights situations (e.g., water towers, scaffolding

alongside a high-rise skyscraper, bridges) where a fall, or

scaffolding or bosun's chair collapse or failure could leave

a worker suspended for an extended period until some means

of rescue arrives at the accident scene. It is one thing to

safely arrest a fall; it is often as serious a challenge to

safely return a worker to a surface where aid is available

or from where a worker could return to his duty station.

The worker may be injured, in shock, or in distress

from an arrested fall. Even an uninjured worker, if left

suspended for an extended period, could suffer harm from

restricted circulation or exposure to environmental

elements. In any event, it is highly desirable that an

individual worker, or the work crew as an entity, have some

means of rapid and safe extraction from a post-fall

suspended configuration. This "means" in most cases could

take the form of a device that is either an integral part of

a work-at-heights fall-safety system or is one which can be

quickly brought alongside the worker, from there to effect a rescue

.

Where the rescue system is an integral part of fallsafety gear, it is typically a mechanical device permitting

a controlled descent from the fall site. As with any other

fall-safety equipment, such a device must have certain

- 47 -
features so that it may serve its intended purpose under

worst-case conditions.

If an accident should leave the worker immobilized, the

device should slowly, safely, and automatically deliver him

to the level below. Alternatively the device could be

controllable by an assistant who is located on an

independent surface.

The device should be lockable or adjustable so that, if

it becomes activated by a fall or collapse of a walk or work

surface, it either acts as a rope grab which then gives the

worker an opportunity to calmly assess his future course of

action, or it begins to lower the worker at a comfortable

rate that allows him to halt his descent should this appear

to be the desirable course of action.

In all events the descending device should not permit

the worker to arrive at the surface below him at too high a speed ajid the device should not run out of rope before the

user reaches a safe surface. Possibly 15 ft/s would be a reasonable maximum "landing" speed. Independent of this

maximum landing speed, the worker should knot his line so

that h._ will automatically stop before he reaches the

surface below.

3.4.3 Class III Systems

Class III systems, as exemplified by the lineman's body

belt and pole strap, is basically a working tool used to

support the worker in the desired location while he performs

his duties. The body belt acts as a back rest and tool

carrier while the pole strap provides him with the balance

necessary to maintain his working position. However, it is

possible for such a system to allow a worker to fall freely

until the pole strap catches on a footrest or other

structural member. Such a fall, if arrested, would not

usually exceed 0.9 m (3 ft).

Lineman's pole straps and belts, the only Class III

system included in this study, are covered by the following

regulations

:

AP-2 (1972) (Edison Electric Institute) [EE-1]

KK-B-151G (ANSI) [NA-1]

29 CFR 1926.959 (OSHA) [CF-8]

29 CFR 1910.268 (OSHA) [CF-4]

- 48 -
Such a system normally consists of:

(1) A body belt with dee-rings positioned at left and

right sides (i.e., at the 3 and 9 o'clock positions).

The belt is usually padded for wearer comfort.

(2) A (pole) strap with snaphooks at both its ends and

which may be adjustable in length.

In use, the strap is first snapped into one or the

other dee-rings; it is then placed around a structural

member and the strap is then secured to the remaining deering. These fall-safety systems are used in climbing poles;

however, they also see service on high-voltage and microwave

transmission towers as well as in construction work

involving re-bars.

The strap and belt must both be adjustable for comfort

and utility as a positioning device. Furthermore, since

Class III devices apply a constant pressure to the worker,

they should be designed to do so in such a manner as to

minimize worker discomfort. For this reason lineman's belts

are typically padded with a 75 to 100 mm (3 to 4 in) wide

inner lining. Weight, bulkiness, and other qualities that

affect worker acceptance must be considered since users of

Class III systems must frequently wear these devices for

hours at a time.

A pole strap repeatedly moved up and down poles and/or

metal struts will abrade in time. It is important that the

pole strap be thick enough so that even after significant

abrasion there is sufficient strength remaining in the strap

to arrest a worst-case fall. Similarly the strapping should

have some built-in indicator that will let the worker know

that a strap has been abraded beyond safe limits and,

therefore, should be discarded.

The assumption is made that a lineman's safety strap

and belt are not "married" and that, due to differential

life expectancies and other factors, a strap or belt will

possibly see more than one mate during its lifetime. It

would appear reasonable that, whatever length belt is used,

its length is adjusted so that the belt at the worker's

waist never spaces him (at waist level) more than about 0.46

m (18 in) from the pole or structural member. With the

strap so adjusted, the worker is assumed to be able to

vertically free fall no more than 0.9 m (3 ft) before being

- 49 -
stopped. It is furthermore assumed that the lineman's pole

strap is never used as a lanyard.

As was the case for Class Ila systems, a Class III

system is typically used in a loaded (but not impacted)

state. As such, the components should be designed to

withstand constant loading without "creeping" or degradation

of breaking strength or extensibility properties. The

forces observed by the strap in a snubbed fall depend

greatly on the angle developed between both sides of the

strap. This angle depends on:

(1) the width of the user (assuming the strap is

snapped on at 3 and 9 o'clock positions).

(2) the diameter of the snubbing obstruction (assumed

to be a right cylinder)

.

(3) the length of the strap and its extension upon

impact

.

(4) the location of the dee-rings, relative to the

buckle, and possibly the shape that the belt must

conform to during impact.

If a lineman should fall, he is likely to suffer a +ax acceleration, performing a reverse jackknife (backbend)

about his waist. This is a dangerous type of flexure and

the opportunity for vertebral damage is high; therefore, it

is recommended that the deceleration limit for lineman's

body-belt/pole-strap systems be tentatively set at 4 or 5 gn

*

Linemen appear to be more safety conscious, on the

average, than is the typical steel construction or industry

worker. As such, worker acceptance is probably less of a problem with Class III than with Class V or VI systems.

3.4.4 Class IV Systems

Class IV systems include, as part -of the system, rope

grabbing and/or shock-absorbing devices that are designed to

give the worker extensive horizontal or vertical mobility.

These systems usually, but not always, include a lifeline

(horizontal or vertical). A lanyard is usually used in

conjunction with the rope grab or shock absorber, but a

- 50 -
rope-grab may be used to connect a body belt directly to a dropline. In any case, the Class IV system is intended to:

(1) Reduce potential free fall distances;

(2) Absorb a significant part of acquired kinetic

energy and, thereby, limit impact forces and

accelerations imposed on a worker as the result of a fall;

(3) Limit fall-arrest system strength requirements by

restricting fall distances, by absorbing fall energy,

and by the use of couplings that do not result in a reduction in system strength.

Class IV systems frequently involve a mechanical

grabbing component but some shock absorbers utilize energy

absorbing tear-webbing. There are, basically, two types of

rope-grabbing devices. These are described in [BE-2]:

"I) Static rope-grabbing device used with lanyard.

The worker moves the device by hand up and down the

dropline with relative ease. It is preferably

positioned above the work level. The device is

actuated during a fall to squeeze the rope or tip in

such a way as to lock onto the dropline by friction.

The fall is thus halted. The lanyard is needed to

provide freedom of movement from the fixed position

rope-grabbing device.

"II) Mobile rope-grabbing device used without lanyard.

No lanyard is used, the safety belt is attached

directly to the dropline. The connecting device floats

freely on the dropline providing freedom of movement

but locks instantly during a fall. The device is

actuated in one system by inertia during a fall with a mechanism comprising three balls floating in a cage

which are forced into a conical wedge and thus onto the

rope. The fall is limited to a few inches. A second

cam-operated lock in some models provides a further

safety feature."

Class IV systems may be shock loaded, if only lightly,

relative to Class V and VI systems; therefore, design

(safety) factors should be introduced to compensate for

component variability and degradation with age,

environmental conditions, and usage.

- 51 -
To quote from [CS-1]

:

"In practice a lifeline is attached to a fixed

anchorage at a point above the working platform; the

rope grabbing device is then attached to this lifeline.

In turn a lanyard is attached to the rope grab and run

to a dee-ring attached to a body belt worn by the

workman

.

"If a fall then occurs the workman drops in free fall

until the lanyard tightens. At this point the rope

grab is actuated and made to 'grab' the lifeline and

thus arrest the worker's fall."

With regard to lifelines, a Class IV system (1) may not

require one; (2) may be compatible with a great many

lifeline materials, diameters and constructions; or (3) may

require and be compatible with only one or a few type

lifelines

.

Mechanical devices such as rope grabs and shock

absorbers may be more severely affected by environmental

conditions than components such as lanyards. The possible

effectr of moisture, grease, dust, grit, heat, cold, and ice

should be considered in the use and testing of Class IV

systems

.

In a recent (1973) CSAO study [CS-1], seven ropegrabbing devices were evaluated. The wearer was represented

by 91 kg (200 lb) rigid weight, M. Peak forces were

measured with a transducer attached just above the weight.

Falls were simulated using a bomb-drop-type quick-release

mechanism. A six foot drop of the test weight was used by

CSAO to represent a worst-case fall situation for each of

the seven Class IV systems. The acceleration for each drop

test was calculated from the measured force, F , , as obs

Acceleration = F

0k s /M • CSAO ' s conclusions and recommendations (explicit and

implicit) and relevant NBS project staff comments are

presented in Table 10.

3.4.5 Class V Systems

A Class V fall-safety system typically consists of a body belt, a lanyard, and an anchorage. It may include a

- 52 -
Table 10. CSAO's

(a) Conclusions and Recommendations Regarding Fall-Safety Equipment with Rope Grabs

CSAO's Conclusions NBS Prolect Staff Comments

The test program clearly indicates that the use

of manila rope for the lifeline or lanyard

constitutes a potential hazard; accordingly,

it is recommended that only poly or nylon

rope be used in field situations.

Agreed, that manila rope be proscribed from use

in fall-safety systems. Nylon, polypropylene and polyester and admixtures thereof all appear to be viable materials at this time.

It is necessary to have detailed installation

and operating instructions supplied with each

rope grabbing device.

Agreed.

Where a mechanical rope grab device was not

available, the triple hitch knot could be used. Agreed

Too much slippage of a rope grab along a lifeline is undesirable.

Agreed. Set slippage limit at 3 ft for a worstcase anticipated fall.

The actions required of a worker to effect a change in the position of a rope grab on a drop

line may produce temporarily unsafe conditions

(e.g., the need for two hands to move the

device was considered unsafe)

.

Agreed. However, this is seen to be more of a purchaser decision than a regulation requirement.

The device should function normally even if the user grabs it as he falls. This is again seen to be a desirable characteristic

but it is not clear how critical this characteristic would be in actual accident situations.

A bounce-type stopping action is undesirable. Agreed. It is suggested that each secondary

impact amplitude be less than 1/2 the (acceptable)

previous peak amplitude.

A device that can be coupled to a lifeline at any point is to be preferred over a device

that must be threaded onto the line from a free end.

Agreed. The regulation need not insist upon this

condition, however.

The device should be clearly labeled as to which

side of it is "up" if it is unidirectional and

should also indicate which type lifeline

materials it is compatible with.

Agreed

.

The grabbing action of the device should not

cut, abrade, crush, fuse or otherwise so weaken

the lifeline as to reduce its strength below

the margin of safety.

Agreed

.

A human faller would incur about half the g's

observed from a similar drop but with a rigid

weight

.

Agreed.

A fall arrest system must be capable of limiting

impact g's to below 10. Agreed. However, a limit of 8 g (when used with

a body belt) is recommended.

a) CSAO = Construction Safety Association of Ontario

b) "Poly" = polypropylene.

#

- 53 -
lifeline between the anchorage point and the lanyard if

mobility greater than would be permitted by the lanyard

alone is required. In any case, these systems are intended

to save a worker after a significant free fall distance by

absorbing the energy of the fall and reducing the forces and

accelerations to tolerable levels.

For the Class V system, it is assumed that all of the

energy is absorbed by the lanyard. The lanyard must

therefore be carefully selected and secured so as to limit

the potential free fall distance, Table 9 proposes a maximum

of 1.8 m (6 ft)

,

to have adequate strength to withstand the

peak force generated in arresting the fall and to elongate

with the force in such a way that the peak acceleration is

not excessive.

As was discussed earlier, a body belt exerts force on

the human body in a way more likely to produce injury than a body harness, i.e. through the soft abdominal tissue rather

than through the skeletal structure. To minimize the

possibility of injury, the belt should be as wide as

practical so as to distribute the force over a large area

and care should be taken to attach the lanyard in the midback, six o'clock position, to limit the tendency for

sideways or backward bending. In addition, the belt must

have sufficient strength to withstand the force generated by

the arrested fall and must not elongate to permit the body

to be released. It should be noted that this elongation

includes not only the stretch of the belt material but also

any slipping or tearing at the buckle.

The anchorage and lifeline, if used, are also assumed

to absorb none of the energy. They are, therefore, required

only to have sufficient strength to withstand the maximum

force generated in arresting the fall. The factors shown in

Figure 5 and Table 5 must be considered if a horizontal

lifeline is used.

Considering the physiological and operational factors

involved with a Class V system, the maximum acceleration

should probably be limited to 8 g and the peak force to

8900 N (2000 lbf )

.

- 54 -
3.4.6 Class VI Systems

A Class VI system differs from a Class V in use of a body harness instead of a body belt. Such harnesses

transmit forces to the body through the skeletal structure

and hence are less likely than a body belt to cause injury

for the same fall conditions. Class VI devices are

generally worn only in very hazardous work environments.

The worker who elects to use such a system is likely to be

safety conscious and motivated towards that end.

Much of the information applicable to the use of Class

VI systems comes from the use and testing of parachutes and

ejection seats. The standard parachute has four riser

straps coming up from the harness and linking with the

parachute above the wearer. The usual Class VI body

harness, however, secures to a lanyard by means of one of

several dee-rings present on the harness. Since man is very

susceptible to sideways, i.e. + a

y

, and backward, i.e. + a x , accelerations, the selection of the point of attachment of

the lanyard is important. A U.S. Navy document [AS-2]

states

:

"Another important factor is the placement of the

fixation point of lanyard on the belt (harness) . This

must be on the back and not the chest in order to avoid

the quick movement of the head towards the back. It is

important to place it as high as possible, so that the

body is vertically suspended after a fall, this means

that the fixation point should be at the point where

the shoulder straps cross in the back at level of the

shoulder bone in an eye provided for this purpose. The

dynamic strain is thereby divided between the two

shoulder straps, transmitted to the safety belt in 4

different places, which assures a good distribution of

the pressure points on the thorax."

It is imperative that the connection between a Class VI

harness and a lanyard only be made high in the back (between

the shoulder blades) or from riser straps coupled to a deering above the head.

Body harnesses are generally adjustable to fit a large

range of sizes. Military specifications call for parachute

harnesses to be adjustable to fit users weighing from 63.5

kg (140 lbs) to 113.5 kg (250 lbs). It might be desirable

to provide two sizes to cover the weight range of 59 kg (130

lbs) to 113.5 kg (250 lbs).

-5 5_
Navy policy [BO-3] limits the use of parachutes to 100

jumps unless it is damaged and retired sooner. Class VI

harnesses may experience forces greater than usually seen

with parachutes. Class VI harnesses and other components

should be regularly checked to determine their

serviceability.

Because of the possibility of a Class VI system being

subjected to high impact loads, the lanyard should always be

tied off in a nonstrength-reducing manner. This can be

accomplished by limiting the length to 1.8 m (6 ft) with

snaphooks on each end or by use of a two-part lanyard having

a steel cable or heavy web strap in contact with any

structural member. Such straps should have a wear indicator

to show when abrasion sufficient to weaken the strap

significantly has occurred.

3.5 Descriptions and Functions of Components

The successful performance of a fall-safety system

depends upon each component functioning in an adequate

manner. A number of components are common to several

classes, while others are limited to use with one or two

classes. For convenience and reference, a number of these

components are described below and their functions are

explained

.

3.5.1 Containment Devices

A containment device serves to insure that the body of

a person involved in a fall accident remains attached to

fall arresting mechanisms, to position the victim's body so

as to minimize the chance of injury, and to transmit the

forces generated to the body. The three types of

containment devices most commonly used are shown in Figure

6. Such devices include:

(1) Body Belt . Generally a wide, padded web belt

having either a friction or tongue buckle so that it

can be adjusted for a comfortably snug fit around the

waist. These belts frequently have a dee-ring or other

arrangement for attaching to a lanyard. With suitable

attachments, these belts are sometimes used to carry

tools. Body belts may be used with Class I, II, III,

IV, and V fall-safety systems.

- 56 -
(2) Chest-Waist Harness . The combination of a belt

around the chest and a waist belt connected by shoulder

straps. A dee-ring for attaching to a lanyard is

generally located in the back between the shoulder

blades. This type of harness distributes the load over

a larger area, but tends to pull up under the arms

unless the waist belt is excessively tight. A chestwaist harness might be used with Class II and

possibly Class IV fall-safety systems.

(3) Body Harness (Parachute Type) A harness similar

to that used with parachutes. The force is applied to

the body skeletal structure through straps around the

upper thigh and pelvic region, a waist belt (primarily

for positioning), and shoulder straps. A dee-ring for

attaching to a lanyard is generally located high in the

back, between the shoulder blades. Body harnesses may

be used with Class II, IV, and VI systems. They are a definitive part of Class VI systems.

(4) Bosun 1 s Chair . A seat attached to ropes for

suspending over the side of a ship, building, etc. to

provide support to a worker during inspection,

pointing, repairing, etc. A bosun's chair might be

used with a Class II fall-safety system.

(5) Other. A variety of special or impromptu

arrangements might be used for particular purposes.

These could vary from a simple rope tied around the

waist to special harnesses for mountain climbers. The

simple, impromptu arrangements should be discouraged

except for emergency use in Class I systems.

3.5.2 Lanyards

A lanyard is a short, generally less than 4.6 m (15

ft), flexible line, rope or strap used to connect the

containment device of a fall-safety system to anchorage or

lifeline. Except for Class IV systems, the lanyard is

assumed to absorb all of the energy of an arrested fall.

Lanyards may be made of a number of materials, including

spun nylon, filament nylon, polyester, polypropylene, and

manila. A lanyard may have snaphooks attached to one or

both ends or may be attached by knotting. Lanyards are used

with all fall-safety systems except some Class III systems

- 57 -
and the few Class IV systems that connect directly onto a lifeline

.

3.5.3

Lifelines

A lifeline is a heavy line used to transfer an

anchorage point to a more convenient or secure site and/or

to give the user considerable horizontal or vertical freedom

of movement. Since a lifeline may be used by several

workers simultaneously and is not considered to be an energy

absorbing component, it will be selected and installed based

on strength considerations. In calculating strength

requirements, the number of workers using the lifeline at

one time and the geometric factors discussed in Section 3.1

must be considered. Heavy fiber rope and steel cable are

candidate materials for lifelines.

3.5.4

Rope Grabs and Shock Absorbers

Rope grabs and shock absorbers are definitive parts of

Class IV systems. These components are intended to provide

mobility along a lifeline while reducing the potential free

fall distance and absorbing a significant part of the energy

generated by the fall. The rope grabbing feature may be

manually operated, requiring the user to deliberately move

it along a lifeline and lock it in place with a cam or

similar mechanical system, or it may be automatic, allowing

free motion along the lifeline until activated by a falling

motion to lock onto the lifeline, usually by an inertial

device. In any case, the system should limit the total fall

distance, including travel along the lifeline. Sweden [SW1] sets one meter (3.3 ft) as the allowable travel of the

rope grab along the lifeline. In addition to the energy

absorbed in the travel along the lifeline, additional energy

absorption may be provided by a mechanical shock absorber or

tear webbing.

3.5.5

Ascent and Controlled Descent Devices

These devices are intended to provide for the egress or

rescue of workers, generally with the assistance of one or

more co-workers. The ascent systems generally incorporate a manual or motorized winch. Such a winch should have

controls, brakes, and/or stops to permit a disabled worker

to be carefully maneuvered around obstacles and through

- 58 -
openings. A controlled descent device may be automatic or

manually controlled, but should limit the descent speed to

less than 4.5 m/s (15 ft/s) to avoid injury from impact at

the end of the descent. Other provisions, e.g. knotting of

the line, should be made to prevent impact with the landing

surface

.

3.5.6 Anchorage

An anchorage is the means for attaching a lanyard,

lifeline or other components to a structural member or other

secure point. The anchorage point is frequently not a part

of the working or walking surface. The anchorage is usually

a beam or an eyehook attached to a beam. A lanyard may be

looped around the beam and tied off with a bowline or

snapped onto itself, or it may be snapped or tied to the

eyehook. In general, the eyehook is preferable since beams

may have cutting or abrading edges that will damage a fiber

line. A portable anchorage consisting of a steel cable or

heavy web strap that can withstand the cutting and abrasion

of a beam can be used. A two-part lanyard, having a web

strap attached to one end, could be considered as a portable

anchorage

.

3.5.7 Other Components

In addition to the principal components discussed

above, fall-safety systems include a variety of components,

generally solid metal or polymeric items, used to couple the

systems together. These items include buckles, carabiniers,

dee-rings, grommets, snaphooks , thimbles, and toggle bolts.

Since these items generally couple to fiber components, it

is important that they be free of sharp edges or burrs that

could cut or abrade. Most of these items will carry some,

if not the major, load during a fall accident, so they must

have adequate strength and should not deteriorate through

corrosion, weathering, or environmental conditions. They

should be subjected to inspection, proof loading, and design

and quality control testing as rigorously as the principal

components

.

3.6 Components, Requirements, and Limitations

In performing the function of preventing or arresting

an accidental fall, the components of a fall-safety system

- 59 -
must meet a number of requirements, specifically those

requirements related to strength, energy absorption, force

distribution on the body, and limiting fall distance. The

requirements will vary for the different classes of fallsafety systems and, to some extent, they may differ

depending upon the particular use. In establishing

requirements that must be met during prototype and quality

control tests, the effects of product variability (due to

material and manufacturing tolerances), use conditions, and

degradation with age, use, environment, etc. must be

considered. Contingency factors are commonly applied for

this purpose. Additional degradation factors may be needed

when specific uses are known or suspected to affect

performance; e.g. tie-off of a lanyard around a beam with

sharp edges will reduce the strength of the lanyard.

3.6.1 Mechanical Requirements

Based upon the information gathered for this report, it

is suggested that the criteria shown in Table 11 be used in

developing the performance requirements for fall-safety

equipment

.

The values given in Table 11 consider that the

acceleration pulse will generally have a duration of 0.1

second or less. This is based upon oscillograph traces from

drop tests by two manufacturers of fall-safety equipment and

computer synthesized drop tests using lanyard

characteristics determined during this program. Pulse

duration was taken as full-width-at-half-maximum amplitude

of pulses that were fairly symmetric. It is also considered

that, based upon information found in the literature, [AS-2,

BI-1, MO-1, NS-1] , a healthy, young male can sustain short-term

accelerations of +a z > 20 gn , ay

= 15 gn , +ax = 15 gn without substantial injury and that other standards [AN-1,

CS — 1 , CS-3] have adopted 10 gn as allowable, supposedly in

the +az direction and presumably with the use of body belts.

The values for Class V systems recognize that the forces are

transmitted to the body through the soft abdominal tissue

rather than through the skeletal structure as for a Class VI

system.

The contingency factors, Ds and Da , are meant to allow

for variability and the effects of aging, use, environment,

etc. on the strength and extensibility of the components,

particularly lanyards. It is also noted that tests made

using a rigid mass will produce higher force and

- 60 -
Allowable

or

Minimum

Test

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M 3 GC/3 d3 - 61 -
acceleration values than would be generated by a falling

human because of the energy absorbing characteristics of the

human body. In many cases, this energy absorption will

essentially introduce a contingency factor, D s = 2 . The use

of a higher contingency factor, Ds, for Class II and III

systems is based upon their sustained loading during use and

the recommendations of the Cordage Group for working loads

for various types of fiber ropes [CG-3] , shown in Table 12.

Table 12. Recommended working load as a percentage of

breaking strength for various fiber ropes [CG-3]

Fiber % Breaking

Strength

Manila 20

Filament Nylon, Goldline 11

Filament Dacron 11

Polypropylene 17

P/D 100 17

P/D 10 17

The energy absorption values are based upon a worst

case fell and estimated lanyard elongation.

3.6.2 Electrical Requirements

When fall-safety systems are used around electrical

systems, they must not only provide protection from falls,

but must also insure adequate electrical isolation for the

worker. Although this is probably most common with Class

III systems, it may apply to all other classes depending

upon the usage.

The dielectric properties of fall-safety equipment are

covered in other regulations and standards [CF-4, CF-8, EE1, NA-1 ] . According to one of these [EE-1], all fabric used

in the construction of safety straps shall withstand an AC

dielectric test of at least 82 000 volts per meter (25 000

volts per foot) when dry for three minutes without visible

deterioration, and leather, fabric, and rope components

shall have leakage current of less than one milliampere for

3000 V AC on electrodes 0.3 m (1 ft) apart.

The above requirements seem reasonable for fall-safety

equipment to be used where significant electrical hazard

exists

.

- 62 -
3.6.3 Environmental

Fall-safety equipment is used in a wide range of

weather and environmental conditions, and fall accidents may

be more likely in adverse environments. It is therefore

appropriate and important that the various components be

known to function properly over the full range of conditions

that may be encountered. Environments of concern and ranges

that might be encountered include:

(1) temperature: -18 to 43°C (0 to 110°F)

(2) humidity: 10 to 100 percent RH

(3) ultraviolet radiation

(4) ice

(5) salt

(6) dust

(7) dirt and grit

(8) industrial solvents

In addition to possibilities under these conditions,

components may be stored so as to have extended exposure to

temperature up to 80°C (175°F) , high humidity, low humidity,

grease or industrial fumes. Each of these factors may

reduce the strength, energy absorbing capability,

reliability, or durability of some components. Unless

available information shows that exposure to these

environments will not affect the performance of a component,

testing may be required.

Figure 8, taken from [DU-3], gives the comparative

sunlight and weather resistance of 1/2 in diameter ropes

exposed to direct Florida sunshine. To quote from [DU-3]:

"NOTE. Exposure conditions for Florida outdoor

exposure tests are extremely severe because the test

items are continuously exposed to sunlight and to

weather elements for prolonged periods of time . The

deterioration observed during such tests is usually

many times greater than that experienced during actual

use of fiber products."

Pertinent information derived from a reading of [BR-2,

DU-3, DU-4, PA-1] regarding the effects of sunlight and

moisture includes:

(1) A Capracyl-dyed, 1/2 inch nylon lanyard should

retain at least 80 percent of its original strength

after worst-case exposure to the elements (sun and rain

- 63 -
BREAKING

STRENGTH,

LBF

Fiaure 8. Comparative Sunlight and Weather Resistance

of Commercial Ropes
for three or more years) . A larger diameter nylon

lanyard will retain a proportionately higher percentage

of its original strength.

(2) Surface grease and dirt probably act to still

further attenuate the degradation effects of

ultraviolet (UV) light on lanyards.

(3) DuPont Dacron polyester ropes will likely retain

more than 90 percent of their original strength after

two or three years of worst-case exposure to the

elements

.

(4) For rope diameters greater than 1/2 inch, the

curves in Figure 8 should tend to flatten out [BR-2].

(5) Various UV inhibiting chemicals can significantly

retard the degrading effects of UV on nylon and

polyester. (Most manufacturers of fall-safety

equipment claimed they purchase nylon ropes so

inhibited .

)

(6) Polypropylene is quite light-sensitive and so must

contain a UV inhibitor. In this regard polypropylene,

containing a black, UV-absorbing pigment, will give the

least UV degradation. However, slightly less effective

yellow polypropylene is recommended since fiber damage

is probably more easily detected than with the black.

Stabilizers make the UV resistance of polypropylene

ropes comparable to ropes of nylon and polyester [PA1 ]

.

(7) A carbon-arc tester (e.g., weatherometer ) is no

substitute for actual outdoor exposure since no

consistent correlation between the two types of data

has been observed. Furthermore, outdoor exposure

(i.e., not under glass) combines the effects of

sunlight, moisture, and heat in one test.

(8) Dry nylon rope can absorb about 4 percent more

energy per unit length than its wet equivalent.

(9) Several sources of information indicate that nylon

is slightly weakened by long-term exposure to moisture.

It would appear, however, that degradation due to UV

light is more significant. The instantaneous loss in

strength of nylon that has been wetted down is

estimated by various sources [DU-3, DU-4] at from 5 to

- 65 -
15 percent. Nylon ropes can be stabilized against

degradation due to moisture. Quoting from [PA-1]

:

"European rope standards now require stabilization of

nylon ropes, while in the corresponding U.S. standards

stabilization is expressly prohibited" (e.g. German

Std. DIN 83 330 vs. U.S. stds . listed in Table 2-5 of

[PA-1] )

.

(10) No synthetic cordage fiber other than nylon shows

noticeable degradation in strength or extensibility

properties with moisture since these fibers absorb

little or no water. In fact polypropylene ropes may

show from 2 to 5 percent higher breaking loads when wet

than when dry due to the reduction in fiber friction in

the rope by water around the fiber itself.

(11) Dacron's properties are essentially invariant

between 0°C (30 C F) and 32°C (90°F)

,

and Dacron is quite

resistant to UV degradation.

An experimental study performed at the National

Parachute Test Range (NPTR) and completed in 1976 [TU-1]

tested manila and various synthetic ropes by submitting them

to a series of conditioning treatments, as formulated in

MIL-STD-810B. Percentage difference, comparing post- and

pre-conditioned breaking strengths, for averages

representing, typically, three samples each are presented in

Table 13. The salient findings given in [TU-1] include:

(1) None of the types of rope tested was significantly

weakened after 24 hours exposure to high temperatures.

(2) Manila loses about 1/3 of its strength and

polypropylene about 1/5 of its strength (when it is

exposed to 71°C (160°F) ambient conditions for 200

hours) . All the other ropes are essentially unaffected

by exposure to these high temperatures for extended

periods

.

(3) Cold has little effect on rope breaking strength

and this effect is to slightly strengthen lanyards of

Dacron and nylon.

(4) Salt spray appears to have little short term bad

effect on the breaking strength of the ropes tested.

(5) Extended exposure to moisture and UV appeared to

weaken "poly-plus" and manila ropes by 10 percent or

more relative to control averages. The other types of

- 66 -
Table

13.

Effects

of

Environments

on

Rope

Strength

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XX - 67 -

"Poly

Plus" =

50/50

polypropylen^/polyester.

Conditions

applied

to

sets

of

(3

each)

130

cm

(51

inch)

lengths

of

various

type

lines

before

they

were

tensile

tested

to

break.
rope were significantly less affected by these

environmental factors.

(6) Manila and polypropylene are readily abraded but

the remaining ropes showed good resistance to abrasion.

(7) Breaking strengths of the type ropes tested were

not significantly reduced by 100 cycles of loading to

4.45 kN (1000 lbf )

.

(8) Manila is somewhat strengthened and nylon somewhat

weakened by equilibration at a high relative humidity

(RH) .

It is, therefore, reasonable to conclude that:

(1) The temperature at which ropes are conditioned is

not a significant strength factor but, at least for

manila and nylon, relative humidity can have a noticeable effect. Strength may be significantly lower

at high temperature.

(2) Heat, cold, moisture, and salt spray do not

significantly weaken the rope types tested, but

possible combinatorial effects remain to be explored.

(3) Abrasion is not a serious problem except for

manila and polypropylene.

Most hardware components are load-bearing. To quote

from [HA-2] : "As the temperature drops from 27 to -18°C (80

to 0 °F ) , the carbon steel becomes increasingly brittle and

the material can endure little impact at subzero

temperatures. Alloy steels, such as 4140, remain tough to

temperatures as low as -185°C (-300°F) .

Figure 9, taken from [HA-2] compares the impact

strength of an alloy and a carbon steel from -73 to 65°C

(-1C0 to+150°F) . Now fall-safety equipment is typically

tested at from 18 to 27°C (50 to 80°F) , yet some units will

probably see service at -20°C (0°F) or slightly below. Due

to adverse conditions at low temperatures, falls are

probably more likely than, say, at 20°C (70°F) . Thus, it is

imperative that the strength of all fall-safety equipment

components remain above the required minimum limits in at

least the temperature range from -20 to +45°C (0 to 110°F)

.

Nylon and Dacron are seen [PA-1] to retain their strengths

in this range and, in fact, they become stronger at low

- 68 -
CHARPY

V-IMPACT

STRENGTH

(FT-LB)

Figure 9. Impact Strength vs. Temperature Curves

for Carbon and an Alloy Steel

- 69 -
temperatures. These synthetic materials do not become

brittle until well below -20°C (0°F)

.

3.6.4 Deterioration in Use

As a result of normal usage, fall-safety equipment will

deteriorate and may be damaged. Periodic inspections,

including daily checks by the user, are essential to insure

that equipment is replaced before it would fail if involved

in a fall accident. Factors that would be of concern

include

:

(1) normal wear

(2) abrasion

(3) cutting

(4) fraying, hackles, etc.

(5) repeated loads and shock loads

(6) bending

(7) cracking

(8) corrosion

(9) failure of protective coatings

(10) environmental exposure

(11) age

Wear indicators can be built into belts and straps that

are subject to wear or abrasion. Components should be

discarded when such indicators appear. Items that pass over

edges or rough surfaces, e.g. structural beams, should be

examined frequently for abrasion and cutting. Lifelines

that are used with rope grabs should also be inspected

frequently for signs of abrasion, crushing, or other damage.

Manila and polypropylene have been found to be particularly

susceptible to abrasion [TU-1]

.

In a study of fall-safety equipment [BO-1] , Boeing

engineers found that:

"Nylon line will stretch up to 40 percent of its length

under impulse loading. However, once shock loaded,

this material does not recover its full elasticity. It

was found, that, for a series of three successive

drops, the shock absorbing characteristics continually

deteriorated. The shock load for the third drop was as

much as 2 gn

'

s

greater than for the first drop."

A paper by Jay Boine [BO-3] also indicates that

repeated, static loading of ropes tends to reduce their

- 70 -
shock absorbing capability even though their strength is not

significantly affected.

Corrosion not only weakens the metal part affected, but

may also degrade synthetic fibers such as nylon. Metal

parts can be corrosion-proofed by plating with corrosion

resistant materials such as cadmium. However, cadmium

plating is brittle and may crack and possibly peel thereby

exposing the base metal. In such cases, the corrosion may

be underneath the plating and not readily visible. The

bending of plated parts, such as thimbles, during assembly

should be minimized, and corrosion testing should be done

after such parts are assembled. The plating may also wear

off with use so that the base metal becomes exposed and

susceptible to corrosion. High strength, low alloy steels

are generally more resistant to corrosion than plain carbon

steel

.

Through numerous conversations with scientists and rope

engineers, the belief was acquired that as a rope aged not

only did its strength decrease but it became stiffer (i.e.,

its extensibility decreased) . In fact it is generally

believed that the embrittlement process proceeds at a greatt. rate than does the reduction in rope breaking

strength.

However, a recent study by Kosmath and Kaminger [KO-2]

included strength tests of 21 nylon climbing ropes. These

ropes varied from 7 months to 8 years old and had seen from

0 to 400 hours of service. Loads and extensions at rope

failure (breaking point) were observed and compared to new

ropes. The results were ambiguous and showed no strong

correlation with age or use. Two ropes (the oldest and one

of the newest) showed higher extensibility while nine showed

significantly reduced extensions, though frequently

associated with reduced strengths. The remaining samples

showed extension that varied from nine percent higher to

eight percent lower than the new ropes.

On the other hand, in the course of this study the

elongation of eight new and 17 used spun nylon lanyards was

measured as a function of load. The used lanyards had been

in service from three months to four years and ranged in

conditions from "good" to "quite dirty, greasy, and

abraded." At 4.45 kN (1000 lbf) the new lanyards showed an

average extension of about 20 percent and the used ones

showed an average of 26 percent. At 13.34 kN (3000 lbf),

the new lanyards averaged about 34 percent elongation and

- 71 -
the used ones averaged 41 percent. In this case, for spun

nylon, the extensibility seemed to definitely increase with

age or use. However, in these same tests, the breaking

strength of the used lanyards averaged 80 to 86 percent of

that for new lanyards, depending upon rope diameter.

Although parachute harnesses do not typically

experience impact forces as great as might be imposed on a Class VI fall-- safety system, U.S. Navy policy [BO-3]

limits the use of parachutes to 100 jumps, or less if damage

is evident.

3.6.5 Other Use Factors

In addition to the possible deterioration of fallsafety equipment with use, some factors inherent in the use

of these systems may affect their performance.

As was shown in Section 3.1, a horizontal lifeline and

its anchorage must be of higher strength than a vertical

line, the amount depending upon the geometry of the system.

It has been observed [CS-1, CS-3] that short lanyards

with free ends will generally be tied off onto eyehooks or

anchor bolts, and that longer lanyards with snaphooks or

free ends are likely to be secured around structural angles,

"H" or "I" beams. It was also shown [CS-3] that securing a lanyard around a beam reduces its strength by 42 to 71

percent (an average of 60 percent) due to the shearing

action of the beam edges. Heat generated as the lanyard

passes rapidly over the metal flange may also melt or

embrittle the fibers. It has also been found [CG-3] that

securing a lanyard with commonly used knots can reduce its

strength by up to 50 percent. It should also be noted that

the nature of these tie-off effects, e.g., cutting, is such

that compensation by use of a larger diameter rope may not

be effective. A more effective procedure might be the use

of a length of steel cable or an abrasion resistant strap to

secure to the beam.

In contrast to the strength reduction when a knot is

used to secure a lanyard, rope engineers claim that a

properly made eye-splice should result in less than 5

percent reduction in rope strength [CG-3] . This agrees with

results from Canadian tests [CS-3]. Therefore, a lanyard's

strength should remain relatively intact if a snaphook.

- 72 -
correctly spliced onto its anchor end, is secured to an

eyebolt.

The knot-holding ability of various lanyard materials

was evaluated at the National Parachute Test Range [TU-1]

.

A bowline knot was tied in each of 10 one-half inch diameter

rope sections of each material. The knotted sections were

then tumbled for 24 or 48 hours and the quality of the knots

was evaluated. The results of these tests are shown in

Table 14. These tests indicate that Dacron and

polypropylene have reasonably good knot-holding ability

while filament nylon and poly-plus (a 50/50 blend of

polypropylene and polyester) are poor in this respect.

Construction workers indicate that spun nylon is superior to

filament nylon in this respect.

3.7 Test Procedures

When examining the various Federal, military, state,

manufacturer, user, and foreign regulations for standards

concerning fall-safety equipment, one is struck with the

widely divergent test parameters, test conditions, and

certification criteria. In some cases components must just

satisfy tensile strength criteria; in other cases, these

components must pass a dynamic test; and in still other

cases, equipment must pass both static and dynamic criteria.

The diversity of requirements for drop tests is evident in

the following tabulation.

Test Weights

- 200 lb (100 kg) , rigid weight [SW-1]

- 250 lb, sand-filled canvas bag [CF-4, EE-1, FE-3,

NA-4 , NI-1

,

US-1]

- 250 lb, rigid simulated torso [AN-1, x-i]

- 300 lb, rigid cylinder or torso [OS-1]

- 300 lb, simulated torso [BS-4, MI-4]

— 350 lb, rigid weight [CA-5

,

NA-2]

Drop Height

— 2 ft (body belt or pole strap) [BS-4, NA-4 , US-1]

- 4 ft (body belt and attachments) [cs-1, CS-5 , EE-1]

- 4 ft (safety straps) [CF-4]

- 5 ft (body belt and lanyard) [CS-1 (conditional)

,

x-l]

- 6 ft (body belt, lanyard, rope [AN-1, BS-4

,

CS-1,

line, tail line) EE-1,

NI-1]

FE-3, NA-2 ,

- 73 -
Table 14. NPTR knot test data [TU-1]

Bowline Knot, 24 Hours (a)

Final Knot

Status Manila Polypropylene Poly Plus Dacron Nylon

Tight 2 6 0 8 0

Slack 8 L 0 1 0

Partially

Undone 0 1 0 1 1 Undone

k 0 1 10 0 9

l

Bowline Knot, 48 Hours (a)

Final Knot

Status Manila Polypropylene Poly Plus Dacron Nylon

Tight 0 6 0 8 0

Slack 6 1 0 1 0

Partially

Undone 2 1 0 1 0

Undone

1 2 2 10 0 10

(a)A bowline knot was tied in ID, 1/2 in diameter rope sections

of each listed fiber (see column headings). The knotted sections

were then tumbled for either 24 or 48 hours. Tabled elements

represent the frequency with which each fiber type rope section

was found in the state specified in column 1.

- 74 -
6 ft (lanyard) [CF-4]

2m (6.6 ft) (lanyard) [SW-1]

3m (9.8 ft) (body belt) [SW-1]

3 ft + lanyard length or 1.5 x [OS-1]

lanyard length

Number of Required Drops

One [BS-4,

Two [NA-4

,

Three [AN-1,

Four [X-l

]

How Unit Tested

Without Failure

CA-5 , CS-1, NA-2, OS-1]

US-1]

FE-3, SW-1]

By itself (lanyard and/or belt) [BS-4, CA-5, CF-4 , CS-1, FE-3, SW-1]

Belt + Lanyard [AN-1, CF-4 , NA-2 , NI-1, x-i]

Belt + Pole Strap [CF-4, NA-4 , US-1]

Anchorage

Anchor- or toggle-bolt into which a snaphook is

snapped [most]

"I" or "L" beam around which a lanyard is tied off

[CS-1

]

Test Criteria (one or more of the following)

No breakage [all]

No release of test weight [all]

Keeper of snaphook not released [CS-1]

Peak force £_ 2500 lbf (body [X-l]

belt)

Peak force < 8750 lbf (body [X-l]

harness

)

Impact force <_ 50 percent of [OS-1]

tensile BS

Force on torso 700 lbf [MI-4]

Tongue buckle moving grommets [BS-4, NA-2

Ripping of belt >3 in [CS-1]

Follow-up tensile pull of 4000 [FE-3]

lbf without failure

The variability in tensile test requirements is seen

from the following:

- 75 -
Hardware and/or Fittings

- 4000 lbf [CF-2

,

CF-6

FE-3, NA-2

- 5000 lbf [MI-4]

5000 lbf (dee-rings) [AN-1, NA-2

- 50 percent proof load of

ultimate tensile strength up

to 2000 lbf

[BS-4]

Lanyard (Strength Requirements)

- 4000 lbf

- 5400 lbf (rope

)

[CF-2]

[CF-6, US-1

- 6000 lbf (rope

)

[MI-4]

- 9000 lbf ( strap) [US-1]

Lifeline

- 4000 lbf

- 5400 lbf

[CF-2]

[AN-1, CA-5

- 7000 lbf (aircraft [US-1]

cable)

Safety Lines

- 2000 lbf [OS-1]

Belt Buckles

- 2000 lbf (with no slippage) [MI-1]

- 2000 lbf (max. deform. < 1/64 in) [EE-1]

- 4000 lbf [AN-1, MI -4

US-1]

Snaphooks

- 1500 lbf (pole strap) [US-1]

- 1500 lbf (positioning line [AN-1]

straps)

- 5000 lbf (break, distort, or [AN-1, EE-1

release ] - 750 lbf :ceeper

)

side load on keeper [EE-1]

Body Belt, Body Harness

4000 lbf (body belt) [CF-2, FE-3

- 5000 lbf (harness

)

[MI-4]

10 000 lbf (webbing itself) [US-1]

, CS-1,

]

, US-1]

]

, CF-6

]

, NA-2,

/ US-1]

]

- 76 -
Fixed Anchorage

- 3400 lbf [AN-1, CF-6]

Since the test procedures and performance requirements

that now exist are so diverse and sometimes inadequately

described, it is suggested that fall-safety system

components be required to meet the performance criteria of

Table 11 when tested as described below.

3.7.1 Static Strength Tests

Although most fall-safety devices are primarily

intended to withstand a dynamic (impact) load in arresting a

fall, it is frequently more convenient and reliable to

determine their strength under static or quasi-static

conditions. Considering the materials and rates of loading

involved, strengths for dynamic and static loading are

probably comparable, and the results of static tests should

be acceptable [CF-9, NE-1] . Dynamic effects may be

significant when lanyards are tied-off around a beam [CS-3].

Static strength tests would usually be conducted by

applying force to the component with a testing machine. The

testing machine should meet the accuracy requirements of

ASTM Method E4 [AS-4] . Fixtures should be provided for the

testing machine so that the component being tested is

mounted in the same manner as it will be in use and so that

the method of applying the load closely simulates use

conditions. The load should be applied smoothly until

failure occurs. The maximum force applied during the test

is the strength value to be reported. Strain and/or

elongation measurements as a function of force may be

desirable during some tests when information in addition to

strength is being sought.

For some tests, particular care must be taken to insure

that the loading conditions and procedures insure validity

and repeatability of the results. Factors to be considered

include

:

(1) For lanyard tests, the tie-off must simulate the

worst-case anticipated in use as proposed by CSAO [CS3] and stipulated in the Canadian Safety Regulation

[CS-1] . It is suggested that tie-offs be made as

- 77 -
listed in Table 15. The same types of anchorages

should be used in testing lifelines.

(2) For consistency, all strength tests of lanyards,

ropes, etc. should be carried out in uniform

atmospheric conditions and on specimens that are in

temperature and humidity equilibrium with the test

environment. The specimens should be exposed to the

test environment for at least 24 hours prior to test.

It is suggested that preconditioning and testing be

carried out in the temperature ranges of 10 to 30°C (50

to 85°F) and at a relative humidity of 40 to 60

percent. It is noted, however, that Federal Test

Method Standard No. 191 [FE-2] calls for a temperature

of 21.1 + 1.1°C (70 + 2°F) and a relative humidity of

65+2 percent.

(3) Since the synthetic fibers generally have large

elongations before failure, the testing machine must

have a long stroke. For test specimens up to 1.8 m (6

ft) in length, a stroke of at least 0.9 m (3 ft) is

required

.

(4) Because of the large elongation and the use of

quasi-static data to predict dynamic performance, a testing speed of at least 0.1 m/min (4 in/min) , and

preferably 0.25 m/min (10 in/min) or more, should be

used

.

(5) The effective strength of a lineman's pole strap,

Class III system, is related to the geometry of its

use. Test fixtures such as those shown in Figure 10

are suggested where the major diameter of the mandrel

is 345 mm (13.5 in) and diameter of the rod loading the

strap is 13 mm (0.5 in).

(6) The fixturing shown in Figure 11 is suggested as

simulating use conditions for a body belt. The mandrel

should have an elliptical form with a major diameter of

345 mm (13.5 in) and a minor diameter of 265 mm (10.5

in) . This gives a circumference of 965 mm (38 in)

.

3.7.2 Elongation (Extensibility) Tests

The load vs. elongation (L/E) relationship for a lanyard type is used in predicting the force and

acceleration levels that will be generated under a variety

- 78 -
Table 15. Anchorages and anchor linkages to be used

when strength testing lanyards

Lanyard 1

Anchor End Length

,

Type Anchorage Type Connection

Linkage L to be Used ( a ) to be Made

^

Snaphook L < 6 ft A D

6 ft < L < 8 ft B E

L > 8 ft C E

Free End L < 6 ft A F

6 ft < L < 8 ft B G

L > 8 ft C £L

^ Where

:

A = eye bolt or the like

B = 3"x3"x3/8" angle iron

C = 10WF33 I-beam

D = snap onto eye bolt

E = loop lanyard around beam once and snap into line

F = tie bowline knot directly to a heavy-duty eye bolt

G = loop lanyard around beam once and tie off with bowline

- 79 -
SIDE HARNESS

Figure 10. A Possible Setup for Tensile Testing of

Linemen's Pole Straps

"D" RING ..

Figure 11. A Possible Setup for Tensile Testing of

Linemen's Pole Belts

- 80 -
of fall conditions. The data required to determine this

relationship can be obtained at the same time that the

static strength test is being made. For this purpose, it is

suggested that a lanyard of 1.8 m (6 ft) length with

snaphooks spliced onto each end be used. For test, the

snaphooks would attach to eyebolts as shown in Table 15.

When possible, it is desirable for the load and

elongation to be automatically plotted on an x-y recorder.

This can be readily done when the testing machine has an

electrical output proportional to load and an electrical

signal proportional to the motion of the moving head can be

obtained. In this case, the signal leads are connected to

the y and x axes of the recorder, respectively. The axes

are scaled to provide nearly full scale records for

anticipated maximum values, and the test is made. Care must

be taken to determine the zero elongation point to coincide

with the first indication of load.

Where autographic recording is not practical, data can

be obtained by observers simultaneously reading the load and

the elongation or position of the moving head. It is

suggested that at least 15 data points, including one at the

first indication of load, be taken to define the L/E curve.

Since the ends of the lanyard (snaphooks, thimbles, and

splices) will not have the same L/E characteristics as the

center (pure rope) section, the results of the above tests

will only represent the length of lanyard tested. However,

if a second set of elongation data for a center section of

the lanyard is taken, the L/E curve for any length of

lanyard can be calculated. This second set of data can be

obtained manually as described in [FE-2] , using a tape to

measure the change in length between two points on the

lanyard. A more convenient method when autographic

recording is used was developed during the study and is

described in Appendix A.

Using the extension of the entire lanyard, AL, the

relative extension of the pure rope section, AZ/Z and

defining the length of the lanyard of interest as A = L + p,

the relative extension of the new lanyard, AA/A

,

can be

found for any force, Fq , as follows:

AA = AL + A

P

But Ap = p AZ/Z

AA/A]

f

= AL/A

]

F

+ p/A(AA/A)]

p

(9)

i i i

- 81 -
where all quantities on the right hand side of Equation 9

are known by definition or experimental measurement. By

calculating a number of such values for various forces an

L/E curve for the new length lanyard can be described.

In conducting elongation tests, factors that must be

given consideration include:

(1) The initial length must be determined under

reproducible conditions. This is generally done by

applying a small load, frequently with weights, to

insure that the rope is straight. The load is

generally based upon the diameter of the rope; for

example [FE-2] calls for a load, in lbf , of 100 d , where "d" is the nominal rope diameter in inches

(approximately 0.7 d^ for force in newtons and diameter

in millimeters) . The procedure followed for this

report, and suggested for general use, was to condition

the lanyard with a 100 d^ lbf load, remove this load

and allow recovery for at least 30 minutes, and then

measure the length under a 22 N (5 lbf) load.

(2) The length of the entire lanyard should be

measured between the inside surfaces of the snaphooks.

(3) Pure rope values should not include sections of

the lanyard closer than 0.1 m (4 in) to a splice.

(4) If data is taken by an observer, care must be

taken to avoid injury from possible whip-like action of

the lanyard when it fails.

3.7.3 Dynamic (Drop) Tests

The ability of a lanyard, body belt, or other

components to withstand the force generated in arresting a

fall and to limit the acceleration to a tolerable level can

be determined through dynamic drop tests. Static tests are

easier to conduct, less subject to experimental variables,

and provide more information for each test, but the

prediction of dynamic performance from static tests has not

been completely verified.

Drop tests are frequently used as pass/fail

specification tests in which a given weight is allowed to

fall freely a specified distance before its fall is arrested

by the lanyard being tested. The lanyard would be judged to

- 82 -
pass the test, and hence indicate that similar lanyards are

acceptable for use, unless:

(1) one or more rope strands or hardware components

broke or deformed excessively;

(2) a peak force greater than specified was generated;

or

(3) a peak acceleration greater than specified was

generated

.

Tests must be made using both maximum and minimum

weights to check for (2) and (3) . The same tests would, of

course, test other components of a fall-safety system

involved (e.g., anchorages, containment devices, and

hardware) . Results from a series of drop tests of different

severity can be used to predict the performance of a lanyard

over a range of tests or use parameters.

A schematic diagram of a drop test is shown in Figure

12. In general either a load cell or accelerometer would be

used, but usually not both. A test is conducted as follows:

(1) The length of the lanyard is measured under a small load (5 lbf or 22 newtons is suggested as for

static tests) and recorded.

(2) The weight is raised to the desired drop point,

and the lanyard is connected to the anchorage and the

weight. The two eyebolts and the center of gravity of

the weight should be a vertical line. The free fall

distance is recorded.

(3) The instrumentation is adjusted and triggering

circuits are set.

(4) The weight is released by a quick release

mechanism that imparts no motion to the weight upon

release

.

(5) The peak force and/or acceleration indicated by

the instrumentation is recorded.

(6) When only force or acceleration has been measured,

the other is calculated from the relationship F = Ma

.

- 83 -
///#/,.

Figure 12. Schematic Diagram of a Drop Test

- 84 -
Factors that must be considered for this type of test

include

:

(1) Provision should be made to catch the weight in

case a component breaks.

(2) The test area should be enclosed to prevent

injuries to personnel in case of a component failure.

(3) The weight should not rotate or swing excessively.

If there is significant motion of this type, the test

should be voided.

(4) The supporting structure must be rigid so as not

to absorb significant energy.

(5) The geometry of the test weight is important when

testing pole straps, body belts, and other containment

devices. A possible test weight configuration is shown

in Figure 13. Possible setups for testing linemen's

pole straps and body belts are shown in Figures 14 and

15.

(oj The load cell can be mounted on the weight instead

of on the supporting structure. This is not

recommended because of problems with the leads and

possible damage to the load cell if a component breaks.

With the arrangement of Figure 12, the measured force

includes that required to accelerate the lanyard. This

effect is considered to be negligibly small.

(7) The length of a lanyard should be measured under

consistent load conditions. Five Ibf (22 N) is

suggested

.

(8) For strength tests, a worst case tie-off

condition, Table 15, should be used. Tests for

acceleration levels should use optimum tie-off

conditions

.

For pass/fail specification testing for strength, the

following tests are suggested:

(1) For Class III systems, a 115 kg (250 lb) mass with

a free fall of 1.2 m (4 ft)

(2) For Class V systems, a 136 kg (300 lb) mass with a free fall of 2.7 m (9 ft).

- 85 -
- 86 -
/

ANCHORAGE

/////// ///

HANDLE USED TO HOIST

TEST WEIGHT AND/OR

TO MAINTAIN BELT'S

POSITION ON WEIGHT

LOAD CELL

EYE BOLT

3/8 in STEEL CABLE

SPLICE OR CLAMP

SNAP HOOK

"D" RING

BODY BELT

Figure 14. A Possible Setup for Dynamic Testing

of Linemen's Body Belts

Figure- 15. A Possible Setup for Dynamic Testing of

Linemen's Body Straps.

- 87-
(3) For Class VI systems, a 160 kg (350 lb) mass with

a free fall of 2.7 m (9 ft)

.

For acceleration level testing, a 60 kg (130 lb) mass

should be allowed to fall the maximum possible free fall

distance anticipated for the lanyards' use. The peak

acceleration measured by an accelerometer or calculated from

force measurements should not exceed 2 a^X / Da ' where ^ax

is the allowable acceleration level for the class of system

being tested (Table 11) , Da is a contingency (safety)

factor (2 is suggested) , and the factor of 2 accounts for

the energy absorption of a human body compared to a rigid

mass

.

3.7.4 Electrical Tests

Existing documents [CF-4 , CF-8, EE-1, NA-1] include

dielectric and leakage current requirements for linemen's

fall-safety equipment. An AC dielectric test of 82 000 V/m

(25 000 V/ft) on dry components for three minutes without

visible deterioration and a leakage current of less than 1

mA with 3000 V AC imposed on electrodes 0.3m (1 ft) apart

are typical requirements. Procedures for testing dielectric

and leakage current properties of wet and dry rope are

contained in parts 1910.268 and 1926.959 of Code of Federal

Regulations, Title 29.

In making the electrical tests, it is important that

good electrical contact be made on the rope or strap under

test. This can be done with narrow strips of clean, heavyduty aluminum foil placed snugly about the test item. The

test length is the free space between the foil strips. This

arrangement is shown in Figure 16.

3.7.5 Other Tests

It is suggested that sunlight and weather resistance

tests be made by direct exposure to Florida weather

conditions for extended periods, up to two years, with

strength, extensibility and electrical property tests being

made at intervals. The use of a carbon-arc tester (e.g.

weatherometer ) is not recommended until correlation with

actual outdoor exposure tests can be shown.

- 88 -
Figure 16. Electric Contact Configuration for

Dielectric Testing of Ropes

- 89 -
All hardware components should be either inherently

corrosion resistant or made with a corrosion resistant

finish in accordance with Federal Test Methods QQ-P-416 or

QQ-Z-325, ASTM Methods A143 or A153, or Military

Specification MS 2204 2, 3 , or 6. These hardware components

should be exposed to a salt spray for 50 hours in accordance

with ASTM Method B117, and then be examined for corrosion

and tested for strength. Thimbles or other parts that are

bent during assembly should be tested after such bending to

detect possible chipping or cracking of protective coatings.

To determine whether strength and extensibility

deteriorate during storage in extreme environmental

conditions, samples of fibrous materials (lanyards,

lifelines, belts, straps, etc.) should be exposed to adverse

temperature and humidity conditions. It is suggested that

these storage tests include at least 200 hours at 80°C

(175°F), 10 percent relative humidity and 100 percent

relative humidity. The storage periods would be followed by

strength and elongation tests using normal testing

conditions

.

3.8 Prototype, Production Line, and Field Testing

There are, basically, three types of inspections that

must be performed on fall-safety equipment:

(1) Before any system or component is marketed,

prototype specimens must be tested to determine if

design features meet performance requirements. This

initial inspectional phase is called "prototype

testing .

(2) Since raw materials, workmanship and the

fabrication process vary with time, a production line's

output must be periodically sampled to ensure that

performance criteria continue to be met. This is

"quality control" or "production-line testing."

(3) When a fall-safety device is first put into

service and at regular intervals thereafter, it should

be carefully inspected for defects that could cause

unsatisfactory behavior or failure. This is called

"field inspection."

Prototype and production line testing are the

responsibility of the manufacturer or assembler of the

- 90 -
component or system. Field testing is the concern and

responsibility of the user and using organization.

3.8.1 Prototype Testing

During the design and development of new fall-safety

equipment, comprehensive analysis must be done to assure

adequate strength and energy absorbing properties. To

verify the design and analysis, tests should be conducted

upon custom-made, prototype models of the device. These

tests are frequently more comprehensive than subsequent

testing and may include the measurement of strains, etc. to

permit stress analysis, determination of load distribution,

and interactions between the various components and the

user. These tests are generally designed, conducted, and

evaluated by trained engineering personnel. Where

certification of a device is required, the results of such

tests should be submitted to the certifying agency for

review and evaluation.

Guidance on the quantity and selection of test

specimens, the assignment of measurement uncertainty values,

and judging the satisfactory or unsatisfactory nature of the

test results can be obtained from statistical handbooks,

e . g . [NA-3 ]

.

3.8.2 Production Line Testing

Production line testing at the proper level will

minimize the chance of faulty products being furnished

because of factors such as:

(1) variability of the materials and purchased

components

;

(2) variability in production line labor; and

(3) variability in the production and assembly

process

.

The testing program must be designed to continuously

monitor critical parameters such as strength, elongation or

energy absorption, and resistance to salt spray. Other

factors, such as weather and ultraviolet resistance, should

be determined for types or lots of materials.

- 91 -
Guidance on the method and rate of sampling can be

obtained from statistical handbooks , e.g. [NA-3], military

specifications, etc. Mil-Spec MIL-H-24460, "Harness,

Safety" [MI-4] recommends the following:

Units in the Units in

Production Lot Sample

£4 0 2

41 to 110 3

111 to 300 4

>300 5

Under this sampling procedure, the lot would be rejected if

any sample failed to meet the requirements of the test.

The ultimate responsibility for production line testing

rests with the manufacturer or assembler of the final

product, even though components have been tested by their

producers. Complete records of production line test

procedures and results should be available to the purchaser

and the regulatory agency.

A large purchaser of fall-safety equipment may also

decide co perform test samplings of delivered lots. This

process is independent of the manufacturer's test program

and might be considered part of a field test program.

3.8.3 Field Testing

In order to provide the best possible continuing

assurance that faulty fall-safety equipment is not being

used, two levels of field inspection are suggested. These

are

:

(1) A visual inspection by the user, supervisor, or

delegated inspector before each day's use, and

(2) A thorough inspection by a knowledgeable,

authorized person at some regular^ designated interval.

This may be a strictly visual inspection, but it could

also include some nondestructive test procedures. The

inspection date, inspector's name, and signature should

be recorded in a company log book along with the

results of each thorough inspection.

- 92 -
Any device found to have a serious defect should be

immediately removed from service. If the defect is not

remediable, the device must be discarded.

Miller and MSA (two manufacturers of safety equipment)

both put out well illustrated booklets giving inspection and

maintenance procedures. U.S. Steel makes available a slide

show on the care and maintenance of fall-safety equipment

and points out ten principal defects in fall-safety

equipment that a worker or inspector should be mindful of

:

(1) cuts or tears of any size

(2) abrasions

(3) burned or melted fibers

(4) molten metal burns or scars

(5) acid, alkali or other chemical burns

(6) dryness

(7) punctures

(8) tar or similar products that penetrate

in the fibers

and harden

(9) cracks in or distortions of hardware

(10) loss of flexibility or elasticity (in

and lifelines)

lanyards

In addition to these factors, the inspector should be

alert for:

(1) Sand and grit in a belt which can cause internal

breakage of fibers. If a fabric component is

excessively sandy, it should be inspected for fuzziness

of inner fibers. (Fuzziness on a rope lanyards'

exterior will occur with use but is not necessarily a sign that the lanyard is no longer satisfactory.

Fuzziness on inner fibers is stronger evidence that a lanyard has been weakened and should be replaced.)

[CG-2

]

(2) Deformed thimbles and buckle tongues and grommets.

Such deformation could be evidence of an unreported

shock load, perhaps from a "near miss." Normal wear on

thimbles, grommets, and buckles will not generally

cause significant deformation.

Toward the end of ensuring that these periodic

inspections are made and within the specified interval, each

system and/or major interchangeable or replaceable component

thereof should contain a permanently affixed tag on which

the next inspection date should be stamped after each

- 93 -
periodic inspection. If the item has a finite life

expectancy then the date by which the device or component

must be removed from service should also be indicated on the

inspection dating tag.

Unfortunately, according to the ARL tests performed for

U.S. Steel on well used and old devices, except for obvious

defects, the appearance of a belt and/or lanyard generally

bears little relationship to its performance under test.

Nondestructive field test methods are needed to sort out

those fall-arrest components which no longer meet breaking

strengths or energy-absorption requirements. These field

tests should not require either elaborate equipment or time.

Since nylon lanyards are relatively inexpensive, any test

that requires more than a few minutes of company time may

not prove cost effective since it could be less expensive to

replace the lanyard than to conduct the test.

A possible nondestructive field test method for

estimating the shock absorbing capability of a lanyard

involves a comparison of the extensibility of a lanyard at a load of 200 d^ lbf (1.4 d^ N) with its extensibility at a relatively large load, 15 kN or 3000 lbf for example. Such

a comparison is shown in Figure 17. There appears to be

some correlation of these two factors, and further

investigation of such a method for estimating energy

absorption capability should be considered.

In any event, daily inspection of fall-safety equipment

and periodic in-depth inspections should be part of every

company's safety program, and all outdated or rejected

devices should be disposed of so that they cannot be reused.

- 94 -
.6r—

.5

£ .4

o

o

o

to

o

_i

.3

.2

.1

0

• 1/2 in. WH., GOLD FIL. NYLON

5/8in.WH., GOLD FIL. NYLON

5/8 in. (OBS.) SPUN NYLON

A 9/16 in. SPUN NYLON

A

A

I 1

.01 .02 .03 .04 .05 .06 .07 .08 .09

AL/Ln (at 200d2

Ibf

)

.10

Figure 17. Correlation Between Lanyard Extensibility

at Two Loads..

- 95 -
4.0 Recommendations

Based upon the information gathered from the literature

search, site visits, and in-house testing that made up this

study, it is recommended that the factors given in this

section be considered in preparing a regulation governing

fall-safety equipment. For convenience, the recommendations

have been grouped as to whether they pertain to (1) design

and fabrication, (2) performance, (3) use, (4) testing, (5)

information to be provided, or (6) areas where additional

work is needed.

4.1 General Considerations

Some general considerations are:

(1) Each requirement of the regulation should involve

a consideration of the following factors:

safety of the user

reasonable anticipated worst-case usage, environmental

and storage factors

worker acceptance/convenience

worker efficiency

cost effectiveness (anticipated impact on worker

safety vs. cost)

technological feasibility

reliability under reasonable abuse

(2) To the degree that it is possible, the addressed

regulation should be of a performance nature.

(3) Any regulation should be written in both SI and

customary units. The intent to eventually convert to

metric units should be explicitly stated in the

regulation

(4) The classification of fall-safety systems into six

classes as proposed in this report should be adopted.

(5) If it is accepted that a lineman's pole strap and

belt are used as a positioning device, backrest, and

tool carrier, then Class III devices may be excluded

from 29 CFR 1910.132a. In this case, 29 CFR 1910. 260g

and 29 CFR 1926.959 should be revised.

- 96 -
4.2 Design and Fabrication

Recommendations relating to the design and fabrication

of fall-safety systems and components include:

(1) Contingency factors should be used to allow for

anticipated degradation with time and/or usage.

(2) Manila rope and leather should be prohibited from

use as a’ load-bearing member of any class of fallsafety system. These materials can, however, be used

in non-load bearing applications such as padding, tags,

and tool pouches.

(3) The use of hard- or soft-lay ropes in lanyards

should be discouraged.

(4) Although the acceleration imparted to the falling

worker is related to the ratio of the free fall

distance to the lanyard length, longer falls are more

likely to cause injury from contact with other objects.

Lanyard length should therefore be such as to limit

free fall distance to the values shown in Table 9.

(3) Lanyards for use with a body harness (e.g. Class

VI systems) should have snaphooks spliced to both ends

and be limited to 1.8 m (6 ft) in length.

(6) To minimize abrasion of lines or straps, thimbles

or rollers (sleeves) should be used wherever a synthetic fiber, load-bearing line or strap is coupled

to metal, load-bearing hardware and the two parts are

free to move with respect to each other.

(7) All stranded lanyard and lifeline splices should

be made with at least four full tucks. Tapered splices

beyond the four-tuck limit can be encouraged but need

not be required. Splices made with clamping devices,

such as those clamps used on wire cables, can be used

if the component so constructed passes all requisite

tests. All stranded endings, whether free or spliced

should be seized, whipped, taped, seared, glued or

otherwise treated to prevent unraveling of the ending

for the life of the lanyard.

(8) Splices should be seized or tightened so that

thimbles cannot be hand turned within the splice.

- 97 -
(9)

A rope lanyard can be spliced around the loadbearing webbing of a body belt by means of a direct

splice (no thimble) or to a load-bearing dee-ring.

Webbing lanyards used on belts without dee-rings should

terminate in a sewn eye of suitable size to accommodate

only (10) the width of the belt.

Any load-bearing or potential load-bearing rope or

strap passing over a shearing edge (e.g., flange or

roof ledge) should be abrasion resistant or padded at

the shearing edge. Use of a sheath that slides up and

down on a line, so as to provide a cushion at the

required point, may be permitted so long as the sheath

does not degrade the operating characteristics of the

line nor significantly abrade the line when moved along

it

(11) Adjustable lanyards should be permitted, but only

if their maximum length is not greater than six feet

(See Section 4.2 (4)).

(12) All synthetic fiber lanyards and lifelines should

contain UV inhibitors where UV degradation is known to

significantly affect the fiber in question.

(13) Uylon ropes and strapping should be stabilized

against the undesirable effect of moisture. Such

stabilization is especially in order with regard to

lifelines used in conjunction with Class II or IV

systems where dimensional changes brought upon by water

absorption could affect the operational characteristics

of a rope grab or controlled-descent device.

(14) Belt sizing should conform to conventional sizing

as follows:

Belt Sizes To Fit Waist Range

Small (S)

Medium (M)

Large (L)

Extra Large (XL)

81 to 102 cm (32 to 40 in)

91 to 112 cm (36 to 44 in)

102 to 122 cm (40 to 48 in)

112 to 132 cm (44 to 52 in)

(15)

Class IV and V body belt load-bearing webbings

should be at least 50 mm (2 in) and no more than 100 mm

(4 in) wide with a manufacturing tolerance of 2 mm

(1/16 in)

- 98 -
(16) No more than four tool loops should be permitted

per belt, and these loops should not be placed in the

front half of the belt.

(17) The cushion part of the lineman's body belt

should

(a) contain no exposed rivets on the inside;

(b) be at least three inches in width;

(c) be at least 4 mm (5/32 in) thick;

(d) have pocket tabs that extend at least one and

one-half inches down and three inches back of the

inside of the circle of each dee-ring for riveting

of plier or tool pockets. On shifting dee-ring

belts, this measurement for pocket tabs should be

taken when the dee-ring section is centered.

(18) The inner core of the pole strap should be of a different color than both outer surface layers (to flag

excessive wear) . The thickness of the surface layers

should comprise, in total, less than 1/4 of the belt

tmckness (exclusive of padding) .

(19) A dee-ring intended for use with a lanyard should

not be located outside the 4 to 8 o'clock zone of a

belt. If dee-rings are located outside this zone they

should be clearly labeled as not safe for use with a lanyard. A belt intended for use with a directly

(soft) coupled lanyard should have a loop placed on the

belt to receive the lanyard. This loop should contain

the strength member of the belt (not the padding, if

any) and should restrain the lanyard from locating

itself outside the 4 to 8 o'clock zone.

(20) Dee-ring spacing (heel-to-heel ) on lineman's belts

should be as in [EE-1]

(21) The use of a liner (sleeve) between dee-rings and

belt webbing should be required to prevent wear between

these components. These sleeves can be made of any

durable, smooth surfaced, metal or synthetic material.

(22) It is suggested that grommets be used on all

tongue buckle holes, and that they be inserted by

spreading the belt weave—not by punching. A similar

- 99 -
suggestion is made for rivets used to attach tags or

labels onto strapping. These need not be requirements,

however, as long as the belt or strap is capable of

passing the prerequisite drop and/or tensile test.

(23) Tongue buckle holes for body belts and lineman's

pole straps should be only large enough to accommodate

the tongue and should be placed no closer than 25 mm

(one inch) apart and no further than 38 mm (1-1/2 in)

apart

(24) The construction of a body harness system with

regard to strap and harness dimensioning, strength, and

location should be equivalent to that for a militarytype parachute. These harnesses should be designed to

distribute the impact forces, due to an arrested fall,

over the buttocks, waist, chest, and shoulders.

(25) The coupling dee-ring of a body harness should be

located between the shoulder blades and high up on the

back. Alternatively, four riser straps, each coming

off a shoulder strap as in conventional parachute

systems, shall be joined into a dee-ring above the

wearer 1 s head level. This dee will then serve as a coupling point for the associated lanyard.

(26) Two size, adjustable body harnesses might be made

available: 60-90 kg (130-200 lb) and 80-115 kg (180-

250 lb). Alternatively, a single adjustable size could

be employed that fits 60-115 kg (130-250 lb) users.

(27) Body harnesses should be designed to avoid undue

stresses in the crotch area (resulting from arrested

falls) even if these stresses will not cause serious

injuries

(28) All hardware components (snaps, dees, sleeves,

carabiniers, thimbles, and buckles) and anchorages

should be smooth and without sharp or pointed edges

where they contact a fiber line. Snaphooks should be

round-nosed

(29) All metal components (hardware, anchorages, rope

grabs, etc.) should be of a corrosion-resistant

material or, if corrodible metal, should be made with a corrosion-resistant finish as specified in:

Federal Specification - QQ-P-416 (Cd plating)

QQ-Z-325 (Zn)

- 100 -
ASTM Method - A-165-7 1 (Cu)

A-153-73 (Zn)

Military Specification- MS 2204 2, 3, 6

(30) Snaphooks or carabiniers and their mating

anchorages (e.g. anchor bolts or eye hooks) should be

of such configuration and dimension as to eliminate the

possibility of rollout. Unless specifically designed

and so designated, snaphooks and carabiniers shall not

be coupled to one another.

(31) If thimbles are to be required in eye splices,

their inside diameters should be not less than 1.75 x the rope diameter (a larger ratio is preferred)

Thimbles should have deep, smooth ridges to prevent

separation of rope from thimble. Thimbles, other than

round-shaped (e.g. pear-shaped), that meet these

requirements should be acceptable.

(32) Where metal thimbles with corrosion-resistant

platings are used, they should be mounted so as to be

able to pass the salt-spray test after mounting (to

insure that the mounting process does not chip or crack

the deposited coating). It is recommended, therefore,

that thimbles be plated in the open position so they

need only be pressed closed to complete a linkage.

(33) The nose of a snaphook should override the keeper

by at least 3 mm (1/8 in)

(34) The construction of an anchorage should,

preferably, be such as to retain the strength of the

lines that will be secured to it. Towards this end,

eye bolt type anchorages are recommended.

(35) Portable anchorages should be readily

transportable, easy to attach and remove, and should

also withstand reasonable abuse.

(36) Whatever body container device is used in

conjunction with a tether line (Class I system) should

be designed so that it couples to the tether line above

the worker's center-of-gravity

(37) The body-restraint component of a Class Ila system

should be so designed as to maintain the worker in an

upright position so that he may be readily extracted

through a narrow orifice.

- 101 -
(38) The body-restraint component of a Class Ila system

should be so designed as to render it impossible for a worker to become separated from the system except by

deliberate effort on his part.

(39) A winch-type mechanism used as part of a Class Ila

safety system should be so geared as to be operable by

one man, even where loads of 113 to 136 kg (250 to 300

lb) are involved.

(40) A Class Ila system should be designed so as to

minimize potential jolts or impacts to users. Such a system should limit the descent rate to about 4.6 m/s

(15 ft/s). The ascent rate can be ungoverned, however.

The hoist should contain an easily-activated locking

(braking) mechanism.

(41) Class lib systems, when designed as a rescue

device, should be capable of descent at a slow constant

speed that will not injure the worker when it is

stopped.

(42) If a rope grab controlled descent device is to be

used with a lanyard then the device should be lockable

so chat it will not ride down its line during nonactive use intervals. This "locking" action must be

readily effected; yet deliberate repositioning should

also be easily accomplished.

(43) A locked device should not travel down a dropline

under dead-weight load of 1.3 kN (300 lbf) until it is

manually released.

4 . 3 Performance

The following performance criteria and related factors

are suggested:

(1) All load-bearing components of a fall-safety

system should have the demonstrated capability to

withstand, without failure, the worst-case peak forces

that they can be expected to encounter. Environmental

factors should be considered.

(2) Components that can be separated should have their

pertinent performance characteristics determined

independently. Even where a belt or harness is spliced

- 102 -
directly to a lanyard, the two should be tested

separately

(3) Components of fall-safety systems should meet the

performance criteria set forth in Table 16.

(4) When a component (e.g. anchorage or lifeline) may

be used by two or more persons simultaneously, the

minimum strength values should be multiplied by the

maximum number of users. Horizontal lifelines must

also consider geometric effects.

(5) The principal peak force is equal to or greater

than 2Ma max/D a , where a max is the peak deceleration

limit for the highest class system the component is

intended for use with and D a is the established g n'

contingency factor for that system. The factor of 2 is

introduced to adjust the impact force to that force a real person (as opposed to a rigid mass) would

experience

(6) Droplines intended for use with Class II or IV

systems should also satisfy the criterion:

BSmln = 100 Mgn /P

BS

where Pbs is the percent of breaking strength shown in

Table 12.

(7) Bounce (secondary impacts) for worst-case falls

(as measured with extreme value weights) should not be

in excess of 4.5 kN (1000 lbf)

(8) Where electrical hazards may be present, fibrous

components should meet dielectric criteria of Section

3.6.2 [AP-2]

(9) To allow for degradation of the extensibility of

lanyard materials with time and use, a contingency

factor for acceleration, , of two is suggested.

(10) A fall-safety system or system component should be

considered to have failed a strength test if any of the

following occur below the specified load:

(a) breaking of one or more strands of a lanyard

or lifeline;

- 103 -
Table

16.

Performance

Criteria

for

Fall

-Safety

Equipment

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(b) slipping of one or more strands from a

splice

(c) breaking or cracking of any hardware

component

(d) deformation of any hardware component

sufficient to release a keeper or belt tongue or

to allow a hook to uncouple from an anchor point;

(e) a buckle tongue cutting through a belt

webbing for more than 25 mm (1 inch)

(f) a friction buckle belt slipping more than 25

mm (1 inch)

(g) body belt elongating more than 100 mm (4 in)

(h) in a drop test, a secondary force peak

exceeding 4.5 kN (1000 lbf) or 50 percent of

primary peak, whichever is least; or

(i) in a drop test, lanyard elongation of more

than 0.9 m (3 ft) with a weight equal to or less

than 115 kg (250 lb) or more than 1.2 m (4 ft)

with a weight greater than 136 kg (300 lb)

(11) For all test requirements involving a binary-type

result (i.e., fail or pass, as in a drop test) all

units comprising a sample (for a sample size of six or

less) should pass the test in order for the system or

component to remain an active candidate for

certification, or for a production lot to be accepted.

(12) For tests involving continuous results (e.g. loadcell tensile test, or dielectric current measurement) a device, design or lot is acceptable if:

(a) the average sample value for the measured

quantity is in the acceptable range;

(b) for prototype evaluation all test specimens

give acceptable responses or for production line

testing fewer than an established percentage (e.g.

five percent) of the test specimens give

unsatisfactory readings; and

- 105 -
(c) no single unsatisfactory test unit deviates

from acceptability by more than 10 percent.

(13) Assume a test is properly conducted, there are two

types of statistical inference errors possible. These

can

:

(a) reject a design or lot although it does in

fact meet all requirements (an "error of the first

kind" or a "Type I error") or

(b) accept a design or lot although it does not

meet all requirements (an "error of the second

kind" or a "Type II error"). Since the

introduction of a defective component into the

market could convert a "near miss" into a tragedy,

it is imperative that Type II errors be guarded

against in all statistical analyses and by proper

sampling design.

(14) Lanyards and lifelines used with Class II or III

systems should not show significant creep after 8 hours

exposure to loads of up to 1.3 kN (300 lb)

.

Preconditioning of a line by loading it with, say 1.3

kN (300 lb), for one hour prior to the creep test

should be permitted. Permanent line extension

(measured under a nominal load) resulting from the

preconditioning should not exceed 5 percent.

(15) The dropline that the device travels along should

be impervious to moisture to the degree that system

behavior is not altered significantly by changes in

temperature or relative humidity or upon being wetted.

(16)

The extensibility of droplines should not exceed

the values given in Table 17 to minimize the chance of

a falling worker striking another object or surface.

Table 17. Recommended Maximum Permissible

drop Line Extensibilities (a)

Load

4.5 kN (1000 lbf

)

8.9 kN (2000)

13.4 kN (3000)

17.8 kN (4000)

Percent Extens ion

6

8

10

14

- 106 -
(17) All load-bearing snaphooks, carabiniers, deerings, buckle frames and other load-bearing hardware

components should be proof-loaded to a substantial

fraction of the required system breaking strength. For

hardware destined for use in Class IV and V systems

17.8 kN (4000 lbf) , and for Class VI hardware 33.4 kN

(7500 lbf) are the tentatively suggested proof loads.

(18) All hardware components should pass a 50-hour salt

spray test as per ASTM B117-73.

(19) Snaphooks and carabiniers should not open at 11 N

(2.5 lbf) load, but should begin to open by a force of

18 N (4 lbf) applied to the keeper latch. The use of

double-locking snaps and self-locking carabiniers

should be encouraged, but their requirement in fallsafety equipment may be premature.

(20) Snaphook and carabinier keeper latches should

withstand 3.4 kN (750 lbf) of applied side load without

suffering a permanent deformation of more than 0.4 mm

(1/64 in)

(21) Sudden impact forces experienced by a winch should

not cause the system to unlock or to unwind at a rate

exceeding 3 m (10 ft) per second. In any event, the

shock should not be transferred directly to the turning

crank in such a manner that a winch operator could

suffer a significant injury.

(22) Repeated operation of an ascending/descending

system under 113 kg (250 lb) loading should not

significantly abrade the lifeline or cause significant

wear to the mechanical components of the system.

(23) The mechanical action of rope grabs and shock

absorbers upon impaction should not be affected to any

significant degree by the presence of moisture, ice,

dirt, grit, or greasy or oily surface contaminants.

(24) An unlocked rope grab should lock upon impact. It

shall be capable of locking in response to a 59 kg (130

lb) man falling 0.3 m (1 ft) into the device as well as

from a 113 kg (250 lb) man falling up to 1.8 m (6 ft)

(depending on the free fall limits imposed by the

system) . A locked rope grab should remain locked upon

impaction

- 107 -
(25) A rope grab or shock absorber, upon impaction,

should activate and arrest the fall within 0.9m (3 ft)

of travel along the dropline (exclusive of dropline

elongation). Rope grab slippage, lanyard extension

and/or tear webbing extension should not, in total,

exceed 0.9 m (3 ft) for any worst-case fall.

(26) Each rope grab test sample should show only

nominal wear after sliding over 100 000 linear feet of

cable in both the up and down directions.

(27) Each rope grab test sample should be moved up and

down a dropline 10 000 times over a distance of not

less than one foot for each movement without

significantly abrading the line. This could be

quantified by the breaking strength of the dropline

after these tests being reduced from the new line

values by less than an average of 10 percent. On the

last 1000 operations, each test sample should correctly

activate without a single failure.

4.4 Use

Recommendations pertaining to the use of fall-safety

equipment include the following:

(1) All fall-safety system components should be

visually inspected by the user or by an authorized

company inspector before each day's use. Every six

months (more frequently for severe usage) each fallsafety system and/or component should be thoroughly

examined by an authorized inspector. Items to be so

inspected include:

(a) lanyards, lifelines, tether lines;

(b) body belts, safety belts;

(c) body and chest harnesses;

(d) pole straps;

(e) rope grabs and shock absorbers.

The inspection date, inspector's name, inspection

findings and the inspector's initials alongside these

findings should be recorded in a company log and should

be available for review upon legitimate request. Each

system, or component that can be separated from the

system, should have a permanent tag affixed to it, and

the date of the next inspection and the life expectancy

expiration date (if any) should be stamped on this tag.

Any system component that exceeds the life expectancy

limit, whatever its apparent condition, should be

discarded

.

- 108 -
(2) Any component of a fall-safety system with one or

more of the following defects should be withdrawn from

service immediately:

(a) cuts or tears of any size

(b) abrasions

(c) burned or melted fibers

(d) molten metal burns or scars

(e) acid, alkali, or other chemical burns

(f) dryness

(g) punctures

(h) tar or similar products that penetrate and harden

in the fibers

(i) cracks in or distortions of hardware

(j) loss of flexibility or elasticity

(k) fuzziness on inner fibers

(l) deformed thimbles, buckle tongues, or grommets

(m) mold

(n) hackles or loose rope strands

(o) permanent deformation or elongation

(p) faulty snaphook retainer springs

(q) alterations or additions that could impair

functioning or efficiency.

(jy If possible, the methods used to couple a lifeline

to an anchorage and/or to a lanyard should minimize

reduction in system strength. If a coupling method is

used that is known to reduce system strength (e.g. use

of knots) , then the system (or affected component)

strength may have to be increased so as to stay within

acceptable limits.

(4) Workers requiring the services of fall-safety

equipment frequently wear heavy gloves in the course of

their duties. Frequently such workers are called upon

to perform their duties at ambient temperatures at

which fine manipulations become difficult. The design

of fall-safety equipment, especially rope grabs, shock

absorbers, controlled descent devices, and the like,

must take into account the potential awkwardness of

their users.

(5) Lanyard pouches should state explicitly that they

should not be used for extended storage of strandedtype lanyards or lifelines since stranded rope may

hackle and be weakened by this method of storage.

Rather stranded rope should be carefully coiled or

- 109 -
stored in the form of a "hank" as is commonly worn by

construction/steel workers.

(6) A lanyard should, by design, or by the method of

securing to an anchorage or lifeline, never permit a free fall of more than 1.8m (6 ft) nor a total fall

distance (free fall + lanyard elongation + rope grab or

shock absorber slippage) greater than 2.7 m (9 ft).

(7) The use of two-part lanyards, as described in

Section 3.8, should be encouraged as a substitute for

the long, free-ended lanyards commonly used by steel

workers

.

(8) Synthetic and natural fiber lanyards in,

essentially, daily use should be discarded after four

years of service, or sooner, if observed defects

warrant such action. Natural fiber lanyards more than

five years old and synthetic fiber lanyards more than

eight years old, independent of use level, should be

removed from service.

(9) Class I tether lines in frequent use should be

discarded at or before their sixth service year. No

tether line used or unused should be retained beyond

the 8th anniversary of its date of manufacture. For

Class I belts/harnesses, these respective retirement

dates should be seven and ten years.

(10) Since Class Ila lines are frequently loaded and

may be abraded by repeated ups and downs, their life

expectancy should be set at four years. Any Class Ila

line more than four years old should be discarded. The

control mechanism need be removed from service only if

it fails a visual inspection or a nondestructive test.

(11) Any fiber lanyard impacted by a force considered

to be in excess of its recommended working load limit

(obtained by multiplying BS x PBS ) should be discarded.

Fall parameters that are estimated to be capable of

generating these limiting forces are presented in Table

18. Alternatively, severity of impact force can be

estimated from distortion of thimbles, permanent line

elongation, or other distortions. When in doubt, the

device should be discarded.

(12) A lifeline should be removed from service if

subjected to shock loading more than 1.5 times that

- 110 -
Table

18.

Fall

Parameter

Limits

Above

Which

Impacted

Lanyards

Should

be

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impact force implied by the drop parameters given in

Table 18, since such an impaction would probably not

reduce the strength of the line.

(13) A body belt or harness that has been loaded (or is

suspected of having been loaded) to more than 70

percent of its rated strength should be removed from

service. Visual evidence of impact damage is also good

cause for replacement of a belt.

(14) If an N+N half-hitch (rope grab) is used to secure

a lanyard to a lifeline N should be 2 or 3, preferably

3.

(15) When a lanyard or lifeline must pass over a jagged, rough surface or a shearing edge, some means

should be provided to protect the line. A sheath or

saddle-type padding may be used. Alternatively, the

line should be of such construction as to resist

abrasion or shear forces.

(16) When possible, a lanyard should secure to an

anchorage or lifeline attached to an independent,

secure walk or work surface or structural member of

appropriate strength. In the case of scaffolding work,

a lanyard must secure to an independent surface, or

better yet, to an independently secured lifeline. The

coupling point should, preferably, be above the

worker's waist level, but it must be such that a free

fall of more than six feet is not possible.

(17) Tether lines should be of fixed length and should

have nominal extensibility. These lines should be as

short as possible and should not be longer than 10 ft

under most circumstances.

(18) A minimum of 12 ft of dropline should always be

allowed below the securing point of a rope grab or

shock absorber. For added security, a knot should be

made at the end of the dropline.

(19) A Class VI lanyard should be no longer than 6 ft

in length and should contain an eye-spliced snaphook

fitting at its anchor end. These criteria are to

preclude its being tied off around a beam. The anchor

snap should secure directly to an anchor bolt.

(20) A lineman's pole strap should never be used as

a lanyard.

- 112 -
4.5 Testing

! I'm

The following are recommendations regarding testing of

fall-safety equipment:

(1) Equipment test criteria must measure quantities

that actually bear on the anticipated behavior of a

system when put to its intended use.

(2) For drop tests, a rigid weight should be used

instead of a sandbag.

(3) Prototype sample lots should consist of at least

six units of each item to be certified.

(4) In addition to regular sampling of each distinct

unit, samples should be taken whenever raw material

suppliers, subcontractors, or personnel changes occur.

(5) Proof-loading, dielectric, and corrosionresistance testing can be performed by secondary

suppliers. The responsibility for the validity of

these tests, however, should reside with the

manufacturer of the ultimate product.

(6) If a manufacturer has more than one factory that

produces a given item one prototype sample will suffice

for all, but each factory should determine production

line (quality control) sampling rates independently of

the remaining factories.

(7) All test samples should be new and previously

unused

(8) The sample size for Class VI systems should be

augmented since these devices tend to be used when the

danger of a fall is greater. '

(9) The entire test drop apparatus should be fenced or

caged off during tests to avoid injuries in cases of

failure. All test personnel should wear safety hats

and glasses and/or should keep clear of the test area

during each drop.

(10) If body belts are similarly constructed, except

for length of belt and dee-ring location, it is

recommended that only one size (preferably M) be tested

in order to certificate all size belts. In the case of

- 113 -
body (or chest) harnesses, only one or two sizes are

indicated. In this case, evaluation of each size

harness is recommended.

(11) Each potential load-bearing component of a fallsafety system that can be interchanged, that is sold

separately, or for which a unique test is prescribed,

must be so tested. However, only medium size body

belts in a line containing various size belts need be

prototype tested.

(12) If a Class II ascent or descent control device or

a Class IV rope grab or shock absorber is permanently

affixed to the lanyard so that if either becomes

defective both must be discarded then lanyard and

device should be tested as a unit.

(13) When measuring the strength of a Class Ila system,

the lifting mechanism and the line should be tested as

a unit

.

(14) A Class lib dropline and an associated controlled

descent device should be tested as a unit.

(±5) Prototype units must in every way be equivalent to

units that will eventually be marketed. If the design

of a unit is modified in a way that could conceivably

modify its intended behavior under load or impact, the

modified unit should be "prototype" tested.

(16) A test weight can be similar in construction to

that form given in CSA Z249.1 [CS-1] but preferably

with an elliptical core. A torso-type weight or

weights can be used to statistically or dynamically

test body belts and/or harnesses.

(17) Multiple drop testing should not be used as a means of evaluating the aging of lanyards.

(18) In making dynamic (drop) tests of lanyards, a number of new, untested lanyards are selected. Half of

them are drop tested for strength and the remaining

half for their energy-absorbing capability.

(19) For either static or dynamic strength testing the

anticipated worst-case tie-off configuration should be

used. For energy absorption testing optimum tie-off

procedures should be followed.

- 114 -
(20) A tumble-type test could be employed to evaluate

the permanency of knots and splices.

(21) Testing and/or preconditioning of all load-bearing

natural and synthetic fiber components should be done

within ambient ranges of 10 to 30°C (50 to 85°F) and 40

to 60 percent relative humidity. The test procedure

should also determine the strength and, where

applicable, energy absorption at anticipated operatingtemperature extremes. An operating temperature range

of -18 to 38°C (0 to 100°F) would appear to be

reasonable

(22) When a lanyard of specific material, type, size

and design is manufactured in a range of lengths, the

range should be specified by the manufacturer. Six

samples of the minimum length in the range and six

samples of the maximum length in the range, should be

tested

(23) In cases where the lanyard length is adjustable,

12 samples of that lanyard should be submitted for

test, six of which should be tested at minimum lanyard

length.

(24) Friction buckles should be strength tested under

anticipated usage conditions such as grease, moisture,

and ice.

(25) A drop test for a Class Ila system could consist

of dropping a rigid test weight of 136 kg (300 lb) 0.6

m (2 ft) into a winch-line combination. An effective

line length of 6 ft should be used. The impact force

generated by such a drop should not cause a system

failure (as defined in item 10 of Section 4.3).

(26) Each pole strap size to be certified should be

tested at both outermost and innermost tongue buckle

hole settings.

(27) Testing of a harness (static, dynamic, force or

acceleration level) requires the services of a torso

shaped dummy or weight. For dynamic strength testing,

allow a 160 kg (350 lb) torso-shaped dummy with harness

snugly affixed to free fall 2.7 m (9 ft) into a

lanyard. For dynamic testing of a lanyard's energyabsorbing ability a 60 kg (130 lb) weight is allowed to

free fall 1.8 m (6 ft).

- 115 -
4.6 Information to be Furnished

Information and instructions that should accompany a

fall-safety system or component throughout its lifetime

should be permanently printed, embossed, or affixed to the

item it pertains to. In addition each fall-safety system or

purchasable component may also require written information

or instructions that need not (or, due to their

extensiveness, cannot) permanently accompany the equipment.

This type of literature should be attached to the equipment

so that the unpacker cannot avoid seeing it. The recipient

should keep this literature on file to be read or reviewed

by appropriate personnel. Recommendations pertaining to

such labels and literature information are given below:

(1) Advertisement- type literature should state the

environmental and usage limitations of such systems

where such limitations are not self-evident.

(2) All prototype certification test data should be

kept on hand by the manufacturer and made available to

legitimate requesters. This data should be available a minimum of seven years beyond the date at which the

item is taken off sale.

(3) The manufacturer (or assembler) of fall-safety

equipment should keep on hand all required productionline test results. These results should be made

available upon written request.

(4) The maker of each component should be readily

determined from unique labeling, markings, or tagging

done by the manufacturer. "Labeling" can be

accomplished using indelible print, embossing, or

imprinting or by means of affixed cloth, leather,

metal, or plastic labels containing the requisite

information. Labeling can also be accomplished by the

use of unique markers or trademarks. However, when

labeling is done it should be readily legible through

the lifetime of the unit and the label should not

impair the operational characteristics of the equipment

it is affixed to.

(5) Instructions and information that should accompany

fall-safety equipment are listed below. In some cases,

these listings can be included on labels; in other

cases, the information is too lengthy or the device too

small to conveniently display the requisite writing.

- 116 -
(a) Acceptable and preferred methods of use,

including preferred tie-off and coupling

procedures and recommended system components

mates

(b) Methods of abuse to be avoided, including

application limits.

(c) Preferred and unsatisfactory use and storage

environments

(d) Recommended field inspection procedure and

schedule

(e) Recommended cleaning and maintenance

procedures, if any.

(f) The breaking strength of the system or

component when used in the normal manner.

(6) All fibrous items (lanyards, lifelines, belts,

straps, and harnesses) should be labeled with the

following

(a) manufacturer's name, city, and state;

(b) model number of component;

(c) date of manufacture or assembly;

(d) Recommended maximum life expectancy or date

by which equipment should be replaced;

(e) Regulation against which a device is

certified; and

(f) Tensile strength and/or highest fall-safety

system class for which the equipment is certified.

(7) Each component should be labeled with the

environmental conditions which will adversely affect

its performance. Possible deleterious environments

include temperature, moisture, grease, oil, dirt, sand,

and organic, or other liquids or vapors.

(8) Since components for Class I sytems are not

designed to withstand any significant impact, these

- 117 -
should be clearly labeled "Certified for Class I Use

Only .

(9) To insure that lanyards are not tied-off leaving

excessive length, any lanyard longer than six feet

should have a permanent mark at the anchorage end (or

at both ends if the device is symmetric) , indicating

the six-foot point from snaphook or belt splice.

(10) Lifelines should state on them the maximum number

of persons that can tie onto them at one time and the

highest class system for which they are certified.

(11) Body belts and harnesses should state the waist

dimensions that they are designed to be used with.

(12) Body belts should state that the associated

lanyard should be positioned within the 4 to 8 o'clock

region at the small of the back. Where a body belt

contains more than one dee-ring, all dee-rings outside

the 4 to 8 o'clock region must be noted as

unsatisfactory as tie-off points for the lanyard.

(13) If conditions such as grease, moisture, ice, etc.

reduce the strength of a belt with friction buckle

below an acceptable level, then this fact must be

stated on the belt tag and on all accompanying

literature and advertisements.

(14) Snaphooks, carabiniers, dee-rings, and the like

should be color, letter, or number coded so that only

compatible components are linked together.

(15) Where a friction buckle is required to be double

passed for the system to achieve its rated strength or

integrity, this fact must be clearly printed on the

belt.

(16) Except where a carabinier is self-closing, it must

be stated in advertisements, on the device itself and

in literature accompanying the device that the rated

strength of the device depends on the loop being

completed by the user.

(17) Load bearing hardware should be clearly labeled

with the proof load value they were subjected to, if

proof loading is required or was performed optionally

by the manufacturer.

- 118 -
(18) When they are unidirectional, mechanical rope

grabs and shock absorbers that fit onto lifelines

should have an arrow and the word "UP" clearly and

legibly printed on them.

(19) Where a rope grab or shock absorber will, upon

impaction, move down a dropline some distance before

locking, the mechanical device should state the minimum

amount of dropline that must always be present below

the working position of the device.

(20) Where a shock absorber is intended for use by a

specific weight range population, it should so state on

the device.

4.7 Suggested Areas for Additional Work

In conducting this study, a number of areas were noted

where additional or better validated information would

assist in specifying, producing, selecting, and using fallsafety equipment. Suggestions of areas for further work

include the following:

(1) A definitive study should be conducted to

determine the feasibility and limitations of using

static load/elongation tests to predict the performance

of fall-safety equipment under dynamic (impact)

conditions

(2) It is recommended that manufacturers and users

periodically subject fall-safety equipment to

destructive tests for the purpose of increasing the

understanding of equipment characteristics as functions

of use, age, and environment. Such sampling could be

coordinated by the manufacturer or by a Federal or

private organization.

(3) Contingency (safety) factors for use with various

fall-safety components should be evaluated and updated

as new materials become available, the accident data

base is developed and data regarding the extensibility

of synthetic-fiber ropes with age and/or use becomes

available

(4) Some means of nondestructively strength testing

anchorages, lanyards, and lifelines should be

developed

- 119 -
(5) Kern mantel rope, a material that has become

popular in mountaineering, should be evaluated for

possible use with fall-safety systems.

(6) The effects of light, moisture, heat, age, and

usage level on body belts, lanyards, and lineman's

equipment as a function of exposure time should be

studied

.

(7) Samples of fall-arrest components with known use

histories should be collected and tested to determine

how strength and extensibility vary with usage, age,

and ambient factors.

(8) A data base for arrested fall case histories is

needed to show how safe such devices are and what are

the problems with their use.

(9) How much impact energy is absorbed by belts and

harnesses relative to lanyards should be evaluated and

how this information might affect regulations for

safety equipment should be determined.

(10) The correlation between lanyard type, composition,

diameter, and tie-off procedure on system strength

should be determined when a lanyard is tied-off around

an L-beam, I-beam, or wide flange for static and

dynamic loading conditions.

(11) The shock-absorbing and strength properties of

Class V systems where the lanyard is spliced directly

to the body belt should be correlated with systems

where coupling is by means of dee-ring and snaphook.

(12) The maximum safe descent and/or arresting speeds

for both conscious and unconscious descenders should be

evaluated

.

(13) Tests should be made to determine the correlation

between lanyard or lifeline length and line strength

and extensibility.

(14) The need for and cost-effectiveness of stabilizing

nylon ropes against moisture should be investigated.

(15) Modifications to fall-safety equipment regulations

that would be required by the entry of women into

- 120 -
trades that require fall-safety equipment should be

determined

(16) An extensive comparative analysis should be made

of new and used safety equipment relative to both

strength and extensibility.

(17) The effects of preboiling nylon lanyards in terms

of their work- to-break ability should be studied.

(18) The psychological and physiological effects of the

suspension of humans as a function of body-containment

system and duration of suspension should be studied.

(19) A realistic test for abrasion resistance of

fibrous components should be developed.

- 121 -
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- 12 *-
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- 129 -
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- 131 -
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- 132 -
APPENDIX A

Experimental Program

A . 1 Introduction

A. 1.1 Purpose

During the course of this study, it became evident that

there was insufficient data available on the performance

characteristics of components of fall-safety systems, in

particular as pertains to energy absorption. In addition,

there seemed to be no generally accepted, convenient method

for using test data to predict the performance of fallsafety equipment under use conditions. It was therefore

decided to conduct a limited experimental program to

demonstrate how the needed data could be readily obtained,

to show how such data could be used to predict performance

and to develop some data on more commonly used items. The

work was primarily on rope type lanyards although some tests

were made on web straps, body belts, and pole straps. The

results of these tests were compared to other data that was

available

A. 1.2 Scope

This experimental work was supplemental to principal

aspects of the study and was not intended to be

comprehensive. Strength and load/elongation data were

gathered from 12 types of lanyards, and the data were

processed to predict the performance of lanyards of various

lengths under a variety of fall conditions. Tables and

graphs were prepared to present the data in a readily usable

form. A mathematical model was developed to assist in

processing the test results. The best methods and

analytical methods used should be useful in developing a

more adequate data base on the strength and energy absorbing

properties of fall-safety equipment.

AA. 2 Rationale

A. 2.1 Rationale for Testing Components Separately

To date most standards and regulations concerned with

fall-safety equipment require that body belts or harnesses

be tested together with their lanyards. In their 1974

report [CS-3] , however, the Construction Safety Association

of Ontario recommends that these components be tested

independently of each other. The basic reasons given in

[CS-3] are:

(1) In actual usage lanyards are replaced far more

frequently than belts. It is possible for the owner of

the belt, in replacing his lanyard, to choose one

having a different length or material and, by doing so,

to create a completely different fall arresting system

for which no certification exists. If, on the other

hand, the belt and lanyard are tested and certified

independently of each other then his new lanyard will,

regardless of length and material, be a certified

product

.

(2) The lanyard, being in essence a large spring and

shock absorber, substantially affects the load

transmitted to the safety belt during a fall arrest.

Variations in lanyard size, length and material produce

significant differences in belt loadings. Thus, when

testing belts and lanyards together, the load

experienced by the belt is controlled by whatever

lanyard the manufacturer wishes to use. There was, in

effect, no common standard that a belt had to meet. A

change to separate component tests ensures that all

belts are subjected to the same test criteria.

(3) Conversely, the loading of the lanyard is

influenced to a degree by the belt and its degree of

stretch during a fall arrest. The belt material,

width, thickness, and stitching vary from product to

product, introducing a variable into the lanyard load.

Separate tests for belts and lanyards removes this

variable

.

In addition to the above, the following factors support

the separate testing of fall-safety system components:

A-2
(1) It is impractical, if not impossible, to insist

that a user continue to purchase lanyards with as good

or better energy absorbing properties than the

discarded ones. Similarly it is unreasonable to expect

a user to throw out a good body belt or harness because

its mate has become defective.

(2) Depending on particular use, a fall-arrest system

may or may not secure to an anchorage through an

intermediate lifeline. The basic system, therefore,

cannot depend on the presence of the lifeline for

meeting performance criteria.

(3) Similarly a fall-arrest system may secure to a variety of anchorages some having modest energy

absorbing ability while others may be quite rigid.

Again the system must meet fall impact force criteria

set down in the regulation independent of anchorage.

(4) A worker should be able to combine only worst-case

certified components and still come up with a satisfactory system.

(5) Simpler test procedures can be used when

components are tested separately.

(6) Separate testing will allow manufacturers to sell

separate components each of which can be certified as

meeting OSHA requirements.

If the premise that all of the energy of an arrested

fall will be absorbed by the lanyard and the body of the

falling person is accepted, the systems will be

conservatively rated, i.e., the accident victim will be less

severely impacted, as a result of energy absorbed by other

components. This provides an additional safety factor for

the worker. We have calculated that various combinations of

body belts and rigid masses having a 1.8 m (6 ft) fall

arrested by a 1.8 m (6 ft) lanyards of 1/2 inch nylon will

be exposed to impact forces 5 to 25 percent lower than

predicted for the lanyard alone. These values were based

upon the difference in energy absorbed by a belt lanyard

combination and lanyard alone at 8.9 kN (2000 lbf) and 13.3

kN ( 3 0 0 0 lbf). Since these would be relatively severe

impacts, the actual reduction in impact force due to the

belt would probably be 5 to 10 percent.

A -3
The effect of testing the components separately and

assuming that all energy absorption is by the lanyard is

seen to introduce a modest additional margin of safety for

the worker. This, in addition to the factors listed above,

seem to justify this approach to testing fall-safety

equipment

.

A. 2. 2 Rationale for Using Static Test Results

to Predict Impact Parameters

In the interest of worker safety, the use of data

gathered from static tests should be used to predict dynamic

performance only if it can be assured that the predictions

will not increase the danger to the worker. Such increased

danger could come from the probability of equipment failure

or from higher impact loads being imposed upon a fall

victim.

With regard to the effect of loading rate on breaking

strength of fibrous materials, the literature generally

indicates higher strength for impact loading [BR-1, KO-1].

Impact strength 20 to 25 percent greater than static

strength was reported in [PA-1]. According to [BO-3] an

increase in strain rate from 2 percent per minute to 200

percent per minute was accompanied by more than 25 percent

increase in breaking strength. This trend towards higher

breaking strengths associated with higher loading rates was

confirmed by a representative of the Cordage Institute for

ropes commonly used in construction of lanyards.

On the other hand, the evidence is that extensibility

decreases with increasing loading rates [BO-3, BR-1, KO-1,

PA-1, SM-1 ] . A 1961 experimental study on tubular rayon

webbing [BO-3] showed a decrease in extensibility at

intermediate loads of about 10 and 20 percent as the

elongation rate was increased from 2 percent per minute to

20 and 200 percent per minute. Newman and Wheeler [NE-1]

concluded that, for 7/16 inch nylon rope, "the energy

required to produce a given stretch in nylon specimens was

greater for impact loading than for static loading."

Support for the use of static data to predict dynamic

performance is found in several places. For example, a 1972

study on braided and twisted ropes [AA-1] concluded that

"velocity of action or impact timing generally seems to have

little effect on the action of nylon rope within cycle

limits of from 7 seconds to 60 seconds." Dr. Bralin [BR-1]

A -4
concludes that "static testing of webbing material gives a good indication of the dynamic properties up to strain rates

of 40 ft/s." Dr. Frank McCrackin of the Polymer Division,

NBS , in a private communication, expressed the opinion that,

at the impact velocities involved, our static-based

predictions are probably a satisfactory representation of

the dynamic L/E behavior for the ropes in question.

Newman and Wheeler [NE-1] concludes that:

(1) the load-extension curve for impact loading is

different from the curve for static loading and lies

above it, and,

(2) "... the energy computed from static-test loadstretch data may also be used to obtain a safe estimate

of the impact energy capacity of a nylon rope of the

length used in these tests."

Motor Vehicle Safety Standard No. 209 [CF-9] calls for

the static testing of (adult) lap/shoulder seat belts

(including most associated, load-bearing hardware) . This

promulgation of this standard implies either that:

(1) DoT is satisfied that the static test requirements

of this standard are valid indicators of the

performance of seat belts in impact, or

(2) The extensive research on auto occupant protective

systems (overwhelming compared to the research done on

fall-safety systems) has yet to uncover evidence that

static tests do not provide valid measures of the

dynamic behavior of restraint equipment.

In actual comparisons impact force peaks generated in

our study from static L/E data (for lanyards alone and with

body belts) were typically greater by from 0 to 30% than

equivalent peak data from manufacturer drop tests. This

observation is contrary to expectations.

In the course of the present work, reasonable agreement

has been obtained in two specific cases between statically

obtained L/E curves and oscillographic traces with

comparable components under dynamic conditions. There is

obviously a requirement to confirm such tests with a wide

variety of cases. However, because of the relatively good

agreement of the comparative records obtained in the project

at hand, it is tentatively proposed to accept the general

equivalence of static-based predictions and dynamic

measurement of arrested fall parameters pending further

investigation of this issue.
A. 3 Experimental Procedures

The static tensile tests were primarily intended to

determine breaking strengths and load/elongation data for

lanyards and body belts. Therefore, the test procedures

differed in some respects from test methods of the Cordage

Institute [CG-5] and Federal Test Method Standard No. 191

[ FE-2 ] . The procedures used may be relevant to other rope

testing situations.

A flow diagram of the testing and analysis procedure is

shown in Figure A-l.

A. 3.1 Test Specimens

A. 3.1.1 Lanyards

The lanyards tested included new ones donated by

manufacturers, old ones donated by users, and a group

assembled from miscellaneous parts provided by

manufacturers. The specimens were made from spun and

filament nylon, polyester, polypropylene, and manila. The

nominal diameter of the rope specimens varied from 13 mm

(0.5 in) to 19 mm (0.75 in).

All lanyards had snaphooks spliced or sewn on at both

ends. Most lanyards tested were of stranded rope; however,

about a dozen were of strap nylon. All rope lanyards had

deeply grooved plastic or metal thimbles inserted into the

splice eyes. For all but a few 3/8 in and 3/4 in ropelanyards tested, inner thimble diameters were about 1 in.

All rope splices contained at least four full tucks except

for two ropes that had only three tucks.

These specimens differ from conventional rope-test

samples in that: (1) they contained snaphooks at both ends,

(2) the thimbles had one inch diameters rather than

equivalent rope test pins or mandrels ranging from twice the

rope diameter to 15 cm (6 in) , (3) most splices contained

four full tucks while rope test samples frequently are made

with tapered four or six tuck splices.

About a dozen new and used strap lanyards were also

tested. These also had snaphooks at each end but these were

secured to the lanyard by means of stitched splices.

A6
\

OBTAIN BELT /

\OR LANYARD j

3

PRECONDITION l CHARACTERIZE

BELT OR LANYARD,

SET UP BELT

OR LANYARD IN STATIC TESTIN6

MACHINE

RECORD

ORIGINAL .LENGTH

SET UP APPARATUS TO TEST 30 iH. PURE

ROPE SECTION

RECORD L/E

CURVE FOR LANYARD

RECORD L/E

OATA FOR PURE ROPE

SECTION I

I

Cp(p(p

RECORD L/E

CURVE FOR BELT

FIT L/E DATA'

TO A 3rd DEGREE

POLYNOMIAL

¥

1

CHECK

GOODNESS

OF FIT

SELECT LANYARD

L LENGTHS, FALL

HEIGHTS l WEIGHTS

INPUT POLYNOMIAL

COEFFICIENTS

{bun model)

OUTPUT IMPACT

FORCES, g'$ l ELONGATION AS

FUNCTIONS OF TIME FOR

SELECTED LANYARD

LENGTHS. FALL HEIGHTS AND WEIGHTS

COMPARE OUR L/E,

BREAKING STRENGTH

OATA AND PREDICTED

PEAK FORCES AND DURATIONS TO DATA FROM OTHER SOURCES

Figure A-l. Flow Diagram of Experimental Procedures

A-7
Although a few of these had leather inserts most contained

no sleeves.

As a result of these lanyard configurations, most

lanyards tested (that did not exhibit hardware failures)

broke at or in their splice zones.

Most lanyards were about 1.5 m (5 ft) in length

(bearing to bearing), although a few were approximately 1.8

m (6 ft) in length.

A. 3. 1.2 Body Belts

All six body belt test specimens were unused belts

donated by various manufacturers.

Tongue buckle belts tested were buckled at the fourth

hole in from the tip of the belt. Friction buckles were

fastened so as to leave approximately 10 to 12.5 cm (4 to 5

in) extended beyond the buckle after double passing the

belt.

A. 3. 2 Testing Apparatus

The tests were conducted using a horizontal ropetesting machine located at the National Bureau of Standards.

This machine has a capacity of 100 000 lbf (450 kN) , but its

lowest range of 10 000 lbf full scale (about 45 kN) was used

for all tests. The load reading dial has markings at 50 lbf

intervals and can generally be read to about + 5 lbf. The

dial was equipped with a pointer follower system that

provided an electrical signal corresponding to the dial

reading. The testing machine had been calibrated in

accordance with ASTM Method E4-72 shortly prior to this

program and found to have the errors shown in Table A-l.

The load is applied by a hydraulic piston having a maximum

stroke of about 0.9m (36= in) . The rate of motion of the

piston varies under load, but rates of 13 to 16.5 cm/min (5

to 6.5 in/min) were used for these tests.

The movement of the piston controlled jaw of the

testing machine, and hence the elongation of the lanyard was

sensed by a potentiometer-type extensometer attached to the

bed of the machine and the movable jaw. The electrical

output of this extensometer was connected directly to the X

axis of an X-Y recorder.
Table A-l. Calibration of Rope Testing Machine

Scale Range (0 - 10000 lbf)

Machine Reading (lbf) Error (%)

1000 -0.42

2000 '3' CN O • 1

3000 -0.56

4000 -0.34

5000 -0.42

6000 -0.45

7000 -0.32

8000 i o • 9000 i o o 10000 -0.86

(a) This calibration was performed May 6,

1975 in accordance with ASTM Method E4-72.

Note that a negative error indicated that

the machine reading is less than the

applied load.

A-9
The potent iometer-type extensometer measured the total,

bearing to bearing, elongation of the lanyard. In order to

adjust this data to represent the total elongation of

lanyards of other length and to compare to data on rope

performance from other sources, the unit elongation of the

center, pure rope portion was desired. Initially this

center section elongation was measured visually using a technique similar to that used by rope engineers [FE-2].

The experimental setup used here is pictured in Figure

A-2. A rubber band y/as looped several times over one of the

circles marking off the 30 inch section. This was looped so

as to be snug but not cutting. A measuring tape was

fastened to this band by sliding it between about half of

the loops and taping it back on itself. The other end of

the tape was brought down towards the other marked circle

and tied with elastic thread to an anchorage point so as to

keep it taut. Masking tape loops were loosely placed over

the measuring tape-rope pair to facilitate reading of the 30

inch mark with respect to the tape rulings. Readings were

taken at predetermined load increments, but this was an

inconvenient method and readings were inadvertently missed.

A more satisfactory method for measuring the center

section elongation utilized an "incremental extensometer"

developed at NBS to provide automated measurements for these

tests. This instrument, pictured in Figure A-3, consists of

a tape with narrow metallic strips deposited perpendicular

to its length at precise intervals. The tape passes through

a slot in an insulating block and under two small "finger"

contacts. As each metallic strip passes under the fingers,

an electrical circuit is closed and the resulting electrical

signal is used to place a pip on the load/elongation curve

being generated for the total lanyard length. An example of

the resulting curve is shown in Figure A-4 . These extensometers (about a dozen was fabricated at

the NBS shops) worked quite well although several were

broken when ropes or hardware destructed. As is evident

from their design, these extensometers were made for use

with ropes; nevertheless, they function equally well with

strap lanyards. The need to rotate these devices about the

rope axis occasionally, as stretched ropes unwound, remained

as problematic for these automated tests, however, as when

measuring tapes were used.

The electrical signals from the pointer follower (load)

and potentiometer-type extensometer were connected to a

A -10
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A- 11

(Pure

Rope)

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A -12

conventional X-Y recorder. The signal from the incremental

extensometer was connected and adjusted to put a small

offset onto the load signal. The recorder has a span

adjustment for each axis that permits nearly full scale for

any anticipated load or elongation.

A. 3. 3 Lanyard Tests

%

A record sheet for a lanyard test is shown in Figure

Rope testing procedures [FE-2] call for preconditioning

of test samples in a standard atmosphere, typically for 72

hours, preceding the test. However, since a conditioning

chamber was not readily available, the specimens for these

tests were stored at about 21°C (70°F) and 50 + 10 percent

relative humidity. The effect of this lack of standardized

preconditioning is not known. The temperature effects were

probably small, particularly for nylon, but there is some

evidence [DU-3, DU-4, TU-1] that nylon and manila are

weakened and polyester is strengthened by exposure to high

humidity.

Each lanyard specimen was prepared for test in the

following way:

(1) One snaphook was fastened onto a crane hook and

was tensed by means of a 5 lb weight (suspended from

the other snaphook) for about one minute. During this

time a bearing- to-bearing length was measured. This

step was to determine the effect of step 2 on the

lanyard length.

2

(2) After removing the 5 lb load a 200 d lbf load was

suspended from the lanyard. (Conventionally, the

diameter (d) „of a rope is supposed to be determined

with a 200 d weight in place.) The "200 d^" value for

strap lanyards was determined by converting to crosssectional area, i.e.,

200 d

2

(lbf) = - (16)

where A, the cross-sectional area, is determined from

the width and thickness for strap lanyards. Suspension

time for each 200 d^ load was at least 5 minutes in

order to condition the, tensed rope. The length of each

lanyard under a 200 d

z load was obtained.

A-14
Figure A-5. Record Sheet for Lanyard Test

SAMPLE » ; SPLICED ; TAGGED ; BROKEN ; DATE BROKEN

TYPE DEVICE - Rope ( ), Strap ( ), Adjustable Rope ( ), Other ( ), describe

BASIC LANYARD PROPERTIES : Composition

Filament /Spun

Color , Lay

IF ROPE: Diameter, Given in Obs. in

# Strands ; # Ply 9

IF STRAP: Pitch 9

Width in; Thickness . Rope/Strap Cross-Sectional Area

SPLICES/THIMBLES/SNAP-HOOKS

LEFT (Moving Side) RIGHT (Stationary Side ) # Tucks

Splicer

Thimble Compo/. .

Manufacturer

Snap Manuf ' rer . .

. Ident. on Snap...

Final Snap Dis- .

position

in2

LANYARD ORIGIN t) ORIGINAL CONDITION (as received] : Donated by , Date Received at NBS

Length of Service (by user)

Type of Service Seen

Condition of Lanyard as Received

Rope/Strap/Webbing Manufacturer

Conments Accompanying Device

PRECONDITIONING OF TIE LANYARD : Original Snap-to-Snap Length (Lanyard wt with 5 lb)

2 200d ^ lbf. Weight Added to Lanyard (>1 min.)

Snap-to-Snap Length of Lanyard + Conditioning wt

Final Pre-Test Lanyard Length, Snap-to-Snap, after >S minute

'Relaxation' Period (Lanyard wtd with S lbs) (L) Increase in Length Due to Preconditioning

STATIC TENSILE TEST RESULTS: Date of Test ; APPROXIMATE SPEED OF PULL i S"/Min

Length of Free-Standing Rope Test Zone (£) ^

Method Used in Measuring Extension of this Zone Breaking Load Ibf Conments

Where Failure Occurred

Final Free-Standing Section (At) (A l/l)

Final Snap-to-Snap Length (L+aL) (AL/L)

Ratio of Above Ratios .

ADDITIONAL COMMENTS

in;

lb; in;

in;

in.

A- 15
The observed diameter each rope lanyard was also

obtained with the 200 d weight in place. Some

disagreements between given and observed rope diameters

were found, almost invariably involving used, spunnylon lanyards. Observed values were used in

subsequent analyses.

2

(3) The 200 d weight was removed and the lanyard left

in an unloaded state. It was soon observed that there

was still significant contraction of some lanyards

after 5 minutes. This rest interval was therefore

increased to 30 minutes or longer. After this rest

interval each conditioned lanyard was loaded with a 5

lb weight and its new length, L, obtained. Relative

lanyard extension (Al/L) values for each load-extension

curve were calculated using this L value.

(4) While the lanyard was loaded with a 5 lb weight

for the second time, a 30-inch, free-standing,

centrally-located rope section was marked off on the

lightly stressed lanyard and the spine of the lanyard

(if it was made of stranded rope) was delineated.

After removing the 5 lb weight (for the second time)

,

the lanyard was mounted in the tensile testing machine

so as to keep its spine straight.

(5) A sample to be pulled was mounted between the

machine jaws by securing each snaphook to a mating

eyebolt. The jaws were originally set at some spacing

less than L (so the lanyard would not be strained

during mounting) and the lanyard length was then

adjusted to L by manually increasing the jaw spacing.

The X-Y recorder was then set and checked for a (0, 0)

setting

.

(6) For central section extension (A£) measurements,

the original position of the measuring tape with regard

to the 30-inch mark on the lanyard was noted before the

test was begun. Alternatively, if central section

measurements were automatic, the extensometer tape was

set so that the contacts rested on a metallic strip

(note the origin peak in the L/E curve presented in

Figure A-3) at the inception of the test pull.

A typical data sheet obtained during an early run when

the tape measure method was being used to measure Al vs. F

values is represented in Table A-2, To obtain AL values

A -16
Table A-2. Typical Data for Manually Obtained

Lanyard-Central-Section L/E Measurement

Sample #14, 1/2 in Dacron Lanyard

Load Reading ^ Extension

0 lbf 39 1/16 in 0 in

100 37 1/8 1.9

200 36 1/2 2.6

300 35 7/8 3.2

400 35 3/8 3.4

500 35 4.1

600 34 1/2 4.6

700 33 7/8 5.2

800 33 1/4 5.8

900 32 1/2 6 .

1000 31 5/8 7.4

1200 30 1/2 8.6

1400 28 3/4 10.3

1600 27 1/2 11.6

1800 26 3/4 12.3

2000 26 1/8 12.9

2500 24 5/8 14.4

3000 23 1/4 15.8

3470 Sudden rope slippage caused

measuring tape to move with

regard to its zero position

stopped measurements.

Original snap-to-snap length, 5 lb weight, 63 in

Length with 50 lb (200 d2 wt) for >1 min, 65 3/4 in

Removed 50 lb and waited for >5 min

Final length (L) with 5 lb weight, 63 1/16 in

a Due to the mounting configuration of the tape measure

in this run the rope appears to be contracting when, in

fact, it is being stretched. Test specimen extensions

were obtained by taking the absolute magnitude of the

differences between the first and subsequent readings.

A-17
from "readings" each reading was subtracted from the initial

length (39-1/16 in).

With the specimen and extensometers installed and

adjusted to the proper initial position and the recorder set

to (0, 0) , the loading control value of the testing machine

was an amount that had been predetermined to produce a head

motion of about 15 cm (6 in) per minute. When the measuring

tape was used to measure center section elongation, the

machine operator called out "read" signals to the tape

observer. The test continued until one or more rope strands

broke or disengaged from a splice, or snaphook failed so

that the lanyard was released, or a stitched splice opened

to release a strap lanyard. A typical load/elongation curve

is shown in Figure A-6 and center section extension data are

presented in Table A-2. Data using the incremental

extensometer is shown in Figure A-4.

A. 3. 4 Body Belt Tests

As with lanyards, the body belt specimens were not

exposed to a special preconditioning environment. The

general test procedures were the same as for lanyards except

for the method of measuring belt length, the mounting in the

machine, and the use of only the potentiometer type

extensometer

.

The method of measuring the belt length is shown in

Figure A-7 . The heavy metal mandrel was used as a spacer

and also as a weight to tense the belt. The same mandrel

was used as a test fixture as shown in Figure A-8. In the

test setup, the dee-ring of the belt is attached to a heavy

hook clamped in the jaw of the testing machine. The deering used was the one furtherest from the buckle. Tongue

buckle belts were buckled at the fourth hole in from the tip

of the belt. Friction buckles were fastened so as to leave

10 to 12.5 cm (4 to 5 inches) beyond the buckle after double

passing the belt.

After mounting the specimen in the testing machine, the

movable jaw was spaced to give the same length, L, as during

the pretest measurement. The X-Y recorder was adjusted to

(0, 0) at this point. The loading control value of the

machine was then opened to provide a head motion of about 15

cm (6 in) per minute. The test was terminated when the belt

broke or uncoupled from either end constraint. Such failure

occurred due to:

A-18
Figure

A-6.

Load-Elongation

Curve

for

9/16

inch

New

Spun

Nylon

Lanyard
Figure A-7. Length -Measurement Configuration for Body Belts

A -20
Tensile

test

con f

i

gu

rn ti

on

for

bo

civ

belt?
(1) webbing breaking;

(2) a dee-ring splitting or deforming to release the

hook;

(3) a tongue tearing completely through the belt

webbing; and/or

(4) a belt end sliding completely through a friction

buckle

.

Typical load vs. elongation curves for tongue and

friction buckle belts are shown in Figures A-9 and A-10

respectively

.

A-22
I

j

I

A- 2 3

dA
LOAD

(KIPs)

Figure A-10. Load-Elongation Curve for a Friction

Buckle Belt

A-24-
A. 4 Data Analysis

The objective of these tests was to provide static test

data that could be used to predict the performance of fallsafety systems, in particular lanyards and lanyard body belt

combinations, under impact loading conditions such as might

be involved in arresting a fall. Such predictions should be

possible for all reasonable combinations of fall distance,

lanyard length, and worker weight. The data analysis

techniques used for this purpose are described below.

A. 4.1 Reduction of Experimental Data

In order for our data to be readily used in the

computer model, third degree polynomial curves were fitted

to the load vs. elongation data for the total lanyard and

the pure rope center section. This was done by computer

using least square techniques. The total lanyard data was

taken from the recorded curve at frequent load intervals.

The pure rope data was taken from the recorded curves at

equal elongation intervals indicated by the pips. Figure A4, or directly from the dat$ taken visually by the observer

using the measuring tape technique. Table A-2. The

resulting equation had the form

Load = A + BAL + CAL2 + DAL3

where AL = elongation; and A, B, C, D = coefficients

obtained from the curve fitting process.

Equations of this form were obtained for lanyards

several lengths of possible interest by using the

relationship

,

AA

t AL

A F . A F . l l + F . l

of

where A = length of lanyard of interest

L = length of lanyard tested

£ = length of pure rope (center) section, and

P = A - L

The output from the computer program using relative

elongation, AA/A, and load as inputs included:

A- 2 5
(1) the coefficients A, B, C, and D;

( 2 ^ predicted (curve) values of load for each

elongation entry;

(3) the differences between the experimental and

predicted (curve) values of load (residuals)

;

(4) the standard deviations for these quantities;

(5) the total lanyard extension, AA and

(6) the instantaneous lanyard length, A + AA.

An example of the computer output is shown in Tables A3 (a , b, and c ) . Since the load sustained by the lanyard at zero

elongation is, by definition, zero, the zeroth order

coefficient (A) should be zero. Although this was not

generally the case, an analysis weighting the zero load

point (0, 0) by 100 changed the average computed peak force

and acceleration values by less than one percent (less than

3 percent maximum) and the average peak duration values by

less than two percent (less than five percent maximum)

.

These differences are considered to be within acceptable

limits and not warranting the introduction of a heavily

weighted (0, 0) point.

Figures A-ll and A-12 show the average load vs.

elongation curves for 13 lanyard types and their pure rope

(center) sections respectively. The curves can be

identified as follows

:

Curve 201 9/16 inch used spun nylon

Curve 202 9/16 inch new spun nylon

Curve 203 1/2 inch filament nylon

Curve 204 5/8 inch filament nylon

Curve 205 3/4 inch filament nylon

Curve 206 1/2 inch gold filament nylon ( Curve 207 1/2 inch gold filament nylon ( Curve 208 5/8 inch gold filament nylon

Curve 209 1/2 inch single-ply polyester

Curve 210 1/2 inch three-ply polyester

Curve 211 1/2 inch polypropylene

Curve 212 5/8 inch polypropylene

Curve 213 3/4 inch manila

The prediction of the response of any length

to various loading conditions would be straightforward if

full lanyards and pure rope sections had the same response.

Unfortunately, this is not the case, and, contrary to

expectations, the percent elongation of the pure rope

sections was generally less than that for the full lanyard

at any given load.

A-26
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44

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•H

o*

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XI

rtf E-r

rtf •H£OC

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X>ao

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CM

'< ') z z Z I c o u otr z >- c x — e: < LJ c c - a U L_ U — C L < C — Q

:: » > 7 _ c C 2

C. = \ a r-

<N t #n I i —

ir

—

*c

m

<r lp a a

H

— ’ co in - r O <N N

CO r*

—

<r IT —— HD I < — — f Ci/ r a rv (v C IT O

<N

a ^ ^ u"

—I c* r.r

i/ iT

a

cr c> in

r o n j — r* r t - <t c 3- — I - - i*

r\

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C if a a < vJU : 1

>- -1 2 r

u*

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lx

lx) CQ5C

yj

A “28 ! ! I
Table

3c.

Typical

Output

from

a

Third

Degree

Polynomial

Fit

of

a

L/E

Data

j O'

1 c o

1

i

1 c 'r>

1 o

1

1 1/ o c if r- X r- o — 1/ if >c if r* X — < rv — o <

— if

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IT if < c X a. -e < c. o X c r, o X — X — r

- X a X <S X c if r- rr c c a if r- o — lT c rs

1/ o < — C Tv ( -C fS a X r* a o if — n4 L rs rv — rs c 3

u. o < r- rs if rv c X O' X X o c X X cr — IX J X < m c X 1

-i r* — r- rc J* c X X fN (S < m r\ c r* c a — a X — if .

• - if rs X r* -c — 0“ v/ c X X >C n a a o X X X 1/ ! o _ I*' <*\ rs <x n X T rs l — r m rs. i — - rv c 1 1 1 1. 1 1 l l 1

• *

i

j

l j !

r~ a CS rx r

1 X X < X 1

; < <\ rv if- — r*~ rv rv X rs fv if < H IT o- a rs <*• X c r* < 1 — rv fv. C X — X < C c <T r' X X X O' e rv rv o X c*\ X

LT X if O' d“ u* rs X — — O' rs — c X — iX <• <. o X

X \S f\ rx O’. rv a — < cr c < rv r*. a o \f — >c c 1 c 1/ < X c if U" X C* a X o X if rv C; >c IT < pv — ro c rv c

C X r- _ r*. rv o m c —. rs C X (N. •c c (+ X rr __ c

u _ r, a < — < rs cc X X < C rx rx rT x X C (X rT fVx X — 1 z if — — — — 1 — — — l l

1 — — — 1

i —

U- 1 1 I i 1 J

j

! i z Q: 1 c 1

i

if > i !‘

!

<S z C c c C c c c c c c c c c r C c c c c c: C c c c

r c o C c c o c c c c c o c c c c c c c o c c c !

i C c c c c c c c c c c c c c c c c c c c c c c c

l, c c Ci r c: c r o c c c c c c c c c c. c c c c c c ,

i

. -

c. c r c a CD c a c c o o c o c o o c c c o c c o

' c u

c** c c. c C) c (_ c c c c c LI cv c c c c: c c Cl c c o ! 0 < c c c c c c c c c c c c c c c c c c c c c c c c i

|

lT -C — >C

lT < — -C

O' f\ X* >C M

r* o c»

O' — X

>0 <X <X rn O C?

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r- C

rv rg

rs rs ri r*.

rx rs. ro rn

• • 1 •

o c

cc o OOXO

X O' C — fX rT X

ro r cc a: o

-c x x rv. <

X Ch rg X.

o x o

x c\ rs

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r-' o >c rs

r a

l c

r S

Ci

c:

l/1

c c

c c

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— t m cf it a o

rs rs rsi rs.

c ( f ( r r c r r t r c rccrr

f> -* r c r r t r ( t C c C C ( i

(

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|

^ -2 9

i
LORD

(KIPS)

No. 400 i|(i COOOlfcr- CwAflTf, (.lUPHir CONTHCUS COMI'OKA’ION IMIMAU'

Figure A-ll. Load/Relative Extension Curves Obtained for 13

Lanyard Types

^ -30
LORD

(KIPS)

70%

No 400 *ni ROf f 0«5'*»C UOAPHIC CdNTBOLS COBfORATtON BU'tAlO

Figure A-12. Load/Relative Extension Curves Obtained for 13

Lanyard Types-- Center Rope Sections

A -31
Figure A-13 shows results that were in good agreement while

Figure A-14 shows considerable variation between specimens

of the same type.

A. 4. 2 Computations Using Analytical Model

In order to predict the performance of fall-safety

systems under impact conditions, forces, accelerations,

elongations, and velocities were computed as a function of

time after impact for a variety of lanyard lengths, test

weights (rigid masses) and free fall distances. The times

at which these factors were computed were themselves

determined by a feedback type internal routine and averaged

approximately 0.01 s. Peak values were estimated using

still finer time gradations; nevertheless, this time scale

"graininess" generated slight additional uncertainties in

computed peak values. The magnitudes of these peak value

errors (induced by time graininess) are estimated to be less

than 1/2 percent.

An effort was made to extend the versatility of our

computerized model to complete (body belt plus lanyard)

fall-arrest systems. This was an attempt to ascertain the

contributions of body belt to various critical arrested fall

parameters. In order to simulate the behavior of lanyardbody belt systems the elongation of each belt at specified

loads was added to the appropriate lanyard elongation at the

same loads. Note that the L/E data used here were obtained

from lanyards similar to those used in the actual drop tests

(i.e., same manufacturers, configurations, compositions and

diameters) . The one difference —lanyard length

necessitated adjusting our L/E data to the length used by

the manufacturer. These modified load-elongation data were

then fitted to third degree polynomials and the four

coefficients from each fit entered into the main program,

which was then run. Oscillograph load vs. time or peak load

data was available, for comparison purposes, from the same

two manufacturers who supplied us with the belts.

Examples of the computer output are given in Tables A-4

a and b.

Using the peak values from the above computations,

tables of peak force and acceleration for a variety of

lanyard types, lanyard lengths, free fall distances, and

mass of test weight or worker were compiled. Examples are

shown in Tables A-5 and A-6.

A-32
LOAD

(KIPS)

Figure A-13. Load/Relative Extension Curves Obtained for 1/2 inch

' Filament Nylon Lanyards.
LOflO

(KIPS)

No. 400 E3Rf COM'IKQ CHA*^¥j GRAPHIC COMP.OlS CORPORATION UiJfFAir

Figure A-14. Load/Relative Extension Curves Obtained for 1/2 inch

Gold Filament Nylon Lanyards

A-34
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Tabic A-5 Summary of calculated peak impact forces for selected fall parameters

IMP A Cl FORCES (IN LOP) FOK A 130 Lb WEIGHT

lANYAWIJ Lf III, IH AND TYPL DPUP = 3 FT 6 F T 9 F T

2 Y 1 X 9 / l 6 I N OSLO SPUN NYLON 2 3 2 2 . + «»**•

8 f T X 9/16U OSLO SPUN NYLON 1 868 . 22 78 . + « + »*«

6 F T X 9 / 1 6 1 N USED SPUN NYLON 1128. 1 729 . 2265 . 8 Y T X 9 / 1 6 I N USED SPUN NYLON 98 8 . 18 28 . 1859.

1 UP T X 9/ 1 6 I N USED SPUN NYLON 8 3 S . 12 36 . 1 598.

2Y T X 9 / 1 6 I N IJE fi SPUN N Y L 0 N 2 2 S 6 • • » 6 * •

8 F T X 9 / l 6 1 N N E A SPUN N Y L U N 1891. 2 3 1 6 . 6 F I X 9 / 1 6 I N NEW SPUN NYLON 1166. 1 786 . 2380 . 8 F r X 9 / 1 6 I N UL U S P U N NYLON 985 . 1882 . 1931.

1 OP T X 9 / 1 6 I N 11 E A SPUN NYLON 868 . 1 286 . 1 665.

2f T X 1/7 111 filament NYLON 2627 . * + «+*«

8 F T X 1 / 2 1 N FILAMENT NYLON 1685 . 2616.

6 F T X 1 / ? 1 N FILAMENT NYLON 1276 . 1 9 75 . 2618.

8 F r X 1 / 2 l n filament NYLON 1 U 7 8 . 1621. 2 13 3.

1 Of I X 1 / 2 I N FILAMFNT NYLON 9 S S . 18 0 9. 1 828 .

2 f 1 X S / 8 1 N FILAMENT nylon 2 661. • •••••

8 F T X 5 / 8 I N FILAMENT NYLON 1 668 . 2 S 7 8 . #»»**

6 f r X S/8 1 11 FILAMENT NYLON 1289. 1960. 2559 . 8 F T X S / 8 1 N FILAMFNT NYLON 1 U86 . 16 13. 2097 .

1 Of T X S/8 1 N FILAMFNT NYLON 96 1. 1808 . 18 0 6.

2F T X 3/ 8 I N filament NYLON 2386 . «*•«» +

8 F T X 3/8 1 N FILAMENT NYLON 1 895 . 23 3 7 . 6 F T X 3 / 8 1 N FILAMENT NYLON 1169. 17 7 1. 2332 . 8 F T X 3 / 8 1 N FILAMENT NYLON 1 UO? . 1 869 . 1 909 .

l <JF T X 3/8 I N filament NYLON 90 1 . 1285 . 1 688 .

2Y T X 1 /? I N GOLD NYLON FILAMENT ( I ) 2 J 7 8 . • »• + * + *•••••

8 Y 1 X 1 / 2 1 M G 0 L 1) NYLON F I L AMENT ( I ) 1268. 2 U 8 3 . • •••*

6 F f X 1 / Z l N gold NYLON FILAMENT ( I ) 9 S 6 • 15 19. 2038 . hf r X l / 2 1 N GOLD NYLON FILAMENT ( I ) 79? . 1 2 32 . 1 683 .

1 OF T X 1 / 2 I N G OLD NYLON FILAMENT ( I ) 69? . 1 U 5 2 . 1 3 9 0.

2 F T X 1 / 2 1 0 G 0 L D NYLON filament ( I 1 ) 2 J9S . • •• + «•

8 f r X 1 / 2 1 M GOLD NYLON FILAMENT ( I I ) 1889 . 2 8 5 2 . 6 F T X 1 / 2 1 N GOLD NYLON FILAMENT ( I 1 ) 112 3. 1826 . 2 8 7 9 . 8 F T X 1 / ? I M GOLD NYLON FILAMENT ( I 1 ) 93 1. 18 7 8 . 1 997 .

1 OF T X 1 / 2 I N GOLD NYLON FILAMENT ( I 1 ) 8 18. 1259. 1 689 .

2F T X 5/8 1 N G 0 L D NYLON FILAMENT 2 5 5 7 . • ••••

8 F T X S / 8 1 N GOLD NYLON F 1 L AMEN T 1561. 2S62 . 6 F T X S / 8 1 N GOLD NYLON FILAMENT 116 1. 1 8 9 U • 2569 . 8 F T X S / 8 I N GOLD NYLON F ILAMtNT 95 1 . 15 18. 2059 .

1 OF T X S / 8 1 N GOLD NYLON FILAMENT 8 2 S . 1 283 . 1731.

2 F T X 1 / 2 I N S I N G L E PLY POLYESTER 1 768 . 8 F T X 1 / 2 1 N SINGLE PLY POLYESTER 1 1 G8 . 1 6 1 J . 6 F T X 1 / 2 1 N SINULF F>LY POL TESTER 896 . 12 8 8 . 1558.

8 F T X 1 / 2 I N SINGLE PLY polyester 789 . 1 u 6 5 • 1 3U8 .

1 uF 1 X 1 / 2 1 N SINGLE PLY polyester 723 . V 5 8 . 1155.

12 v i

******

Z 7b3.

2 26U . 1VJ6. ****** ••••••

Z J 5 8 . 2U 1 8 .

••••«•

3 2 11 . 2613.

222 7 . *»••••

••*•••

JUS.

2 5 8 7 . 2 18 1 . *•*•••

••••••

2ttb3.

2328 . 1990.

***•••

***•*•

2 S 2 8 . 2 U 2 7 . 17 18. ••••••

3 U V 6 • 28 y 3 . 2 l j3 . ******

******

32 l 1 . 2 S 6 J . 2 1 6 3 . ****** ••••••

1 8S6 .

1 S 8 8 .

1 3 8 3 .

A-37
Table A ^ (continued)

2ft X 1/2 In three ply polyester 3289   ** **** ******

sr t X 1 / 2 I N THREE PLY PULYEbTEK 2 1 6 M . 3 3 R 7 . ••***• ••••••

6F r X 1 / 2 I N THREE PLY PULYEbTEK 17 11.* 2616. 3 M 2 u . M 1 t> 3 •

fl f T X 1 / 2 I N TfiKLE PLY PULYEbTEK 1 Mb7 . 2 l 92 . 2 8 M 8 . 3 M o 6 •

i u f r X 1 / ? I N 1 Ft K L L PLY PULYEbTEK 1 292 . 1 9 1 M . 2 M 7 2 • 2990 .

2 F T X l / ? I N F’OL YPKOP YLENE 2 H 3 1 • ••••• ***•*• ••••••

MF T X 1 / 2 I U POL YPKOP YLENE 1 HRM . 2 7 16. •*••••

61- 1 X 1 / 2 I N POLYPROPYLENE 1609. 2 166. 2676 . 3 1 1 0 . «r r X 1 / 2 I N F’UL YPKOPYL E N F 1296. 1836. 2278 . 26o8 .

1 UF I X 1 / 2 I N POLYPROPYLENE 116 3. 162 7 . 2009 . 2 3 M U .

2F T X 5 / H I N POLYPROPYLENE 3 126.

MF 1 X 6 / H I N POLYPROPYLENE 2 1 68 . 3 l M H . ••••••

6 F T X b / H I N POLYPROPYLENE 1 7M6 . 2676 . 3 1 M l . 3 6 d 2 . HF T X S / H I N POL YPKOP YLlNE 16 18. 2 1 6 M . 2 7 0 M . 3 1 e> 0 .

1 UF r X b / U I N POLYP ROF'YLtNl 1 368 . 19 19. 2 3 H M , 2b 16.

2 F T X 3/M I N MANILA 3896 . »••••• •••••• ••»•••

MF 1 X 3/ M I M MANILA 3 U 0 7 . M / M H . •••••* ••••••

6 F T X 3/M 1 N MANILA 263 3 . 3906 . 6 U 9 9 . 6 19 7.

HF T X 3 / M I N MANILA 2 2 13. 3389 . M M 0 2 • 6329 .

i UF T X 3/M I N MANILA 1989. 3 U 3 9 . 3936 . M 72 7 .

A-38
Table A-6. Summary of calculated peak impact decelerations for

selected fall parameters

G*3 FOR A 13;; LH WE I GH T IAN YARD LENGTH AND TYPE D K <> P = 3 F T 6 F T 9 F T 12 El

?F 1 X 9 / 1 6 I N USED SPUN NYLON B . 9 3 • • • •

4E T X 9 / 1 6 I N USED S P U N N Y L 0 N S . 6 3 8.76

6E T X 9/ I 6 1 N USED SPUN NYLON 4.32 6 • 6 S B . 7 1 10.63

8E T X 9 / 1 6 I N USED SPUN NYLON 3 • 6 S b . 99 7.1b H . 69

lilt 1 X 9/ 1 6 ! N USED SPUN NYLON 3.21 4 . 7 S 6.1b 7.4b

2E T X 9/ I 6 1 N UFA SPUN NYLON 8.68

4t T X 9 / 1 6 I N N E kV S P U N N Y L 0 N S . 73 8.91

6E T X 9 / I 6 I N NEW SPUN NYLON 4 . 4 B c.87 9 .00 10.98

H f T X 9 / 1 6 I N N F H SPUN NYLON 3.79 b . 7 0 7.43 9 . Ub

1 UF T X 9/ 1 6 1 N N E rt SPUN NYLON 3.34 4.9b 6.40 7.7b

2E T X 1 / ? 1 N filament nylon 1 U . 1 U * * * • * • • • *

4 F T X i / ? I N FILAMENT NYLON 6.33 1 U • 0 6

6 F T X 1 / ? I N F ILAHFNT NYLON 4.91 7 . 60 10.0b 12.3b

BF T X 1 / 2 I N FILAMENT NYLON 4 . 1 S 6.23 8 .20 1 U . US

1 UE T X 1 / ? I N FILAMENT NYLON 3.6 7 b . 4 2 7.03 B . b 7

2 F T X b / 8 I N FILAMENT NYLON 1 U . 23

4 F T X b / 8 I N FILAMENT NYLON 6 • 4 U 9.92

6 Y T X b / 8 I N FILAMENT NYLON 4.96 7 . b 4 9.84 11.9b

8F T X S / 8 I N F i lament nylon 4.18 6.20 8.07 9.80

1 uF T X S/8 I N FILAMENT NYLON 3 . 70 b . 9G 6 . 9 S B . 39

2 Y T X 3/ 4 I N filament NYLON 9.02

4 F T X 3 / 4 I N FILAMENT NYLON S . 7S B . 99

61 T X 3/4 i N FILAMENT NYLON 4 . SU 6.81 8,97 1 1 . u 1 8 F T X 3/ 4 I N FILAMENT NYLON 3 . 8 S b . 6 S 7.34 8 ,9b

1 UF T X 3 / 4 I N FILAMENT NYLON 3.47 4.94 6.32 7.6b

2 Y T X 1 / 2 I N GOLD NYLON FILAMENT (I ) 7.99 t * * 4 F T X 1 / 2 I N GOLD NYLON FILAMENT (I ) 4 . 88 7.86

6E r X l / 2 I N GOLD NYLON FILAMENT (I ) 3.68 b . 84 7.84 9.72

bf r X 1 / 2 1 N GOLD NYLON FILAMENT (I ) 3 . OS 4.74 6.32 7 • B j

l UF T X 1 / 2 I N GOLD NYLON FILAMENT (I ) 2 .66 4 . Ub b . 3b 6 . b 9

2 F T X 1 / ? I N GOLD NYLON FILAMENT (I 1 ) 9.21

4 F T X 1 / 2 I N GOLD NYLON FILAMENT (I I ) S . 7 3 9.43 * * * • * 6 F T X 1 / 2 1 N GOLD NYLON FILAMENT (I I ) 4.32 7 . U 2 9. S3 11.91

BF T X 1 / 2 I N GOLD NYLON FILAMENT (I 1 ) 3 . SB b . 6B 7.68 9 . b 9

1 UF T X 1 / ? I N GOLD NYLON FILAMENT (I 1 ) 3.13 4.84 6 . SO d . 0 9

2F 1 X S / 8 1 N GOLD NYLON FILAMENT 9.83 • • * •

4 F T X S / 8 I N GOLD NYLON FILAMENT 6 . OU 9.8b

6 F I X S/ 8 I N GOLD NYLON FILAMENT 4.47 7.27 9.88 12.33

RF T X S / 8 I N gold nylon filament 3*66 b . 84 7.92 9 • d j

1 uF r X S / 8 I N GOLD NYLON FILAMENT 3.17 4.93 6.66 B . 32

7 F T X 1 / 2 I N single ply polyester 6.78

4 F T X 1 / 2 I N SINGLE PLY POLYESTER 4.26 6.19

6 F T X 1 / 2 I N SINGLE PLY POLYESTER 3 • 4 S 4.80 b . 99 7.14

BF T X 1 / 2 I N SINGLE PLY POLYESTER 3.03 4 . 1 U b . 03 b . 92

1 UF I X l / 2 I N SINGLE PLY POLYESTER 2 • 7 B 3.67 4.44 b . 1 7

A -39
Table A-6 (Continued)

2ft X 1/2 in three ply polyester 12.65 ***** ***** ******

4 F T X 1 / 7 I N three: ply polyester R .32 13.03

AF T X 1 / 2 1 N HKtt PLY POLYESTER A . Shi l O . OA 13.15 1 6 . u 1 6b T X 1 / 2 I N THREE PLY POLYESTER S . AO 6.43 10.95 10.29

1 OF T X 1 / ? I N THREE PLY POLYESTER 4.97 7.36 9.51 1 1 . 5 j

2 f r X 1 /2 I N POLYPROPYLENE 10.89

41 T X 1 / 2 I N polypropylene 7 . 2S 10.44

6F T X 1 / 2 I N POLYPROPYLENE S . 80 8.29 10.29 11.96

HFT X 1 / 2 1 N polypropylene 4.98 7.06 8.76 1 0 . 22

i u b r X 1 / 2 1 N POLYPROPYLENE 4.43 6.26 7.73 9,jJ

2 b T X 5 / y I N POLYPROPYLENE 12.02

4 F 1 X S / 8 I M POLYPROPYLENE 8.30 12.11

6 F T X S/8 I N POLYPROPYLENE 6.72 9.7 1 12.08 14.16

HF 1 X S / 6 I N POL YPROP YLENE S . 84 8.32 10.40 12.15

1 OF 1 X S / 8 1 N POLYPROPYLENE S .22 7.38 9.17 IU.8J

2F T X 3 / 4 I M MANILA 14.98

4 f r X 3/ 4 I N MANILA 11.57 18.26 * * • A F 1 X 3/4 I N MANILA 9.74 15.02 19.61 2 3.80

HF T X 3 / 4 I N MANILA 8.51 13.03 16.93 2 o • 5 o

1 OF T X 3/ 4 I N MANILA 7 , A 5 11.69 15.13 18.16
For simplicity in presentation and conveniences of use,

these data are presented in terms of peak force and

acceleration as a function of lanyard type, mass of test

weight or worker, and ratio of free fall distance to lanyard

length (h/L) . These data are presented in Tables A-7 and A8. The peak acceleration values for the extreme values of

worker weight, 59 kg (130 lb) and 113 kg (250 lb), are

plotted in Figures A-15 (a through m) . It will be noted

that in nearly all cases the points are reasonably

represented by a straight line function of acceleration as a function of the ratio h/L. The data presented are

representative of lanyard length of 0.6 to 3m (2 to 10 ft)

and free fall distance of 0.9 to 3.7 m (3 to 12 ft)

A. 4. 3 Model Validation and Comparison with Other Results

Attempts were made to validate our static-to-dynamic

impact parameter-prediction model. Steps (1) through (4)

below represent checks of the basic L/E data obtained and

the general methodology by which the data were converted to

polynomial coefficients and then to arrested fall impact

predictions. Steps (5) and (6) represent comparison of our

impact parameter predictions (based on static L/E data) with

actual, dynamic drop test results performed on similar

equipment

(1) Relative L/E data calculated from our L/E data for

pure rope sections of lanyards were compared to

industrial and research generated data on similar type

ropes. Some such comparisons are shown in Figure A-16.

The comparisons are considered to be generally

satisfactory (i.e., not indicating serious

disagreements) , considering the high variability in

rope behavior--a fact verified in our experimental

program. Some observed differences may be due to

variations between the project method for measuring

and the methods used by others.

(2) Another check of our output was made as follows.

The energy involved in a fall begins as potential

energy, PE, which is measured from the point at which

free fall begins to the point at which the test weight

bottoms out and starts back up again. For a mass, M,

and a fall distance, h, PE = Mgh . Now PE so

calculated is equivalent to the area under an L/E curve

from zero up to the peak impact force, Fpea]< . Thus

the area under an L/E curve up to the peak impact force

A-4
Table

A-7a.

Calculated

Peak

Impact

Forces

for

Selected

Fall

Parameters

-H CM T—1 o ON i—1 o oo NO 00 bO NO U0 CM ON CM UO n nO CO no <r CM rH 40 co CM UO CM 00 uo CM ON CM 1—1

00 NO

—1 m o in o on uo

O uo o m oo oo NO rH oo n- 00

m o rH CM CM co co CO 1—1

CM CM CO CO co rH CM CM cn CO UO uo

CMVM

m U0 on UO i—i

CM rH rH 00 co 00 ON ON o CO NO

m i—1Ob uo NO

CO

rH

on o m

m CM CM 00 ON CO NO NO CM 43 CM r*^ U0 CM CM 00 NO i—1

43 ON rH CO UO rH 43 00 i—1

CO

m rH ON CM in Ob

rH i—1

rH rH CM rH rH rH rH CM

H rH rH rH CM

H o CM 00 CM CO 00 ON <r 00 CM CM CM ON oo NO Ob 00 UO ON X 00 i—l

on CM

m CM 00 UO rH ON NO rH ON 43 CO

m 00 CM 00 1 CO CO cm o m CM CO 00 CM r- I—1

in CO <r ON

m o o ON

rH rH CM CM CO CO i—1 i—1CM CM cn CO rH rH CM CO CO <r

x-v oCM

CM oo Ob CO oo c- CM Ob rH <T

m in oo i—1 1—< o ON

X rH o i—1

T—1UO 4) o o o CM CM rH NO uo -<r CM NO

m Ob rH » 1 OO nO oo o CM co uo Ob NO 00 o CM \J- m Ob NO 00 r—1

co UO CM

rH rH 1—1

rH rH rH

H rH

r

—1

rH rH rH rH rH

H CN

bC

1-J MM 00 o o ON UO <r oo rH NO CM uO 1—1

CO NO oo i—1 00 CO CO i—1 X X on O'* nO CO OO CM ON ON o co ON CO ON 00 CO o NO rH

oc rH

r—1 m

O CO 40 rH O- rH NO o <r .H 00 CM CM o m

<u •H rH <—1

CM CM CM CO co t—1

rH CM CM CM CO CO rH rH CM CN CO CO o <u /'~N

J-i o O ON

Pm 1-1 rH cn V ' CO 43 CO Oo o 00 CO CM 43 NO co cn CM CM CO

m uo CM

CD CO o rH 40 ON OO 00 CO rH

O 00 ON CO ON o NO oo NO

CT3

H NO

n) 00

m on o rH co 43m ON o CM co

m ON CM COm ON

PM '-a •Hw 1—1 rH rH rH rH

H rHH rH rH rH rH

•H

PS 14-1 nO rH o oo rH uo 00 CO 43 NO uo rH CM CM o 00 CM <r <r rH rH 3 •H NO CO 40 CM o CO 00 NO rH r—1 CO 00 CM o m ON CN

Mm

H o CO o CO CM o CO r\ rH CO

H

m O' co NO o 00 o o 1—1 H rH CM CM CM CO rH H rH CM CM CM CO rH r—1

rH CM CM CO CO

C/3 nC

CD

03 rH

CMm o o CM CO 00 ON NO NO rH CM uo 00 rH co

Om o s uo o cm CO o m m rH 00 <r rH o ON NO 00 o CO

nO ON o CM <r <r NO ON o CM

m <r NO oo o rH co

rH rH l—1 rH rH rH rH rH rH rH

00 NO VnD 4) NO UO

m NO com 00

r

—1 4-1 in <r ON 40 rH CO b£> NO 00 OO rH r—1 UO m co CM rH rH

rJO CO CM *<r CM co 00 NO 00 rH o CO 00 ON CM NO ON CM 43 CN

rH oo i—1 Ob CM C'vr

—1 rH

T 1 CM CM CM rH rH rH CM CM CO

/*"N i—1 rH r—1 rH CM CM OCO1—1 rH o CO OO rH m ON 43 ON rH NO o o m oo 43 00 rH 00

r^» o 40 40 rH CM 00 1 1 43 ON ON co CM NO CM ON NO CN O'm CO m no 00 o CM CO m NO 00 o CM UO 00 ON rH i—1

rH rH rH rH rH o o m o O o o o o m o o o o o o m o O o o 1— CO m o CM in o CO m o CM m o CO m o CM m o X o o o T-M rH rH CM o o o rH rH rH CM o o o rH rH rH CM

nj

j-ct i rO T3 3 CD c CD CD P rH P

CO in c P o •H o l 3 o rH Hi rH 1—1 C 3n >.

Mp Sn •H JS

p c H S3 nO c

•H

U

cd no 3 rH 3 CM

p

D. 1—1 3 a \ aj >n CD ON in i—1 e

E- on Cfl

,!

A 42
Table

A-7b.

Calculated

Peak

Impact

Forces

for

Selected

Fall

Parameters

A-43

l
Table

A-7c.

Calculated

Peak

Impact

Forces

for

Selected

Fall

Paranete

(!) u

A -44
c

S-i <u

4-1 01B

CO

)-l (0 &H

CO

pL|

XI

<u

01

c/n

CO

cuCJ

J-l o

CJ

to(XB

CO

<u

CL, X

<u

4-4 COH3

CJI CO oX

r-~I <

-Q

CO H

A -45
C/) H

a) H

0)&

03H

03

P-. rH

rH

03

P~J X3

0)

cj

0) i

1 a) znwo

4-1

CDCO

cD3V

rH

0)u

CJ <coD

3-Ed

OJ COX

0> uD

r—i3o

1—1TO

C_J

CC 00I <

Qj H

JQ

aj H

O CM o-. CM O' CO <r 40 CM to 4C oo rH LO O' MT rv CO 04 UO rH o rH o oo 00 m o o rH rH o r\ CM CO 40 00 On o

CM

'w'

C CO U0 40 40 r- 04 CO u-l 40 r^. 04 CO Mf to 40 00 1—1 00 H

CO.

1 rHo CO o rH u-i 04 CM CM 00 rH o. oo O' 40 LO co UO <r

V CM

C rH 1—1 CM CM 04 o o rH CM CM CM O' 04 CM cr. o. 1—1 co

_o CM 00

cO i—; CO <J- to, 40 40 oo 04 CO <r LO 40 04 CO LO 40 04

r

—1 N H o s 00 o

CM

M <H

pH #v

*4 OJ cO H

•H o 

4-J 3 o UO 00

O O-i o. CM 00 u-i rH 40' CO 40 mT <r 00 o CO 04 00

T 1 03 co 3 rH rH CO CM o CM O' i—1

Csl co CO CM CM co to. 04

H o CO 40

H to •H 00 • 0) c co LI-1 40 o- 00 04 CO <r U0 40 P-. 00 o CO <r LO oc- O' H • 1 H rH H

<3

H 40

CJ rH oo u CD c

MH

03 o

0) Oh CD />—

N

L/0 r—-1U0 40 <r CO co CM rH CO n- o H CM O' MJ*

CD o r—

H

CM <r <r CM <r <M CM CO to 4C

m LO, LO UO o CO CM 40 O'

D vO S rH 3 CO <r uo 40 00 o co Mf LO 40 00 o CO <r 40 00 04

H | ' oo r—1 H H j CO

r>v

rH CM 4C

m

m CO <3* 00 CM r- U0 rH 00 rH 0C o UO o CM CO UO 40 40 CO 00 o 04 40 O' CM 40 UO c CO CO 3 H 00 CO <r LO 40 r-* oc o co m 40 00 o CO 40' OC o CM

rH

HHH

04

UO

rJ o o uO o c o o o o UO o o o o o o m o o o o "v. co IT) O- o CM u-i o co LO o CM LO o CO LO r^- o CM U0 o X • O o O 0 rH rH rH CM o o o rH rH rH CM lo o o H H H CM x H H 3 D <u >4 X) E c 0) 3 3

CO CD c a; c H J 3 o 3 o *H

rH rH P-l 4-1 C >4 c >4 o •H z •H z c

•H c

(1) 40 c 40 c o a rH 3 rH 3 CM H

kO \ a \ a. V. >4

FTMc 04 0) 04 CD

H z

II tu

CO

A -46

force

generated

by

rigid

mass.

Factor

of2

accounts

for

energy

absorbed

by

human

body.
rt

'C

o;

0) COo

0)ou<o

<0CuB

coa> p*T3

0>

CO oX

COI

XI

CO H

II IX

A-47

force

generated

by

rigid

mass.

Factor

of2

accounts

for

energy

absorbed

by

human

body.
Table

A-8c.

Calculated

Peak

Impact

Accelerations

for

Selected

Fall

Parameters

A -4 8

force

generated

by

rigid

mass.

Factor

of2

accounts

for

energy

absorbed

by

human

body.
Table

A-8d.

Calculated

Peak

Impact

Accelerations

for

Selected

Fall

Parameters

A- 4 9

force

generated

by

rigid

mass.

Factor

of2

accounts

for

energy

absorbed

by

human

body.
ACCELERATION,

g

n

Fiqures A15a-m. Calculated Peak Impact Acceleration as a Function

of the Ratio of Free Fall Distance, h, to Lanyard Length, L.

Figure A-15a

A -50
A-51
A-52

Figure A-15e U I A -5 4 i
Figure A-15f

'

A-55
Figure A-15g

^ -56

Figure A-15i

A -58
A-59
Figure A-15k
ACCELERATION,

g

n

7\ -6
A £ 9
LOAD(klpt)

LOAD

(kips)

'

LOAD

(kip*)

Figure A-16. Comparison of Test Results with Cordage

Institute L/E Data

A-6 3
the area under an L/E curve up to the peak impact force

should be identical to the quantity Mg n (h + Al)

,

where

h is the free fall distance and AL is the maximum

lanyard elongation. Areas under L/E curves up to Fpea k

for various type lanyards were measured by means of a planimeter. This comparison, as given in Table A-9, is

quite favorable. However, it merely checks the

internal consistency of our model/analysis and does not

confer any validity on our basic static- to-dynamic

assumption

.

(3) Another internal type check that was made was to

test our entire analysis process using an imaginary

spring that obeyed Hooke's law. A spring constant of

12 500 lbf was assumed and a straight-line load vs.

relative-extension curve was drawn. Load-elongation

points were visually interpolated from the curve and a third degree polynomial fit performed. Quite

reasonably the coefficients of this fit were:

k

Q = 0.00006

k

1 = 12 500

k

2 = 0.0004

k

3 = 0.0008

These coefficients were then input into the main

program and impact forces were computed. A comparison

of generated impact forces with those computed from

Hooke's law is given in Table A-10. Again the

agreement, while excellent, is merely a check of the

static validity of our basic model and does not purport

to confer a blessing on our dynamic predictions.

(4) Observed lanyard breaking strengths were compared

to the respective strengths as given for pure ropes.

This comparison is detailed in Table A-ll. Although

differences were expected (due to rope variability and

test condition differences) , these differences are

generally within the inherent variabilities of the

materials themselves. That commercial rope testing is

done using large diameter mandrels and tapered splices

(in an attempt to determine the strength of pure rope)

should have produced specified strengths higher than

our measured forces. That many of our measured

strengths were actually greater than specified values

A- 64
Table A-9. Comparison of Absorbed Energy as Measured

with a Planimeter and Calculated Using a Computerized Model (a)

Rigid Weight, W

Free

3 ft

fall

6 ft

distance, h

9 ft 12 ft

150 lb o

r-H 1 <1 <1

200 4 <1 <1 2

250 <1 <1 2 3

300 <1 1 3 NA

350 <1 2 NA NA

(a) These data are for a 6 ft lanyard. The computerized

model essentially uses the L/E curve as input data.

(b) Each element in matrix represents a quantity,

Iqq

,

(Area under curveto appropriate elongation) - W(h+AL) , (Area under curve to appropriate elongation)

A -6 5
1

Forces

Law %

Error 0

.4%

0.1 0.2

0.04 Pp to xi p - — O CD P < xc p xi o o •—1

T3

O *H

C XI ~ "O cm oo co oo P P cu tc h <T

cp '

p

h

m

h to

P3 c cu cm cm ro -sr CD -h Ip p — P aj X) rH X) \ P O XI PI O <3 \ i—1 tP PI tp PCX < XI

<J -H l—1 p x: X

ip

a i O u-| o o O C/3 Pi m o m

II 1 h oi oo in

C P CM CM ro o to HI II to CD IP •H H K p Ip p p • a a/ 6 p • p 0 O -H >p

CJ P

on (n tN P >p ro in cx> • <1 • • • • o i—1 rH rH i—1

T—\| < p

a) ip

rH JC X3 in in o o P rH rH

Eh

X)i—1 2 uo o o o o in in m

cm ro cm ro

XI<1 . c P TJ 0 6 CD *H P P P P P o O

tp

H •H

C0 CD

C

rH P *H

CD

a

ip CO CO H p - c CD c

•H P p p 0 x: CUP p

CD >1 P re rp CD CP c x: 0 p X3P B •v •H p CO p CD Cp P P 0 2 c P CP CD CU -H e

<p CD P CD

CD P P . P C CP P P P P

ip cu o 6 P o O P CD • o H P

in c P

CD CP CD

Cl) SZ *rH XI n P CO c O >i CM *H P t—\CD x: CD C P p XI

CD P •H

PCC 5 rp P P i—1

-P P to i—1 P CD P

to 0 P P

tp rH P c fd O

pi

D > P p XI

A- 6 6
Table

A-ll.

Comparison

of

Given

Breaking

Strengths

(BS)

with

Average

Values

for

Various

Lanyards I ’

CO S X /—

X-N X“*S o X X X o "O 'w' rH 01 rH X X CTn X Osl X X i rH CO rH rH i 1 rH

03 <3 4~>

II 1 X)

01 P > cn (0 i-i o o o O o X o o o

CQ > 01 CN

X O' iH r—

00 1

•H CO coXXX CO CO LO

X

00

X •* * + <3 s-x o rH •O" rH i i i X

01 01 4-i X > X o o o o o CO o o o

CO l-i rH CN rH CO <r

X i—lX O'

X 0) '-X r^- LT)

X

XX rH

01 CD + > X cn X

X <x

XXX <rX <r

<C

OX

4-< 10) o x CO 3 4-1 • CO a 00 CN CNI CN

X

X CN CN o <0 01 p 01 6 £

4-1 c X o o o o o o o o o

01 rH o o o o o o o o X > <r CN <r <r CN CN X

•H r. o CO X o X o X X <r X rH »—

rH

1-

01 •u c

01 •H C4

X CN

X CN CNI

X E '-x \ \ \ \ \ \ \

03 rH

X CO rH uO rH rH LO CO

•HQ

>-i 01 0) 01 0) o 4-) 4-i 4-J X X 4-J rH •H •H •H rH rH •H i i 1 o X X X o o X i i 1 u 5 3 3 X X 3 i i 1

01

p c o c 01 •H o rH U rH

•H ph a.

CO z o o c x 03 a • o CL 1 1 6 03 1-1 pH •H O rH u rH a o •H 03 o cti tH Q PL, 2

<D X

CO

X

Xo c o X X

CL

X

X

o)

x

p c o X

CO CQ

XX

X 3

4-1

U

•H CO

u 3 01 o 3 X i—

CO

i-i 03

X

X > CO a 01 01 01 X

t—1 X

X 3 C X c X X CO X X X CO X

4-1

CM

X

X 01

01

X

pH

X

X

rH 03 CO

01XX

XX

03O CO E O 01 •H X X E 3 o o X

1-1 1-1 •r! CL 4h CO Cl <x

03 3

01

X

X

X o O 03 o X X

CO

a

X 0) C0

>-i

X P

03 03 CO >>C CO X

03 01 P X 3 01 ,—1 CO X 03 01 O > X

lx CL X • 01 01 PQ CO X 3 X • 03 P X CO CO

01

X 01X

CO > p CJX

X *H 01 c CO x O x 0) pH X X X p C CO 01 CO 0) • <x X 3 X u 4H X c •H X X

CO 01

X

X 3

CO o X X X 01 P U CO X <X X 03 X o X 01 X CO

03

p

X CO

01O 01 c

l-i

X CO 01 o X P 01 01 •rH X x X X X CL X X

01

X 01

X o > 01 >-t CL X U 01

01

X CO CO 01

CO

XX 01 Cl

X CL 01

X

O

O CO coH

X

03

X

n

r '—

A- 6 7
indicate that the use of small thimbles in commercial

lanyards does not result in a significant reduction in

breaking strengths. Note that our interest is in the

characterization of real lanyards and not with rope

strengths, per se.

(5) Several sets of dynamic drop test data, involving

unused lanyards of varying lengths, were made available

to us by two safety equipment manufacturers. These

data included either peak impact forces or peak force

oscillograph traces. Components of these data sets for

which we could generate comparable data were used to

check our model. These comparisons, presented in

Tables A-12 and A-13, indicate that:

(a) Calculated peak forces for impacted lanyards

are, typically, slightly higher than those

generated by actual impacts and observed as

oscillograph traces of load cell measurements.

These differences are attributed, in part, to real

sample variations, energy absorption by one or

more elements in the experimental setup or to

approximations and assumptions that went into the

model

.

(b) As is evident from Table A-13, peak duration

calculations appear to give quite good comparisons

with the experimental data. These durations are

of use in validating the model, of course, but are

also required to evaluate potential injury levels.

(c) If peak force calculations are acceptable

then their counterpart peak deceleration

calculations should also be accepted. Similarly

if peak forces and times are valid then lanyard

elongation calculations, for which no comparable

real world data were found, can also be assumed to

be valid.

(6) Several impact force calculations made for 1.8 m

(6 ft) falls of 68 and 113 kg (150 and 250 lb) rigid

weights into 1.8 m (6 ft) lanyards of 1/2 inch nylon

were compared with similar parameter calculations for

lanyard-plus-belt (friction and buckle) combinations.

These comparisons indicated that peak impact forces for

lanyard plus body belts were about 5 to 25% lower than

for the respective forces for lanyards alone. For a 1.8 m (6 ft)

,

3/4 inch manila rope inclusion of a body

belt will reduce impact forces by about half.

A-68
Table A-12. Comparison of calculated peak impact forces with comparable values as experimentally

determined by equipment manufacturers

t Peak Impact Forces^

Lanyard

NBS Manufac- Type Type Drop Drop Manufac- Sample Sample Percent turer lanyard belt length height weight turer 1 peak 2 peak difference

6

X 1/2 in nylon None 6 ft 6 ft 250 lb 2597 lbf 3319 lbf 2729 lbf i7S

6 ft 350 3896 4560 3726

8 250 2277 2754 2287

8 350 3130 3823 3152

10 250 1910 2371 1999

10 350 3143 3322 2786 $

5/8 in nylon None 6 6 250 2565 3314 3363 30

6 350 3410 4429 4341 29

8 250 2465 2737 2826 13

8 350 3145 3692 3698 17

10 250 2330 2359 2474 4 10 350 2930 3212 3257 10 1/2 in polyester None 6 6 250 4130d

4302 4286 4

6 350 <5330q

5620 5581 5 8 250 3762 , 3610 3617 -4

8 350 <5060

a 4736 4830 -5 10 250 3483 3154 3176 -9 10 350 4582 4147 4163 -9 3/4 in manila None 6 6 250 <4460d

6334

a 6417a 43

6 350 3915

a 8181

a 8348

a

8 250 4062 S470

a 5548a

36

8 359 2930

a 7082 7060a

10 250 3962 4855a 4951

a

24 10 350 -- 6303

a 6267

a -- 1/2 m nylon Friction 6 6 212 1770

d 2168 2120 21

12 M990a 3423 3324 M3

Tongue 6 6 212 1770 1894 1815

6 2100,

-4 12 M830a

2784 2806

3

12 3100

%-6

12 150

c 1465 2153 2095 45 3/4 in manila Tongue 6 6 212 M664d 2938

a %9

2750 . 12 212 ^3205°

4075

4891

a -- M4

Y 1/2 in nylon Friction 6 5 250

C 1830 2923 60 Tongue 1660 2661 60 1/2 in polyprop. Tongue 6 5 250 2250 2619 -- 16

aRope failed. For co. X or Y force represents observed force at the break point. An "a" by NBS force

indicates computed peak force above NBS observed breaking strength.

^The L/E curves for samples 1 and 2 differed considerably for 1/2 in gold nylon. Were the percent

differences given in column 10 based on sample #2 only better agreement (i.e., smaller peak force differences)

would have been obtained.

cSandbag weights. All other weights are rigid metal.

dMeasurements superscripted with d went off oscillograph chart scale. Where < sign appears limits were

estimated by experimenters; where 'c sign appears peak forces were extrapolated from existing parts of curves.

0Elements in this column represent 100 [(NBS) - (X or Y)]/(X or Y) values. Where two equivalent NBS or X or

Y measurements are listed, they have been averaged to produce the final difference.

^--indicates value not available or not developed.

®A11 peak impact forces in columns 7 through 9 are for single samples; these measurements in column 7 are due to manufacturer "X" or "Y," as listed in column 1, while those forces in columns 8 and 9 represent

model calculations based on L/E data developed by this study.

A-69
Table A--13. Comparison of calculated peak impact durations with comparable values

as determined by equipment manufacturers

Manufacturer

Type

lanyard

Type

belt

Lanyard

length

Drop

height

Drop

weight

Peak Widths, FWHM

3

Manufac turer

NE

Sample 1

s

Sample 2 Percent

0 difference

X 1/2 in nylon None 6 ft 6 ft 250 lb .12 s .09 s .11 s -17

6 350 .11 .09 .12 - 5 8 250 .14 .11 .13 -14

8 350 .15 .11 .14 -17

10 250 .18 .12 .16 -22

10 350 .16 .13 .16 - 9 5/8 in nylon None 6 6 250 .13 .09 .10 -27

6 350 .13 .10 .10 -23

8 250 .14 .11 .11 -21

8 350 .15 .12 .12 -20

10 250 .16 .13 .12 -22

10 350 .17 .14 .14 -18 1/2 in polyester None 6 6 250 .07 .07 .07 0

6 350 <.09d

.07 .08 -17

8 250 • 08d.09 .09 13

8 350 <.08d

.09 .09 13 10 250 .10 .10 .10 0 10 350 .10 .11 .11 10 3/4 in manila None 6 6 250 <.06d

• 05

c

. 05

C - 17 f

6 350 . 05

C

• 05

c

.05C 1

8 250 .07 .06

C

.06C -14

8 350 . 05

C .06° .06C 10 250 .07 .07

c .06

c

- 7 10 350 -- .07° . 07c --

1/2 in nylon Friction 6 6 212 •!3d

.12 .12 - 8 12 %.lld

.10 .11 - 5 Tongue 6 6 212 .13 .15 .14 -

1 ? 6 .13,

LL

12 'v. 12d.14 . 13c

12 .11

1 / 12 150b

.16 .13 .12 -22 3/4 in manila Tongue 6 6 212 'v. 07d

.10c -- 43

12 212 'v.lO4 uIs o -- -30

Y 1/2 in nylon Friction 6 5 250

b

.11 .10 -- - 9 Tongue .12 .11 -- - 8 1/2 in polyprop. Tongue 6 5 250 .10 .11 -- 10

aAll peak durations, computed as full-width-at-half-maximum (FWHM) times are based on single sample measurements; those measurements in column 7 are due to manufacturer "X" or "Y," as listed in column 1, while those times in columns 8 and 9 represent project staff data.

DSandbag weights. All other weights are rigid metal.

°Rope failed. Times for manufacturer X and Y are to break while NBS times with designation "c" are based on L/E curves where ropes broke below peak force.

‘^Measurements superscripted with d went off oscillograph chart scale. Where £ sign appears limits were estimated by experimenters; where 'v sign appears peak durations were extrapolated from existing parts of

curves.

eElements in this column represent 100 [(NBS) - (X or Y)]/(X or Y) values. Where two equivalent NBS or X or Y measurements are listed, they have been averaged to produce the final difference.

indicates element not available or was not developed due to uncertainties in subordinate values.

A -70
Peak impact forces for lanyards secured to body

belts which, in turn, were wrapped snugly about rigid

cylindrical weights represent the combined action of

lanyard and belt in absorbing impact energies. The

versatility of our model would be extended if, by

appropriately combining L/E data for lanyard and belt,

impact parameters for the combined system could be

calculated. As is seen in Table A-12 agreement between

our (static-based) force calculations and experimental

(dynamic) values is generally good considering the

inherent variability of the devices tested. In all

cases manila rope gives the poorest fit. The large

differences obtained when a sandbag was used can be

attributed, in part, to the energy absorbing nature of

this type test weight.

One consideration that should be borne in mind

when comparing synthesized fall impact parameters

(based on static L/E data) with actual drop test

results is that most interference factors in drop

testing (e.g., give in the anchorage, non-Z axis

motions, including rotations, imparted to the test

weight by the release mechanism, etc.) tend to reduce

the observed impact forces.

A- 7
A. 5 Computation of Load vs. Elongation Functions

for Various Length Lanyards

In order to facilitate the comparison of data generated

in this project with results of other load vs. elongation

tests of lanyards, the coefficients of the polynomial

equations for complete 1.8 m (6 ft) lanyards (lanyard with

snaphooks spliced onto each end) and center (pure rope)

sections of these lanyards are given in Tables A-14 and A15, respectively. The equations with these coefficients

correspond to the curves of Figures A-ll (adjusted for a lanyard six feet long) and A-12

.

The information in Tables A-14 and A-15 can also be

used to calculate values for lanyards of other lengths of

interest by using Equation 9 (page 81) . An example giving

calculated data points for a 3 m (10 ft) lanyard of new,

9/16 inch spun nylon is given in Table A-16 . The computed

values of Al/L and A£/£ were found by an iterative process

from Tables A-14 and A-15. The values of AA/A were then

calculated using Equation 9,

AA/A = ^

x

+ X

where A =10

L = 6

p

= A - L = 4

An equation predicting the load vs. elongation function

for a 3 m (10 ft) lanyard can be obtained by fitting a third

degree polynomial to the values in the last and first

columns of Table A-16.

M

£

A-72
Table

A14.

Coefficients

of

the

Polynomial

Equations

for

1.8m

(6

ft)

Lanyards

CO

Coefficients

of

equation

Force =A+B

(AL/L) +C

(AL/L) +D

(ALA-)
Table

A-15

Coefficients

of

the

polynomial

equations

for

pure

rope

sections

of

lanyards f—1 1 3 $ < ms in o in

m CO r- o CO ro CO *r r—1

ms • • , f ^r oo 04 o o 1—1 in 04 «—1

uo 00 o 00

in Si

std in in vr o 1—1

in in in r- ^r

r—1

in in ) i—1 1—1 i—1

ID 04 o '3* oo oo i—l

in OOm 04 in O'-

m in in 04 o' oo r- oo 04

O o er. in t-~ 00 in in -a* 00 oo r- in O O' co

r- ro 00 o oo oo 0- o CO f" 04 00 rin 04 00 00 in in 00 i—i i—1

00 00 04 in

—1 l—1 r

—1 i—l 1—1

04 04 1 i—1

in

ujj

in 00 in 00 oo oo o 04 04 •o* o i—i

in o r- oo 04 1—1

in in

O

O or 00 00 or

^r 00 in

m in ^r Co e'- OO r- 00 04 o o 04 oo 00 in O'. OO er 00 r- UO CO 04 i—i

04 04 i—l

00 i—i

^r

m 1 oo in oo i—i i 1 1 1 l i 1 i UO

CQ< 1—1

04 OO or in in e'- 00 co o » 1 04 OO o o o o o o en o o I—1 1 1 i—1 .—1

04 04 04 04 04 04 04 04 04 04 CM 04 04 G0I I &a

in *8G

•Ht—I \CT 8i—l &amCci—I \ C

G 0 O

M

HH

G

G c G 0 G O 0 0 -P 0 i—i 1—1 1—1 W -P

!>i :x >1 0 CO C c c >i 0

r—H

3x

-P -p -p 0 1—1 G G C

-P -PC

4-1 44 44

•H *H -H

4-1 4-1 4-1 ms ms ms i—i i—i i—i o

as as & 8 8 i—I i—I

>i >i >i ^ Uj Qj

Dj o o I G G

ai0h d)

aa tn $ Ex Ex

C

-H

CM 00

in oo

tm Cr co

a c C C c c

•H •H *H •H

04 00 04 04 04 \1 \ \ \ \ 1 uo 1 1 1 1 1 1 A- 74 a

a

•5 .5

00\m

^r\00

oo

04 00 in 04 04 r- 00 OO 04 o I—1

<r in i ex' <1 uo ro 00 CO CO cr uo 04 r- i—1

CO oo 1—1 f in r-~ 1—1

CO i—1

0- o cr oo 04 in 04

uo uo in CO oo cr o 04 in CO OO l—

Q 1

04 uo uo 00 oo r~ 00 in I—1

uo OO 1 +

04

uo i—1 oo in 1 1 CO oo 04 in oo o 04 sr i \

<3 o i—1 r—1

00 o •—1 04 i—1 o o rH o *,

U 1 t i i 1 I 1 I 1 1 i 1 \v + 3\ii \ex’ <3

13 in CO 04 04 oo 04 oo in •*r rH 04 *ii

CQ+ r <

fO
Table A-16 Elongation of 9/16 inch new spun nylon lanyard

computed from test data

Elongation

Load 6 ft. lanyard

(b) Pure rope 10 ft. lanyard

lbf percent percent percent

1000 18.96 18.18 18.65

1500 23.45 22.47 23.06

2000 26.91 25.58 26.38

2500 29.76 28.08 29.09

3000 32.22 30.18 31.40

3500 34.38 32.02 33.44

4000 36.33 33.65 35.26

(a) A/L, computed using coefficients given in Table A-14

(b) M/l, computed using coefficients given in Table A-15

(c) AX/X =0.6 AL/L + 0.4 Ad/H

A-7 5
.
NBS-1 14A (REV. 7-73)

U S. DEPT. OF COMM. 8IBLI0GRAPHIC DATA

SHEET

1. PUBLIC ATION OR R H PORI NO. NBSIR 76-1146

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SURTITLF 5. Publication Date

A Study of Personal Fall -Safety Equipment

6. Performing Organization Code

7. AUTHOR(S)

Harold L. Steinberg

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. 4410433

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Occupational Safety and Health Administration

Division of Safety Standard Development

Department of Labor

3rd 5 Constitution Avenues, N.W. , Wash., D.C. 20210

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Codt

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) A study has been made of the basic requirements for personal safety equipment that

is designed to protect workers at heights against the danger of falls. The project

was undertaken for the Occupational Safety and Health Administration as part of an effort to update the Code of Federal Regulations on fall-safety equipment. The

investigation included an intensive literature review, numerous field visits, and a limited laboratory examination of some components. Some unique testing and

evaluation approaches were developed, and a novel extensometer was designed.

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) Body belts ; body harness ; fall-arrest equipment; fall-safety

systems; impact accelerations; impact forces; lanyards; linemen's equipment;

load- extension data; occupational safety and health; performance standard; regulation;

tensile testing; worker safety equipment.

18. AVAILABILITY [^Unlimited

cz For Official Distribution. Do Not Release to NTIS

2 Order From Sup. of Doc., U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. C 1 3

I~X1 Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

218

22. Price

*7-75

USCOMM-DC 20042-P74