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Author: Perner, Judd, J Title: Effects of Lanyard Leg Variation on Maximum Average Arrest Force in

Energy Absorbing Lanyards Used for Fall Protection The accompanying research report is submitted to the University of Wisconsin-Stout, Graduate School in partial

completion of the requirements for the

Graduate Degree/ Major: MS Manufacturing Engineering

Research Adviser: John Dzissah, Ph.D.

Submission Term/Year: Summer, 2013

Number of Pages: 71

Style Manual Used: American Psychological Association, 6th edition

I understand that this research report must be officially approved by the Graduate School and that an electronic copy of the approved version will be made available through the University Library website

I attest that the research report is my original work (that any copyrightable materials have been used with the permission of the original authors), and as such, it is automatically protected by the laws, rules, and regulations of the U.S. Copyright Office.

My research adviser has approved the content and quality of this paper. STUDENT:

NAME Judd Perner DATE: 08/02/13

ADVISER: (Committee Chair if MS Plan A or EdS Thesis or Field Project/Problem):

NAME John Dzissah DATE: 08/02/13

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This section for MS Plan A Thesis or EdS Thesis/Field Project papers only Committee members (other than your adviser who is listed in the section above) 1. CMTE MEMBER’S NAME: DATE:

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--------------------------------------------------------------------------------------------------------------------------------- This section to be completed by the Graduate School This final research report has been approved by the Graduate School.

Director, Office of Graduate Studies: DATE:

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Perner, Judd J. Effects of Lanyard Leg Variation on Maximum Average Arrest Force in

Energy Absorbing Lanyards Used for Fall Protection

Abstract

Industrial fall protection is an ever expanding category of occupational health and safety. Unlike

other forms of hazardous energy such as electrical or mechanical, gravitational potential energy

is universal and affects every organization. To combat the dangers associated with working at

height, fall protection equipment manufacturers have developed a plethora of devices to safely

arrest a worker in the event of a fall. Although there are many different types of fall protection

devices, some of the most common are energy absorbing lanyards. Energy absorbing lanyards

are tested to national standards to ensure they meet all applicable performance requirements.

When dynamically tested, the critical performance measurement for energy absorbing lanyards is

the Maximum Average Arrest Force (MAAF). It has been observed that when tested using

different lanyard leg materials, energy absorbing lanyard produce different MAAF values. To

grow the body of knowledge related to the effects of lanyard leg materials on MAAF results, this

study performed a variety of dynamic and static tests to evaluate this relationship. Descriptive

and inferential statistical techniques were employed to analyze the experimental data. The

statistical data obtained during this study suggests that there is a strong correlation between

lanyard leg material properties and MAAF measurements.

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Table of Contents

............................................................................................................................................. Page

Abstract ...................................................................................................................................... 2

List of Tables .............................................................................................................................. 5

List of Figures ............................................................................................................................. 6

Chapter I: Introduction ............................................................................................................... 7

Statement of the Problem ................................................................................................. 8

Purpose of the Study ........................................................................................................ 9

Assumptions of the Study ................................................................................................ 9

Definition of Terms ......................................................................................................... 9

Limitations of the Study ................................................................................................ 10

Methodology ................................................................................................................. 10

Chapter II: Literature Review .................................................................................................... 12

Industrial Fall Protection Can Save Lives ...................................................................... 13

Types of Fall Protection ................................................................................................. 14

Common Fall Protection Products, Past and Present ...................................................... 16

ANSI Z359 Committee and Related Standards .............................................................. 19

Testing Products to ANSI Z359 Standards ..................................................................... 22

Energy Absorbing Lanyards Designed to Meet the ANSI Z359.13 Standard .................. 23

Summary ....................................................................................................................... 25

Chapter III: Methodology .......................................................................................................... 27

Lanyard Selection and Description ................................................................................ 28

Instrumentation and Test Equipment .............................................................................. 29

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Data Collection Procedures ............................................................................................ 29

Determination of Lanyard Leg Stiffness ........................................................................ 30

Strain Rate Analysis ...................................................................................................... 31

Descriptive Statistical Analysis ...................................................................................... 32

Inferential Statistical Analysis ....................................................................................... 32

Limitations .................................................................................................................... 32

Assumptions of the Study .............................................................................................. 33

Summary ....................................................................................................................... 33

Chapter IV: Results ................................................................................................................... 34

Descriptive Statistical Analysis ..................................................................................... 34

Inferential Statistical Analysis ...................................................................................... 37

Tear Webbing Velocity Response Analysis .................................................................. 45

Chapter V: Discussion ............................................................................................................... 49

Discussion .................................................................................................................... 50

Limitations ................................................................................................................... 51

Conclusions ................................................................................................................... 52

Recommendations ......................................................................................................... 53

References ................................................................................................................................ 55

Appendix A: Descriptive Statistics ............................................................................................ 57

Appendix B: Graphical Data and Images ................................................................................... 59

Appendix C: Collected Data ...................................................................................................... 65

Appendix D: Inferential Statistics .............................................................................................. 68

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List of Tables

Table 1: Published ANSI/ASSE Z359 Standards ....................................................................... 21

Table 2: Descriptive Statistics - Ambient Condition .................................................................. 36

Table 3: ANOVA: Two-Factor With Replication ...................................................................... 38

Table 4: Single Factor ANOVA - Ambient Condition ............................................................... 40

Table 5: Tukey’s Range Test – Hot Dry Condition Single Factor ANOVA................................ 41

Table 6: Lanyard Leg Stiffness Comparison Tests ..................................................................... 42

Table 7: Regression Analysis of Mean MAAF versus Strain – Hot Dry Condition .................... 45

Table 8: Tear Web Strain Rate Analysis .................................................................................... 47

Table 9: Regression Analysis of Average Force versus Velocity ............................................... 48

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List of Figures

Figure 1: Example of force versus time graph for steel cable leg EAL ....................................... 35

Figure 2: Bar chart of mean MAAF results for lanyard leg materials in the ambient condition ... 37

Figure 3: Mean MAAF versus strain in the hot dry condition .................................................... 43

Figure 4: MAAF versus impact velocity .................................................................................... 46

Figure 5: Average force versus velocity..................................................................................... 47

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Chapter I: Introduction

In the natural world there are fundamental forces that govern all things and impact human

life at every level. Although some of these forces are easier to recognize than others, the

universally understood force is that of gravity. As civilization continues to build taller buildings,

bridges, and structures, the dangers associated with gravity become more prevalent to those

working at height. When a fall hazard cannot be eliminated through engineering controls, a

common safety practice is the use of fall protection equipment. If not properly controlled the

forces applied to the human body during a fall can cause serious injury or death. To combat

these forces, industrial fall protection products have been developed to gradually decelerate

workers and reduce their exposure to bodily harm.

In general industry a typical product used as a deceleration device is the energy absorbing

lanyard (EAL). This type of fall protection system is used to connect a user’s full body harness

to an appropriate anchor point capable of withstanding the forces generated during a fall. The

full body harness and energy absorbing lanyard are examples of personal protective equipment

(PPE). Historically, EALs are manufactured from synthetic woven products such as polyester or

nylon webbing but can be produced from a variety of different materials. The fundamental

components of an EAL consist of an elongating energy absorber, a fixed length lanyard leg, and

a connector at each end. Although every manufacturer produces energy absorbers to their own

specifications, the two most common forms of energy absorber are the tear web style and

Partially Oriented Yarn (POY) style. Due to varying customer requirements, EAL manufacturers

produce lanyards with multiple leg material options ranging from steel cable to polyester

webbing.

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Prior to marketing and selling energy absorbing lanyards, manufacturers must subject the

devices to rigorous performance criteria to ensure they meet or exceed all applicable standards.

In the United States the most common fall protection standards are developed by the

Occupational Safety and Health Administration (OSHA) and the American National Standards

Institute (ANSI) Z359 committee. Historically, the OSHA and ANSI test requirements for EALs

included dynamic tests which measured maximum arrest forces (MAF) generated by dropping a

specified weight a specified distance.

In recent years, the ANSI committee has determined that the maximum arrest force

method is not satisfactory for evaluating EALs and has switched to a maximum average arrest

force (MAAF) test criterion. The MAAF method differs greatly from the MAF method as it

measures the average force over an extended period of time while the MAF method only

measures peak forces which are often presented in milliseconds. The ANSI Z359 committee’s

decision to adopt MAAF test criteria was due to research on the ergonomic effects of impulse

loading on the human body. Since the MAAF method has been adopted, there has been little

research done in regards to how different lanyard leg materials or constructions affect final

MAAF test results.

Statement of the Problem

Manufacturers that design, test, and certify EALs to standards which include MAAF test

criteria have observed correlations between lanyard leg material characteristics and MAAF

variance. Energy absorbers that respond differently to dissimilar leg materials pose to increase

EAL development costs due to additional testing requirements. MAAF variance also reduces

product interchangeability and predictability when combined with other fall protection devices.

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Purpose of the Study

The purpose of this study is to determine the relationship between EAL leg material

characteristics and MAAFs when tested in accordance with ANSI Z359 requirements. All

observed correlations will be used to improve product consistency, reduce costs associated with

testing, and add to the body of knowledge relating to personal fall protection equipment.

Assumptions of the Study

Due to the minor variability in test set up and measurement devices, this study will

assume that all tests were conducted without error and or inconsistency. In addition to test setup,

it will also be assumed that all tests were conducted using the same calibrated test equipment.

Also, all EAL samples tested during this study will be assumed to have zero manufacturing

related defects that influence test results.

Definition of Terms

Aramid. “Any of a group of lightweight but very strong heat-resistant synthetic aromatic

polyamide materials that are fashioned into fibers, filaments, or sheets and used especially in

textiles and plastics” (“Merriam-Webster,” para. 1, 2013).

Arrest force. Force generated when decelerating a human body or test weight from free

fall to a complete stop.

Constructional stretch.

When a load is applied to a wire rope, the helically laid wires and strands react in a

constricting manner, compressing the core and bringing all of the elements of the rope

into closer contact. The result is a slight reduction in diameter and an accompanying

lengthening of the rope. (“Wirerope Works, Inc.,” para. 2, 2013)

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Deceleration device. A component within a fall protection system that limits the forces

applied to the body during a fall by controlling the rate of deceleration.

Tear element. A component of tear webbing comprised of synthetic yarn that joins two

plies of webbing together and absorbs energy through plastic deformation during separation.

Tear web. A two ply webbing that is specifically woven to separate at a predetermined

load and maintain consistent resistance to separation while in tension.

Partially oriented yarn. “A continuous synthetic filament made by extruding a polymer

so that a substantial degree of molecular orientation is present in the resulting filaments, but

further substantial molecular orientation is still possible” (“Encyclo,” para. 2, 2013).

Webbing. “A strong narrow closely woven fabric designed for bearing weight and used

especially for straps and upholstery” (“Merriam-Webster,” para. 1, 2012).

Limitations of the Study

Because there are many fall protection equipment manufacturers, each producing a

variety of EALs, the effects of all lanyard leg materials cannot be practically studied. The scope

of lanyard leg materials will be limited to: polyester webbing, nylon webbing, steel cable, aramid

webbing, and nylon/polyester rope. Additionally, the style of energy absorber will be limited to

one product family and based on a tear web style lanyard. A simplified drawing of tear webbing

showing a two ply construction woven together with tear elements is shown in Appendix B.

POY style lanyards will be excluded from this study as the POY energy absorber acts

independently of the tubular lanyard leg.

Methodology

To provide background information on energy absorbing lanyards, lanyard testing, and

fall protection systems, a literature review has been included within this document. The

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literature review section describes the purpose of industrial fall protection products and how they

are tested to meet OSHA and ANSI Z359 standards. Following the literature review is a detailed

report on how the study was conducted and all methodologies related to testing, data collection,

and analysis. The results of this study are discussed in chapter IV and include detailed statistical

analysis. A final recommendation follows chapter IV and includes discussions, conclusions, and

recommendations based on the data obtained during this study.

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Chapter II: Literature Review

Although hazards can be found in almost any work environment, hazards associated with

falls are some of the most common due to the universal constant of gravity. Whether building a

skyscraper or climbing stairs in a factory, the risks associated with working at height are the

same and can be fatal if not controlled properly. To aid the workforce in the continuous goal of

working safely, manufacturers of safety equipment have developed new and innovative products

to protect individuals working at height. As materials and technology progresses so do the

devices that are used to protect individuals working at height. Some of the most common forms

of fall protection devices include energy absorbing lanyards that are used to tether a worker to an

anchorage and safely arrest them in the event of a fall.

During the development of new energy absorbing lanyards, manufactures rigorously test

designs to comply with national standards. Although OSHA standards are the only group of

standards required by law in the United States, ANSI standards have become increasingly

popular and often required by organizations. One of the main differences between OSHA and

ANSI energy absorbing lanyard test requirements is the adoption of maximum average arrest

force measurements (MAAF) by ANSI compared to the maximum arrest force measurement

(MAF) method used by OSHA. The MAAF method was implemented by the ANSI Z359

committee in 2009 and is currently used during the qualification testing of all EALs designated

as ANSI Z359 compliant. There has been little research conducted on the correlation between

lanyard leg material characteristics and their effect on MAAFs when tested using ANSI

requirements. This deficiency in technical information requires fall protection equipment

manufactures to perform a greater amount of research and development tests.

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While energy absorbing lanyards are the focal point of this study, they are only a

subsystem within larger fall protection systems. Other components that typically make up a fall

protection system include an anchorage, full body harness, connectors such as EALs or self-

retracting lifelines, and rescue or controlled decent devices. Each of these product categories

have been developed to address challenges associated with fall protection. The information

presented in this literature review will provide a detailed view of the importance, history, and

progression of fall protection. This background information will be related to OSHA and ANSI

standards which have helped shape the fall protection industry. In addition to giving background

information on fall protection, this literature review will also describe the different types of fall

protection products and how they are tested in accordance with national standards.

Industrial Fall Protection Can Save Lives

Industrial fall protection equipment can be found in nearly all industrial settings because

of OSHA regulation. Although fall protection PPE is easily accessible and commercially

available in every state, workers still fall from height every day. According to Dunhamel (2012)

the bureau of Labor Statics reported that 605 workers were fatally injured in 2009 and

approximately 212,760 workers were involved in serious accidents due to falling one level or

less. Fall related statistics are published yearly by OSHA and show the severity of occupational

hazards associated with working at height. Falls were the leading cause of fatalities in the

construction industry during 2011 and accounted for 35% of all work related deaths (OSHA,

Construction’s “Fatal Four”, para. 4). In addition to OSHA, other government agencies

periodically publish statistics related to falls. Bickrest (2009) explains that according to the U.S.

Department of Labor (DOL), falls are related to 8% of all occupational deaths from trauma in the

United States and that this number makes falls a primary cause of occupational fatalities. The

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Department of Labor also published reports that indicated at least 442 construction worker

fatalities were attributed to falls in 2007 (Bickrest, 2009). Bickrest (2009) also explains that

roofs are some of the most dangerous fall hazards in the construction industry and were related to

686 deaths between 2003 and 2007. Due to the importance of fall protection on worker safety,

industrial fall protection is key topic among employers, regulators, and end users.

Types of Fall Protection

Fall protection is needed wherever a fall hazard exists. OSHA regulation requires the use

of fall protection when working at 4 feet above a walking/working surface in general industry or

6 ft and higher in construction (Epp, 2007). The best approach is to eliminate the fall hazard by

using passive methods such as guardrails or covers over holes (Denis, 2010). In addition to their

simplicity, passive fall protection systems are also preferred due to their low training

requirements. Torres (2007) explains that:

Railing systems are popular because the worker doesn't have to go through any type of

training in order to stay protected. Once the guard rail is erected, usually on rooftops, the

workers are automatically safer. The only way that a worker is in danger is if he climbs

over the guard rail. (p. 35)

Sometimes passive protection is too costly or cannot be justified given the small amount

of exposure or frequency of fall hazards (Denis, 2010). When passive fall protection cannot be

implemented the use of fall restraint PPE is often the second best option (Denis, 2010). When

fall protection is needed there are multiple types of fall protection systems (FAS) that can be

used depending on the situation. Fall restraint is a type of FPS that does not allow the worker to

fall at all by keeping them away from the fall hazard (Epp, 2007). If work must be done near a

fall hazard, fall arrest and work positioning systems are often needed. Feldstein (2007) describes

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a work positioning system as a subsystem within a fall arrest system that is utilized to stop a fall

from taking place. Work positioning systems must be used in combination with fall arrest

systems to ensure the worker is always protected from a fall in the event that the work

positioning system fails. Fall or work positioning systems are required to limit a workers free

fall to two feet or less (Epp, 2012). According to Denis (2010) “If fall restraint is infeasible, fall

arrest is the next preferred method of fall protection” (p. 48). If a worker falls while using the

appropriate fall arrest equipment, the fall will be arrested so that force and clearance

requirements are maintained (Denis, 2010). As the need for better and more innovative fall

protection equipment increases, so does the need for proper training, planning, and testing.

Torres (2007) states:

Despite all the innovations in technology in the past few years, experts point out that fall

arrest systems and equipment, while important, only are part of the solution to reducing

fall-related injuries and deaths. Employers and workers share the misconception that just

having the right fall protection equipment is the best solution to keep workers safe. (p.

32)

It is not uncommon for employers that have fall hazards to provide formal fall protection

training in addition to providing the required fall PPE (Denis, 2010). There are times when

providing PPE and training is still not enough to protect workers at height. Denis (2010)

explains that an important factor in any safety program is that the fall hazards are continuously

surveyed and the program is updated to reflect a changing work environment. If an organization

does not have the expertise or knowledge to implement a fall protection program, they can look

to the ANSI Z359.2 standard for direction (Denis, 2010). Another important factor in any fall

protection plan is the amount of clearance required for the specific equipment being used. Self-

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retracting lanyards require less fall clearance than shock-absorbing lanyards and therefor can be

used in different settings. The typical required clearance for a six foot shock-absorbing lanyard

is 17.5 ft and includes: free fall, deceleration distance, D-Ring height, harness stretch, and a

safety factor (Epp, 2007).

Rescue is also an important category of fall protection because it is common for

individuals to become incapacitated during or after a fall. Being unconscious while hanging in

fall protection equipment increases the likelihood of suspension related injury. Because of this,

it is imperative that rescue efforts are carried out as soon as possible. Epp (2007) states that

“The final misconception is that calling 9-1-1 automatically fulfills the employer’s responsibility

for rescue planning. Depending on the situation calling 9-1-1 may or may not work. Hang time,

height and available equipment are the true determining factors” (p. 33). Even when all of the

components associated with a fall protection system perform as intended the user can still

become fatally injury due to suspension trauma (Epp, 2007, p. 34). Not only is it important to

use fall protection equipment, it is also important to plan and train for rescue situations.

Common Fall Protection Products, Past and Present

Looking back 50 years, it was difficult to find fall protection equipment and often

workers would resort to crudely made rope lanyards tied around the waist. While this practice

might have stopped workers from hitting the ground, it caused extreme bodily harm in the

process. For this reason, the technology surrounding fall protection has perpetually improved

and continues to reduce workers exposure to injury. Today there are thousands of fall protection

products but many can be categorized into the three categories of anchorages, body support, and

connecting devices. Dunhamel (2012) explains that a simple way to remember the components

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of a fall arrest system is to think of the ABCs where A is anchorage, B is body support, and C is

connecting device.

Anchorages need to be rated to 5,000 lbs per person to be in compliance with OSHA for a

fall arrest system (Epp, 2007). Ellis (2012) describes that an anchorage can be used to support

many fall protection devices ranging from safety nets to EALs and should be designed to

withstand the loads associated with a fall. If a suitable anchorage is not available, the use of fall

protection equipment such as energy absorbing lanyards will not protect the worker. Bickrest

(2009) describes that “Selecting inadequate anchorages is a major problem. The best harness

with the best lanyard or lifeline cannot arrest a fall if unsuitable anchorages are selected” (p. 37).

Another important factor when selecting an anchorage is its location and nearby obstacles.

When investigating a potential anchorage, the qualified person should choose one that is

positioned overhead, will reduce the possibility of swing falls, and allow rescue if needed

(Bickrest, 2009). It is recommended that any anchorage used for fall protection be reviewed and

approved by an engineer with fall protection knowledge (Ellis, 2002).

A full-body harness can be defined as “a body support device that distributes fall arrest

forces across the shoulders, thighs and pelvis and has a center back fall arrest attachment for

connection to the connecting device” (Dunhamel, 2012, p. 44). Although the variety of

harnesses on the fall protection market is similar to the vast number of lanyards styles, the

common theme involves a back D-Ring located between the shoulder blades. Ellis (2012)

describes that the back D-Ring is often allowed to slide and is popular because it distributes the

arrest forces across the harness straps, permits the user to breath comfortably when suspended,

and reduces the possibility of whiplash related injury. Even when harnesses are designed for

specific applications they are still required by ANSI to have a back connection point such as a D-

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Ring. A properly designed D-Ring should be circular and include geometry that will inhibit the

accidental disconnection of snap hooks (Ellis, 2002). It is not uncommon for harness

manufactures to produce various styles for different applications that can include welding, rope

access work, and rescue applications. Ellis (2002) explains that full body harnesses are

traditionally tested for a six foot free fall and must be adjusted properly to ensure the user does

not fall out in the event of a fall.

Connecting devices can take on a variety of forms but are typically self-retracting

lanyards (SRLs) or shock-absorbing lanyards (Dunhamel, 2012). Self-retracting lanyards are

different from EALs as they arrest falls more rapidly (Ellis, 2012). Bickrest (2012) explains that

“One common example is that many contractors buy shock-absorbing lanyards and use them in

areas with inadequate fall clearance. A retractable lifeline or a fall limiter should be used in

certain circumstances” (p. 36). SRLs typically contain a lifeline that is wound on a drum and can

be unwound when slight tension is applied to the device. During a fall the SRL will

automatically lock in a similar fashion to a car seatbelt. Once the SRL is locked, it will arrest the

fall in under 3.5 feet to comply with OSHA and ANSI standards (Duhamel, 2012).

Energy absorbing lanyards do not typically self-retract and are often manufactured from

synthetic materials such as polyester. Lanyards can be described as “a short, flexible rope or

strap webbing that connects a worker’s safety belt to the anchorage point or the grabbing device

on a lifeline” (Ellis, 2002, p. 43). Spotts (1998) describes that EALs are used to increase the

deceleration distance of a fall and subsequently are able to reduce the forces generated during a

fall by 65 to 80 percent which is below the threshold for injury as specified by OSHA.

Two common types of EAL include models with the energy absorber inside a tubular

webbing cover and models based on tear webbing that tears apart in a controlled manner during a

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fall. The tear web based energy absorbers can be added to lanyards that typically are not used

for fall arrest (Spott, 1998). Energy absorbing lanyards are often produced in user specified

lengths which can cause safety concerns if the user does not understand the products limitations.

Wingfield (2010) explains that certain industries such as wind energy and aerospace create

hazards that require the use of a 12 ft free fall EAL which has historically not fallen within the

scope of ANSI. It is not uncommon for users to misuse EALs designed for six foot free falls in

ways that allow a 12 ft free fall (Ellis, 2012). Allowable fall clearance is also a topic of concern

when employees utilize 12 ft free fall EALs. Because of this type of issue in the marketplace,

ANSI has introduced testing criteria for 12 ft free fall lanyards to standardize their construction

and performance characteristics (Wingfield, 2012).

Another common type of fall protection device is the lifeline which can be used

horizontally or vertically (Ellis, 2002). Both horizontal and vertical lifelines can be constructed

of similar materials but their applications can be very different. Ellis (2002) describes vertical

lifelines as “a flexible line for connection to an anchorage point at one end, to hang vertically; it

serves as a means of connecting other components of a personal fall arrest system to the

anchorage” and horizontal lifelines as “an engineered rail, rope, wire or synthetic cable installed

horizontally and used for attaching a worker’s lanyard or lifeline device while moving

horizontally; it is used to control dangerous, pendulum-like swing falls” (p. 44). As with all fall

protection equipment, lifelines are tested and qualified to meet the requirements of their intended

application in accordance with OSHA and ANSI Z359 standards. A component that is regularly

used with vertical lifelines is the rope grab. As their name implies, rope grabs are a type of fall

arresting devices that are connected to vertical lifelines and grab the rope in the event of a fall

(Ellis, 2002).

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ANSI Z359 Committee and Related Standards

The ANSI Z359 committee is a group of safety professions that create standards relating

to fall protection under the provision of the American Nation Standards Institute. The Z359

committee was chartered in 1988 and published the Z359.1 standard four years later in 1992

(Tech Safety Lines, 2009, para. 2). The standard remained essentially unchanged from 1992

until 2007 when multiple revisions were made to improve the performance of fall protection

products baring the Z359 stamp. Since 2007, numerous ANSI Z359 standards have been

published to address specific areas of fall protection. If overlap occurs between the base Z359.1

standard and newly published standards, the new standards will “supersede sections detailed in

the current Z359.1” (Tech Safety Lines, 2009, p. 2). The American National Standards Institute

(2012, code package) has compiled a list of active ANSI/ASSE standards that can be purchased

for use by end users or fall protection equipment manufactures. Table 1 includes all of the ANSI

standards currently being used today (American National Standards Institute, 2012, code

package).

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Table 1

Published ANSI/ASSE Z359 Standards

Title Year Published Description

Z359.0 2007 Definitions and Nomenclature Used for Fall Protection and Fall Arrest

Z359.1 2007 Personal Fall Arrest Systems, Subsystems, Components

Z359.2 2007 Minimum Requirements for a Comprehensive Managed Fall Protection Program

Z359.3 2007 Positioning and Travel Restraint Systems

Z359.4 2007 Assisted-Rescue and Self-Rescue Systems, Subsystems and Components

Z359.6 2009 Specifications and Design Requirements for Active Fall Protection Systems

Z359.7 2011 Qualification and Verification Testing of Fall Protection Products

Z359.12 2009 Connecting Components for Personal Fall Arrest Systems

Z359.13 2009 Personal Energy Absorbers and Energy Absorbing Lanyards

Z359.14 2012 Safety Requirements for Self-Retracting Devices For Personal Fall Arrest and Rescue Systems

Some of the major differences between the ANSI standards and OSHA requirements

include a connector gate face strength increase from 220 pounds of force to 3,600 pounds of

force, an increased lanyard test weight, and rescue systems (Tech Safety Lines, para. 5). Also,

unlike OSHA standards which are required per federal law, the Z359 standards are non-

mandatory. Other differences are pointed out when (Firl & Wolner, 2008) describe “Rescue and

Self-Rescue Systems, Subsystems and Components (ANSI/ASSE Z359.4-2007). These topics

are not addressed in detail in any OSHA standard. Therefore, when people seek guidance on

positioning, travel restraint or rescue, the code provides assistance” (p. 50). One reason that the

ANSI Z359 series standards are becoming popular in the United States is that they are

22

continually updated to reflect current work practices and technologies. Epp (2007) describes that

although OSHA standards are often questioned or confused which has led to over 365 letters of

interpretation by OSHA.

The latest ANSI Z359 standard in regards to energy absorbing lanyards was the Z359.13

standard which was published in 2009. This standard supersedes the original Z359.1 energy

absorbing lanyard requirements and includes a broad range of improvements. The new standard

is tougher and provides specific requirements for EALs from performance criteria to labels and

instructions (Wingfield, 2007). The new standard also includes new testing requirements that are

aimed to improve the performance of fall protection products regardless of the application

(Wingfield, 2007). Overall the Z359.13 standard is a more stringent qualification standard that

will push manufacturers to produce better, more reliable, and safer products. Another important

aspect of the Z359.13 standard is the detailed testing criteria for twin leg or Y-Lanyards. To

reduce the possibility of product misuse, the Z359.13 standard has additional test requirements

for Y-Lanyards and specifies the use of special labeling if products do not meet the Y-Lanyard

tests (Wingfield, 2007). In addition to Y-Lanyard specific testing, the new standard also requires

abrasion testing of wrap around energy absorbers which was not included in previous ANSI

standards (Wingfield, 2007).

Testing Products to ANSI Z359 Standards

The testing required for fall protection equipment has changed dramatically in the past 20

years. A new qualification and testing standard was published in 2011 and is described by

Griffith (2012, p. 34) as “the minimum requirements for the test laboratory, whether that is a

third party or the manufacturer’s in-house lab, as well as the unique equipment to properly test

fall protection equipment covered by any ANSI/ASSE Z359 standard”. This type of standard

23

will benefit the industry by ensuring all manufacturers who mark their product to the ANSI

standard have performed the appropriate testing. The new ANSI standard is titled ANSI Z359.7

and gives manufacturers and or test labs defined test protocols that must be in place prior to

marking a product as meeting ANSI (Griffith, 2012). Griffith (2012) goes on to explain that the

quality requirements of this standard are vital to the industry by keeping non-conforming

products out of circulation.

In addition to ensuring products are tested correctly, the new ANSI standard also requires

manufactures that test their own products to attain ISO 17025 accreditation. The main reason

behind requiring manufacturer test labs to attain ISO certification is to reduce the possibility of

biased test procedures (Griffith, 2012). For a test lab to become ISO 17025 accredited, various

measures must be taken. One of the first things that a test lab needs to do is “establish and

maintain a quality control management program which encompasses the product being tested”

(Griffith, 2012, p. 74). Griffith (2012) also explains that after a product has been qualified in a

17025 accredited test lab, it must be labeled with the appropriate Z359 standard as well as the

Z359.7 standard.

Energy Absorbing Lanyards Designed to Meet the ANSI Z359.13 Standard

Energy absorbing lanyards that have been designed to meet the ANSI Z359.13 standard

are evaluated for both their static and dynamic properties. Although the forces applied to the

human body during a fall cannot be definitively re-created, the Z359 standard has been designed

to simulate real life fall situations. To ensure that the forces recorded when dropping a steel test

weight are representational of the forces applied to the human body, a 1:1.1 test weight

conversion factor has been agreed upon by the Z359 committee. Wingfield (2010) describes that

“Using a more accurate conversion factor and, therefore, a greater weight will model energy

24

absorbers during testing that will more closely represent applications by the workings in the

field” (p. 75). Historically, the factor between a steel test weight and human body has been 1:1.4

but was changed in 2009 based on extensive research conducted by Gravitec Systems

(Wingfield, 2010). By applying the 1:1.1 factor to the maximum user weight recognized by

ANSI, a test weight of 282 lbs was determined. In addition to using a representative test weight,

the Z359.13 standard also specifies that EALs be tested in a variety of environmental conditions

to simulate real world work settings. Among the ambient dynamic tests, EALs are also

dynamically tested when wet, cold, and hot. After the EAL has been dynamically tested using the

282 lb test weight, the sample is then statically tested to ensure its structural integrity post

deployment. Various static tests are specified in the Z359.13 standard but the one constant is

that an energy absorbing lanyard shall be capable of withstanding a 5,000 lb static load for a

period of one minute. Although not new to the Z359.13 standard, the need for multiple static

tests is exemplified by:

Concerns over potential misuse of twin-leg shock-absorbing lanyards prompted

additional test requirements and warnings for these products, which were not mentioned

in the 1999 version. The new standard includes a 5,000 lb static test of the joint between

the two lanyard legs. (Feildstein, 2007, p. 47)

One goal of the final static requirement is to reduce the possibility that a lanyard will fail after it

has successfully arrested a fall. Another reason that the 5,000 lb static requirement exists is to

provide protection against falls that exceed the energy absorbing capacity of the EAL.

When comparing the new and old ANSI Z359 testing requirements, the most profound

changes are the use of a heavier test mass, an increase allowable energy absorber elongation,

different classes based on free fall allowance, and the use of MAAFs versus MAFs. Since its

25

first publication in 1992, the Z359.1 standard has specified that energy absorbing lanyards be

tested using a 220 lb test weight (Wingfield, 2010). This 220 lb test weight requirement

remained part of the standard for 17 years until the release of the Z359.13 standard in 2009.

Wingfield (2010) explains the importance of having two classes by stating “Until now, standards

for lanyards that were manufactured for a free fall greater than 6 ft did not exist” (p. 74). The

new 12 ft class has allowed manufacturers to produce ANSI approved products that are used in

this application. As the test weight increased so did the maximum allowable elongation from 42

inches to 48 inches for 6ft EALs and 60 inches for 12ft EALs which allowed arrest forces to

remain within acceptable ranges (Wingfield, 2010).

Lastly, the Z359.13 committee adopted the MAAF measurement method in place of the

traditional MAF method. Prior to 2009, all EALs were tested to a pass/fail criterion that only

allowed arrest forces up to 900 pounds force (lbf) regardless of duration. The Z359 committee

elected the MAAF method based on research that impulse forces below a particular duration

were not detrimental to the human body and sustained forces are the leading cause of injury

during fall arrest. Using the MAAF measurement method, the Z359 committee specified that the

MAAF shall not be greater than 900 lbf after a 6 ft free fall or 1,350 lbf after a 12 ft free fall.

Although the MAAF method is utilized in the Z359.13 standard, a MAF of 1,800 lb is specified

for both 6 ft and 12 ft free fall EALs.

Summary

Industrial fall protection is a continually growing category of occupational safety due to

the widespread exposure to fall hazards. Falling from height has historically proven to be one of

the leading cases of workplace fatalities in the U.S. and a major contributor to employee injuries.

Workplace accidents related to falling from height have caused an influx of interest in fall

26

protection from workers, employers, and government agencies. Over the past 50 years, fall

protection has become a large and diverse industry. This new industry has generated many new

practices and techniques to protect workers from falls. Fall restraint, fall arrest, work

positioning, and rescue systems are all examples of the perpetually evolving methods used to

ensure worker safety. In addition to various types of fall protection, there are also many different

types of fall protection products that are used for specific applications. Oftentimes the design,

function, and performance of fall protection devices are governed by national standards such as

OSHA and ANSI. These national standards impose strict guidelines on the qualification testing

of safety products to ensure reliability. Some of the most recent developments related to fall

protection standards include the ANSI Z359.13 standard which was published in 2009 and

relates to energy absorbing lanyards.

27

Chapter III: Methodology

When evaluating an industrial setting for workplace hazards it not uncommon to find

unguarded elevated work surfaces. If elevated work surfaces cannot be guarded or eliminated

through engineering controls, the use of personal protective equipment is a common solution to

protect workers at height. While there is an abundance of fall protection products available to

organizations around the world, some of the most common fall protection PPE devices are

energy absorbing lanyards used to connect a workers full body harness to an anchorage.

Although the construction of energy absorbing lanyards differs from manufacturer to

manufacturer, the fundamental principles of operation are similar due to standardized testing.

Historically, U.S. manufacturers have designed, built, and tested EALs to meet OSHA

requirements which specified that the maximum arresting force applied to the human body could

not exceed 1,800 lb. As PPE technology progresses and standards organizations such as ANSI

investigate how falls affect the human body, standards are ever changing to improve product

performance. Although not required by law the ANSI Z359.13 fall protection standard has

become widely adopted in the U.S. fall protection market. One of the most significant

differences between the ANSI Z359.13 fall protection code and OSHA regulations is the use of

maximum average arresting force criteria during dynamic testing of energy absorbing lanyards.

When EALs are tested using ANSI prescribed dynamic test methods, the MAAF results have

varied depending on the material and construction of the lanyard legs.

The topics described in the methodology portion of this study are closely related to the

testing procedures as required by the ANSI Z359.13 standard for EALs. These procedures

include test set up, equipment, measurement, and data acquisition. In addition to the testing of

28

EALs, the methodology used to interpreted, statistically analyze, and draw conclusions from test

data will also be described.

Lanyard Selection and Description

The energy absorbing lanyards selected for this study include 6 ft free fall models based

on ANSI Z359.13 requirements and exclude all 12 ft free fall models. While similar in

constriction to the 6 ft free fall lanyards, the 12 ft free fall models include additional webbing

within the energy absorber for greater energy absorbing capacity. Higher capacity models were

excluded due to their construction and use being similar to 6 ft free fall models. A drawing that

describes a typical single web leg energy absorbing lanyard can be found in Appendix B. All

test samples were built in a production setting from computer generated work orders to improve

product consistency. The specific lanyard leg materials chosen for this study included all of the

materials commonly offered by fall protection equipment manufacturers. The following lanyard

leg materials were dynamically tested during this study:

Polyester webbing (8,000 lb tensile strength)

Polyurethane coated polyester webbing (9,800 lb tensile strength)

Polyester tubular webbing (6,600 lb tensile strength)

Nylon webbing (13,000 lb tensile strength)

Aramid webbing (9,800 lb tensile strength)

Nylon/polyester static kernmantle rope (10,000 lb tensile strength)

Galvanized Steel Cable (7,000 lb tensile strength)

All test lanyards consisted of one tear web style energy absorber, one lanyard leg, and two ANSI

qualified connectors. Dual leg lanyards were not tested during this study as they have a similar

construction to single leg lanyard with the exception of two legs versus one.

29

Instrumentation and Test Equipment

The instrumentation and test equipment utilized for this experiment included the

following: 282 lb test weight, 10,000 lb rated strain gauge load cell, Microsoft Windows based

data acquisition software program, calibrated measurement equipment per ISO 17025, electronic

quick release mechanism, and desktop computer. Auxiliary equipment such as data cables and

connecting carabiners was also used to couple the various components together. In addition to

the drop test equipment, an environmental conditioning chamber was utilized to condition the

samples to the ambient wet, cold dry, and hot dry environmental conditioning requirements in

accordance with ANSI Z359.13. Lastly, the structure used to perform the tests was built and

tested to meet the structural and frequency requirements specified in the ANSI Z359.13 standard.

Data Collection Procedures

The data collection procedure employed during this study involved taking measurements

from the load cell at a frequency no less than 1,000 Hz during each dynamic drop test. When

testing the 6 ft free fall EALs the 282 lb test weight was raised 6 ft and dropped using the quick

release mechanism. In total a series of 84 dynamic tests were conducted using twelve samples of

each lanyard leg material. Each group of twelve samples was divided into subgroups of three

and tested in accordance with the conditioning requirements of ANSI Z359.13. For each lanyard

leg type the following tests were performed: three ambient dry, three ambient wet, three cold dry,

and three hot dry. The measurements were then imported into the desktop computer via the data

acquisition software. Once the test was complete, the data acquisition software was used to

appropriately filter the data and convert it into a usable form. After data processing, the test

results were transferred into a formal test report document which includes values such as MAF,

MAAF, initial lanyard length, and final lanyard length. All of the procedures, documentation,

30

and test protocols utilized during this study met the requirements of an ISO 17025 accredited

testing laboratory.

Determination of Lanyard Leg Stiffness

For purposes of this study, the lanyard leg materials were treated as ideal springs where

all deformations are elastic and strain energy is recoverable in the form of mechanical work.

Under this assumption, stress and strain values of the lanyard legs are proportional up to the

material proportionality limit and follow Hooke’s law (Cutnell & Johnson, 1992). While some

lanyard leg deformation is not elastic, it is assumed to be related to constructional stretch of the

leg material and not due to plastic deformation. Hooke’s law can be described as:

(1)

where F is the force required to stretch or compress a spring, k is the spring constant or stiffness,

and x is elastic deformation. This relationship between force and elongation was used to

determine the stiffness of each lanyard leg material.

To benchmark the lanyard leg materials against each other, a standardized test was

developed to determine the stiffness of each material. The basis of this test was to gather force

versus elongation data by statically pulling each leg material at a rate of two inches per minute

and measure elastic deformation while under load. Seven test specimens were produced using

the applicable lanyard leg materials and included a 2 ft effective length between stitch patterns or

swage fittings. Although 6 ft free fall EALs typically utilize lanyard legs longer than 2 feet, this

length was used due to tensile test equipment height restrictions. It should be noted that material

stiffness is proportional to length and longer test specimens would result in lower spring

constants. The samples were measured before, during, and after being tensile tested to 1,800 lb

and constructional stretch was then subtracted from elongation measurements. To ensure the

31

samples were in tension prior to initiating the test, a preload of 20 lb was used to set initial

length.

Strain Rate Analysis

During dynamic testing of EALs, it is often observed that higher velocities produce

higher average arrest forces. This information is widely accepted in the fall protection industry

and is typically available through free fall versus MAAF charts in EAL user instructions. To

verify this concept, nine 6 ft free fall energy absorbers were tested using steel cable test lanyards.

Three samples were dynamically tested using 2 ft, 4 ft, and 6 ft free falls. The data collected

from these tests was then plotted versus impact velocity to determine any correlation. The

velocity at impact can be calculated using the general kinematic equation for constant

acceleration (Cutnell & Johnson, 1992):

(2)

which reduces to:

√ (3)

where is velocity at impact, is the acceleration due to gravity (32.2 ft/sec), and y is free fall

distance.

In addition to testing tear web in a dynamic context, tear webbing samples were also

tensile tested in a quasi-static setting at various rates to establish any relationship between

velocity and MAAF at low speeds. The test procedure included a tear web sample being tensile

tested in a tensile testing machine at velocities of 0.25, 1.00, 4.00, 10.00, and 20.00 inches per

minute. The duration of each test was modified according to the velocity to elongate one inch of

tear webbing only. Using this data, the average force required to elongate one inch of tear

webbing at a particular speed was calculated.

32

Descriptive Statistical Analysis

Standard descriptive statistical analysis techniques were used to organize the data

obtained during this experiment. The overall sample population was broken down into multiple

subpopulations so that descriptive statistical values could be calculated for individual lanyard leg

types and conditions. Environmental test conditions are a major factor in product performance

and therefore were used to separate the data. The values associated with each lanyard leg type

were tabulated and can be found in Appendix A. Bar charts and other graphical descriptions of

the data can be found in Appendix B.

Inferential Statistical Analysis

After the data was collected and organized, various inferential statistical analysis

techniques were used to determine if the relationship between lanyard leg materials and MAAFs

is statistically significant. Hypothesis testing was conducted where the null hypothesis states that

the lanyard leg material has no effect on MAAF measurements and the alternate hypothesis

states that the lanyard leg materials causes a statistically significant effect on MAAF

measurements. An alpha value (α) of 0.05 was consistently used during this study to obtain a

minimum of 95% confidence. Other inferential statistical analysis methods were utilized and

included: linear regression analysis, one-way Analysis of Variance (ANOVA), two-way

ANOVA with replication, Tukey’s range test, and normality tests. Various graphs, tables, and

plots relating to the inferential statistics performed during this study can be found in Appendix

D.

Limitations

Because of the wide variety of energy absorbing lanyard styles available, this study was

limited to one brand. This brand only utilizes one type of energy absorber which is a propriety

33

product supplied by one webbing manufacturer. Also, all EALs tested during this study were

designed to meet the 6 ft requirement of ANSI Z359.13. Test results from standards that do not

require MAAF measurements such as CSA and OSHA were not included with this study.

Lastly, due to the small sample sizes for each environmental condition and lanyard leg

combination, normality testing was limited.

Assumptions of the Study

Based on the requirements necessary to become an ISO 17025 Testing Laboratory, all

measurements taken during this study were assumed to be correct. Also, it was assumed that all

documentation and procedures were conducted accurately. Other sources of variation such as

manufacturing related defects and material variation will be assumed to be zero. Lastly, it was

assumed that all data sets obtained from testing are normally distributed.

Summary

The energy absorbing lanyards tested for the purposes of this study were chosen to

represent common fall protection equipment found in nearly all industries with workers at height.

Due to stringent testing procedures and requirements set forth by ANSI, this study is

representative of the testing required for a manufacturer to qualify products to ANSI Z359.13.

The statistical analysis resulting from this study will increase the body of knowledge surrounding

the testing of fall protection equipment.

34

Chapter IV: Results

The purpose of this study was to determine the effects of lanyard leg construction

variation on MAAF measurements when testing energy absorbing lanyards in accordance with

ANSI Z359 requirements. The information obtained from this study will be used as a reference

in the future development of energy absorbing lanyards used for fall protection. To simulate the

testing requirements of a new lanyard product line, eighty-four dynamic drop tests were

conducted. Seven lanyard leg materials were studied in combination with a specific 6 ft free fall

energy absorber. Each of the seven lanyard models was subjected to four different

environmental conditions prior to performing the dynamic drop tests. The data collected from

these tests was analyzed using descriptive and inferential statistical methods to determine if

lanyard leg materials have an effect on MAAF measurements.

Descriptive Statistical Analysis

As described in the methodology portion of this study, standard descriptive statistical

values were calculated using MAAF measurements taken during dynamic drop tests per ANSI

Z359.13. The MAAF measurement is obtained by dynamically dropping a test sample and

recording the force versus time data as shown in Figure 1.

35

Figure 1. Example of force versus time graph for steel cable leg EAL.

After the data has been collected, all data points above 500 lb are combined and divided by the

total number of data points to calculate the MAAF. Figure 1 is an example of a cable leg lanyard

dynamic drop test. When compared to the force versus time graphs of web and rope leg

lanyards, there is a noticeable difference in response curve shape. It is typical for lanyards with

synthetic leg materials to have higher force values near the end of the dynamic test. Examples of

polyester web and polyester/nylon rope leg lanyard force versus time graphs are shown in

Appendix B.

Because environmental conditioning can affect MAAF measurements, values for each leg

type were calculated four times to separate the different environmental test results. The

descriptive statistical values for the ambient test condition are shown below in table 2:

36

Table 2

Descriptive Statistics - Ambient Condition

Aramid Nylon Polyester Polyester, Tubular Polyester/TPU Steel Cable Polyester/Nylon

Mean 830.33 850.67 854.33 828.67 858.33 842.67 874.00

Standard Error 4.18 13.84 5.24 9.82 19.06 10.84 7.51

Median 834.00 864.00 853.00 828.00 859.00 853.00 867.00

Standard Deviation 7.23 23.97 9.07 17.01 33.01 18.77 13.00

Sample Variance 52.33 574.33 82.33 289.33 1089.33 352.33 169.00

Skewness -1.69 -1.73 0.65 0.18 -0.09 -1.73 1.72

Range 13.00 42.00 18.00 34.00 66.00 33.00 23.00

Minimum 822.00 823.00 846.00 812.00 825.00 821.00 866.00

Maximum 835.00 865.00 864.00 846.00 891.00 854.00 889.00

Count 3.00 3.00 3.00 3.00 3.00 3.00 3.00 Confidence Level (95.0%) 17.97 59.53 22.54 42.25 81.99 46.63 32.29

The lanyards with the highest mean MAAF were models that included lanyard legs constructed

from polyester/nylon rope. It should also be noted that the rope leg models accounted for the

second highest MAAF value following polyester/TPU lanyard leg models. The lanyards with the

lowest mean MAAF were those constructed with tubular polyester webbing legs. Models with

tubular polyester legs also produced the lowest MAAF values. A bar chart that graphically

describes the difference in leg type means is shown below in Figure 2.

37

Figure 2. Bar chart of mean MAAF results for lanyard leg materials in the ambient condition.

Bar charts for each of the environmental test conditions were created to visually represent how

lanyard leg materials affect MAAF measurements. Bar charts for the cold dry, hot dry, and

ambient wet environmental test condition can be found in Appendix B.

Inferential Statistical Analysis

To properly understand how lanyard leg materials affect MAAF measurements, the data

collected during this study was analyzed using standard inferential statistical techniques. The

first statistical test that was performed was the two-factor Analysis of Variance (ANOVA) with

replication test. This test was used to determine if the mean MAAF results were significantly

different between environmental test conditions, lanyard leg types, and to evaluate interaction

between both variables. Table 3 describes the calculated results from the two-factor ANOVA

with replication.

38

Table 3

ANOVA: Two-Factor With Replication

Summary Aramid Nylon Polyester Polyester, Tubular Polyester/TPU Steel Cable Polyester/Nylon Total

Ambient Count 3.00 3.00 3.00 3.00 3.00 3.00 3.00 21.00

Sum 2491.00 2552.00 2563.00 2486.00 2575.00 2528.00 2622.00 17817.00

Average 830.33 850.67 854.33 828.67 858.33 842.67 874.00 848.43

Variance 52.33 574.33 82.33 289.33 1089.33 352.33 169.00 492.36

Cold Dry Count 3.00 3.00 3.00 3.00 3.00 3.00 3.00 21.00

Sum 2765.00 2777.00 2708.00 2563.00 2614.00 2553.00 2658.00 18638.00

Average 921.67 925.67 902.67 854.33 871.33 851.00 886.00 887.52

Variance 345.33 2809.33 554.33 456.33 1952.33 721.00 589.00 1575.26

Hot Dry Count 3.00 3.00 3.00 3.00 3.00 3.00 3.00 21.00

Sum 2425.00 2584.00 2456.00 2498.00 2529.00 2326.00 2829.00 17647.00

Average 808.33 861.33 818.67 832.67 843.00 775.33 943.00 840.33

Variance 404.33 120.33 956.33 16.33 837.00 440.33 169.00 2809.23

Ambient Wet Count 3.00 3.00 3.00 3.00 3.00 3.00 3.00 21.00

Sum 2624.00 2480.00 2566.00 2480.00 2518.00 2548.00 2424.00 17640.00

Average 874.67 826.67 855.33 826.67 839.33 849.33 808.00 840.00

Variance 30.33 190.33 52.33 1166.33 80.33 460.33 76.00 641.20

Total Count 12.00 12.00 12.00 12.00 12.00 12.00 12.00 Sum 10305.00 10393.00 10293.00 10027.00 10236.00 9955.00 10533.00 Average 858.75 866.08 857.75 835.58 853.00 829.58 877.75 Variance 2213.48 2134.63 1270.75 483.54 897.45 1439.72 2692.75 ANOVA Source of Variation SS df MS F P-value F crit Sample 32290.52 3.00 10763.51 20.04 5.98E-09 2.77 Columns 20196.07 6.00 3366.01 6.27 4.40E-05 2.27 Interaction 60092.31 18.00 3338.46 6.22 6.05E-08 1.79 Within 30072.67 56.00 537.01 Total 142651.57 83.00

Using the probability values (P-values) from Table 3, it can be concluded that there is a

statistically significant difference in mean MAAF results between leg types, environmental test

39

conditions, and there is significant interaction between the two independent variables. The null

hypothesis (H0) that the lanyard leg mean MAAF results, environmental mean MAAF results,

and interaction between results are equal can be rejected and the alternate hypothesis can be

accepted. All P-values obtained from this test were below an alpha (α) value of 0.05 which

indicates a greater than 95% confidence in the analysis results.

The second statistical test that was performed was a single factor ANOVA. The single

factor ANOVA was used to determine if the difference between the MAAF results for each

lanyard leg type was statistically significant. This single factor ANOVA was performed for each

of the four environmental test conditions. Table 4 describes the results of the ambient condition

single factor ANOVA. The null hypothesis (H0) states that the mean MAAF values for each leg

type will be equal. The alternate hypothesis (HA) states that the mean MAAF values for leg type

are different. An alpha (α) value of 0.05 was used to test for 95% confidence.

40

Table 4

Single Factor ANOVA - Ambient Condition

Groups Count Sum Average Variance Aramid 3.00 2491.00 830.33 52.33 Nylon 3.00 2552.00 850.67 574.33 Polyester 3.00 2563.00 854.33 82.33 Polyester, Tubular 3.00 2486.00 828.67 289.33 Polyester/TPU 3.00 2575.00 858.33 1089.33 Steel Cable 3.00 2528.00 842.67 352.33 Polyester/Nylon 3.00 2622.00 874.00 169.00 ANOVA Source of Variation SS df MS F P-value F crit Between Groups 4629.14 6.00 771.52 2.07 0.12 2.85 Within Groups 5218.00 14.00 372.71 Total 9847.14 20.00

The calculated P-value for Table 4 was 0.12 which indicates that the null hypothesis can be

accepted and the data does not indicate a statistically significant difference in mean MAAF

measurements between lanyard leg types in the ambient condition. A single factor ANOVA was

performed on the cold dry, hot dry, and ambient wet environmental condition data sets and

produced P-values of 0.06, 4.12E-06, and 0.01, respectively. These P-values indicate that the

null hypothesis can be accepted for the cold dry condition and rejected for the hot dry and

ambient wet test conditions. This is evidence that during the hot dry and ambient wet condition

dynamic drop test, there is a statistically significant difference in MAAF measurement between

lanyard leg types. Single factor ANOVA results for the cold dry, hot dry, and ambient wet test

conditions can be found in appendix D.

Using the single factor ANOVA statistical test results, a Tukey’s range test was

performed on the ANOVA data from the hot dry and cold dry condition dynamic drop tests. The

purpose of the Tukey’s range test was to determine which leg materials were statistically

41

different from each other as the ANOVA test only described that there was a difference within

the group. The Tukey test statistic was calculated using the mean square (MS) within groups and

sample size (n) data from the hot dry and cold dry single factor ANOVA in combination with a

value from “a studentized range statistic (q) table” (“Duke,” para. 1, 2013). After the test

statistic was calculated, the difference between lanyard leg type means was determined and

compared against the Tukey statistic. The Tukey’s range test showed that polyester/nylon rope

lanyard leg mean MAAF results were significantly different than all of the other leg types in the

hot dry condition. The hot dry condition Tukey’s range test also showed that the steel cable

mean MAAF results were significantly different than the nylon, tubular polyester, and

polyester/TPU lanyard legs mean MAAF results. Table 5 describes the Tukey’s range test for

the hot dry condition single factor ANOVA and highlights the significantly different leg types.

Table 5

Tukey’s Range Test – Hot Dry Condition Single Factor ANOVA

q-value MS n Tukey Test Statistic

4.83 420.52 3.00 57.18 Groups Average 1st 2nd 3rd 4th 5th 6th

Aramid 808.33

Nylon 861.33 53.00

Polyester 818.67 10.33 42.67 Polyester, Tubular 832.67 24.33 28.67 14.00

Polyester/TPU 843.00 34.67 18.33 24.33 10.33

Steel Cable 775.33 33.00 86.00 43.33 57.33 67.67

Polyester/Nylon 943.00 134.67 81.67 124.33 110.33 100.00 167.67

42

A Tukey’s range test for data calculated from the cold dry condition single factor ANOVA can

be found in Appendix D.

As described in the methodology portion of this document, seven test specimens were

tensile tested to determine the lanyard leg stiffness characteristics. The values calculated from

the data obtained during these tests are related to elastic deformation, stiffness, and strain. Table

6 is shown below and describes the results obtained from the lanyard leg stiffness comparison

tests.

Table 6

Lanyard Leg Stiffness Comparison Tests

Initial Length

(Li) Final Length

(Lf) Elongation Under Load

Constructional Stretch

Elastic Deformation

(δ) Stiffness (k) Strain (ε)

in. in. in. in. in. lb/in. in./in.

Aramid Webbing 34.63 35.00 1.53 0.38 1.16 1558.44 0.03

Nylon Webbing 35.50 36.50 2.25 1.00 1.25 1440.00 0.04

Polyester Webbing 36.50 38.00 3.65 1.50 2.15 837.21 0.06

Polyester, Tubular Webbing

32.50 34.00 3.85 1.50 2.35 765.96 0.07

Polyester/TPU Webbing 35.00 35.25 2.20 0.25 1.95 923.08 0.06

Steel Cable 38.13 38.16 0.22 0.03 0.19 9442.62 0.00

Polyester/Nylon Rope 33.25 34.13 4.91 0.88 4.04 446.10 0.12

Based on the lanyard leg stiffness comparison tests, it is evident that the leg material with the

highest spring constant is steel cable. The material with the lowest spring constant was the

polyester/nylon rope with a k value of 446.10 lb/in. and a strain value of .12 or 12 percent.

Using the mean MAAF data obtained during dynamic drop tests and the stain data from Table 6,

43

a regression analysis was performed to evaluate the relationship between these variables. A

scatterplot of the mean MAAF versus strain relationship for the hot dry environmental condition

is shown below in Figure 3. In addition to the individual data points, a trend line and linear

equation have been added to the scatterplot to show the positive correlation between mean

MAAF and strain. The hot dry condition scatterplot was chosen due it having the highest

coefficient of determination (R2) value which was equal to 0.76. This R2 value indicates that

approximately 76 percent of the variability in the data set can be associated with the relationship

between mean MAAF and strain. Mean MAAF data from each of the environmental condition

was plotted versus strain and the R2 values for the ambient, ambient wet, and cold dry condition

were 33 percent, 45 percent, and 0.2 percent, respectively. This information suggests that during

the ambient and hot dry condition tests there is a direct relationship between mean MAAF and

strain. The ambient wet condition data suggests that there is an inverse relationship between

mean MAAF and strain. Based on the R2 value being nearly zero for the cold dry condition tests,

a relationship between mean MAAF and strain could not be determined.

Figure 3. Mean MAAF versus strain in the hot dry condition.

44

The fourth statistical analysis technique utilized to determine the effects of lanyard leg

variation on MAAF was linear regression analysis. Using the same data from the mean MAAF

versus strain scatterplots, a regression analysis was performed on the hot dry and ambient wet

data as they produced the highest R2 values. Table 7 shows the results from the hot dry condition

mean MAAF versus strain linear regression analysis.

45

Table 7

Regression Analysis of Mean MAAF versus Strain – Hot Dry Condition

Summary Regression Statistics Multiple R 0.87

R Square 0.76 Adjusted R Square 0.71 Standard Error 28.55 Observations 7.00 ANOVA df SS MS F Significance

F Regression 1.00 12690.08 12690.08 15.57 0.01 Residual 5.00 4075.70 815.14 Total 6.00 16765.78 Coefficients Standard

Error t Stat P-value Lower 95% Upper 95%

Lower 95.0%

Upper 95.0%

Intercept 771.96 20.41 37.81 0.00 719.48 824.43 719.48 824.43 Velocity 1253.48 317.69 3.95 0.01 436.84 2070.12 436.84 2070.12

Using the P-value from Table 7, the null hypothesis that there is no significant linear correlation

between variables can be rejected and the alternate hypothesis can be accepted. This indicates

that there is 95 percent confidence that the mean MAAF values will increase when lanyard leg

strain values increase during the hot dry condition tests. The ambient wet condition linear

regression analysis is shown in Appendix D and also includes a P-value of less than 0.05

indicating the null hypothesis can be rejected and there is an inverse relationship between mean

MAAF.

Tear Webbing Velocity Response Analysis

As described in the methodology portion of this study, the MAAF data obtained from

dynamic testing nine energy absorbers was plotted versus impact velocity which was determined

from free fall distance. Figure 4 describes the data using a scatterplot and also includes a trend

46

line with linear equation and R2 value of 0.54. Linear regression analysis was also performed on

this data set and can be found in Appendix D. The linear regression analysis showed a P-value

of 0.02 which indicates that the null hypothesis can be rejected and the alternate hypothesis that

there is a relationship between MAAF and impact velocity can be accepted.

Figure 4. MAAF versus impact velocity.

To verify if tear webbing MAAF results are related to velocity at low speeds, a tensile

test was developed as described in the methodology portion or this study. The tensile test

procedure was related to tensile testing tear webbing through a distance of one inch at five

different velocities. The test was performed three times and then averaged to accumulate the 5

data points as shown below in Table 8.

47

Table 8

Tear Web Strain Rate Analysis

Velocity Average Force Elongation Energy

(in./min) (lb) in. (ft·lb)

0.25 1313.12 1.00 109.43

1.00 1222.82 1.00 101.90

4.00 1097.86 1.00 91.49

10.00 1031.39 1.00 85.95

20.00 1046.82 1.00 87.24

The data points were then averaged and plotted against velocity as shown in Figure 5.

Figure 5. Average force versus velocity.

A trend line was fitted to the data and shows an inverse relationship between velocity at low

speeds and average force. The R2 value of 0.54 indicates that 54% of the variation can be

attributed to this relationship. In addition to the scatter plot with linear equation, a linear

48

regression analysis was performed on the data. Table 9 includes the regression analysis data for

average force versus velocity.

Table 9

Regression Analysis of Average Force versus Velocity

Summary Regression Statistics

Multiple R 0.73 R Square 0.54 Adjusted R Square 0.50 Standard Error 84.01 Observations 15.00 ANOVA df SS MS F Significance

F Regression 1.00 105752.98 105752.98 14.98 0.00 Residual 13.00 91754.99 7058.08 Total 14.00 197507.97 Coefficients Standard

Error t Stat P-value Lower 95% Upper 95%

Lower 95.0%

Upper 95.0%

Intercept 1223.18 30.10 40.64 0.00 1158.15 1288.20 1158.15 1288.20 Velocity -11.46 2.96 -3.87 0.002 -17.85 -5.06 -17.85 -5.06

The linear regression analysis for average force versus velocity produced a P-value of 0.002

which allows the null hypothesis to be rejected and the alternate hypothesis accepted. This gives

95% confidence that the average force to elongate one inch of tear webbing is related to the

velocity. To test the normality of error for this linear regression analysis, an Anderson-Darling

normality test was performed on the residual data. The normality test produced a P-value of 0.39

which indicates that the error within the analysis is normally distributed. A plot of the

Anderson-Darling normality test for residuals can be found in Appendix B.

49

Chapter V: Discussion

Energy absorbing lanyards have the potential to dramatically reduce the likelihood of

injury during a fall by limiting arrest forces. Historically, manufactures of energy absorbing

lanyards have reduced arrest forces by utilizing the elastic properties of rope. As fall protection

standards become more stringent, so do the tests associated with qualifying energy absorbing

lanyards, making rope lanyards obsolete. To ensure equipment compliance, manufacturers

typically use woven products such as polyester or nylon webbing in the construction of energy

absorbing lanyards. Because every work environment is different, so are the requirements of

individuals who use fall protection equipment. This variation in equipment requirements has

driven manufactures to produce energy absorbing lanyards in a multitude of configurations.

Because every material reacts differently under stress, the force generated from different lanyard

leg materials can affect test results, which causes variability within product lines. This

variability adds development cost to new EAL projects due to the additional research and

development testing needed to verify materials.

Based on the historical information presented in this study, it is apparent that testing of

fall protection device is an important and continually changing process. Fall protection

equipment manufactured in the United States is typically tested to OSHA standards which only

require MAF measurements as well as the Z359.13 standard for EALs that requires both MAF

MAAF measurements. The MAAF requirement has only been in use since 2009 and little data

has been published as to how different lanyard leg materials affect MAAF test results. The

testing and analysis of this study was related to MAAF measurements and lanyard leg variation

and employed a variety of statistical tests to determine the significance of the observed data. Test

results from this study compared MAAF data with lanyard leg types, environmental test

50

conditions, leg stiffness, and impact velocity. Each of these tests yields insight into how tear

webbing based energy absorbers react when tested using various leg materials.

Discussion

The data and analysis from this study suggest that there is a direct relationship between

MAAF measurements and lanyard leg stiffness when tested dynamically in accordance with the

ANSI Z359.13 standard. The seven lanyard leg materials that were tested ranged from steel

cable to polyester/nylon rope and had a wide range of spring constants. The first portion of the

analysis was to use descriptive statistics to organize the data for subsequent analysis. Once the

data was organized, descriptive statistical techniques such as ANOVA, linear regression,

Tukey’s range test, and normality tests were utilized. By using the one way and two-way

ANOVA tests, it was determined that there was a significant difference in MAAF forces between

leg types and test conditions. The ANOVA results also indicated that the only statistically

significant differences between leg materials occurred during the hot dry and ambient wet

condition tests. Although these tests are based on small data sets, they are beneficial in

determining how 6 ft free fall EALs will react when tested using different leg materials. By using

the Tukey’s range test, it was established that the polyester/nylon rope leg MAAF results were

the most significantly different from the other leg materials.

The environmental test condition that showed the highest correlation between lanyard leg

stiffness and MAAF was the hot dry condition. The linear regression analysis was based on

MAAF versus strain data which is the ratio of elastic deformation in relation to initial length.

This relationship was mirrored by the ambient condition tests but with less statistical confidence.

The ambient wet condition tests showed the opposite effect and displayed a negative correlation

between MAAF and strain. Data obtained from the cold dry tests did not show a significant

51

correlation between MAAF and lanyard leg material strain. The material the highest amount of

leg strain was the polyester/nylon rope and accounted for two of the four test conditions highest

MAAF results.

Another aspect of energy absorber performance that was analyzed during this study was

that of energy absorber response to strain rate or impact velocity. Two tests were set up to

collect quantitative data on the MAAF versus velocity relationship. The first test involved

dynamically drop testing lanyards from different heights and measuring the MAAF. It was

found that MAAF results show a positive correlation with impact velocity at high speeds. The

second force versus velocity test involved tensile testing tear webbing in a quasi-static state at

five different velocities. This series of tests produced the opposite effect as the dynamic MAAF

versus velocity tests and showed a negative correlation between strain rate and average force to

separate one inch of tear webbing.

Limitations

The major limitation of this study was sample sizes. Because each data set only included

three data points for each lanyard leg material/test condition combination, the normality of the

data could not be adequately verified. Small sample size also contributes to percent error as the

data cannot be fully representational of the greater population. Another limitation to this study

was the lanyard leg stiffness comparison tests only being conducted in the ambient condition and

with test samples approximately half the length of a typical 6 ft free fall lanyard leg. Due to

stiffness being directly proportional to length, the spring constant values obtained during this

study are conservative. Also, because the properties thermoplastic materials such as nylon and

polyester are greatly affected by temperature, the stiffness tests at room temperature are not fully

representative of the lanyard legs during environmental conditioning tests. Lastly, because the

52

majority of lanyard leg materials are based on woven products such as webbing or rope, the

mechanical analysis of these materials is limited and computer based simulation programs are

not sufficient to accurately model the internal geometry and fiber interactions of lanyard leg

materials.

Conclusions

In conclusion to this study, it has been observed that tear web style energy absorbing

lanyard MAAF test results are affected by different lanyard leg materials. When tested in the

ambient and hot dry condition, lanyards with legs comprised of high stretch materials such as

polyester/nylon rope typically exhibit higher MAAF forces. Lanyards constructed with stiff leg

materials such as steel cable are less susceptible to this issue. When tested in the ambient wet

condition, the opposite effect has been observed and lanyard leg stiffness is negatively correlated

with MAAF. A correlation between lanyard leg stiffness and MAAF was not observed when

tested in the cold dry condition. The literature review portion of this study described how testing

of EALs has evolved throughout the past 50 years and the importance of adequate testing on fall

protection equipment performance. The energy absorber was described as an integral part in

many fall arrest systems and understanding how EALs react during fall events is paramount to

safety and user wellbeing.

It has also been observed that at high speeds such as during a dynamic fall event, the

MAAF measurement will increase with velocity. Increasing free fall height yields this effect as

impact velocity is a function of free fall distance. When tested at speeds less than two feet per

minute, tear webbing shows signs of increased average force per unit distance as speed

decreases. This observation does not mirror the material properties when tested at high speeds.

By calculating the amount of energy required to elongate one inch of tear webbing at various

53

speeds, it is apparent that as speed decreases from impact velocity to zero, the amount of energy

absorbed per tear element increases. When combined with the lanyard leg stiffness correlations

and force versus time graphs of dynamic tests, the velocity versus average force at low speeds

results indicate a relationship between leg stiffness and strain rate of tear elements.

Collectively, all of the analysis and data from this study show that higher strain values for

lanyard legs will produce higher MAAFs when tested in the ambient and hot dry condition.

Because materials such as polyester webbing and polyester/nylon rope become less stiff when

heated, the hot dry condition amplifies this effect. The data suggests that during the initial

portion of energy absorption, each lanyard leg material will perform in a similar manner. As the

test weight velocity is decelerated, the relationship between dynamic event speed and high

MAAF is decreased and the effect of higher MAAFs at lower speeds ensues. When looking at

the last few inches of elongation at the tear element level, the leg materials connecting the energy

absorber to the weight are allowed to elastically deform and then recover as each tear element

plastically deforms. Upon loading the subsequent tear element, the lanyard leg material must

elongate which determines the speed in which tear elements are loaded. Stiff materials such as

steel cable or aramid, quickly load the tear element and the high MAAF at lower speeds

correlations is attenuated. High elongation materials such as polyester/nylon rope are less stiff

and require more time to transfer the load to the tear element. By increasing the amount of

energy required to elongate the tear webbing, the MAAF will increase. The specific mechanism

that causes tear webbing to absorb additional energy at lower speeds is unknown but has been

observed through empirical data.

Recommendations

54

Based on the analysis and observations of this study, it is recommended that more data

be captured in relation to the effects of lanyard leg variation on MAAF in energy absorbing

lanyard used for fall protection. Although multiple tests were conducted and showed statistically

significant evidence that a relationship exists between lanyard leg stiffness and increased MAAF

results, additional testing will improve the reliability of this study. Also, the elastic properties of

lanyard legs should be studied in greater detail and under all environmental test conditions. This

will enable better conclusions to be drawn based on MAAF versus stain linear regression tests.

Other testing procedures that include elements such as high speed photography and or

videography should be implemented to visually capture the dynamic free fall event. This will

provide better insight into what is happening as each tear element absorbs kinetic energy.

Further mathematical dynamic analysis should also be performed using material properties

obtained from lanyard leg material manufacturers. Lastly, it is important that manufactures of

fall protection equipment consistently verify that the products they produce meet all applicable

standards for quality, reliability, and safety. By diligently analyzing each component within

systems and how those components interact with the system as a whole, fall protection

equipment manufactures will continue to advance the products people depend their lives on.

55

References

American National Standards Institute. (2012). ANSI/ASSE Z359 fall protection code package.

Retrieved from http://webstore.ansi.org/RecordDetail.aspx?sku=ANSI/ASSE Z359 Fall

Protection Code Package

Bickrest, E. (2009). Fall protection: Failure is not an option. EHS Today, 2(3), 34.

Cutnell, J., & Johnson, K. (1992). Physics (2nd ed.). Hoboken, NJ: John Wiley & Sons, Inc.

Denis, K. (2010). Best practices in fall protection. Professional Safety, 55(11), 47-48.

Duhamel, K. (2012). Five things to consider before implementing a fall arrest system. EHS

Today, 5(9), 43.

Duke University. (1998). The studentized range statistic (q)*. Retrieved from

http://www.stat.duke.edu/courses/Spring98/sta110c/qtable.html

Ellis, J. (2002). Personal fall arrest systems. Professional Safety, 47(12), 42.

Encyclo online encyclopedia. (n.d.). Partially oriented yarn. Retrieved from

http://www.encyclo.co.uk/define/partially oriented yarn

Epp, R. J. (2007). Fall protection misconceptions & myths. Professional Safety, 52(9), 26-34.

Feldstein, J. (2007). ANSI/ASSE Z359 fall protection code. Professional Safety, 52(9), 47-51.

Firl, C., & Wolner, T. (2008). Standards developments. Professional Safety, 53(11), 50.

Griffith, R. (2012). Testing fall protection products. Professional Safety, 57(1), 34.

OSHA. (n.d.). Commonly used statistics. Retrieved from

http://www.osha.gov/oshstats/commonstats.html

Spotts, S. (1998). Critical link in fall protection. Occupational Hazards, 60(11), 77.

Tech Safety Lines. (2009, November). ANSI Z359 fall protection code. Retrieved from

http://techsafetylines.com/ANSI Z359 1-TSL 2009NOV.pdf

56

Torres, K. (2007). New frontiers in fall protection equipment. Occupational Hazards, 69(6), 31.

Merriam-Webster.com. (2012). Webbing. Retrieved September 21, 2012, from

http://www.merriam-webster.com/dictionary/webbing

Wingfield, R. (2010). New standard for energy-absorbing lanyards what you need to know.

Professional Safety, 55(6), 74-75.

Wirerope Works, Inc. (2008). Elevator rope stretch. Retrieved from

http://www.wwwrope.com/product_pdfs/EL_TB_05.pdf

57

Appendix A: Descriptive Statistics

Table A1

Descriptive Statistics - Cold Dry Condition

Aramid Nylon Polyester Polyester, Tubular Polyester/TPU Steel Cable Polyester/Nylon

Mean 921.67 925.67 902.67 854.33 871.33 851.00 886.00

Standard Error 10.73 30.60 13.59 12.33 25.51 15.50 14.01

Median 927.00 949.00 901.00 863.00 876.00 866.00 893.00

Standard Deviation 18.58 53.00 23.54 21.36 44.19 26.85 24.27

Sample Variance 345.33 2809.33 554.33 456.33 1952.33 721.00 589.00

Skewness -1.19 -1.60 0.32 -1.53 -0.47 -1.73 -1.19

Range 36.00 98.00 47.00 40.00 88.00 47.00 47.00

Minimum 901.00 865.00 880.00 830.00 825.00 820.00 859.00

Maximum 937.00 963.00 927.00 870.00 913.00 867.00 906.00

Count 3.00 3.00 3.00 3.00 3.00 3.00 3.00 Confidence Level (95.0%) 46.16 131.67 58.49 53.07 109.76 66.70 60.29

Table A2

Descriptive Statistics - Hot Condition

Aramid Nylon Polyester Polyester, Tubular Polyester/TPU Steel Cable Polyester/Nylon

Mean 808.33 861.33 818.67 832.67 843.00 775.33 943.00

Standard Error 11.61 6.33 17.85 2.33 16.70 12.12 7.51

Median 814.00 855.00 810.00 832.00 831.00 768.00 950.00

Standard Deviation 20.11 10.97 30.92 4.04 28.93 20.98 13.00

Sample Variance 404.33 120.33 956.33 16.33 837.00 440.33 169.00

Skewness -1.17 1.73 1.16 0.72 1.55 1.38 -1.72

Range 39.00 19.00 60.00 8.00 54.00 40.00 23.00

Minimum 786.00 855.00 793.00 829.00 822.00 759.00 928.00

Maximum 825.00 874.00 853.00 837.00 876.00 799.00 951.00

Count 3.00 3.00 3.00 3.00 3.00 3.00 3.00 Confidence Level (95.0%) 49.95 27.25 76.82 10.04 71.87 52.13 32.29

58

Table A3

Descriptive Statistics – Ambient Wet Condition

Aramid Nylon Polyester Polyester, Tubular Polyester/TPU Steel Cable Polyester/Nylon

Mean 874.67 826.67 855.33 826.67 839.33 849.33 808.00

Standard Error 3.18 7.97 4.18 19.72 5.17 12.39 5.03

Median 875.00 832.00 859.00 819.00 844.00 839.00 812.00

Standard Deviation 5.51 13.80 7.23 34.15 8.96 21.46 8.72

Sample Variance 30.33 190.33 52.33 1166.33 80.33 460.33 76.00

Skewness -0.27 -1.48 -1.69 0.96 -1.71 1.66 -1.63

Range 11.00 26.00 13.00 67.00 16.00 39.00 16.00

Minimum 869.00 811.00 847.00 797.00 829.00 835.00 798.00

Maximum 880.00 837.00 860.00 864.00 845.00 874.00 814.00

Count 3.00 3.00 3.00 3.00 3.00 3.00 3.00 Confidence Level (95.0%) 13.68 34.27 17.97 84.84 22.27 53.30 21.66

59

Appendix B: Graphical Data and Images

Figure B1. Example of force versus time graph for polyester web leg EAL.

Figure B2. Example of force versus time graph for polyester/nylon rope leg EAL.

60

Figure B3. Bar chart of mean MAAF results for lanyard leg materials in the hot condition.

Figure B4. Bar chart of mean MAAFs for lanyard leg materials in the ambient wet condition.

61

Figure B5. Bar chart of mean MAAF results for lanyard leg materials in the cold dry condition.

Figure B6. Simplified drawing of tear webbing

62

Figure B7. Mean MAAF versus strain in the ambient condition.

Figure B8. Mean MAAF versus strain in the ambient wet condition.

63

Figure B9. Mean MAAF versus strain in the cold dry condition.

Figure B10. Example of a typical single web leg energy absorbing lanyard.

64

Figure B11. Anderson-Darling normality test for residuals.

65

Appendix C: Collected Data

Table C1

Collected Data

Leg Materials Free Fall (ft) Condition MAAF (lb) MAF (lb) Elongation (in.) Aramid 6 Ambient 834 1101 37.25 Aramid 6 Ambient 822 1060 37.75 Aramid 6 Ambient 835 1029 37.25 Aramid 6 Cold 901 1173 31 Aramid 6 Cold 927 1198 30 Aramid 6 Cold 937 1205 29.75 Aramid 6 Hot 786 1017 40 Aramid 6 Hot 814 1093 39 Aramid 6 Hot 825 1070 39 Aramid 6 Wet 869 1064 33.5 Aramid 6 Wet 880 1152 32.25 Aramid 6 Wet 875 1173 34.25 Nylon 6 Ambient 823 1149 38 Nylon 6 Ambient 865 1192 35.5 Nylon 6 Ambient 864 1236 35.5 Nylon 6 Cold 865 1092 33 Nylon 6 Cold 949 1203 30.25 Nylon 6 Cold 963 1376 26.25 Nylon 6 Hot 874 1312 36.5 Nylon 6 cold 855 1291 36.25 Nylon 6 Hot 855 1192 33.5 Nylon 6 Wet 832 1132 40 Nylon 6 Wet 811 1154 38.5 Nylon 6 Wet 837 1138 38

Polyester 6 Ambient 846 1083 36.75 Polyester 6 Ambient 864 1119 36.25 Polyester 6 Ambient 853 1058 36.25 Polyester 6 Cold 880 1226 32.5 Polyester 6 Cold 927 1096 31.5 Polyester 6 Cold 901 1081 31.5 Polyester 6 Hot 853 1153 37 Polyester 6 Hot 793 1131 41.5 Polyester 6 Hot 810 1118 38.25 Polyester 6 Wet 859 1091 35.5 Polyester 6 Wet 860 1078 34.25 Polyester 6 Wet 847 1112 31

66

Polyester, Tubular 6 Ambient 812 1245 34.25 Polyester, Tubular 6 Ambient 828 1310 30 Polyester, Tubular 6 Ambient 846 1303 26 Polyester, Tubular 6 Cold 830 1276 32 Polyester, Tubular 6 Cold 870 1312 29.25 Polyester, Tubular 6 Cold 863 1376 27.75 Polyester, Tubular 6 Hot 837 1333 32 Polyester, Tubular 6 Hot 829 1353 30.5 Polyester, Tubular 6 Hot 832 1350 29.5 Polyester, Tubular 6 Wet 797 1261 34.5 Polyester, Tubular 6 Wet 819 1223 33 Polyester, Tubular 6 Wet 864 1153 32.75 Polyester/Nylon 6 Ambient 866 1295 37 Polyester/Nylon 6 Ambient 867 1241 36.5 Polyester/Nylon 6 Ambient 889 1238 34.25 Polyester/Nylon 6 Cold 859 1142 34.5 Polyester/Nylon 6 Cold 893 1123 33.5 Polyester/Nylon 6 Cold 906 1265 33 Polyester/Nylon 6 Hot 928 1315 33 Polyester/Nylon 6 Hot 951 1240 33.25 Polyester/Nylon 6 Hot 950 1298 34.25 Polyester/Nylon 6 Wet 798 997 37.5 Polyester/Nylon 6 Wet 812 1089 37.25 Polyester/Nylon 6 Wet 814 1198 35.75 Polyester/TPU 6 Ambient 859 1098 35.5 Polyester/TPU 6 Ambient 825 1178 35 Polyester/TPU 6 Ambient 891 1214 34.25 Polyester/TPU 6 Cold 876 1106 31.5 Polyester/TPU 6 Cold 825 1137 30.75 Polyester/TPU 6 Cold 913 1220 28 Polyester/TPU 6 Hot 831 1160 37.5 Polyester/TPU 6 Hot 822 1128 36.5 Polyester/TPU 6 Hot 876 1154 34.5 Polyester/TPU 6 Wet 845 1189 37.5 Polyester/TPU 6 Wet 829 1184 35.25 Polyester/TPU 6 Wet 844 1190 34.5

Steel Cable 6 Ambient 854 1110 34 Steel Cable 6 Ambient 821 1140 34 Steel Cable 6 Ambient 853 1070 33.5 Steel Cable 6 Cold 866 1090 32.5 Steel Cable 6 Cold 867 1202 31 Steel Cable 6 Cold 820 1210 31 Steel Cable 6 Hot 768 1033 40

67

Steel Cable 6 Hot 759 965 39.5 Steel Cable 6 Hot 799 1037 36.75 Steel Cable 6 Wet 839 1127 34.5 Steel Cable 6 Wet 835 1232 34.5 Steel Cable 6 Wet 874 1253 31.5

68

Appendix D – Inferential Statistics

Table D1

Single Factor ANOVA – Cold Dry Condition

Groups Count Sum Average Variance Aramid 3.00 2765.00 921.67 345.33 Nylon 3.00 2777.00 925.67 2809.33 Polyester 3.00 2708.00 902.67 554.33 Polyester, Tubular 3.00 2563.00 854.33 456.33 Polyester/TPU 3.00 2614.00 871.33 1952.33 Steel Cable 3.00 2553.00 851.00 721.00 Polyester/Nylon 3.00 2658.00 886.00 589.00 ANOVA Source of Variation SS df MS F P-value F crit Between Groups 16649.90 6.00 2774.98 2.62 0.06 2.85 Within Groups 14855.33 14.00 1061.10 Total 31505.24 20.00 Table D2

Single Factor ANOVA – Hot Condition

Groups Count Sum Average Variance Aramid 3.00 2425.00 808.33 404.33 Nylon 3.00 2584.00 861.33 120.33 Polyester 3.00 2456.00 818.67 956.33 Polyester, Tubular 3.00 2498.00 832.67 16.33 Polyester/TPU 3.00 2529.00 843.00 837.00 Steel Cable 3.00 2326.00 775.33 440.33 Polyester/Nylon 3.00 2829.00 943.00 169.00 ANOVA Source of Variation SS df MS F P-value F crit Between Groups 50297.33 6.00 8382.89 19.93 4.12E-06 2.85 Within Groups 5887.33 14.00 420.52 Total 56184.67 20.00

69

Table D3

Single Factor ANOVA – Ambient Wet Condition

Groups Count Sum Average Variance Aramid 3.00 2624.00 874.67 30.33 Nylon 3.00 2480.00 826.67 190.33 Polyester 3.00 2566.00 855.33 52.33 Polyester, Tubular 3.00 2480.00 826.67 1166.33 Polyester/TPU 3.00 2518.00 839.33 80.33 Steel Cable 3.00 2548.00 849.33 460.33 Polyester/Nylon 3.00 2424.00 808.00 76.00 ANOVA Source of Variation SS df MS F P-value F crit Between Groups 8712.00 6.00 1452.00 4.94 0.01 2.85 Within Groups 4112.00 14.00 293.71 Total 12824.00 20.00

Table D4

Tukey’s Range Test – Cold Dry Condition Single Factor ANOVA

q-value MS n Tukey Test Statistic

4.83 293.71 3.00 47.49 Groups Average 1st 2nd 3rd 4th 5th 6th

Aramid 874.67

Nylon 826.67 48.00

Polyester 855.33 19.33 28.67 Polyester, Tubular 826.67 48.00 0.00 28.67

Polyester/TPU 839.33 35.33 12.67 16.00 12.67

Steel Cable 849.33 25.33 22.67 6.00 22.67 10.00

Polyester/Nylon 808.00 66.67 18.67 47.33 18.67 31.33 41.33

70

Table D5

Regression Analysis of Mean MAAF versus Strain – Ambient Wet Condition

Summary Regression Statistics

Multiple R 0.71 R Square 0.50 Adjusted R Square 0.38 Standard Error 13.65 Observations 6.00 ANOVA df SS MS F Significance

F Regression 1.00 756.73 756.73 4.06 0.11 Residual 4.00 745.20 186.30 Total 5.00 1501.93 Coefficients Standard

Error t Stat P-value Lower 95% Upper 95%

Lower 95.0%

Upper 95.0%

Intercept 852.61 10.69 79.76 0.00 822.93 882.29 822.93 882.29 Velocity -316.53 157.06 -2.02 0.11 -752.59 119.53 -752.59 119.53

71

Table D6

Regression Analysis of MAAF versus Impact Velocity

Summary Regression Statistics

Multiple R 0.73 R Square 0.54 Adjusted R Square 0.47 Standard Error 11.67 Observations 9.00 ANOVA df SS MS F Significance

F Regression 1.00 1100.22 1100.22 8.08 0.02 Residual 7.00 953.34 136.19 Total 8.00 2053.56 Coefficients Standard

Error t Stat P-value Lower 95% Upper 95%

Lower 95.0%

Upper 95.0%

Intercept 719.79 18.35 39.22 0.00 676.39 763.20 676.39 763.20 Velocity 3.25 1.14 2.84 0.02 0.55 5.95 0.55 5.95