HSE Health & Safety

Executive

A review of criteria concerning design, selection,installation, use, maintenance and training

aspects of temporarily-installed horizontal lifelines

Prepared by Safety Squared for the Health and Safety Executive 2004

RESEARCH REPORT 266

HSE Health & Safety

Executive

A review of criteria concerning design, selection,installation, use, maintenance and training

aspects of temporarily-installed horizontal lifelines

D Riches BSc (Hons) Safety Squared

11 Cordell Close St Ives

Cambridgeshire PE27 6UL

A temporarily-installed horizontal lifeline (HLL) is a line that is stretched between two extremes of travel in a workplace, to provide a continuous anchor for the attachment of fall-arrest equipment, providing protection against falling from a height over a convenient span. If a worker falls, they will be arrested in a similar manner to the way in which an aircraft catches the arrester wire when landing onboard an aircraft carrier, i.e. the lifeline deflects into to a “V” shape whilst absorbing the energy.

To look at, temporary-installed HLLs are very simple. But in terms of the fall-arresting process, they are very complex. Consequently, the design and installation of temporary-installed HLLs is not just a matter of stringing up some randomly chosen rope in an improvised manner, and in the process relying on a good degree of guesswork. HLLs are engineered systems and require engineering disciplines and approaches in order to ensure that they will perform as intended.

There is a general lack of understanding of the criteria involved in the design, installation and control of fall-arresting systems (FAS) based on temporary-installed HLL, particularly by those who have to select and install these systems at the workplace. This applies to organisations who either choose proprietary systems from fall-arrest manufacturers or those who take it on themselves to fabricate their own designs.

This research gathers together and reviews technical information in order to provide a greater understanding into how these FAS are designed, how they work, and how they are controlled. This includes: key factors regarding selection, installation, use and maintenance; recommendations for those organisations that fabricate and install their own designs; recommendations for training; and information that could be put into HSE guidance.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

HSE BOOKS

© Crown copyright 2004

First published 2004

ISBN 0 7176 2892 2

All rights reserved. No part of this publication may bereproduced, stored in a retrieval system, or transmitted inany form or by any means (electronic, mechanical,photocopying, recording or otherwise) without the priorwritten permission of the copyright owner.

Applications for reproduction should be made in writing to: Licensing Division, Her Majesty's Stationery Office, St Clements House, 2-16 Colegate, Norwich NR3 1BQ or by e-mail to hmsolicensing@cabinet-office.x.gsi.gov.uk

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Acknowledgements

The author acknowledges with gratitude the assistance from the following in the production of this review:

· Document Supply Centre, Research Services and Worldwide Searches Department of The British Library for document search and provision;

· The National Engineering Laboratory for permission to review and document various archived film material for research purposes;

· The Wright Image Company for the production of DVD copies of the above material;

· Paul Jones of the HSE for retrieving accident data from the HSE’s FOD database.

And in addition, the author acknowledges with thanks the assistance from the following manufacturers for the supply of information:

· Dunn and Cowe Ltd

· Latchways plc

· Proteq Ltd

· Sala Group Ltd

· Spanset Ltd

· Tractel Ltd

· Uniline Safety Systems Ltd

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CONTENTS

EXECUTIVE SUMMARY… … … … … … … … ix

1. INTRODUCTION … … … … … … … … 1

1.1 PURPOSE … … … … … … … … … 1

1.2 BACKGROUND … … … … … … … … 1

1.3 RESEARCH METHOD … … … … … … … 4 1.3.1 Literature search and review … … … … … … 4 1.3.2 Survey of UK manufacturers and suppliers … … … … 5 1.3.3 HSE FOD Database … … … … … … … 5 1.3.4 Review of archived film material … … … … … … 6

1.4 DEFINITIONS … … … … … … … … 6 1.4.1 Permanently-installed HLL … … … … … … 6 1.4.2 Temporarily-installed HLL … … … … … … 6 1.4.3 Single-span HLL … … … … … … … … 6 1.4.4 Multi-span HLL … … … … … … … … 6 1.4.5 Span … … … … … … … … … 6 1.4.6 Sub-span … … … … … … … … 6 1.4.7 Travelling device … … … … … … … … 6 1.4.8 Interconnecting fall-arrest equipment … … … … … 6 1.4.9 Energy-absorbing lanyard … … … … … … 6 1.4.10 In-line energy absorber … … … … … … … 7 1.4.11 Free fall … … … … … … … … … 7 1.4.12 “V” deflection … … … … … … … … 7 1.4.13 Deflection angle … … … … … … … … 7 1.4.14 Load ratio … … … … … … … … 7 1.4.15 System safety factor … … … … … … … 7 1.4.16 Wire/rope construction … … … … … … … 8

2. FALL ARRESTING SYSTEMS BASED ONTEMPORARILY-INSTALLED HORIZONTAL LIFELINES … … … 11

2.1 BASIC FAS … … … … … … … … … 11

2.2 FAS BASED ON TEMPORARILY-INSTALLED HLL … … … … 13

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CONTENTS

3. LITERATURE REVIEW ... … … … … … … 21

3.1 AMERICAN RESEARCH… … … … … … … … 21

3.2 FRENCH RESEARCH … … … … … … … 22 3.2.1 Static analysis … … … … … … … … 22 3.2.2 Static testing to destruction … … … … … … 23

3.3 CANADIAN RESEARCH … … … … … … … 24 3.3.1 Ontario Hydro … … … … … … … … 24 3.3.2 Canadian steel erection industry … … … … … 29 3.3.3 Retractable arresters… … … … … … … … 31

3.4 AUSTRALIAN RESEARCH … … … … … … … 32 3.4.1 Initial research … … … … … … … … 32 3.4.2 Further research … … … … … … … … 34 3.4.3 Points worth noting from further testing … … … … … 37 3.4.4 Long single-span systems with multiple workers … … … 41

3.5 UNITED KINGDOM RESEARCH … … … … … … 44 3.5.1 Drop-tests involving multiple-dummy releases … … … … 44 3.5.2 Drop-tests: simultaneous and staggered double-dummy releases … 46 3.5.3 Static tests to destruction … … … … … … 48 3.5.4 Research and development … … … … … … 50 3.5.5 Design and performance details … … … … … … 55 3.5.6 Single-spans versus multi-span HLLs … … … … … 56 3.5.7 Free space requirement … … … … … … … 58

3.6 GERMAN RESEARCH … … … … … … … 60

3.7 OFFICIAL DOCUMENTS … … … … … … … 62 3.7.1 United Kingdom Legislation … … … … … … 62 3.7.2 American Legislation … … … … … … … 65 3.7.3 Official guidance … … … … … … … … 67 3.7.4 British standards … … … … … … … … 70 3.7.5 British standard BS EN 365 … … … … … … 70 3.7.6 British standard BS EN 795 … … … … … … 73 3.7.7 British standard BS 7883 … … … … … … 74 3.7.8 American national standard ANSI A10.14 … … … … 75 3.7.9 Canadian national standards … … … … … … 76 3.7.10 Australian / New Zealand standard AS/NZS 1891.2 … … … 77

3.8 ACCIDENT DATA … … … … … … … … 78

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CONTENTS

4. SURVEY OF UK MANUFACTURERS AND SUPPLIERS … … 79

4.1 GENERAL … … … … … … … … … 80

4.2 INEXPERT, UNPROFESSIONAL OR UNTRAINED ORGANISATIONS … 81

4.3 INSTALLATION AND DESIGN APPROACH … … … … 824.3.1 Computer analysis … … … … … … … 82 4.3.2 Graphical and tabular approaches … … … … … 84 4.3.3 Modelling multiple-fall scenarios … … … … … 84 4.3.4 Controlling design changes … … … … … … 85

4.4 SERVICING AND ANNUAL EXAMINATION … … … … 85

4.5 PRODUCT DESIGN … … … … … … … … 86 4.5.1 Terminations … … … … … … … … 86

4.6 INSTALLATION AND USE … … … … … … … 87 4.6.1 Attaching to structure … … … … … … … 87 4.6.2 Multiple use situations … … … … … … … 88 4.6.3 Tensioning … … … … … … … … 88 4.6.4 Attachment of fall-arrest equipment … … … … … 89

4.7 RESCUE … … … … … … … … … 90

4.8 APPLICATIONS … … … … … … … … 91

4.9 TRAINING … … … … … … … … … 91

4.10 FALL ACCIDENTS … … … … … … … … 91

4.11 STANDARDS … … … … … … … … 92

4.12 PRODUCT ABUSE … … … … … … … … 92

4.13 INSTRUCTIONS FOR INSTALLATION AND USE … … … … 92 4.13.1 Application … … … … … … … … 92 4.13.2 Restraint systems … … … … … … … 93 4.13.3 Fall-arrest systems … … … … … … … 93

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CONTENTS

5. CONCLUSIONS … … … … … … … … 97

5.1 KEY FACTORS IN REGARD TO DESIGN AND PERFORMANCE … … 97

5.2 KEY FACTORS IN REGARD TO SELECTION … … … ...103 5.2.1 General considerations … … … … … … ...103 5.2.2 Product considerations … … … … … … ...104

5.3 KEY FACTORS IN REGARD TO INSTALLATION AND USE … .. 106 5.3.1 Fundamental considerations … … … … … .. 106 5.3.2 Product considerations … … … … … … .. 110

5.4 KEY FACTORS IN REGARD TO MAINTENANCE … … … . 112 5.4.1 General considerations … … … … … … . 112 5.4.2 Fundamental considerations … … … … … . 112

5.5 RECOMMENDATIONS FOR NON-PROPRIETARY INSTALLATIONS . 113 5.5.1 General considerations … … … … … … . 113 5.5.2 Specific considerations … … … … … … . 114

5.6 RECOMMENDATIONS FOR THE TRAINING OF INSTALLER-USERS . 117

5.7 RECOMMENDATIONS FOR FURTHER WORK … … … . 118

6. REFERENCES ... … … … … … … . 119

7. APPENDIX: LIST OFARCHIVED NEL CINE FILM, U-MATIC TAPE AND VIDEO TAPE … … … … . 123

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EXECUTIVE SUMMARY

There is a general lack of understanding of the criteria involved in the design, installation and control of fall-arresting systems (FAS) based on temporary-installed horizontal lifelines (HLL), particularly by those who have to select and install these systems at the workplace. This applies to organisations who either choose proprietary systems from fall-arrest manufacturers or those who take it on themselves to fabricate their own designs.

To look at, temporary-installed HLLs are very simple. But in terms of the fall-arresting process, they are very complex. Consequently, the design and installation of temporary-installed HLLs is not just a matter of stringing up some randomly chosen rope in an improvised manner, and in the process relying on a good degree of guesswork. HLLs are engineered systems and require engineering disciplines and approaches in order to ensure that they will perform as intended.

To address this need, approximately 60 articles, including research papers, legislation, official guidance, standards and various technical literature from National, European and International sources were studied, for the purposes of:

· Providing a greater understanding into how these FAS are designed, how they work and how they are controlled

· Identifying the key factors that organisations need to address when selecting, installing, using and maintaining these types of FAS

· Providing recommendations for those organisations who take it on themselves to fabricate and erect their own temporary-installed HLLs

· Providing recommendations for the training of personnel who are expected to install these types of FAS

· Providing information which could be put into HSE guidance format

Apart from the information drawn from the results of the literature review, a number of UK manufacturers were either contacted or visited, in order to learn from their approach and to understand the issues as they saw them in the market place. In addition the HSE FOD accident database was interrogated, and a review was undertaken of archived research film material, held at the National Engineering Laboratory. The author also utilised his own experience in the design and computational analysis of HLL based FAS, and as the current Convenor of CEN/TC 160 WG1, the Euro-standards committee responsible for the standard BS EN 795.

The results of this research have been presented in this report. Various issues are examined, including:

· The large number of parameters which affect the fall-arrest performance of a temporary-installed HLL and how changing these parameters can change performance and risk

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· In the event of a fall occurring, the need to be able to determine the arrest force that a worker could experience, the distance that the worker could fall through, the loads that could be generated in the FAS, and the loads transmitted to the end-anchors, which typically are a magnification of the arrest force

· The need to be able to apply the above performance information to ensure safe installation

· The importance of dynamic and static testing approaches, and interaction and compatibility issues between HLLs and other fall-arrest equipment that may be attached

· Fall-arrest performance of HLLs when the fall of two or more attached workers is simulated by test, either by simultaneously releasing the test surrogates, (test weights or dummies), or by releasing at staggered time intervals

· Users of temporary-installed HLLs are likely to be the installers, i.e. temporary-installed HLLs are user-installed like most other kinds of FAS, e.g. FAS based on energy-absorbing lanyards or retractable arresters. However, the installation of temporary-installed HLLs have more exacting requirements, and performance and safety is correspondingly affected by error or negligence to a greater extent than with other types.

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1. INTRODUCTION

1.1 PURPOSE

The purpose of this research was to:

· Gather together and review technical information on temporarily-installed horizontal lifelines (HLL), in order to provide a greater understanding into how these fall-arresting systems (FAS) are designed, how they work and how they are controlled.

The results of this review can be found within Sections 2, 3 and 4 of this report. Key factors concerning design and performance can be found in clause 5.1.

· Identify the key factors that organisations who use temporarily-installed HLLs need to address when selecting, installing, using and maintaining these types of FAS.

This information can be found in clauses 5.2 to 5.4.

· Provide recommendations for those organisations who from time to time consider the fabrication and erection of their own temporarily-installed HLLs in the workplace, (i.e. not proprietary temporarily-installed HLLs that are marketed by safety equipment suppliers).

This information can be found in Clause 5.5.

· Provide recommendations for the training of personnel who are expected to install temporarily-installed HLLs.

This information can be found Clause 5.6.

· Provide information which could be put into HSE guidance format.

The information contained within Section 5 could be used as a basis for HSE guidance.

1.2 BACKGROUND

Workers in the UK have been protecting themselves from the harmful effects of falling from a height by using FAS over a number of decades - the state of the art in the late 1950’s is described in Shand (1960), and the UK’s first fall-arrest standard was published as BS 1397 (1947).

FAS work by arresting the fall of a worker by stopping it soon after it starts, i.e. the total falling distance is limited at the onset.

Over the course of time, a requirement emerged at the workplace for a FAS which would provide fall protection whilst moving over a considerable distance in the horizontal plane.

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Companies requiring this protection adopted “aerial ropeway” technology, whereby a horizontal cable was temporarily suspended between the extremes of travel at the workplace, and was tensioned so that it adopted an approximate horizontal attitude. A lanyard and safety harness could then be attached. The idea was that in a fall, a worker would be arrested, (Figure 3), in a similar manner to the way in which an aircraft catches the arrester wire when landing onboard an aircraft carrier, Fuller et al (1980).

These horizontal cables were fabrications made to suit the workplace. Very little if any engineering analysis or testing was usually performed in order to ascertain if the cable could stop a man from falling. The perceived simplicity of the cable belied the complexity of the fall-arresting process. Experimental testing showed that in some cases such a cable could have failed, (which would have caused a fall to the ground), or the amount of cable stretch would not have prevented an impact with the ground.

These dangers continue to threaten in present times because of the lack of available information and understanding in the market place of these visually simple yet inherently complex FAS.

Safety equipment manufacturers developed more sophisticated, permanently-installed versions of the above, in doing so coining the name “horizontal lifeline” (HLL). Specialist installation companies are trained and authorised to install various configurations of these HLLs, because each has to be tailor-made to suit the structure to which it will be attached. Engineering analysis and testing is performed, because it is known that the factors which affect the arrest performance and strength requirements of the HLL, and its anchors, vary from installation to installation. The factors are significant and numerous, such as: overall span, cable type, cable pre-tension, numbers of intermediate support anchors, where the fall occurs on the HLL, the free fall distance, bending the cable around corners, more than one worker falling simultaneously or near-simultaneously, and the type of fall-arrest equipment attaching the worker to the HLL.

Safety equipment manufacturers modified this technology in the supply of temporarily-installed HLLs, Figure 1. These are HLLs which facilitate temporary installation and subsequent removal at the workplace. The idea is that any trained personnel at the workplace would be able to install a temporary HLL in accordance with installation instructions, which contain procedures to control the fall-arrest performance and specify strength requirements of anchoring structure. However it has not stopped the relatively easy fabrication and installation of temporary HLLs, without engineering analysis, by companies who wish to avail themselves of this approach.

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iHLL

Energy-absorbing lanyard

Temporarily- nstalled

Figure 1 FAS based on a temporarily-installed HLL

At the present time there is a lack of understanding of the technical criteria involved in the installation of temporarily-installed HLL, particularly by those who have to select and install these FAS at the workplace. There are also questions in regard to the control of these FAS, in particular: What are the selection criteria and what systems are available? What degree of research has been conducted? What is the nature of training and who supplies it? What maintenance is conducted? The lack of understanding has been caused by factors amongst which include: the perceived simplicity of HLL; the lack of written information, and the difficulty in obtaining that which is available; and the decline in numbers and expertise of technical personnel within the fall-arrest industry.

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1.3 RESEARCH METHOD

The following method was used to deliver the research.

1.3.1 Literature search and review

A computerised search was undertaken for documents with the assistance of the British Library Research Service, which utilised the DIALOG and GEM on-line host services. The following key words were used:

· horizontal lifeline· static wire· running line· horizontal line· fall arrest system· arrester cable· aerial ropeway

The databases searched were:

· INSPEC – a database for physics, electronics and computing, with articles dating back to 1898.

· NTIS – National Technical Information Service database consisting of summaries of unclassified, publicly available US government-sponsored research, development and engineering, from agencies such as NASA, DOD, DOE, HUD, DOT, Dept of Commerce and some 240 other agencies.

· Ei Compendex – an engineering database which provides abstracts from the world’s significant engineering and technological literature. This covers approximately 4,500 journals and selected government reports and books, and additionally over 480,000 records of proceedings from engineering and technical conferences.

· TRIS – Transportation Research Information Services – a database relevant to the planning, development, operation and performance of transportation systems, providing international coverage of ongoing research projects, journal articles, state and federal government reports, conference proceedings, research and technical papers and monographs.

· Energy Science and Technology – a database containing worldwide references to basic and applied scientific and technical research literature.

· SciSearch – a scientific database of a international multidisciplinary nature, covering science, technology, biomedicine and related disciplines produced by the Institute for Scientific Information (ISI).

· UBM Industry News – contains the full text content of 57 leading UK business publications covering a broad range of industrial sectors.

· Occupational Safety and Health (NIOSH) – a database which includes citations to more than 400 journal titles as well as over 70,000 monographs and technical reports, covering all aspects of occupational safety and health.

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· PIRA Management and Marketing Abstracts (MMA) - provides information on all aspects of management and marketing practice and customer and industrial relations in the single European market and worldwide.

· RAPRA – database dedicated exclusively to rubbers, plastics, adhesives and polymeric composites covering technical, academic commercial and marketing aspects of the industry.

· AEROSPACE (formerly Aeroplus) – containing the International Aerospace Abstracts (IAA), is one of the world’s most comprehensive sources for published literature in the field of aerospace (aeronautics and astronautics) and the related areas of chemistry, materials, geosciences, physics and computer sciences.

· COPAC – an on-line database and a consortium of 24 UK University libraries holding 20 million items.

· NASA 1 and 95 - National Aeronautics and Space Administration databases which hold approximately 250,000 references each.

Articles were also searched for using the names: Arteau J., Sulowski A. C. and Dayawansa P. H. as these were known authors in the research field.

Relevant articles were obtained from the British Library Document Supply Centre, which has access to at least 150 million books, journals, reports and theses, covering almost every subject in every language.

Other articles were retrieved from Safety Squared’s own library holdings, which included standards, legislation, official guidance, accident statistics and research papers.

1.3.2 Survey of UK manufacturers and suppliers

This reviewed the marketing, technical, installation and training approach adopted by manufacturers / suppliers.

Information was gathered mainly by way of internet and telephonic enquiry. The more notable suppliers were visited for the purpose of technical discussion and interview. Further details can be found in Section 4.

1.3.3 HSE FOD Database

In order to try and supplement accident evidence obtained from elsewhere, permission was obtained to study cases recorded in the HSE Field Operations Directorate (FOD) database. The search used the keywords: “LIFELINES” “FALL-ARREST” and “LANYARDS”. The search revealed that 270 accidents contained one or more of the keywords, occurring between April 2001 - June 2003.

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1.3.4 Review of archived film material

In the course of the research, a number of cine films, “U-matic” tapes and video tapes were discovered in the National Engineering Laboratory (NEL) archives, which, from titles, were felt to be of importance to present and future research. With permission from the NEL, a review of the material was made, and copies were transferred onto DVD format for the purposes of HSE research. The vast majority of this material relates to UK fall-arrest research dating back to the 1970’s, and a list giving brief details of each item can be found in the appendix.

1.4 DEFINITIONS

For the purposes of this report the following terms and definitions are used, together with the corresponding SI units of measurement:

1.4.1 Permanently-installed HLL

A HLL which once installed, is not intended to be removed or dismantled in the foreseeable future. These HLLs are usually of the multi-span type.

1.4.2 Temporarily-installed HLL

A HLL which is repeatedly installed, used, removed after use, transported and then reinstalled, used, and the cycle continued. These HLLs are usually of the single-span type.

1.4.3 Single-span HLL

A HLL with no intermediate anchors.

1.4.4 Multi-span HLL

A HLL with one or more intermediate anchors.

1.4.5 Span

The overall length of the HLL, measured from one end-anchor to the other.

1.4.6 Sub-span

The distance between two adjacent intermediate anchors in a multi-span HLL.

1.4.7 Travelling device

A device which attaches to and slides along a HLL, and to which a worker connects an energy absorbing lanyard or other interconnecting fall-arrest equipment.

1.4.8 Interconnecting fall-arrest equipment

Fall-arrest equipment which connects a worker’s full body harness to the travelling device.

1.4.9 Energy absorbing lanyard

A lanyard with an integral energy or shock absorber.

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1.4.10 In-line energy absorber

A component, usually inserted between the end of the HLL and the end anchor point, which is used to increase the energy absorbing capacity of the HLL and hence control the loads experienced at the end-anchor.

1.4.11 Free fall

The distance a person falls through when subjected to the forces of gravity and air resistance only, i.e. the distance from the onset of the fall to the point where the FAS just begins to resist the downward motion.

1.4.12 “V” deflection

The vertical displacement between the HLL at the onset to a fall and at maximum deflection as a result of a fall, so called because the HLL adopts a shape similar to the letter “V” (Figure 3).

1.4.13 Deflection angle

The angular difference (Figure 3) between the HLL when at rest and when deflected under load, when measured at the end anchor, (in the case of a single span system), or at the intermediate support flanking the sub-span under load, (in the case of a multi-span system).

1.4.14 Load ratio

The ratio of load at an end anchor to that of the arrest force applied perpendicular to the HLL which produced it. End anchor loadings are a magnification of the applied arrest force.

1.4.15 System safety factor

For design purposes, this is a measure of the reserve of strength a system may have, over and above that which is required when the maximum arrest force occurs. In mathematical terms:

System safety factor = the highest force that can be sustained before system failure the maximum arrest force

both forces being applied in a direction perpendicular to the HLL, and both being expressed in the same unit of measurement

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1.4.16 Wire/Rope Construction

Wire rope construction (Figure 2), is commonly designated by two figures, the first indicating the number of strands, and the second, the number of wires per strand. So 7 x 7 construction refers to 7 strands each containing 7 wires; 6 x 25 construction refers to 6 strands each containing 25 wires. Some ropes have a core (central element) made from fibres (fibre core), some have an independent wire rope core (IWRC). Diagrams representing these constructions commonly show the cross-section arrangement which confirms the designation.

(i) 7 x 7 (ii) 6 x 25 filler with IWRC

each black dot represents a wire and each each of the larger black dots group of 7 dots represents a strand represents a wire and each group of 25

large dots represents a strand. The strands in this case are interspersed with smaller filler wires. The core is a 7 x 7 independent wire

Figure 2 Cross-sectional examples of wire rope constructions

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HLLi

(i)

End anchor

Travell ng device

Energy-absorbing lanyard

At the onset of the fall

Defl

l

( ll

ection angle

“V” Def ection

ii) At the end of the fa

Figure 3 Deflection of temporarily-installed HLL during fall-arrest

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2. FALL-ARRESTING SYSTEMS BASED ON TEMPORARY­INSTALLED HORIZONTAL LIFELINES

2.1 BASIC FAS

A FAS consists of a number of fall-arrest equipment components which are connected together in series to make a physical link between the worker and the workplace structure, Riches (1998). In the most basic type (Figure 4), the components consist of:

· a full body harness which is worn by the worker; · an anchor device or anchoring structure, which provides a reliable means of connection

to the workplace; · an interconnecting attachment such as an energy-absorbing lanyard, which links the

harness to the anchor device / structure; · connectors, which join the above components to each other.

Once in the full body safety harness, and once all the connections are made to the anchor device, the worker and workplace structure in effect become integral parts of the FAS.

Connectors

Full body harness

Anchor device

Energy-absorbing lanyard

Figure 4 FAS based on an energy-absorbing lanyard

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If a fall occurs, (Figure 5), the worker is arrested by virtue of being connected to the workplace structure, i.e. the structure provides resistance to the downward motion of the fall. At such a stage in a fall, the energy absorbing lanyard becomes taut, and the sudden resistance exerted by the structure causes the worker to decelerate abruptly, principally at a rate which is controlled by the energy absorbing qualities of the lanyard and its design. In Figure 5 the energy absorption is depicted by the tearing apart of a special “tear web” strip.

(i) (ii) (iii) (iv)

Key (i) worker falls off and lanyard begins to get taut (ii) lanyard becomes fully taut and energy absorber begins to absorb energy (iii) maximum extension of the lanyard occurs; worker swings back towards structure (iv) worker in post-fall arrest suspension awaiting rescue

Note: some structure detail omitted for clarity

Figure 5 Typical sequence of events that occurs when a worker falls whilst using a FAS based on an energy-absorbing lanyard

Fixed single-point anchor devices such as the eyebolt shown in Figure 4 are the most simplest in the family of anchor devices, but their use severely restricts the range of movement of the user, this being controlled by the position of the anchor device and the length of the energy-absorbing lanyard. This arrangement also leads to the danger of striking adjacent objects through pendulum or swing falls when users move to an extreme horizontal position from the anchor device. Alternatively, HLLs provide a “continuous anchor” for an energy-absorbing lanyard. As Ellis (1993) puts it: “HLLs are designed to help minimise the potential for dangerous pendulum-like swing falls that can result from moving laterally away from a fixed anchor point. Swing falls can generate the same forces as falling through the same distance vertically, but with the additional hazard of striking an obstruction”.

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2.2 FAS BASED ON TEMPORARILY INSTALLED HLL

A FAS based on a temporarily-installed HLL (Figure 6) consists of:

· the lifeline itself, which may either be cable, rope or webbing based

· two fixed end-anchor points on structure from which the HLL is suspended

· anchor connections, which connect the end-anchors to the HLL, e.g. a strop

· some form of tensioning device to eliminate the sag in the line

· a travelling device, which attaches to the HLL, and in turn provides a point for interconnecting fall-arrest equipment, such as an energy-absorbing lanyard

· energy absorbing lanyard or other interconnecting fall-arrest equipment which links a harness to the travelling device

· full body harness

· connectors, which join the travelling device and harness to the interconnecting fall-arrest equipment

Optionally, (Figure 7), other components may be fitted, e.g.

· a number of intermediate anchors, which support the HLL at pre-set intervals

· in-line energy absorbers, fitted at either or both ends of the HLL

A temporarily-installed HLL is typically installed to stretch across any straight line horizontal access route and its length can be adjusted to suit the workplace. It can be used to bridge and therefore provide fall protection across gaps which have no intermediate supporting structure, and hence are a solution in the steel erection industry.

Travelling devices are designed to engage onto and slide along the HLL. They may be simple karabiner type connectors or other types of fitting, but are designed to prevent inadvertent disengagement from the lifeline. They also provide a means for interconnecting an energy-absorbing lanyard or other fall-arrest equipment between the HLL and harness. This interconnection governs how far a worker may move away from the HLL.

During use, the travelling device is pulled along the HLL in response to the worker’s movement. Providing that the interconnecting fall-arrest equipment is not too long, the travelling device will remain in close proximity to the worker, ensuring that in the event of a fall, any swinging action is minimised.

In some cases if structure is available, intermediate anchors can be utilised. These components support the HLL at pre-set intervals and can provide important fall-arrest performance improvements over single-span configurations. In such cases a special travelling device is normally required, which can pass through the intermediate anchor component without the need for the worker to disconnect from the HLL. The alternative is to disconnect before reaching the intermediate anchor, and then to reconnect on the opposite side. This is a dangerous practice as the worker is exposed to falling during this operation, and is not advised.

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Tensioning device (with excess

HLL

ion

lany

i

ll

End anchor

Anchor connect

Energy-absorbing ard

Travell ng device

rope pu ed through)

Figure 6 FAS based on a temporarily-installed HLL

Intermediate anchor

In-line energy absorber

Figure 7 FAS based on a temporarily-installed HLL with intermediate anchor and in-line energy absorber

14

An alternative is to have two lanyards or a lanyard with two “tails”. This allows the worker to remain attached by one connection before the intermediate anchor, whilst a second connection is made at the opposite side of the anchor. When this “upstream” connection is made the downstream connection can be broken. This is a manual technique that requires self-discipline, whereas the special travelling device is automatic and is to be preferred.

If a fall occurs, a complex sequence of events occur, which can be followed by studying the sequences in Figure 8. Although 5 distinct views are shown, each is only a snapshot in time and the whole event may take less than a second from start to finish. So although the energy-absorbing lanyard is shown extending in view (iv), it may have already begun to operate in view (iii).

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(i) at the onset to the fall

(ii) worker falls and lanyard becomes taut

(lli i li i

iii) lifeline begins to stretch and deflect; trave ng dev ce s des down l feline

Figure 8 Typical sequence of events that occurs when a worker falls whilst attached to a FAS based on a temporarily-installed HLL: sequences (i) – (iii)

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(v)

i i

i

(iv) li iicii ;

ii

energy absorbed; lifeline tends to oscillate up and down about an equilibr um position until res dual motion is fully damped; worker adopts post-fall suspension position awa ting rescue

feline at max mum deflection, providing suff ent reaction force for energy absorb ng lanyard to extendapplied arrest force transm tted to and magnif ed at end-anchors

Figure 8 continued Typical sequence of events that occurs when a worker falls whilst attached to a FAS based on a temporarily-installed HLL: sequences (iv) & (v)

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Design criteria that have to be considered when designing a single-span HLL under fall-arrest conditions, include:

· the magnitude of forces acting on end-anchors versus the strength of the structure

· the magnitude of forces acting in the system versus the strength of the system

· the magnitude of forces acting on the worker versus permissible limits

· the total amount of vertical fall distance versus free space underneath worker before fall occurs

· the total amount of horizontal displacement versus the amount of obstruction free space in the horizontal plane

There are several parameters which affect the performance of a FAS based on a HLL. These parameters are most comprehensively listed and schematically shown in Figure 9 from Sulowski and Miura (1983). A change to any single parameter affects the overall performance, and this is why HLL performance is so complex. Factors include:

· Length of the HLL span

· Length of the interconnecting fall-arrest equipment

· Elastic properties of the HLL, interconnecting fall-arrest equipment, (whether energy-absorbing lanyard, or other) and harness

· Energy absorbing characteristics of any energy absorbing mechanism including in-line energy absorber (if fitted)

· Initial tension in the HLL

· Sub-spans between intermediate anchors (if installed)

· Amount of free fall (where the fall starts in relation to the level of the HLL)

· Position of fall (in relation from end-anchor)

· Weight of the worker(s)

· Friction at corner units and intermediate anchors

· End-anchor and anchor connection stiffness

· Arrest characteristics, compatibility and interaction between interconnecting fall-arrest equipment (e.g. retractable arresters) and the HLL

· Number of workers who fall, and whether they fall simultaneously or at staggered intervals (i.e. with an appreciable time difference)

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ii

Key: MAL = max mum anchor load MAF = max mum arrest force TFD = total fall distance

Figure 9 Parameters affecting performance of FAS based on HLLs after Sulowski and Miura (1983)

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3. LITERATURE REVIEW

A number of documents were found during the literature search which were identified as being relevant and are reviewed here. However no attempt has been made to fully report on the contents of these documents, since to do so would have detracted from the main purpose of the present research; a selective reporting approach has therefore been taken, based on the relevancy of the material. Full reference details are given of all the documents that were studied, (see Section 6), and the reader is encouraged to obtain these if further reading on the subject is desired.

Whereas some of the results reviewed apply to permanently-installed HLLs, they have been included in the body of the report because the principles can also be applied to the temporarily-installed versions. Indeed, most of the development work and thinking applied to the temporary versions has been adopted from work previously done to bring the permanent versions to market.

3.1 AMERICAN RESEARCH

A relative early statement on single-span HLL performance can be found in Steinburg (1977), in which a simple static analysis is carried out. By this, Steinburg determines that the greatest load in the HLL (and hence on the end-anchors) occurs when the angle of deflection is small, and when the impact occurs in the middle of the span, (Figure 10). This relationship is expressed in terms of the ratio of tension generated in the HLL (T1) to that applied in the connecting lanyard (T) for various angles, see Table 1.

T

T1

Deflection angle

Figure 10 Static load “T” applied to HLL

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Table 1 Ratio of tension in HLL to tension in lanyard after Steinburg (1977)

Deflection angle (º) Ratio T1 : T

2 14.33

5 5.74

10 2.87

15 1.93

30 1.00

45 0.71

60 0.58

75 0.52

80 0.51

85 0.50

Note: load applied at mid-span

Further, in Steinberg 1977, (one purpose of which was to recommend criteria for a OSHA performance standard that was in the course of being drafted), mention is made of situations when HLLs will be used by two or more persons simultaneously. In this case, Steinberg argues, that the minimum strength values should be multiplied by the number of users, taking into account the geometrical factors involved with HLLs.

3.2 FRENCH RESEARCH

3.2.1 Static analysis

In Caisse Nationale de L’Assurance Maladie Note technique No 167 (1980), (translated as National State Health Insurance Office Technical Note No 167), the efficiency of a safety harness is described by reference to the limited range of movement obtained when connected via a lanyard to a fixed anchor point. This is compared to the safe and increased range of movement gained when attaching the same lanyard to a cable that has been stretched between two points.

The note gives information about the choice and fastening of the cable. It makes reference to use of a 6 x 37 construction steel cable with fibre core of 13.2 mm and 15.4 mm diameter and a requirement that end-anchors should be able to sustain 40 kN. The maximum arrest force permitted to be experienced by the user is stated to be 6.0 kN.

There then follows a mathematical formula which expresses the relationship between the span (single), the weight of the cable, it’s stiffness (assumed to be constant), initial tension, and tension when a load of 6 kN is applied perpendicular to the line. The formula is a static analysis only, i.e. it takes no account of the motion or energy gained during a fall-arrest event. A series of graphs are provided based on the formula to give a “ready reckoner” into how a system may behave. The first shows end-anchor loads verses system span when a 6 kN static load is applied for a range of initial tensions. The second shows initial sag and “V” deflection verses system span when a 6 kN static load is applied for a range of initial tensions. The graphs are repeated for the different cable sizes.

22

It is worth noting that this static analysis predicts that a 6 kN mid-span load generates a 30 kN end anchor load, for a 10 m span of 13.2 mm diameter cable at an initial tension of 2 kN, and produces a “V” deflection of 0.5 m.

Technical Note No. 167 makes the vital point that since loads at the end-anchors can be very high, it is important that some verification is made of their ability to sustain them, as well as the structure to which they are installed to. Also that safety factors need to be applied to both anchor and structure to ensure that there is a sufficient reserve of strength should loads be applied of the magnitudes predicted.

Mention is also made that the manufacture of the anchor point, the fastening of the cable to the anchor, and the tensioning of the HLL all require “meticulous execution” and a careful inspection before initial use. The note goes on to recommend that the installed HLL should be tested by carrying out a fall simulation.

3.2.2 Static testing to destruction

In CEBTP (1984) a series of static tests are described on a 9-metre long length of HLL, made from 8 mm diameter stainless steel cable of 7 x 7 construction. It was installed with two intermediate supports as to give a configuration of 3 x 3 m sub-spans. In the tests, an increasing load was applied slowly, (as opposed to rapidly in drop-testing), and perpendicular to the HLL at the mid-point of the middle sub-span (i.e. in the direction in which a fall-arrest loading would be applied). A load cell was inserted at one of the end-anchors. The load was gradually increased until failure occurred.

In one test the cable failed completely, when the measured end-anchor load was 25 kN. Reconstruction of the cable showed that the failure had occurred where the cable had beared on one of the intermediate anchor supports, Figure 11. In order to check that the minimum strength of the cable was correct for that type of cable, and to ensure that a defective cable had not been used for test, an undamaged section was cut from the test specimen and was tested to destruction in tension. Failure occurred at 37.3 kN, which was comparable to the minimum breaking strength of 38 kN. This proved that the cable was not defective, but that the cable-support bracket interface had reduced the strength of the cable by a factor of 35%. This was due to the cable reeving over a relatively abrupt edge, with little area of contact, causing a stress concentration.

Cable failure at intermediate bracket

AnchorHLL rope Travelling device

Applied loading

Figure 11 Test set-up and static loading failure as in CEBTP (1984)

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3.3 CANADIAN RESEARCH

3.3.1 Ontario Hydro

In Sulowski and Miura (1983) a substantial project within the Ontario Hydro Research Division is described in which results of experimental and theoretical research work is disclosed. The aim of the research was to develop a method of designing and/or selecting a FAS based on a HLL and on other components, which would ensure the safety of the user and would comply with the appropriate safety regulations. In addition to the test methods and results arising from 75 drop-tests contained within this 120 page report, a specially developed HLL analysis computer program is described.

The main stimulus for the research came from requests for information, which had been received from operational departments within Ontario Hydro, in conjunction with a lack of serious experimental data in existing literature. The report describes the main uses of HLLs at the time which were in situations where a large range of protected horizontal movement was required by the user, e.g:

· Traversing a narrow, elevated unprotected element (eg: I-beam)

· Traversing a narrow, elevated unprotected structure (eg: bridge without superstructure, tower crane arm, top of hydraulic dam)

· Working along the edge of an opening (eg: hatches)

The test program itself covered 8 different configuration-parameters of HLL based FAS and their variations as described in Table 2. This approach was commensurate with the analysis under Figure 9.

Due to the relatively large number of different components employed in a FAS based on a HLL, and the complexity of the problems involved, the research method included theoretical analysis as well as experimentation.

The theoretical analysis was conducted at an early stage in order to estimate the behaviour of the FAS under test as a whole. A computer program was developed to carry out the analysis, and was later modified and refined by incorporating the experimental data obtained in the tests.

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Table 2 Configurations and variations chosen for Ontario-Hydro research testing

after Sulowski & Miura (1983)

Configuration-parameter Variations

)

) ///

HLL rope (six types

3/8 inch diameter 1/2 inch diameter IWRC wire rope 5/8 inch diameter 5/8 inch diameter “permacable” 5/8 inch diameter nylon synthetic rope 1 inch diameter polypropylene

Interconnecting equipment (six typesbetween HLL and drop weight

5/8 inch diameter nylon 7/8 inch wide nylon webbing 5/16 inch diameter aircraft cable “Miller” type 216 s a lanyard. “Zorba” s a & 5/16 inch diameter aircraft cable “Zorba” s a & “Sala” retractable lifeline

without energy absorption

with energy absorption

HLL span (four lengths) 3 m, 10 m, 30 m, and 50 m

HLL terminations & end-anchors (three types)

Clipped eye (Crosby clip, U-bolt clips) and eyebolt anchor Flemish eye splice and eyebolt anchor HLL rope tied around support column

300 N and 500 N for 3 m span Two different initial tensions for each 500 N and 1 kN for 10 m span span length 1 kN and 3 kN for 30 m span

3 kN and 6 kN for 50 m span

Three different locations along the span for releasing the drop mass

Mid-point of the span One quarter point of the span 1 m from the end anchor

Three different heights for releasing drop mass To generate free falls of 1.0 m, 1.285 m, and 1.5 m

Number of drop masses Single 100 kg mass 100 kg mass and a 110 kg mass released simultaneously

Note: s/a denotes “shock absorbing”

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Test findings

Sulowski and Miura (1983) report the following findings on tests which were conducted on single-span HLLs:

· Considering the span parameter, it was observed that greater spans produced lower forces at the end-anchors and lower fall-arrest forces, but greater falling distances. The maximum end-anchor load seemed to occur somewhere between the 3 and 10 m size. Surprisingly, the end-anchor loadings for the 3 m spans were lower than those for the 10 m spans. It was suspected that anchor stiffness, rope termination method and anchoring structure stiffness were factors more pronounced in shorter span situations.

· As initial tension in the HLL was increased:

o higher end-anchor loads were produced (upper view of Figure 12) o greater falling distances were produced (lower view of Figure 12) o lower arrest forces were produced (middle view of Figure 12)

although the initial tension did not seem to affect performance to such an extent as originally envisaged, particularly in a short span.

· As expected, longer free fall distances produced higher end anchor loads, higher arrest forces and greater falling distances.

· The HLLs using wire rope produced higher forces at the end-anchor, higher fall-arrest forces, and shorter falling distances. The HLLs using synthetic rope produced lower forces at the end-anchor, lower fall-arrest forces, but greater falling distances.

· Among the interconnecting fall-arrest equipment tested, the energy-absorbing lanyards produced the lowest fall-arrest forces.

· Regarding the anchoring methods, the Flemish eye splices produced slightly higher forces at the end-anchor, higher fall-arrest forces, and shorter falling distances than the HLLs with clipped eyes. When the HLL rope was looped around the end supporting columns and secured with Crosby clips, they produced lower forces at the end-anchor, but higher fall-arrest forces and greater falling distances than the HLLs with Flemish eyes or clipped eyes connected to eye bolts on the support columns.

· The tests examining drop-test location revealed that maximum forces at the end-anchor and maximum falling distance occurred when the mass was released at the mid-point of the span. However, the arrest force became higher as the drop location moved closer to the end-anchor.

· In the experiments which simulated two workers falling together, the maximum forces at the end-anchor and maximum falling distances were recorded when the two test masses were released at the mid-point of the span. However the individual arrest force experienced by each mass was lower than that under single mass drop conditions.

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, m

3 10 30 50

3 10 30 50

m

m

initial tension

initial tension

initial tension

Note: HLL based on 1/2 inch diameter steel rope 6 x 25 IWRC construction, clipped eyes on each end. Interconnection equipment consisted of a 5/8 inch nylon lanyard of 1.0 m overall length. Free fall distance 1.285 m, drop mass of 100 kg.

Figure 12 End anchor load, maximum arrest force and total fall distance verses HLL span for various initial HLL tensions. After Sulowski & Muira (1983)

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· The computer program was developed so that it could be employed either in an analytical mode or in a design mode. The difference between the two modes lay in the introduction of safety margins into the design mode in order to assure that any potential error in the computer calculation would be on the safe side whilst taking account the strength of materials in the load path and the worker’s tolerance to fall-arrest forces.

· Because of the complexity of the HLL as a whole, with many uncertain factors involved in the FAS, a highly accurate prediction of performance was not deemed possible. A comparison of tests results and computer prediction revealed that the majority of test results fell in ± 10% of the computer prediction for the end-anchor forces and fall-arrest forces, and between -10% and +15% for the falling distance. When employed in the design mode, the program automatically increased analytical values by 10% for the end-anchor forces and fall-arrest forces and by 15% for the falling distance so that the prediction for each factor was on the safe side rather than the average.

· Likely sources of error lie in the assumptions behind the analysis, e.g: the mass of the lanyard and HLL rope was assumed to be negligible and the HLL rope modulus was assumed to be constant irrespective of applied load. This latter factor was modified during later computer program development.

Conclusions

In Sulowski and Miura (1983) the conclusions drawn were:

· In general the “Permacable” synthetic rope showed superior one-man fall performance when compared to the other ropes tested, and it was easier to install when compared to the wire equivalents. A 5/8 inch diameter wire rope is stipulated for the two-man fall situation.

· An important point that was made, was that the choice of HLL rope cannot be made without examining the conditions of each application individually.

· The worst case scenario for end-anchor forces and falling distance was a fall at the mid-span point.

· The Flemish eye splice showed a slightly better performance for HLL terminations. However, for the anchoring method, insufficient data was obtained to draw any definite conclusion.

· Although graphs were drawn up as a guide to performance under limited conditions, an attempt to produce a more comprehensive design guide in graphical form was only partially successful because of the large number of parameters involved, due to the wide variation of configuration and conditions representing field applications.

· Data for designing a HLL based FAS in the field could be obtained by requesting a computer analysis. The information on the application and the conditions would have to be supplied by the user (a standard format is described). The choice of sizes and materials of the system components would be limited to those which had undergone testing. Also there was a limit to the accuracy of the computer program.

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· With the HLL installed, the cable sag measurement at 1.5 m from the end anchor could be used as an indicator for the initial tension in the HLL rope. This method would need to be studied and developed.

· Further work would be needed to test other sizes and potential components that could be incorporated into future HLLs, and for extending the capability of the computer program.

· Comment was made about the initial extension of a new HLL rope under fall loading, which was very large1. The elongation of the rope in the first drop test is reported to have been almost 50% more than in the third drop on the same rope.

· Comment was also made that in the field of operations, HLL ropes are replaced with new items after a fall-arrest incident, i.e. after the rope has been subject to a impact loading. This is because of the safety critical nature of the FAS. The same stance was taken during the testing, i.e. it was decided to replace each rope with a new one after each test.

In assessing the performance envelope for HLL configurations, the following limits were established:

· The maximum end-anchor load permitted was 1/3 the minimum breaking strength of the HLL rope, including a 10% safety margin; i.e. the rope would be at least 3 times as strong as any load transmitted through it to the end-anchor.

· The maximum arrest force permitted to be experienced by a worker was 8 kN2

including a 10% safety margin.

· The maximum total fall distance permitted was 5.0 m including a 15% safety margin.

The third limit also enabled the establishing of a minimum clearance beneath the worker, measured from the datum of the HLL to the nearest obstacle below. Setting of such a clearance prevented a falling worker from colliding with an obstacle before completion of the fall.

Protocol is mentioned by which the person on site has to amass the geometrical information, carry out either a graphical or computer analysis, and ensure that the results obtained do not exceed the limitations for the HLL.

3.3.2 Canadian steel erection industry

In Arteau and Lan (1992), reference is made to the introduction of HLLs in the Canadian steel erection industry, where in 1981 steel erection workers had a daily absentee rate of 82.6 per 1000 workers.3 This was mainly due to falls from a height. A simplified means of mathematically analysing HLLs is presented, based on static analysis alone. This neglects the capacity of the HLL rope to dissipate energy. Results are presented graphically and it was hoped that this would simplify design of the HLL on site. However the accuracy of such calculations is not reported.

1 This is due to the twisting and seating of individual wires and strands when a load is applied. A rope is a complex mechanism, consisting of wound strands which themselves consist of a number of wound wires. 2 Allowable under Canadian standards 3The number of workers absent each working day per 1000 workers

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In Arteau and Lan (1994) the work in Arteau and Lan (1992) is repeated, but some additional dynamic test work is reported. This focuses on tests using posts as the end-anchoring means and demonstrates that the degree of rigidity (or flexibility) of the end-anchor arrangement can have an affect on performance.

The static analysis method is mentioned in Corbeil et al (1996), in that it necessitated the production of very heavy anchor posts (in the order of 50 kg). This drove forward the idea of more efficient posts as described in Corbeil et al (1996) which would be deformable and hence provide energy absorption at the end-points of the HLL.

This would have the effect of lowering end anchor forces and reducing the decelerations on workers, which is reported to be in the order of 10 g 4. Figure 13 demonstrates the concept.

Notes: View (a) prior to fall View (b) instant when HLL begins to deform View (c) anchor posts deform in response to loading

Figure 13 Components and fall-arrest operation of HLL based FAS using collapsible energy-absorbing end anchor posts. After Corbeil et al (1996)

4 There is no mention, but the author assumes that energy-absorbing means were not fitted in the worker’s lanyard between body harness and HLL

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Testing

Corbeil et al (1996) goes on to describe the experimental drop-test methodology, in order to study the energy-absorbing effects of the collapsing end anchor posts. This includes, interestingly, performance under temperatures of -40ºC, -25ºC, and +25ºC, since ambient temperature affects the impact properties of steel.

Also worthy of note is that different steel test masses were used to represent different sizes of workers. These were: (i) 80 kg mass, representing a worker’s weight in the 50th percentile5, and (ii) 100 kg mass, representing a worker’s weight in the 95th percentile6. A single 200 kg mass was used to simulate two workers falling simultaneously.

The HLL under test consisted of a 6 x 25 IWRC grade 110/120 steel wire of 12.7 mm diameter stretched between two anchor posts 0.9 m high.

For the dynamic strength tests, which were tests to assess strength safety factors, the same type of wire rope was used for the interconnecting lanyard, but for dynamic performance, a 3-strand nylon lanyard of 16 mm diameter and 1.2 m length was utilised. This was chosen in order to represent as faithfully as possible the conditions prevailing on construction sites.

Following a dynamic performance test, the residual static strength was checked by doubling the test weight, and suspending it from the horizontal wire for 5 minutes, “the period of time corresponding to a rescue”7. Corbeil et al (1996) then go on to describe another dynamic test, which they claim reproduced a “failed rescue attempt”, and, from what can be discerned from the description of this, assumes that the Rescuee8 becomes inadvertently detached from the rescue system, falls, and impacts the HLL a second time9. The free fall for this test was 1.2 m, which subjects the energy-absorbing end-anchor posts to a second amount of rapidly applied energy, which they had to withstand if the test was to be successful.

Only one set of results is presented which involves a drop test of 2.4 m free fall with a test mass of 100 kg. The end-anchor posts deformed, limiting the end-anchor load to 11 kN and the load on the mass to 5 kN.

3.3.3 Retractable arresters

In Sulowski (1991) reference is made to the use of retractable type fall arresters whilst connected to anchors of low stiffness, (susceptible to springing, e.g. a cantilevered beam). Concern had been expressed because of the tendency for such an anchor to spring up and down at the point of arrest, and that the frequency and magnitude of these vibrations might cause the locking mechanism (commonly ratchet pawls) to disengage. This would result in a subsequent fall which would have to be arrested again. This phenomena could easily be envisaged when connected to a HLL. The cycle of “ratchet bounce” might be repeated until the amplitude of the HLL vibrations had subsided. This could create a danger where the free space beneath a worker was at a minimum. Sulowski (1991) recommends a simple, non-instrumented drop test in those situations where such a phenomenon is suspected.

5 50th percentile is a statistical measure and means 50% of the measured population had a mass which was less than 80kg and 50% had a mass which was more than 80 kg. 6 95th percentile is a statistical measure and means 95% of the measured population had a mass which was less than 100kg and 5% had a mass which was more than 100 kg. 7 The author assumes that this corresponds to the static weight of two persons, the rescuer and the rescuee 8 Person being rescued 9 It should be noted that there is no mention as to the method of rescue

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3.4 AUSTRALIAN RESEARCH

3.4.1 Initial research

In Dayawansa et al (1989), a 39 page report sets out the results of a theoretical and limited experimental investigation carried out on the behaviour of “static line systems” (their term for HLL based FAS) for the Victorian Occupational Health and Safety Commission. A theoretical (computational) method was developed to determine the forces required for strength design of the HLL and the force experienced by the person falling. The theoretical method was verified by a limited series of experiments consisting of 12 drop tests on a single span HLL of 3.7 m overall length.

The report claimed that the elastic properties of the cable and the interconnecting lanyard influence the performance of the FAS more than their respective breaking strengths. These parameters were measured experimentally, for two sizes of steel cable (10 mm and 12 mm diameter round strand 6 x 24 fibre core) and for polyester rope (12 mm diameter).

Development of the Static Line Analysis Program “SLAP”, a relatively basic computer program for performing calculations, is described. As with engineering calculations in general, assumptions are usually made so as to minimise their complexity. In this case they were:

· That there would be sufficient friction between the HLL and the travelling device to prevent it from sliding down the lifeline in a fall

· That there would be no friction between intermediate supports and the HLL

· That the deflection angles in a fall would be large

· That the stiffness of the supports and harness could be represented by linear springs

· That elements of the system would not absorb energy through plastic (permanent) deformation

As cited elsewhere, e.g. in Drabble and Brookfield (1998) and in Riches (1992a), solvable equations cannot be obtained when modelling such complex real time dynamics as the trajectory of a falling man being decelerated by a HLL. Dayawansa et al (1989) confirms that the system of equations can only be solved by using an iterative solution necessitating the use of computers.

Once the parameters that would influence the behaviour of the HLL under fall-arresting conditions had been identified, one of the objectives became the investigation into how each of the parameters would influence the loads within the HLL and interconnecting lanyard. Dayawansa et al (1989) goes on to state that the fall arrest load in the connecting lanyard is directly proportional to the deceleration felt by the person falling, and the loads in the HLL are important from the design point of view of the whole FAS.

Test findings

In Dayawansa et al (1989) static testing of the cables was performed to determine stiffness and strength properties. The stiffness of the cables was found to increase due to repeated loading, an important aspect as the performance of the HLL can be significantly affected by alteration in cable stiffness.

32

Whilst it was acknowledged that HLLs in practice have multiple sub-spans, a single span was tested since it was felt sufficient to verify the computer program model. Both a steel block and a dummy, each of 80 kg mass, were used in the experiments to represent a falling person.

The specification of the dummy is not described, but from the photographs in Dayawansa et al (1989) it would seem to have been a simple human–shaped sandbag, tied at points to give approximate arm and head shapes, (legs are not discernible from the photographs). The idea was to use the rigid steel mass to verify the computational model, and then to compare results with these tests using the dummy, thus enabling the energy-absorbing characteristics of the dummy to be identified.

The following observations were made after the results of the testing were studied in conjunction with computer analysis. These observations rely to a much greater extent on the computer analysis than on the experimental results:

· The force in the interconnecting lanyard decreased when lanyard stiffness, HLL stiffness, free fall and mass of the person were decreased

· The force in the interconnecting lanyard decreased when initial HLL tension and intermediate span were increased

· The force in the HLL decreased when lanyard stiffness, HLL stiffness, intermediate span, free fall and mass of person were decreased

· The force in the HLL decreased when the initial tension in the HLL was increased

· For a given system, the forces in the HLL and interconnecting lanyard were a minimum when the loading point was at the centre of the HLL span and at the centre of an intermediate span. The forces increased when the eccentricity of the loading point increased both with respect to the total span and with intermediate span.

Conclusions and recommendations

Dayawansa et al (1989) concludes that:

· The effective elastic stiffness of both steel cable used as the HLL component and polyester used as the lanyard component greatly influence the behaviour of the whole system

· The stiffness of the HLL cable increases with repeated loading

· The computer model was verified against experimental results. This enabled analysis of HLL based FAS to be made, so that system forces, reactions of supports and deformations could be calculated

· From the viewpoint of potential injury to the person experiencing a fall, the forces in the lanyard appeared to be excessive for most of the static line configurations considered10

· The harness would not significantly reduce the force in the lanyard

10 author’s note: lanyard forces recorded varied from 12.28 to 16.51 kN without an energy absorber fitted

33

· The performance of the system could be significantly improved by incorporating energy absorbers of the permanent deformation type

Dayawansa et al (1989) goes on to emphasise that the utilisation of energy absorbers in the lanyard are very effective in reducing the forces experienced by a person during a fall. Given the HLL configurations considered, high lanyard forces would be experienced if the energy-absorbing strategy relied solely on the energy-absorbing capability of the HLL cable and the polyester lanyard. In addition the important point is made that the reduction of forces on the person in a fall will result in lesser forces being transmitted to the HLL and hence through to the end-anchors.

3.4.2 Further research

Building on the efforts described in Dayawansa et al (1989), further work is described in Dayawansa and Ralph (1997), in which more comprehensive testing is summarised, based on a programme of sixty-eight tests that are fully documented in Dayawansa and Ralph (1996).

Of particular interest is the reference to the use of test results in justifying specifications in preparing the subsequent Australian Standard AS/NZS 1891.2. The intention behind this standard was the provision of guidelines and performance requirements which would be generally applicable to all HLL based FAS, so that commercially available systems would be required to satisfy those requirements. AS/NZS 1891.2 would also provide information for a set of prescribed configurations of HLL based FAS which could be set up by users without the need for testing or for engineering calculations, i.e. those systems would be deemed to comply with performance requirements.

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Three test system configurations with their variants were described, see Figure 14:

Figure 14 Schematic (plan) diagrams of system configurations used for testing After Dayawansa and Ralph, (1997)

Referring to Figure 14, Configuration 1 consisted of a straight line system with three sub­spans11. This configuration was the most important in the research, since it was considered to be the most common installation in practice. Accordingly forty-eight tests were conducted on this configuration. Variations included the investigation of three different cable diameters, namely 8, 10 and 12 mm - Dayawansa and Ralph (1997) stating that: “the stiffness of the cable increases when the diameter is increased”. Cable type is reported as “general purpose 6 x 24 fibre core galvanised steel rope”. Similarly it is stated that: “the overall stiffness of a system increases when the overall span is decreased”. Hence two nominal spans were used to investigate that effect, namely 36.6 m and 18.3 m. Lengths of sub-spans were also varied.

Configuration 2 consisted of a “Z” shaped system with two internal 90º corner angles and five sub-spans. Twelve tests were conducted on this configuration using 10 mm diameter cable.

Configuration 3 consisted of a flattened “Z” shaped system with two internal 135º corner angles. Six tests were conducted on this configuration using 10 mm diameter cable.

11 Each sub-span can be defined as the distance between adjacent letters in the three views of Figure 14

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Other testing parameters included:

· the use of chain interconnecting lanyards

· different kinds of energy absorbing lanyards

· the use of a karabiner (made from 12 mm diameter steel bar) as the travelling device

· the use of a 100 kg test mass to represent a worker

· different pre-tension of the HLL rope (0.5, 1.5 and 3.0 kN)

· different fall positions (middle of span, ¼ span and near to support)

No in-line energy absorbers were tested.

Test Findings

An interesting point worth emphasising comes from results of static HLL stiffness testing (see Table 3) conducted in Dayawansa and Ralph (1997). As in other research, reference is made to the usual practice of replacing HLL cables once they have been subjected to a fall-arrest loading, because such a loading tends to increase cable stiffness, which can significantly increase system and anchor loadings in a second or subsequent fall-arrest loading.

Two samples of each cable diameter were tested. Each sample was loaded to a pre-determined force, had the load removed, and then was subjected to the same procedure again for at least 5 times. The average stiffness in Table 3 was calculated as the average of values corresponding to a third, fourth and fifth loading cycle. (It was found that although stiffness increased after the first and second cycles, it did not change significantly after the third, fourth and fifth cycle).

Table 3 Stiffness of cables After Dayawansa and Ralph (1997)

Cable Test No. Stiffness Increase in Stiffness Diameter (kN/mm) (%) (mm)

First Cycle Average

8 C8A 1201 2483 106.7

8 C8B 1372 2216 61.5

10 C10A 3094 3700 19.6

10 C10B 2521 3251 29.0

12 C12A 2614 4410 68.7

12 C12B 2533 4400 73.7

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The increase in stiffness between the cable in a virgin state and the average was calculated as shown in Table 3. It is interesting to note that stiffness could change by over double in the 8 mm case and by 2/3 in the 12 mm case. The 10 mm case appears less significant. Also the assertion that “cable stiffness increases with increased diameter” is not fully supported by the above results; whilst admittedly, a doubling in stiffness between the 8 and 12 mm sizes is clear, there is next to no difference between the 10 and 12 mm sizes. In fact in one case the 10 mm size is stiffer. The difficulty behind this approach is that it assumes that cable stiffness is constant, but realistically cable stiffness varies according to load in the virgin state, Riches (1997). An example of stiffness test results shown in Dayawansa and Ralph (1997) also shows this non­linear stiffness relationship as depicted in Figure 15. As can be seen, the first slope (arrowed) is curved and so its gradient, (the measure of stiffness), at any load is different to the next, (as shown by the three double-lined positions).

Figure 15 Graph of load v extension (appended) after Dayawansa and Ralph (1997)

The above evidence establishes a very good reason to justify the replacement of HLLs after being subjected to fall-arrest loadings, (apart from other safety-critical reasons). If a HLL is left in place after sustaining a fall-arrest loading, then the stiffness of the HLL will certainly be at a much higher level than it was when it was originally installed.

Since stiffness has a significant effect on a HLL’s capability to absorb energy, and hence how much force is transmitted to end-anchors, it follows that in the event of a second fall-arrest loading being applied, sufficient loadings may be generated within the cable or at the end anchors to cause system failure, resulting in a worker falling to the ground or other substantial platform. In other words, any calculation or analysis made when the system was originally installed, which was performed in order to assess loadings and system performance, will no longer be valid, because any increase in the value of stiffness will significantly increase the loadings transmitted through the system.

3.4.3 Points worth noting from further testing

End anchor loads and lanyard loads

The maximum value of load recorded at the end-anchors was 18.3 kN with a corresponding force in the lanyard of 7.16 kN (no energy absorber fitted). This was recorded on a Configuration 1 system, based on 10 mm diameter cable of 16.64 m overall span. Three drop tests had been conducted on this system previously, so cable stiffness will have increased from that when the cable was in a virgin state.

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The test was conducted in the end sub-span of 7.0m length, near to an intermediate anchor. The length of the chain lanyard was 1.5 m and this was set so as to allow the test mass to free fall through a distance of 0.5 m. Maximum “V” deflection at first impact is given as 208 mm.

This shows that in this case the applied force in the lanyard is multiplied by a factor of approximately 2.5 by the time it is felt at the end-anchor. This is mainly due to the fact that the sub-span in which the fall takes place is deflected into a characteristic “V” shape in an attempt to resist the downward motion of the test mass. This creates a proportionately higher tension within the HLL which, apart from the applied load in the lanyard and other factors, is dependent on the deflection angle.

With energy absorbing lanyards employed, the maximum value of load recorded at the end-anchors was 9.6 kN, with a corresponding lanyard force of 3.8 kN. This gives an end-anchor to applied load ratio of 2.52. This was recorded on a Configuration 1 system, based on 10 mm diameter cable of 34.94 m overall span. Eleven drop tests had been conducted on this system previously, so cable stiffness will have increased from that when the cable was in a virgin state. The test was conducted in the middle sub-span of 10.0m length, at the mid-point. The length of the chain lanyard was 1.5 m and this was set so as to allow the test mass to free fall through a distance of 1.5 m. Maximum “V” deflection at first impact is given as 385 mm. Energy absorber extension is given as 980 mm.

The end-anchor loads are reported to be lower when the position of the fall simulation was next to an intermediate anchor. Dayawansa and Ralph (1997) suggest that this may be due to a reduction in the effectiveness of the HLL’s energy absorption capability, with the result that the system behaves more like a lanyard which is directly connected to an intermediate anchor.

The test results also show that end-anchor loads tend to increase when the total span of the HLL or the length of sub-spans is decreased. The latter observation is less pronounced than the first.

Intermediate anchor loads

The maximum value of load recorded at an intermediate anchor was 8.9 kN with a corresponding lanyard load of 8.7 kN (no energy absorber fitted). This was recorded on a Configuration 2 system, based on 10 mm diameter cable of 29.74 m overall span.

Nine drop tests had been conducted on this system previously, so cable stiffness will have increased from that when the cable was in a virgin state. The test was conducted in an internal sub-span of 7.0m length, near to an intermediate anchor. The length of the chain lanyard was 1.5 m and this was set so as to allow the test mass to free fall through a distance of 0.5 m. Maximum “V” deflection at first impact is given as 193 mm.

Karabiner sliding

In tests where the release of test mass was next to the intermediate support, the travelling device (karabiner) slid down the cable towards the centre of the “V” deflection during the first few rebounds. In test number SL9LM59, for example, the test mass is recorded as slipping a horizontal distance of 1700 mm in an internal sub-span of 7.0 m length.

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Cable size and stiffness

Higher loads were expected at the end anchors with cables of larger diameter, on the basis that these were stiffer than their smaller counterparts. This was supported by the results from the 8 mm cable diameter tests, as they produced the lowest loads. However, results from the 10 mm diameter tests were higher than those from the 12 mm diameter tests. This indicates again that other factors may come into play that affect a cable’s stiffness and energy absorbing ability which are masked when considering size alone. Stiffness and therefore energy absorbing capability are, for example, a function of load, and it would be a worthwhile exercise to study how results are affected when applying different loads, to determine how energy absorbing rates are affected.

Initial tension

The vast majority of tests were conducted with an initial tension of 0.5 kN, but some were carried out at 1.5 kN and 3.0 kN. Dayawansa and Ralph (1997) do not make definite conclusions, but observe that (i) loads generated appear to be lower when the initial tension is higher, and (ii) the influence of initial tension on loads does not seem significant when the magnitude is “within practically feasible limits of 0.5 – 1.5 kN”.

Multiple falls

Dayawansa and Ralph (1997) report on tests made with a Configuration 1 HLL which simulated the arrest of two men falling at different time intervals. Table 4 summarises the results. Three load-time histories are disclosed but these have not been reproduced here.

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Table 4 Comparison of drop-test results simulating the arrest of two men

by releasing two test masses at different time intervals after Dayawansa and Ralph (1997)

Measured force (kN)

Description V deflection (m) End anchors Intermediate

anchors Lanyards

North South North South A B

15. Two simulated falls in middle 7.0 m sub-span at mid-point, 600 mm apart, test masses released 1.187 19.2 19.9 5.7 6.2 7.8 5.8

near-simultaneously

16. As above 1.224 18.8 18.9 5.4 5.8 6.5 5.5

17. Two simulated falls in middle 7.0 m sub-span at mid-point, 600 mm apart, test masses released 1.25 18.5 20.1 5.8 5.8 5.7 6.9

50 ms apart

18. Two simulated falls in middle 7.0 m sub-span at mid-point, 600 mm apart, test masses released 1.14 14.0 14.3 3.6 5.1 7.5 7.5

200 ms apart

19. Two simulated falls in middle 7.0 m sub-span at mid-point, 600 mm apart, test masses released 1.164 13.4 13.2 3.3 5.8 8.8 6.8

300 ms apart

20. Two simulated falls, one in end 7.0 m sub-span and one in middle 7.0 m sub-span, both at 1.108 12.9 13.7 2.4 5.7 6.6 5.1 mid-point in respective sub-spans, test masses released 300 ms apart

Notes: (i) North and South end-anchors refer to the two end-anchors of the system

(ii) North and South intermediate anchors refer to the two intermediate anchors flanking the sub-span in which the drop-test was located

(iii) Designations “A” and “B” refer to the two arresting lanyards. 1.5 m chain lanyards were used (no energy absorbers), set so that each of the 100 kg test masses would freefall 0.5 m upon release

(iv) Tests were conducted on Configuration 1, (10 mm diameter, 34.94 m overall span)

(v) Initial tension 0.5 kN. 4 drop tests had been conducted previously on same HLL

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Referring to Table 4, Dayawansa and Ralph (1997) make the following points:

· In Test 15, where the two test masses were released almost simultaneously12, the maximum load recorded at the end anchor was 19.9 kN, in comparison with 13.2 kN which was recorded when a single test mass was released in identical configuration and conditions

· When the two simulated falls are separated by a stagger of 200 – 300 ms, the lanyard load experienced by the test mass which reacts against the cable first is similar to the lanyard force obtained for a single simulated fall of the same height. However, in considering the second mass, it has to fall further than the first before reacting against the cable, since the cable by that time will have been pulled downwards into the characteristic “V” shape, caused by the first mass. Therefore, the second mass experiences a higher lanyard force than the first. (It should be understood that no energy absorbers were utilised in these tests). Also at the moment of impact of the second mass, the level of tension in the HLL may be higher due to the load induced by the first mass.

· In Test 20, where the two test masses were released within 300 ms of each other in separate but adjacent sub-spans, comment is made that lanyard loads and end-anchor loads are similar to those obtainable when under single test mass conditions. This is because when viewing the load-time histories, one can see that the force being applied by the reaction of the first mass against the cable has virtually decayed by the time that the second mass starts to react. Although not tested, Dayawansa and Ralph point out that if the time stagger between releases in adjacent sub-spans were eliminated to produce the simultaneous releases of Tests 15 and 16, the end anchor loads may show a load trend similar to the said tests.

3.4.4 Long single-span systems with multiple workers

Further work is described in Dayawansa and Ralph (1997) as: “tests on long-span static line systems”. These tests were conducted on single-span HLLs of 17 m and 33 m length. HLL material included galvanised steel, stainless steel and kernmantel rope.

Comment is made that “long span” HLL systems, i.e. long single-span systems, are generally used when intermediate supports cannot be provided at the location in question. Typical situations are described as aircraft hangars and during construction and maintenance of long structures. The system tested was designed to span 35 m as a single-span system, and to allow the simultaneous attachment of 4 workers.

A test frame is described, to which the HLL was attached 7 m above ground level. Six outriggers, which could be moved along the top flange of the test frame beam, gave the capability to drop up to 6 test masses from a height of up to 2.5 m above the level of the HLL, either one at a time, or simultaneously.

The galvanised steel cable was 12 mm diameter of 6 x 24 fibre core construction. The stainless steel cable was 12 mm diameter and is described as made from “G304” material. The kernmantel rope is described as being 19 mm in diameter.

12 “Near or almost simultaneously” is not defined. However from the load-time histories in the report the test masses appear to have been released simultaneously, with the maximum arrest forces occurring within 25 ms of each other

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The energy absorbing lanyards used to connect the 100 kg test masses to the HLL were 1.8 m long and of 6 kN rating. In-line energy absorbers were employed but these are not described.

In the tests which involved the multiple release of test masses, all masses were released approximately simultaneously, (no error given).

A summary of the 11 tests is shown in Table 5. Note that not all details are disclosed.

Table 5 Summary of test results of multiple near-simultaneous fall simulations on long

single-span HLL after Dayawansa and Ralph (1997)

Test No

Cable type / span (m)

No. of test masses released

Free fall (m)

No. of in-line energy absorbers

Maximum end anchor load (kN)

01 Galv / 33 1 1.0 - 17.7

02 Galv / 33 1 2.0 - 19.8

03 Galv / 33 1 2.0 - 20.3

04 Galv / 33 2 2.0 1 16.0

05 Galv / 33 4 2.0 2 27.2

06 Galv / 33 6 1.3 3 26.8

07 SS / 33 4 1.3 2 19.3

08 Galv / 17 2 1.3 1 17.4

09 Kern / 17 2 1.3 - 8.4

10 Galv / 33 2 1.3 - 25.2

11 SS / 17 2 1.0 - 33.3

Notes: (i) Cable type: Galv = galvanised steel SS = stainless steel Kern = kernmantel

(ii) No individual “V” deflections were given except the maximum values stated in the text immediately following this table

Observations are made as follows:

· Except in Test 05 and 11, the arrest forces in the energy absorbing lanyards remained below 6 kN. In Test 05 one reading was 7.5 kN, and in Test 11 one reading was 6.2 kN. It was noted after test that the energy absorbing elements of the two energy absorbing lanyards were completely exhausted. This could indicate either that the items were of defective manufacture or that they had been subjected to energy levels beyond their capacity to absorb.

· For tests with a single mass on a 33 m span the maximum “V” deflection was 2080 mm

· For tests with two masses on a 33 m span the maximum “V” deflection was 3545 mm

· For tests with four masses on a 33 m span the maximum “V” deflection was 3900 mm

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· For tests with two masses on a 17 m span the maximum “V” deflection was 1700 mm

· For the test with two masses on a 17 m span using the kernmantel rope the maximum “V” deflection was 1260 mm. The deflection in the 17 m span steel cable was higher than that of the kernmantel type because of the additional extension of the in-line energy absorber.

· In most of the tests that simulated multiple fall situations, it was noted that the attachments to the HLL slid along the cable towards the bottom of the “V” deflection after the first impact causing the masses to collide with each other. Some of the masses touched the ground during this process13.

· The maximum “V” deflections between galvanised and stainless steel cables did not appear to differ greatly

· For a given cable type and size, “V” deflection depended on:

o Span o In-line energy absorber extension o Position of falls o Free fall heights o Number of near simultaneous falls

· Since the test programme did not cover sufficient combinations of the above parameters in order to determine the maximum “V” deflection, a reasonable safety factor would have to be applied if any of the recorded deflection measurements were ever used in calculating the minimum free space required beneath a HLL, in order to avoid collisions with the ground or other substantial obstacle.

· Significantly high loads can be generated at end-anchors of long single-span HLLs in comparison to those supported with intermediate anchors

· Multiple near-simultaneous falls increase end-anchor loads in comparison to single falls

· In-line energy absorbers can reduce loads at end-anchors significantly

· The loads at end-anchors can be significantly lower in kernmantel based HLLs than those generated in steel cable based HLLs, but may lead to greater “V” deflections

· “V” deflections in long, single-span HLLs, extension of in-line energy absorbers, and extension of personal energy absorbing lanyards in multiple fall situations requires special attention by designers and users of HLLs. The combinations of these displacements may become sufficiently large to pull other workers away from their position of work, (i.e. the first person who falls may pull others off-balance). Also, the excessive deflection of the HLL may cause second and subsequent workers to experience excessive free falls before being arrested by the HLL.

13 Authors note: although it is claimed that the measured maximum “V” deflection and maximum end-anchor loads may not have been affected by these ground collisions, it would be logical to check the respective force-time histories first (which were not shown)

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3.5 UNITED KINGDOM RESEARCH

3.5.1 Drop-tests involving multiple-dummy releases

In Drabble (1995), a series of drop tests on a multi-span HLL are analysed, most of which entailed the simultaneous release of four anthropomorphic-articulated test dummies each of 100 kg mass.

One set of results is shown in Table 6. This corresponds to a straight line multi-span HLL, using 12 mm diameter 7 x 7 construction stainless steel cable, of 28 m overall span. Sub-spans were at 4 m intervals with a single sub-span of 8 m. The four dummies were connected to the HLL in the 8.0 m sub-span, via 2 m long energy absorbing lanyards connected at the dorsal harness attachment point, (energy absorber nearest harness), and were simultaneously released such that their free fall amounted to 4.0 m before the HLL started to deflect14, Figure 16.

Load cells were inserted at the end anchors, at the connection point between HLL and lanyard, and at the connection point between harness and lanyard. The latter two positions enabled the recording of force at either end of the lanyard, as there are often differences.

Table 6 Summary of test results of 4 simultaneous releases of anthropomorphic dummies on

multi-span HLL after Drabble (1995)

Load cell position Maximum load record@ time from release (

ed (kN) ms)

Time from release at onset of arrest (ms)

End anchor left hand side 32 @ 1100 1000

End anchor right hand side 30 @ 1100 1000

Dummy 1 HLL connection 5.0 @ 1050 970

Dummy 1 harness connection 4.5 @ 1050 950

Dummy 2 HLL connection 5.2 @ 1425 1050

Dummy 2 harness connection 5.2 @ 1410 1100

Dummy 3 HLL connection 5.2 @ 1090 1045

Dummy 3 harness connection 4.8 @ 1090 1020

Dummy 4 HLL connection 5.6 @ 1090 1040

Dummy 4 harness connection 6.1 @ 1090 1030

As can be seen from Table 6, the maximum end-anchor loadings occurred simultaneously, and within a time interval of 10 – 50 ms after the maximum arrest forces had been transmitted by each of the four dummies. The exception is dummy 2 which had a much later maximum arrest force. What is interesting to note is that although the four dummies were released simultaneously, (the margin of error is not stated), the time at which onset of arrest commenced varied between each dummy. This is the time at which the HLL and energy absorbing lanyard just start to resist the downward motion of the dummy, i.e. the HLL just begins to deflect and the lanyard is taut. These onset times (at the HLL connection point) were: 970, 1050, 1045 and 1040 ms for dummies 1-4 respectively, i.e. 80 ms between the first and last onsets.

14 i.e. they were released approximately 2.0 m above the level of the HLL

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The end-anchor loadings were in the region of 30 kN, for near-simultaneous applied loadings of 5kN arrest force per dummy (dummies 1, 3 and 4), plus dummy 2’s contribution of 4 kN at the 1050-1090 ms time frame, which later peaked at 5.2 kN. This shows that the forces transmitted to end-anchors are magnifications of the applied arrest forces and that applied arrest forces can be accumulative if they are applied within a short time frame. If, however the dummies had been released, or had impacted the HLL over a greater range of time, the end-anchor loadings may have been smaller. What is significant, is that the combined energy applied of 4 x 100 kg dummies, each free falling through 4 m, and dissipating that energy at a rate of 5 kN nominally, only produced end-anchor loadings of 30-32 kN, for a “V” deflection of 0.85 m, and a energy-absorber extension of 1.5 m. This means that although four persons were falling simultaneously in the same sub-span, the distance that they were decelerated through was only 2.35 m for a 4.0 m free fall. Whilst this can be partly be explained by the energy-dissipating nature of the harness-clad dummy, which attempts to model a real man-fall more accurately that by using a steel test mass, Riches (2002), the main mechanism at work is the fact that the cable was supported at intervals throughout it’s length, as opposed to a single-span system, and the stiffness characteristics of the cable allowed a significant amount of energy to be dissipated whilst restricting excessive deflection.

Fig 16 Four dummies impacting HLL near-simultaneously, after Riches (1997)

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3.5.2 Drop-tests involving simultaneous and staggered double-dummy releases

In Monks, (1991), a series of drop tests on a multi-span HLL are analysed, most of which entailed the simultaneous release (SIMREL) and staggered release (STAGREL) of two anthropomorphic-articulated test dummies each of 100 kg mass, Figure 17. A number of test variations were attempted. The HLL configuration tested comprised of a multi-span HLL, using 12 mm diameter 7 x 7 construction stainless steel cable, of 30 m overall span. Sub-spans were at 3 m intervals with a single 90º corner arrangement. Sub-spans were numbered 1-4 from the left hand end-anchor to the corner, and were numbered 5-8 after the corner to the right hand end-anchor. Sub-span numbers 4 and 5 flanked the corner arrangement and sub-span numbers 1 and 8 were adjacent to the end-anchors.

Fig 17 STAGREL of two dummies at 500 ms interval, after Riches & Feathers (1998)

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The dummies were connected to the HLL and were released in various sub-spans, see Table 7, via 1 m long energy absorbing lanyards connected at the dorsal harness attachment point, (energy absorber nearest HLL), and were released such that their free fall amounted to 2.0 m before the HLL started to deflect15. Other interconnecting equipment was also tested. Load cells were inserted at the end-anchors and at the connection point between HLL and lanyard. A summary of the test schedule is shown in Table 7.

Table 7 Summary of test configurations after Monks (1991)

Test No.

No. of dummies

Drop sub-span No

Drop position in sub-span

Attaching equipment between HLL and harness

Release type

1 1 6 Mid-sub-span Energy absorbing lanyard -

2 1 3 Mid-sub-span Retractable lifeline -

3 1 3 Mid-sub-span Retractable lifeline -

4 1 6 Quarter sub-span

Energy absorbing lanyard -

5 2 7 Mid-sub-span Energy absorbing lanyards

500 ms STAGREL

6 2 6 and 7 (one dummy in each)

In respective mid-sub-spans

Energy absorbing lanyards

500 ms STAGREL

7 2 7 Quarter and three-quarter sub-span

Energy absorbing lanyards

500 ms STAGREL

8 2 2 Quarter and three-quarter sub-span

Energy absorbing lanyards SIMREL

9 2 2 and 3 (one dummy in each)

In respective mid-sub-spans

Energy absorbing lanyards SIMREL

10 2 3 Mid-sub-span Energy absorbing lanyards SIMREL

11 2 8 Mid-sub-span Energy absorbing lanyards SIMREL

12 2 4 and 5 flanking corner (one dummy in each)

In respective mid-sub-spans

Energy absorbing lanyards SIMREL

Directly over

13 2 6 one support bracket and near

Energy absorbing lanyards SIMREL

to same bracket

14 2 - Directly on corner unit

Energy absorbing lanyards SIMREL

Note: SIMREL = simultaneous release of dummies STAGREL = staggered release of dummies at 500 ms intervals

15 i.e. they were released approximately 1.0 m above the level of the HLL

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Points of interest16 and conclusions drawn from Monks (1991) are:

· for this type of configuration and with the two types of retractable arrester tested, no ratchet-bounce17 could be detected;

· in the cases of 500 ms STAGRELs (staggered releases at 500 ms intervals) in the same sub-span, at mid-sub-span, the first arrest was virtually complete before the second arrest started. Arrest forces were virtually identical, with end-loadings slightly higher and taking a longer time to decay with the second arrest than that of the first. This was probably due to the fact that the first dummy had deflected the HLL before the second dummy struck it. Hence the second dummy would impact the HLL with a higher velocity and with a greater amount of energy to be absorbed than that of the first, because of the extra distance through which it would have to fall.

· in the cases of 500 ms STAGRELs with one dummy being released in each of two adjacent sub-spans, arrest characteristics were more similar to each other than those conducted within the same sub-span. Forces also occurred over a shorter time, probably due to the fact that each dummy fell through the same distance, i.e. the “V” deflection caused by the first dummy striking the HLL would not affect the distance through which the second dummy would have to fall through, as the vertical position of the second target sub-span would be unaltered.

· In the cases of 500 ms STAGRELs in the same sub-span, but at quarter and three-quarter positions within the sub-span, arrest forces were slightly higher for the second dummy than for the first, the differences being greater than those where the release points were mid-sub-span;

· In the cases of the SIMRELs (simultaneous releases), lanyard forces were generally the same as in STAGRELs, but were additive to produce approximately 50% higher end-anchor loads than those recorded in STAGRELs.

· In the cases of the SIMRELs in extremity sub-spans, end-anchor loads were approximately 80% higher than those recorded in STAGRELs.

3.5.3 Static tests to destruction

In Monks (1990) a series of tests are described on rope samples which are of interest. The tests entailed the application of a static load to different rope samples, so affixed as to represent a HLL of 3 m span. This load was applied slowly, (as opposed to dynamic testing which applies a rapid loading as that experienced in fall conditions). Loads were applied in mid-span, perpendicular to the rope as to cause a static “V” deflection, as per Figure 19. Load cells were fitted at one end termination of the HLL and at the hydraulic ram providing the applied load. A displacement transducer also recorded “V” deflection.

The purpose of the tests was to compare the failure loads of different rope constructions when deflected into a “V” shape. Results are shown in Table 8.

16 Full technical details not disclosed 17 See Section 3.3.3, 3.5.4 and 3.7.2

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Table 8 Summary of test results after Monks (1990)

Test Rope Maximum Failure “V” System safety factor

load in deflection at One person Two persons No. construction applied load (kN) cable (kN) failure (mm) arrested at arrested at 6 kN

6 kN each (12 kN)

1 8 mm Ø 7x7 18 37

2 10 mm Ø 7x7 29 60

3 12 mm Ø 7x7 37 74

8 mm Ø

216 3 1.5

204 4.83 2.42

216 6.17 3.08

4 59 172 4.33 2.16“dyformed” 26

9.5 mm Ø5 dyformed” 31 75 (iii) 160 5.17 2.58

6 8 mm Ø 7x7 12 28 168 2 1

7 8 mm Ø 7x7 18 37 240 3 1.5

Notes:

(i) Ø is the engineering symbol for diameter

(ii) maximum applied load is that load applied in a direction perpendicular to HLL which caused the HLL cable to fail

(iii) dyformed construction is a type of rope construction which uses shaped strands to reduce airspace in the rope structure and hence provide a greater strength than conventional round-stranded structures

(iv) in all cases except test 5, the rope failed at the mid-span point. In test 5 the applied load was held at 31 kN, (without failure), since the maximum measurement capacity of the load cell at the end-anchor was 75 kN

(v) in Tests 6 and 7, the same ropes were tested but with different travelling devices

(vi) system safety factor is the maximum applied load divided by the maximum arrest force generated by a single person (6 kN) or by two persons being arrested simultaneously (12 kN)

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In Monks (1990), apart from test 5, all rope failures occurred at the mid-span point, where the load was applied, and where the rope was caused to bend through a sharp radius. This causes a stress concentration, causing local weakening. As a result in some of the above cases the rope failed prematurely, i.e. at a load lower than that if it had been pulled in direct tension, (which is the normal direction of stressing, for a rope). For example, the 8 mm 7 x 7 rope has a minimum breaking strength of 38 kN when loaded in direct tension. This is a minimum, and is generally some 10% higher in practice. However, Tests 1, 6 and 7 recorded a lower figure, (37, 28 and 37 kN respectively), indicating that a weakening effect had taken place.

Similarly 12 mm 7 x 7 rope has a minimum breaking strength of 81 kN when loaded in direct tension. Test 3 recorded a lower figure of 74 kN, indicating that a weakening effect had taken place.

In Tests 6 and 7, the same ropes were tested but with different travelling devices for the connection of a lanyard. The results of these tests underline the absolute necessity to test for interaction and compatibility between device and rope in actual loading conditions. The device in test 6 was of good design for its intended function, but of poor design in how it interacted with the rope. It’s relatively abrupt edges effectively sliced through the rope at an applied load of only 12 kN. In comparison, the device in Test 7, with its relatively smooth edges, did not cause the rope to fail below an applied loading of 18 kN.

It is also worth mentioning that these type of static tests also demonstrate the “system safety factor”. In strength terms this shows how much reserve of strength a system may have, over and above that which is required when the maximum arrest force is applied. In other words, the highest load that can be applied to the HLL before failure, in a direction perpendicular to the HLL, divided by the maximum arrest force. For example, assuming a maximum arrest force of 6 kN per person, Test 6 would have a system safety factor of two (12 ÷ 6). All the other tests exhibited a system safety factor of at least 3, (e.g. Test 5, 31 ÷ 6 = 5.17). However when a two-person simultaneous impact is considered, these factors reduce. In this case 12 kN is applied, so in Test 6’s case, the rope would almost certainly fail. Also in Test 1 and 7 the safety factor would only be 1.5 (18 ÷ 12)18.

3.5.4 Research and development

In Riches and Feathers (1998) an account is given of research, development and testing of multiple-use, multi-span HLLs from the design perspective. Designing a FAS is a very demanding activity because great care has to be exercised when analysing the moral, legal, technical and commercial aspects, before making decisions. Often, the first three aspects require significant attention before the latter can be properly realised, with all the attendant pressures. The designer has to be painstakingly conscientious, and must be able to work with a clear conscience, because fundamentally the task is not to protect limbless wooden dummies or steel test masses from colliding with the test house floor, but is to prevent the injury or death of a real person. Any design mistake not detected during an inadequately designed test programme can result in someone’s death.

Amateur fabrications

A number of different HLL fabrications were studied in Riches and Feathers (1998). The components involved had been made without production tooling and were for one-off type installations. As a result a number of welds had been used to join parts together.

18 This assumes that when the load was applied with two travelling devices, the weakening effect on the rope would be the same as that with one device. In practice it may be better or worse.

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Welding and the necessary stress-relieving heat-treatment afterwards can be difficult processes to carry out, and poor welds can be prone to sudden brittle fracture. This is especially true when the welded area is within a load path which is likely to be dynamically stressed.

Testing of such components did reveal these types of weaknesses, and in some cases caused catastrophic system failure, e.g. Figure 18. It is worth highlighting that the termination component in Figure 18 also incorporated a spring to act as an in-line energy absorber. Springs do not really dissipate energy, unless they permanently deform in some manner. They usually just store the energy and then release it back into the system at some stage. In any event this particular spring failed when the welds failed.

Failure points

Figure 18 Example of a welding failure on a fabricated HLL component

In another one-off type fabrication, a travelling device had been made, for the connection of a worker’s lanyard. It had an unconventional profile. As an experiment, it was decided to incrementally load this component to destruction, together with the HLL rope, in the manner in which it would be loaded in a fall-arrest occurrence, i.e. perpendicular to the HLL, Figure 19.

Anchor

Applied loading

HLL rope

Line of HLL, prior to loading

Travelling device

Figure 19 Incremental loading of travelling device on HLL

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At an applied loading of 15 kN the device cut completely through the rope, indicating that the interaction between device and rope constituted a serious weakness. The profile had been contributory to the cutting action. This test also showed that when individual components are combined together in a system, as would be the case in practice, the strength of the whole system may be different to the individual strengths of each component. Consequently, and especially with FAS based on HLLs, it is essential to assess how the whole system performs from a dynamic performance and strength viewpoint.

Retractable arresters

Riches and Feathers (1998) discuss the benefits and problems of attaching retractable arresters to HLLs. The benefits are a greater range of movement for the worker in the vertical and horizontal plane, with generally better fall-arrest performance over that of fixed length energy absorbing lanyards.

The first problem with using these devices, is that their performance has to modelled for incorporation into a computer program, or other method of calculation, which can then be used to determine end-anchor loads, arrest force and total fall distance.

The second problem is that of the “ratchet bounce” phenomenon. In a fall, the rapid extraction of the lifeline element from its housing causes the reel on which it is wound to accelerate. At a pre-determined angular velocity, spring-loaded locking pawls which are mounted to this reel are inertially thrown out and engage a braking ring. This causes the lifeline to lock-up and prevents further extraction, providing the arrest resistance. In normal use the locking pawls are held away from the braking ring by springs, which allows the lifeline to be extracted and retracted in response to worker movement, without locking-up.

In a fall, once the locking pawls are engaged into the braking ring, it is important that they stay in place. In normal fall-arrest circumstances they are held in place by the tension in the lifeline element, caused by the arrest force, and subsequently by the weight of the worker in post-fall arrest suspension.

When ratchet bounce occurs, the locking pawls are allowed to disengage the braking ring, because the tension in the lifeline element decays, and the springs pull the pawls away from the ring. This allows the worker to free fall again, causing more extraction of the lifeline element, until at such time when the pawls can re-engage. This cycle can be repeated several times until the pawls finally lock and stay in place. Obviously ratchet bounce has to be avoided otherwise it submits the worker to several arrests and increases arrest distance.

An example of this can be seen in Figure 20. This shows the force-time trace of a drop test conducted on a retractable type arrester that was attached to a fixed anchor. The test was conducted with no free fall and with a 75 kg solid mass. The five major peaks showed that it required five attempts before the locking pawls could finally engage, i.e. the test mass bounced five times.

Retractable arresters are particularly prone to ratchet bounce when the load path or anchor is not stiff enough, i.e. when it is too springy19. This can cause the lifeline element of the retractable arrester to relax too much after the moment of first impact, allowing the pawls to disengage the braking ring. This can be greatly exacerbated when the anchor point is flexible, such as the situation when attached to a HLL.

19 See clause 3.7.2

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In Riches and Feathers (1998), the approach to dealing with this problem was to design a special type of retractable arrester for use with HLLs, which contained locking pawls with anti-ratchet bounce features, to prevent the release of the pawls in a fall situation.

Notes: Numbers in circles 1-5 show the five locking pawl engagements and immediate disengagements; intervals between locking attempts are shown with dotted arrows

Figure 20 Force-time graph of drop-test on retractable arrester showing “ratchet bounce” (author’s private collection)

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Another interesting case study is brought up in Riches and Feathers (1998), in regard to maintenance deficiencies. The gusting conditions on board an oil-rig had caused a cable-based HLL to wear within its intermediate support bracket, (Figure 21). Several wires had broken before the damage was detected; this would have caused a serious weakening of the cable in a fall-arrest incident.

Figure 21 Broken cable wires after wearing against bracket (author’s private collection)

Some dangerous situations are not necessarily easy to foresee, as highlighted in Riches and Feathers (1998), and as shown in Figure 22. As part of a research programme, two full anthropomorphic, articulated dummies were simultaneously released whilst attached to a HLL via energy absorbing lanyards. This was to simulate two workers falling together at the same time, as had been reported in some case studies of accidents, Health and Safety Executive (1985).

The pre-release point was such that the dorsal harness attachment point, to which the lanyard was attached, was approximately 1.5 m above the level of the HLL. This simulated the lifeline being installed at walk way level. After the drop-test, the review of the high speed photography revealed that one dummy caught the HLL under its armpit during the fall, which caused the arm to be pushed upwards, as Figure 22 shows. In a real life incident this could have severely injured the worker, and so the test highlighted one hazard when allowing a worker to work with a HLL installed at the level of the feet.

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Figure 22 SIMREL of two dummies being arrested by way of a HLL with attached energy absorbing lanyards; dummy “George” (right hand side) catches his arm during the fall. After Riches and Feathers, (1998).

3.5.5 Design and performance details

A number of design and performance features are discussed in Riches (1992b), which are worth highlighting:

· System safety factor (as described in clause 3.5.3). The reserve of strength afforded by the system safety factor is required for a number of reasons:

o Degradation over time due to environment o Degradation over time due to wear and tear o Damage due to abuse o Variation in manufacturing technique and materials o Misuse leading to overload

Manufacturers may apply different safety factors on their products. Standards require a minimum safety factor of between 2 - 2.5 in general. Fall arrest loading takes place over a fraction of a second; FAS that have been loaded in a fall situation are invariably scrapped, or critical components are replaced or closely examined afterwards.

· Design for installation – whereas design for use and function are important, they should not be at the expense of design for installation. Installation should be relatively simple without undue complication, in order to avoid errors. Component design should facilitate safe installation.

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· Design for minimising degradation – due consideration should be given to those environmental factors which can cause degradation to the materials and manufacturing processes chosen in the make up of the product. Examples include: abrasion, wear, corrosion, sunlight. Water traps should be avoided; anti-icing features should be considered; performance should be considered in adverse conditions.

· Stress concentrations – Where cables are bent around a point, (e.g. through and around an intermediate anchor bracket or corner arrangement, or at the bottom of a “V” deflection), where the contact area between components is very small, and where there is the possibility for high friction generation, these areas become more severely stressed than when the cable is stressed in direct tension. Stress concentrations should be eliminated where possible or minimised.

· Energy absorption – All components should in some way contribute to energy absorption if possible whilst maintaining system integrity.

· Fall indication – There should be some sort of indication to readily show that a fall has occurred on a system.

· Terminations – joining methods used to join cable to fitting to end-anchor should be as close as possible to 100% joint efficiency, (this is the situation where the minimum breaking strength of cable is the same before and after joining). Where joining methods reduce joint efficiency this needs to be taken into account when limiting loads in the system.

· Tensioning – tensioning method should be capable of being implemented in practice. Tensioning components should not effect the strength of the HLL unduly by their gripping or joining methods.

3.5.6 Single-span versus multi-span HLLs

In Riches (1992b), some advantages and disadvantages between permanently-installed and temporarily-installed versions of HLL are discussed, summarised in Table 9. The points are based on the general market disposition that permanently-installed versions tend to be of the multi-span type and temporarily-installed versions are of the single span type.

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Table 9 Summary of advantages and disadvantages between single-span and multi-span HLLs

after Riches (1992b)

Aspect Single span HLL Multi-span HLL

Relatively inexpensive and quick to install More expensive and slower to install

Installation Substantial tensioning is required to Tensioning requirements are substantially maintain horizontal attitude of lifeline, reduced which can deplete strength reserves

Fall forces and anchor loads are substantially reduced

Fall distances are substantially reduced

Considerably less likelihood of first fall pulling second worker off balance

Calculation or analysis (if performed) is relatively simple

Any rope type can be adopted in “home made” approach but more likely to have a system failure due to poor analysis, understanding or installation

More professional approach is required

System performance is verified by computational and engineered means

Systems are less likely to be installed by amateurs

Design / calculations

No special travelling device needed

Simple karabiner attachment can produce wear

Simple karabiner attachment can cause local stress concentration between HLL and karabiner at bottom of “V” deflection in fall situation

Special travelling device needed to pass through intermediate supports without requiring the worker to disconnect and reconnect

Travelling device designed to minimise wear and stress concentrations

Travelling device

Fall forces and anchor loadings are high

Fall-arrest Fall distances are invariably excessive

performance First worker to fall can pull second worker from work surface resulting in second fall; second worker will fall further than first

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3.5.7 Free Space Requirement

Arguably the most important aspect of any FAS is that it must stop the fall of a worker quickly enough before such a fall allows the worker to collide with the ground or other substantial structure, Riches (1997). FAS stop the downward motion of a free fall by applying an arresting force until the worker is brought to a complete halt. Consequently there has to be enough free space beneath the worker to ensure that, if a fall occurs, it will be arrested safely before a collision can occur, i.e. the free space must be greater to some degree than the distance the worker falls through.

This creates the requirement to know how much space is needed beneath a worker in case of a fall, and is a legal requirement for manufacturers’ instructions for use according to the PPE Regulations (2002) – Statutory Instrument No 1144.

The free space can be computer-modelled by considering such factors such as: worker’s mass, free fall, arrest performance characteristic of the equipment being used, harness stretch, height of worker and safety clearance. An example is shown in Figure 23 after Riches and Feathers (1998).

The free space can also be determined by testing with the full FAS, with a full representation of a human being, i.e. a full anthropomorphic, articulated, dummy. This can be seen from Figure 23, wherein the free space is simply the sum of items 1, 2 and 3. The safety clearance is similar to the philosophy of a safety factor and is set to take into account such factors as variations in stature height and mass of people, in arrest performance of equipment, in harness stretch, in environment and to allow for dynamic rebound, which cannot be assessed unless viewed by high speed photography methods.

If for whatever reason neither computer modelling nor full FAS testing is carried out, a calculation based on the arrest distance contribution of each of the components in the FAS has to be performed. Some of these contributions may have to be estimates, based on individual component performance tests, which may not represent how the component will actually be used, and invariably will not be the same value as when tested in combination with a HLL. Such a calculation is difficult and is prone to error.

The importance of the free space requirement cannot be overemphasised. In Wolner (1992), a situation was described in which a company had fabricated their own temporarily-installed (single-span) HLL to provide fall protection in an advertising board application. This company approached DBI Sala, (a leading American fall-arrest manufacturer), with a request for verification of their HLL design calculations. These calculations were based on a static analysis. No dynamic factors had been taken into account. T Wolner, being the Senior Engineer of DBI Sala at that time, declined the invitation and instead, offered a full-scale test.

Accordingly, the subject HLL was erected, complete with the necessary fall-arrest lanyards and strategically placed load cells for load measurement. The height of the HLL was set according to the height needed to do the work task, not the performance of the system. Two test masses of 100 kg mass each were connected in, and were simultaneously released according to where workers would be located in a real life situation. Both masses struck the ground with some force, showing that the workers, had they fallen when connected to such an installation, would have been seriously injured or killed. This FAS extended to such an extent that it could not arrest the fall of two workers, and showed the unreliability of purely static mathematical analysis.

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Before the fall At the end of the fall

l

Wal

EA IA HLL

1

2

3

Ground leve

k way

Key: EA: end anchor

IA: intermediate anchor

1: lanyard length + energy absorber operation + “V” deflection

2: harness stretch + distance between harness attachment point and feet

3: safety clearance

RFS: recommended free space = 1 + 2 + 3

Figure 23 Example of recommended free space for a FAS based on a multi-span HLL and energy-absorbing lanyard after Riches & Feathers (1998)

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3.6 GERMAN RESEARCH

In Lobert (2004), some very interesting drop-tests are described which investigate the effects of five workers falling and being arrested at or near the same time, whilst connected via an energy absorbing lanyard to a common, fixed anchor. The weight of the five workers was represented by using five 100 kg test masses, each connected to its own energy-absorbing lanyard.

A load cell was incorporated at the fixed anchor to measure arrest force with respect to time. The overall length of the energy absorbing lanyard was 2.0 m. The test masses were released in the tests so that they would free-fall through 2.0 m, and at different time intervals between each other. A summary of results can be found in Table 10, together with some comments. This information cannot be readily transferred to the HLL situation, but it nevertheless shows the relationship between time interval of falls and resultant maximum arrest force at the anchor.

Note that no information regarding arrest distance is given.

One school of thought that commonly arises in multi-fall discussions is that it is impossible for five workers to fall simultaneously, so there is no need to design for it. Taking this route automatically allows some manufacturers to be able to make fantastic claims for their products by making such a sweeping statement, because the level of forces that the product is subjected to in a “no need to design for it” test is much lower than that required for the simultaneous scenario, i.e. worst case. However, in practice, if near-simultaneous falls did impact their product, it would probably fail, allowing several falls to the ground. The real problem is that manufacturers are reluctant to modify or create new products to withstand larger loads caused by simultaneous or near-simultaneous loadings. They may also be reluctant to design and produce better energy-absorbing components which could limit loads by absorbing the greater amounts of energies generated in simultaneous or near-simultaneous loadings. This subject area is not helped by the lack of guidance in standards and in other documents20.

In the other school of thought, a number of manufacturers have recognised the need to test with simultaneous release of multiple test masses, and generally test to their own (higher) standard. The main trend to deal with the larger amounts of energy generated in such tests is to employ innovative or supplementary energy-absorbing techniques, and is one of the reasons behind the adoption of in-line energy absorbers.

20 in clause 5.6, a recommendation for future research is made to address this deficiency

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Table 10 Summary of test results after Lobert (2004)

Test No.

No of test masses & energy absorbing lanyards

Time interval between individual test mass releases (ms)

Maximum arrest force (kN)

Comment21

1 1 0 4.0 An expected result, occurring at 2.5 s after release.

An expected result, five forces of 4.0 kN 2 5 0 20.0 accumulating to give a total force of 20 kN occurring

at 2.5 s after release.

3 5 2.5 19.0 Test masses impact so close to each other, (near to 2.5 s after release), there is little difference to test 2.

4 5 5.0 17.0 Test masses impact so close to each other, (2.5 s after release), there is little difference to test 2 or 3.

Forces are again accumulative, but by now the interval between release is allowing the first arrest

5 5 10.0 15.5 force to decay before the second mass impacts and so on; this results in a lowering of the total arrest force.

6

7

8

5

5

5

50.0

100

200.0

16.0

14.0

10.5

At this point forces are still accumulative, but test trace begins to show the separation of the five arrest sequences; however none of the individual arrest forces can decay before the onset of the next.

Forces are still accumulative, but test trace shows clear distinction between individual arrest sequences; clear indication of arrest force decay before onset of next. There is approximately 100 ms of time between each arrest peak; each peak is a s follows: 4.0 kN, 7.0 kN, 10.0 kN, 12.5 kN and 14 kN. (Note 100 ms of time is equivalent of 49 mm of free fall).

Forces become less accumulative; arrest sequence of previous test mass almost complete before onset of next; rate at which load is being applied to anchor is less (indicated by slope of graph).

Forces are virtually non-accumulative; test trace shows that each of the arrest sequences are virtually

9 5 500.0 7.5 complete before the next begins; only a slight increase in arrest force between successive arrests (4 kN to 7.5 kN).

21 Comment from D Riches

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3.7 OFFICIAL DOCUMENTS

3.7.1 United Kingdom legislation

The text in clause 3.7.1 reviews some parts of UK legislation. It is a summary only and must not be referred to or used for legal, operational, safety or assessment purposes of any kind. For accuracy and completeness, reference must be made to the regulations themselves.

There are duties under various UK regulations which apply to HLL based FAS, for example the Personal Protective Equipment (PPE) at Work Regulations (1992)22. From a design and manufacturing viewpoint regulation 4 (3) (e) makes a stipulation that “PPE shall not be suitable unless it complies with any enactment (whether in Act or instrument) which implements in Great Britain any provision on design and manufacture with respect to health and safety in any community directive listed in Schedule 1 which is applicable to that item of PPE”. Schedule 1 lists the Council Directive 89/686/EEC (1989), which was transposed into UK Law as the PPE (EC Directive) Regulations 1992. These regulations have subsequently been updated and revoked by the PPE Regulations (2002).

Design and manufacture for sale

With a few exceptions, employers have to ensure that any PPE that they purchase complies with the PPE Regulations (2002). These regulations require that PPE such as temporarily-installed HLLs to be certified by an independent body, (known as a Notified Body) which will, if the PPE meets certain basic health and safety requirements, issue a EC type-examination certificate23. This involves examination and testing of the PPE and assessment of technical documentation. Subject to meeting the necessary requirements, the manufacturer or organisation submitting the product for certification is then able to display the “CE” mark on the product. It is illegal for suppliers to sell PPE unless the product bears the CE mark.

In many cases PPE was and is still made to harmonised European standards, which steadily replaced national standards in the various Member Countries of the European Community. PPE conforming with these standards is deemed to demonstrate compliance with the basic health and safety requirements of the PPE Regulations (2002). However there is still a general duty that no person shall supply any PPE unless that PPE is safe24.

Apart from the information that must be supplied by the manufacturer, either in instructions or other documentation, the fundamental basic health and safety requirements of the PPE Regulations (2002) that apply to temporarily-installed HLLs are as follows:

· The FAS must incorporate a body harness and an attachment system which can be connected to a reliable anchor point.

· The FAS must be designed so that under the foreseeable conditions of use the vertical drop of the user is minimised to prevent collision with obstacles and the braking force does not, however, attain the threshold value at which physical injury or the tearing or rupture of any PPE component which might cause the user to fall can be expected to occur.

22 See also “European Commission” in clause 3.7.5 23 See also “European Commission” in clause 3.7.5 24 The PPE Regulations (2002) defines “safe” as PPE when used and maintained in accordance with its intended purpose could not compromise the health and safety of the user

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· The FAS must also ensure that after braking the user is maintained in a correct position in which he may await help if necessary.

· The manufacturer’s notes must specify in particular relevant information relating to:

o the characteristics required for the reliable anchor point and the necessary minimum clearance below the user

o the proper way of putting on the body harness and of connecting the attachment system to the reliable anchor point.

Pre-use checks and ongoing maintenance

Maintenance of PPE and storage is required under regulations 7 and 8 of the PPE at Work Regulations (1992). An effective system of maintenance is essential to make sure that the equipment continues to provide the degree of protection for which it was designed. This, where appropriate, includes cleaning, disinfection, examination, replacement, repair and testing. The responsibility for carrying out maintenance should be laid down, together with details of procedures to be followed and their frequency.

A product such as a temporary-installed HLL, which undergoes frequent repeated cycles of installation/de-installation/reinstallation, in all kinds of outdoor environments, and in heavy industrial conditions, and given it’s safety critical nature, would certainly need a regular planned preventative maintenance programme. This programme would probably be carried out at 3­monthly or even monthly intervals, depending on the durability of the design in question. However manufacturers’ maintenance schedules and instructions should normally be followed: any significant departure from them should be discussed with the manufacturers or their authorised agent.

The requirements of regulation 7 of the PPE at Work Regulations (1992) extend to examination before use. Such examinations should be carried out by properly trained staff in accordance with manufacturer’s instructions. Regulation 8 requires that employers need to ensure that storage is provided for PPE so that it can be safely stored or kept when not in use. Such arrangements should be adequate to protect the PPE from contamination or damage by harmful environments, e.g. damp or sunlight.

Training

Regulation 9 of the same regulations requires that the employer is to ensure that the worker using the PPE is provided with information, instruction and training as is adequate and appropriate to enable the employee to know:

· The risks which the PPE will avoid or limit

· The purpose for which and the manner in which the PPE is to be used

· Any action to be taken by the employee to ensure that the PPE remains in an efficient state, in efficient working order and in good repair

Training should involve both theoretical and practical elements; in the case of a temporary-installed HLL, this would include the method of installation.

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Design, manufacture and installation

Section 6 of the Health and Safety at Work Act (1974) applies to organisations who are contemplating designing, manufacturing, importing, supplying or installing HLL based FAS.

It shall be the duty of any person who designs, manufactures, imports or supplies any article for use at work –

· To ensure, so far as is reasonably practicable, that the article is so designed and constructed as to be safe and without risks to health when properly used.

· To carry out or arrange for the carrying out of such testing and examination as may be necessary for the performance of the duty above.

· To take such steps as are necessary to secure that there will be available in connection with the use of the article at work adequate information about the use for which it is designed and has been tested, and about any conditions necessary to ensure that, when put into use, it will be safe and without risks to health.

· It shall be the duty of any person who undertakes the design or manufacture of any article for use at work to carry out or arrange for the carrying out of any necessary research with a view to the discovery and, so far as is reasonably practicable, the elimination or minimisation of any risks to health or safety to which the design or article may give rise.

· It shall be the duty of any person who erects or installs any article for use at work in any premises where that article is to be used by persons at work to ensure, so far as is reasonably practicable, that nothing about the way in which it is erected or installed makes it unsafe or a risk to health when properly used.

Other relevant provisions are found in the Construction (Health, Safety and Welfare) Regulations (1996), which in Schedule 4 makes requirements for equipment provided for the purpose of arresting the fall of any person. This clearly would include a temporarily-installed HLL. The requirements are that the equipment:

· shall be suitable and of sufficient strength to safely arrest the fall of any person who is liable to fall

· shall be securely attached to a structure or to plant and the structure or plant and the means of attachment thereto shall be suitable and of sufficient strength and stability for the purpose of safely supporting the equipment and any person who is liable to fall

· suitable and sufficient steps shall be taken to ensure, so far as practicable, that in the event of a fall by any person the equipment does not itself cause injury to that person.

These requirements are likely to be updated and replaced with requirements under the proposed Working at Height Regulations, the draft of which, Health and Safety Commission Consultation Document 192 (2003), is currently (March 2004), under consultation. These regulations will require work equipment to be selected considering the risks associated with installation, use, dismantling and rescue.

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3.7.2 American legislation

It of significant interest that in the Code of Federal Regulations 29 Pt 1910.66 (1996), U.S. regulations require that:

· HLLs shall be designed and installed as part of a complete personal fall arrest system, which maintains a safety factor of at least two, under the supervision of a qualified person.

· Connectors shall not be used as a means of connection to HLLs, unless of a locking type designed and used to prevent disengagement from the HLL.

· Personal fall-arrest systems or components subjected to impact loading shall be immediately removed from service and shall not be used again for employee protection unless inspected and determined by a competent person to be undamaged and suitable for reuse.

· The employer shall provide for prompt rescue of employees in the event of a fall or shall assure the self-rescuing capability of employees.

· Before using a personal fall-arrest system, and after any component or system is changed, employees shall be trained in the safe use of the system.

· Personal fall-arrest systems shall be inspected prior to use for degradation and defective components shall be removed from service if their strength or function may be adversely affected.

· The system’s performance should be evaluated taking into account the range of environmental conditions for which it is designed to be used.

· Depending on the angle of sag (deflection angle, the term used in this research) and the HLL’s elasticity, the strength of the HLL and the anchors to which it is attached should be increased a number of times over that of the lanyard (Author’s note: referring to the fact that any applied load as that generated in a fall-arrest situation would be multiplied as it was transmitted through the system to the end-anchors).

· Extreme care should be taken when considering a HLL (single span) for multiple simultaneous use. The reason for this is that if one employee falls, the movement of the falling employee and the HLL during the arrest of the fall may cause other employees also attached, to fall. HLL and anchor strength should be increased for each additional employee attached. For these and other reasons, the design of systems using HLLs must only be done by qualified persons. Testing of installed HLLs and anchors prior to use is recommended.

· Sufficient distance must be allowed for free fall, elongation and deceleration distance and must be maintained between the employee and obstructions below, to prevent an injury due to impact before the system fully arrests the fall. Elongation and deceleration distances should be available with the instructions for use and must be added to free fall distance to arrive at the total fall distance before an employee is stopped.

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· If self retracting equipment25 is connected to a HLL, the sag in the HLL should be minimised to prevent the device from sliding down the lifeline to a position which creates a swing hazard during fall arrest. In all cases, manufacturer’s instructions should be followed.

Construction industry

Another set of U.S. regulations, the Code of Federal Regulations 29 Pt 1926.500 (1996), which are more applicable to the U.S. construction industry, repeat much of the above, but in addition brings attention to problems which may occur when retractable type fall arresters are attached to HLLs:

· Most manufacturers warn in the user’s handbook that safety blocks / retractable lifelines26 must be positioned above the attachment point on the harness (above the workspace of the intended user). Attachment of a retractable device to a HLL near floor level may result in increased free fall due to the attachment point on the harness being some five feet higher than the attachment point of the HLL. Impact forces may exceed the maximum arrest force permitted27, with the potential for swing falls increased.

· Manufacturers recommend an anchor for the retractable lifeline28 which is immovably fixed in space and is independent of the user’s support systems. A movable anchor is one which can be moved around (such as equipment or wheeled vehicles) or which can deflect substantially under shock loading (such as a HLL or very flexible beam). In this case a shock load applied during fall-arrest can cause oscillation of the HLL such that the retractable brake mechanism may undergo one or more cycles of locking/unlocking/locking (ratchet effect) until the HLL deflection is dampened. Therefore, this use involves critical engineering and safety factors and should only be considered after fixed point anchors have been determined not to be feasible.

· HLLs used as an anchor present an additional hazard due to amplification of the horizontal component of arrest force of a fall transmitted to the points where the HLL is attached to the structure. This amplification is due to the angle of sag (deflection angle) and is most severe for smaller angles.

25 retractable type fall arresters 26 retractable type fall arresters 27 At the time, 11.2 kN was the maximum arrest force permitted where the body containment was a full body harness, or 5.6 kN where it was a waist belt. Testing was conducted with a 100 kg mass with the measuring instrumentation response frequency set at 500 Hz 28 retractable type fall arresters

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3.7.3 Official guidance

HSG 33

In the UK, HSG 33 (1998) makes the very important point that when a HLL is attached to the structure, the advice of the equipment supplier and the structural designer should be sought to make sure that the imposed loads generated during a fall can be sustained by the workplace structure, and should a HLL be attached to a working platform, that the platform must be secured against overturning. A further mention is made in that guard rails on roof purlin trolleys used for laying roof surfaces are unlikely to be strong enough to sustain arrest loads from HLL based FAS.

Rescue after a fall is also emphasised: “consideration should also be given to how a person would be rescued after an arrested fall”, particularly from high structures”.

Attention is also drawn to the fact that adequate information, instruction, training and supervision should be given when a FAS is used, e.g:

· How to wear the harness and adjust it to the body · How to manage the lanyard and other equipment · How to self-rescue or rescue others in a fall · How to inspect the equipment and recognise significant defects · How to assemble the system correctly, including “recognising safe anchorages”, which

conflicts with: “the safe performance of a FAS depends completely on a suitable anchor being provided. The adequacy of all anchorages including the ability of the supporting structure to carry the loads, should be verified by calculation or testing”

INDG 367

In the UK, INDG 367 (2002) gives advice predominantly on inspection regimes for energy-absorbing lanyards made from webbing or rope. It also states that the principles described can be applied to other textile-based fall-arrest equipment. This would apply to webbing- or fibre rope-based HLLs.

Recent research is mentioned in INDG 367 (2002), as disclosed in Health and Safety Laboratory (2002), in which a number of potential causes of degradation of synthetic fibre webbing lanyards was confirmed. These included:

· abuse · general wear and tear · edge/surface damage · ultraviolet light (UV) · dirt/grit · chemicals

The research also highlighted that there is no well-defined boundary concerning usable life separating those lanyards that are safe and those that are not. The conclusion was that if lanyards were to continue to provide the required level of fall protection, then it would be essential that they were subjected to an effective inspection regime.

The scope of such an inspection scheme described in INDG 367 (2002) covers pre-use checks, detailed and interim inspections.

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Pre-use checks are described as essential and should be carried out prior to each use. Detailed inspections are described as in-depth inspections and are recommended to be carried out every six months. In cases of frequent use, the suggestion is to increase the frequency of the six-monthly inspection to every three months, particularly where equipment is used in arduous environments.

Interim inspections are highlighted as a possible requirement in addition to pre-use and detailed inspections. These may be needed where a risk assessment has identified a risk that could result in rapid deterioration, affecting the safety of the equipment before the next inspection is due. Examples of such situations given in INDG 367 (2002), are:

· transient arduous working environments involving paints, chemicals or grit blasting operations

· acidic or alkaline environments

Examples of defects and damage are given as:

· cuts on edges of webbing/ropes

· surface and edge abrasion

· stitching damage

· knots, other than those intended by the manufacturer

· chemical attack (local weakening and flaking)

· heat or friction damage (hardening and glazing)

· UV-degradation (loss of colour and powdery surface)

· partly-deployed or operated energy-absorber

· contamination with dirt/grit/sand etc (which may cause internal abrasion)

· damaged/deformed fittings

· damage to sheath and core of kernmantel ropes (rucking)

· internal damage to a laid rope

Static line fall arrest systems

In an Australian Government document, Queensland Government (2002), guidance is given in order to inform principal contractors, employers, designers, riggers and other workers of the need for HLL based FAS to be properly designed and fit for use.

The reason for the guidance arose because there had been a large increase in the number of HLLs being fabricated and erected by steel erection companies. There was concern that not all of these HLLs were being adequately verified as fit for purpose, and there was a suspicion that some of the systems or support structure could fail in the event of a fall occurring.

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Attention is drawn to the fact that some configurations of HLLs may require more than 8 m of clear space underneath the lifeline, in order to prevent any collisions if a worker should fall.

On buildings under construction, the building designer should be consulted to determine if the existing structure is strong enough to withstand potential fall-arrest loadings at the locations where the HLLs are needed.

Queensland Government (2002) goes on to make some sound recommendations in respect of HLL verification, which should include factors such as the following:

· Any verification should include all parts of the FAS, as used on site, and not parts in isolation, (e.g. the end-anchor fittings may be very strong in themselves, but if the anchoring structure or method of attachment is structurally inadequate the FAS may fail when a person falls resulting in a drop to the ground).

· The design of end-anchor components and the method of attaching the HLL to the structure via these.

· The minimum strength of the supporting structure.

· Specification of the HLL: material, type, size, pre-tension etc.

· Maximum span.

· Minimum amount of free space required to underneath the lifeline.

· Maximum number of persons to be attached to the HLL at any one time.

· Where the HLL or connecting lanyards can contact an edge, verification that the line will not fail due to damage on contact, (which may be verifiable by on-site testing).

Reference is made to Australian Standard AS/NSZ 1891.2 (2001) as one means of verification. Some recommendations are also made in regard to testing:

· Where testing is selected to verify the system, it should reflect the way that the HLL is set up and used on site and should be severe enough to demonstrate that the system will not cause injury to the user. It is also advisable for testing to be undertaken by an independent testing organisation that has experience in the testing of FAS.

· When performing tests it may be necessary to:

o select a test weight with a suitable safety factor (i.e. the test weight should be heavier than the heaviest person(s) using the FAS)

o drop the test weight so that the free fall of the weight, prior to the FAS starting to arrest the fall, is at least equivalent to the maximum free fall that may be experienced by a user

o drop the test weight in the worst possible locations to maximise the loads at the anchors and in the lifeline

Any testing should demonstrate that the HLL does not catastrophically fail.

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3.7.4 British standards

British Standards or British Standard equivalents of European Standards contain requirements in relation to HLL based FAS. It should be understood that they are minimum requirements only; by just designing, testing, manufacturing and generally controlling products to the level required by the standard may not be enough. It is often thought that when marketing products, that if the product meets a standard’s requirements, then that will be sufficient, and that by gaining a CE mark in the case of PPE means that the PPE will be suitable for the particular task for which it is being sold. This is not necessarily the case as the testing in the relevant standard is often limited to checking standardised parameters under laboratory conditions and therefore may not cover the specific circumstances of use. A lot more may have to be done in excess of the standard to ensure that products are safe and satisfy legislation, e.g. the PPE Regulations (2002) and the Health and Safety at Work Act (1974).

It should be noted that all British Standards or British Standard equivalents of European Standards contain the following warning at the front of the standard: “Compliance with a British Standard does not of itself confer immunity from legal obligations”.

3.7.5 British standard BS EN 365

The British Standard BS EN 365 (1993) contains useful information on maintenance and other general requirements that should be contained in manufacturers’ instructions for use. In regard to maintenance the standard states that instructions shall contain the following information:

· For textile material components, an instruction that in the event of becoming wet either in use or due to cleaning, it shall be allowed to dry naturally away from an open fire or other source of heat.

· Instructions for storage. Where environmental or industrial factors affect the materials, instructions should be given for proper storage.

· Instruction that the system or component be examined – or where deemed necessary by the manufacturer, serviced – at least once every 12 months by a competent person authorised by the manufacturer.

BS EN 365 (1993) is due to be replaced by a more comprehensive updated version in 2004, the final draft of which is prEN 365 (2003). This draft standard contains requirements that manufacturers have to include in their instructions for use, maintenance, periodic examinations and repair. Selected points relevant to temporarily-installed HLL are:

Instructions for use

This document has to contain:

· statements describing the equipment, its intended purpose, application and limitations;

· a warning about medical conditions that could affect the safety of the equipment user in normal and emergency use;

· a warning that the equipment shall only be used by a person trained and competent in its safe use;

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· a warning that a rescue plan shall be in place to deal with any emergencies that could arise during the work;

· a warning against making any alterations or additions to the equipment without the manufacturer’s prior written consent, and that any repair shall only be carried out in accordance with manufacturer’s procedures;

· a warning that the equipment shall not be used outside its limitations, or for any purpose other than that for which it is intended;

· sufficient information to ensure the compatibility of items of equipment when assembled into a system;

· a warning of any dangers that may arise by the use of combinations of items of equipment in which the safe function of any one item is affected by or interferes with the safe function of another;

· an instruction for the user to carry out a pre-use check of the equipment, to ensure that it is in a serviceable condition and operates correctly before it is used;

· the features of the equipment that require the pre-use check, the method of checking, and the criteria against which the user can decide whether or not the equipment is defective;

· a warning stating that it is essential for safety that equipment is withdrawn from use immediately should any doubt arise about its condition for safe use, or if it has been used to arrest a fall, and not used again until confirmed by a competent person in writing that it is acceptable to do so;

· the requirements of the anchor device or structural member chosen to serve as the anchor point(s), in particular the minimum required strength, the suitability and the position;

· instructions on how to connect to the anchor device or structure;

· an instruction detailing the correct harness attachment point to use, and how to connect to it;

· for equipment intended for use in FAS, a warning to emphasise that it is essential for safety that the anchor device or anchor point should always be positioned, and the work carried out in such a way, as to minimise both the potential for falls and potential fall distance. Where it is essential that the anchor device/point is placed above the position of the user, the manufacturer shall make a statement to that effect;

· an instruction that a full body harness is the only acceptable body holding device that can be used in a fall arrest system;

· a warning to emphasise that it is essential for safety to verify the free space required beneath the user at the workplace before each occasion of use, so that, in the case of a fall, there will be no collision with the ground or other obstacle in the fall path;

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· information on the hazards that may affect the performance of the equipment and corresponding safety precautions that have to be observed, e.g: extremes of temperature, trailing or looping of lanyards or lifelines over sharp edges, chemical reagents, electrical conductivity, cutting, abrasion, climatic exposure, pendulum falls;

· instructions as relevant on how to protect the equipment against damage during transportation;

· information on the meaning of any markings and/or symbols on the equipment;

· a statement of any known limit to the safe useable life of the product or any part of the product and/or advice on how to determine when the product is no longer safe to use.

Instructions for maintenance

This document has to contain:

· cleaning procedures;

· a warning that when the equipment becomes wet, either from being in use or when due to cleaning, it shall be allowed to dry naturally, and shall be kept away from direct heat;

· storage procedures, including all necessary preventative requirements where environmental or other factors could affect the condition of components, e. g. damp environment, sharp edges, vibration, ultra-violet degradation;

Instructions for periodic examination and repair

This document has to contain:

· a warning to emphasize the need for regular periodic examinations29, and that the safety of users depends upon the continued efficiency and durability of the equipment;

· a recommendation in regard to the frequency of periodic examinations, taking account of such factors as legislation, equipment type, frequency of use, and environmental conditions. The recommendation shall include a statement to the effect that the periodic examination frequency shall be at least every 12 months;

· a warning to emphasize that periodic examinations are only to be conducted by a competent person for periodic examination and strictly in accordance with the manufacturer’s periodic examination procedures;

· where deemed necessary by the manufacturer, e. g. due to the complexity or innovation of the equipment, or where safety critical knowledge is needed in the dismantling, reassembly, or assessment of the equipment, (e. g. a retractable type fall arrester), an instruction specifying that periodic examinations shall only be conducted by the manufacturer or by a person or organisation authorised by the manufacturer;

· a requirement to check the legibility of the product markings;

29 Periodic examination is a European term for scheduled servicing or in-depth examination

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· any repair shall only be conducted by a competent person for repair, who has been authorised by the manufacturer, and that the repair procedure shall be strictly in accordance with the manufacturer’s instructions.

3.7.6 British standard BS EN 795

As mentioned under clause 3.7.1, PPE conforming with harmonised European standards are deemed to demonstrate compliance with the basic health and safety requirements of the PPE Regulations (2002). The standard which covers temporarily-installed HLLs (where they are categorised as a “Class C” product) is BS EN 795 (1997). Selected points from BS EN 795 (1997) relevant to temporarily-installed HLL are:

· the travelling device must not be capable of unintentional detachment from the HLL; if it is fitted with a device to allow it to be manually separated from the HLL (to allow access at specific points), it has to be designed so that it can only be detached or attached by at least two deliberate manual actions

· the minimum breaking strength of the cable, rope or webbing which constitutes the HLL, has to be at least twice the maximum tension that can be generated within the HLL in a fall-arrest occurrence, (including when two or more persons are simultaneously connected)

· other load bearing components have to be capable of withstanding twice the maximum tension that can be generated within the HLL in a fall-arrest occurrence

· lifeline, fittings and terminations have to be capable of withstanding 1.5 times the manufacturer’s permitted design force (an in-line test, not perpendicular to lifeline)

· in the dynamic test, the end-anchor loads/lifeline tension and deflection is not allowed to vary by more than ± 20% from that determined by the manufacturer’s calculation / method of performance prediction

· the dynamic test ensures that a force of 6 kN is imparted to the HLL

· a dynamic strength test ensures that a force of 12 kN is imparted to the HLL

· the following information is to be displayed either by marking or tagging the HLL or by using a wall plate:

o maximum number of attached workers permitted o the need for energy absorbers o ground clearance requirements

At the time of writing, (March 2004), BS EN 795 (1997) is undergoing a substantial technical revision.

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European Commission

In European Commission Communication (2000), a statement was made by the European Commission that the clauses within BS EN 795 (1997) which covered HLLs (and other products), would no longer be a means to demonstrate compliance with the basic health and safety requirements of Directive 89/686/EEC30. This was due to legal and other problems as to what constituted an anchor, (HLLs in BS EN 795 being described as: “anchor devices employing horizontal flexible lines”).

Subsequently, it has been shown that European Commission Communication (2000) is probably flawed, since both the European Manager, (who is responsible for Directive 89/686/EEC), and the PPE Consultant, (who is engaged by the European Commission, and is responsible for the supervision of European standards such as BS EN 795), have both agreed that temporarily-installed HLLs are PPE, Riches (2003) and Dirscherl (2004).

Despite this, a commonly held (but mistaken) view is that European Commission Communication (2000) says that “HLLs are now no longer PPE”. European Commission Communication (2000) does not in fact say this, and in Finch (2003), the Department of Trade and Industry31 also agree that European Commission Communication (2000) does not say this. What it does say is that the relevant clauses of BS EN 795 (1997) cannot be used to demonstrate compliance. Therefore HLLs are PPE under the PPE Regulations (2002), but test specifications other than those in BS EN 795 (1997) need to be used to demonstrate compliance. This means manufacturers will have to use their own test specification.

This has important ramifications for the UK market since temporarily-installed HLLs may end up being tested in quite different ways in order to meet the PPE Regulations (2002).

3.7.7 British standard BS 7883

A code of practice was written in support of devices covered in BS EN 795, BS 7883 (1997) and is currently under revision. Selected points relevant to temporarily-installed HLL are:

· It is essential that a safe means of access is provided for personnel installing HLLs

· HLLs should not be used if they have been modified without the manufacturer’s permission

· HLLs should only be installed on structure with sufficient stability and strength to withstand any fall-arrest loadings imposed

· HLLs should be installed at a height in order to keep any potential free fall to a minimum

· Energy absorbing lanyards and connectors should not be allowed to trail over sharp or abrupt edges in normal use or when pulled taut during a fall-arrest occurrence

30 This is the European document which was transposed into UK national law as the PPE Regulations (2002). 31 The UK Government Department responsible for the PPE Regulations (2002).

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3.7.8 American national standard ANSI A10.14

The American National Standard ANSI A10.14 (1991) contains requirements relating to the use of HLLs in the construction industry. Points relevant to HLL include:

· HLLs are to have a tensile strength capable of supporting a static load of at least 2273 kg mass per employee using the lifeline, applied anywhere along the lifeline32. A qualified engineer should be consulted in the application of the HLL.

· HLLs are to have a maximum of two persons connected at any one time between supports.

· Anchorages for HLLs are to be specified by a qualified person and shall be capable of sustaining the loads specified above. They are to be capable of supporting a mass of 2273 kg per employee attached, or shall be designed, installed and used as part of a complete FAS under the supervision of a qualified person maintaining a safety factor of at least two. Angle of sag and pre-tensioning are essential considerations when installing.

· Lifelines33 are to be designed, installed and used as part of a complete FAS under the supervision of a qualified person maintaining a safety factor of at least two.

User’s responsibilities

There are some interesting requirements relating to user’s responsibilities, selection and use in ANSI A10.14 (1991):

· Users are to be trained by a competent person34 before using HLLs in the application limits, installations, proper anchoring and connecting techniques, method of use, inspection and storage of equipment. Retraining should be repeated at regular intervals. The employee is also to receive training in the choice of suitable anchor points.

· HLLs should be installed as to limit the free fall of any employee to 1.5 m and to prevent collision with any lower level.

· Each HLL shall be inspected periodically, but not less than twice annually by a competent person according to the manufacturer’s recommendation. Equipment showing any defect is to be withdrawn immediately.

· HLLs subjected to impacts caused by a fall or by testing are to be removed from service and should not be used again.

· HLLs are to be visually inspected prior to each use.

32 It is not clear whether the tensile strength relates to the static load being applied perpendicular to the lifeline or directly in-line with it. 33 Lifelines are defined in the standard as being either vertical or horizontal in orientation. 34 Defined as one who is capable of identifying existing and predictable hazards in the surroundings or working conditions that are unsanitary, hazardous or dangerous to employees, and who has the authority to take prompt corrective measures to eliminate such hazards.

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· A snap hook is not to be connected back on its integral lanyard, (the connector on a lanyard should not be passed over the HLL and then connected back onto the lanyard to form a loop around the HLL).

· Wire rope is not to be used where electrical hazards are present.

· Fall-arrest harnesses are to be connected to the FAS by using the dorsal attachment point.

Product marking and instructions for use

Aspects of ANSI A10.14 (1991) relating to markings and instructions for use include:

· HLLs are to be marked or tagged with equipment length, rating, and the number of attached people permitted.

· Instructions for use are to explain the following:

o Installation requirements o Direction for use o Directions for maintenance o Directions for inspection

3.7.9 Canadian national standards

In CSA (1999), a Canadian draft standard for “flexible horizontal lifeline systems” is disclosed, and contains some modern thinking and approaches, virtually identical to those contained in the International draft standard ISO/CD 16024 (1999). Relevant matters include:

· Permanently-installed HLLs and temporarily-installed HLLs are differentiated in the definitions. The former is defined as “a HLL designed to be installed and not intended to be dismantled in the foreseeable future”, and the latter as “a HLL intended and designed to be installed and used for a foreseeable short term period of use”.

· The minimum tensile strength of finished HLLs made from wire rope is to be at least twice the maximum arrest load generated in the lifeline, but this factor is to be increased to three times for HLLs finished from fibre rope or webbing.

· Intermediate supports have to withstand a static loading requirement of 16 kN35 in a direction perpendicular to the HLL and in the direction of the resultant loading.

· The dynamic test configurations for single-span HLLs have to include:

o At least one specimen at the shortest recommended span o At least one specimen at a mid-range span o At least one specimen at the longest recommended span

35 Based on the possibility that a person may fall when the travelling device is directly over an intermediate support bracket. The maximum arrest force permitted to be transmitted to the worker’s harness attachment point under this draft standard is 8.0 kN; a safety factor of 2 has been applied to produce a test load of 16.0 kN.

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· Dynamic tests are conducted with 100 kg test masses, on a basis of one test mass per each worker permitted to be simultaneously attached to the HLL. Test masses are connected to the HLL via the attachment subsystem, (whether this is an energy absorbing lanyard, retractable lifeline, or other), permitted for use in conjunction with the HLL. Test masses are released simultaneously. Each type of attachment subsystem authorised for use with the HLL has to be evaluated in separate tests.

· When the configuration that shows the highest end-anchor load has been determined from the dynamic tests, this configuration has then to withstand to a static loading of 2.0 kN for each test mass used during the dynamic test, applied centre-span, in the same direction as a fall36.

· The above static test requirement has been increased to 12 kN in ISO/CD 16024 (1999), reflecting a different philosophy. This test in effect applies a FOS of 2 to the maximum arrest force permitted under that standard of 6 kN.

3.7.10 Australian / New Zealand standard AS/NZS 1891.2

In AS/NZS 1891.2 (2001) and supplement, an Australian standard for “horizontal lifeline and rail systems” also contains some modern thinking and approaches, a large portion of which is based on previous research as reported in Dayawansa and Ralph (1997). Points of interest include:

· The standard differentiates between:

o “proprietary systems” – HLL based FAS for which the fall-arrest performance of any design layout can be determined by a method or program which has been verified by means of performance testing of prototypes over an adequately representative range of layout configurations, and

o “prescribed systems” – HLL based FAS set up in accordance with configurations and components prescribed in tabular form within the supplement to the standard.

· The standard also differentiates between use for fall-arrest, restraint and work positioning / personal suspension purposes. Use for work positioning is discouraged unless the system is specifically designed for such a purpose.

· The combined HLL and terminations used, has to withstand twice the maximum load in the HLL for any fall-arrest event in the case of steel wire rope, and four times in the case of fibre rope or webbing.

· In-line energy absorbers are only allowed in proprietary systems. They have specific requirements in order to prevent inadvertent operation and to ensure that sufficient integrity remains even when the energy absorbing means has been fully exhausted.

36 1 kN reproduces the weight of a worker of 100 kg mass, which would be applied when the fall-arrest sequence was over and the worker remained motionless in suspension. Applying a safety factor of 2 produces a test load of 2 kN. This test appears to simulate suspension forces on the HLL after the arrest.

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· Where snap hooks and karabiners are the direct means of attachment to the HLL, in order to prevent wear from frequent travelling along the lifeline, they have to be selected for both the suitability of their material and section. Surface finish should not damage the lifeline.

· Either a test mass, torso dummy or full dummy37 of 100 kg mass is allowed to be used as the test surrogate in the dynamic test.

· Prescribed systems are limited to 100 m span with maximum sub-spans of 10.0 m. Maximum number of attached users is limited to 4 and the lifeline material is limited to 8, 10 or 12 mm diameter galvanised steel cable, (depending on application), of 6 x 24 fibre core construction, to an Australian standard.

· Mention is made of the potential for sliding down a leg towards the bottom of the “V” deflection and swinging during a fall-arrest, especially where a fall occurs some distance away from the centre of a long sub-span.

· Assessment of structure to which a HLL is to be anchored is to be carried out by an engineer or other competent person.

3.8 ACCIDENT DATA

Various accident data were searched such as those in Cloe and Breslin (1979), which described 98 falls from roofs, though ceilings or other surfaces with a fatal outcome, but no reference to falls when attached to a HLL could be found. In Steinberg (1977) more than 100 possible sources of fall-related injury data were contacted, in situations involving attachment to FAS.

At least half of the data obtained involved FAS that were not correctly secured to an anchor, i.e. the falling worker did not remain linked to the anchor under the impact of the fall. Steinberg comments that “these falls generally resulted in fatalities and serve more to illustrate the misuse of FAS than the effectiveness when properly secured”.

Only about 35 cases involved falls which were arrested by correctly secured FAS. In two of these the lanyards failed upon impact, probably due to sharp edges on the structural members they were attached to. In the remaining cases, the falls were successfully arrested with no significant injuries. The few injuries that were received came from contacts with other surfaces during the fall. No specific mention is made about attachment to a HLL.

In order to try and obtain more substantial evidence, permission was obtained to study accident cases recorded in the HSE Field Operations Directorate (FOD) database. The search used the keywords: “LIFELINES” “FALL-ARREST” and “LANYARDS”. The search revealed that 270 accidents contained one or more of the keywords, occurring between April 2001 - June 2003. Whilst at least one case might have been the result of a poorly installed HLL, it was not clear from the report whether this was the actual case. No other cases were able to be attributed to the use of HLLs.

A dummy that is anthropomorphic (resembling the human form), anthropometric (of a set size and with set proportions relating to a statistical population), and with articulating joints, similarly disposed as with the human body and with anthropometric ranges of movement.

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4. SURVEY OF UK MANUFACTURERS AND SUPPLIERS

This survey reviewed the marketing, technical, installation and training approach adopted by manufacturers / suppliers.

Information was gathered mainly by way of internet and telephonic enquiry. The more notable suppliers were visited for the purpose of technical discussion and interview. A questionnaire was utilised, with a range of headings and sub-headings as follows:

· Product name

· Product features & limitations - lifeline type, tensioning features, anchoring method, travelling device, fall-arrest equipment attached, length of equipment if relevant, number of simultaneous users, mass of users, height of system above walk level, single or multi-span, overall span, corners, entry points.

· Installation - Who installs and how is this done? Installation instructions, design criteria control: forces, free space requirements, calculation method & what factors can be taken into account in calculation; example of calculation; chafing and sharp edges, rebound, tensioning, rating plates.

· Use & maintenance - User instructions, precautions, pre-use, regular inspection and examination frequency; criteria for rejection? environment, product vulnerability, wear, life?

· Training - Who supplies it? Training requirements?

· Applications - Restraint as well as fall-arrest? Where and when are these products specified/used: steelwork? Rescue considerations.

· Research and development and testing - Available test data, CE marking, high speed video, failure mode of product, technical philosophy, factors of safety, future developments.

· Product abuse - Accident/incident occurrences, products installed or used incorrectly, amateur fabrications, product used outside limits, accident simulation.

· References - Literature, research reports, articles?

Technical literature was gathered where available; this included: marketing literature, research and development information, test results and instructions for installation / instructions for use.

The purpose of this survey was not to extol certain manufacturers or discredit others, nor was it to compare manufacturer to manufacturer.

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Due to the remit of the research not all UK suppliers were directly consulted. Other suppliers were indirectly consulted, e.g: some information was taken from suppliers’ websites as would be done normally with a preliminary enquiry, i.e. not necessarily with their knowledge. This does not mean that the organisations who were not directly consulted were in any way seen to be inferior or less reputable than those who were. Nor does it mean that the contributions that were received directly were in any way superior to those that were received indirectly.

Some product information was gathered from U.S, Canadian and Australian sources, to give an international perspective.

As a result of the above approach, individual organisations are not referred to in respect of the information that they supplied. The purpose was to report on current trends of the supply industry and its approach to the marketplace. This kind of information is particularly useful because: (i) it shows that different approaches can be made to solve the same problem, with varying degrees of success, and (ii) it identifies common deficiencies and the particular problems that need to be faced and overcome by all interested parties in order for the industry to progress, commensurate with safety for the user.

All of the organisations who were contacted or visited were marketing permanently-installed versions of HLLs, and nearly all were marketing temporarily-installed versions.

Whereas some of the results of the survey that follow apply to permanently-installed HLLs, they have been included in the body of the report because the principles can be generally applied to the temporarily-installed market. Indeed, most of the development work and thinking applied to the temporary versions has been adopted from work previously done to bring the permanent versions to market.

4.1 GENERAL

Overall, there seemed to be a lack of technical personnel and inclination towards research, development and technical matters. It was clear that those companies who are inclined towards research and development tended to be more aware of the main issues and problems to do with HLLs, (and have taken steps to address those situations), than those companies who were less inclined.

Some companies had a clear research and development outlook and were on the look out for areas in which they could improve their product and their approach to market.

There was a substantial decline in standards committee attendance, which would seem to indicate a lack of importance attached to standards. Only one manufacturer is active in CEN/TC 160 WG1 – the European standards committee which is responsible for BS EN 795 (1997), the standard which specifies HLL test requirements.

Temporarily-installed HLLs appear not to be a significant part of company sales, especially when compared to the permanently-installed versions.

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4.2 INEXPERT, UNPROFESSIONAL OR UNTRAINED ORGANISATIONS

Several recurring themes came from the interviews. One such theme is that of companies, who, having no expertise or experience in the fall protection field, set out to design and install HLLs with little regard for design, testing and certification requirements. One such situation was described during interview where a technical representative from company “A” contacted and visited four companies “B”, “C”, “D” and “E”. They all acted as distributors of various fall protection equipment, and they had been trying to install fabricated HLLs on their own initiative, without attempting to CE mark the product. Whilst claiming that the product met BS EN 795, no documentary evidence could be offered. Companies “B”, “C”, “D” and “E” were also unsure as to what class in BS EN 795 their respective products would be categorised under38.

A further example of a recurring theme within inexpert organisations is the belief that the maximum arrest force that can be generated in a FAS is equal to the user’s weight. It is a commonly held view but which is in error. Two notes of explanation are needed:

· The unit of the Kilogramme (kg) refers to mass, i.e. the amount of substance in an object, not to the forces that are imposed on it. The unit of force is the Newton (N). If one is referring to force or load then the unit of Newtons should be used.

· 100 kg is the size of the test mass used in drop-testing, the dynamic test method used to simulate a person who falls. It represents the weight of a 100 kg person, which is, technically speaking, 981 N. Weight is the force on the object as a result of being in the Earth’s gravitational field. As a result, if one attached a lanyard and a 100 kg mass to a HLL, then slowly lowered the mass until it became wholly supported by the HLL, the lanyard would register a force of 981 N. This is because, with the mass stationary, the lanyard would have to apply an upward force of 981 N to balance out the downward force of 981 N on the mass. If the mass was then raised, and then this time released so as to drop, as opposed to being lowered slowly, so that the HLL had to arrest it, then the force in the lanyard would be considerably higher than 981 N. This is because not only would the lanyard have to apply an upward force of 981 N to balance out the downward force of 981 N on the mass, but an extra force is needed to slow down the mass, which at this point would be travelling with significant velocity. A simple proof of this is to stand on bathroom scales to measure one’s weight. If one then jumps onto the bathroom scales and watches the scale at the same time, the reading is always higher than that when one stands on the scales and remains stationary.

Considerable comment was received about unscrupulous installation companies who do not test HLL systems, or do not test to the degree necessary. These companies also offer solutions which do not solve the particular problem at hand; no thinking goes into the design of the system. These factors makes competing with them difficult, because professional companies feel obliged to thoroughly test their products, and analyse customer’s problems to make sure the right design is installed. Education is seen as part of the selling process.

38 A reference to BS EN 795 (1997) quickly shows that HLLs come under the Class “C” categorisation

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Generally, experienced and competent manufacturers find it difficult to compete with inexpert, inexperienced organisations who offer products for sale with no technical back-up, but make substantial claims as to what their product is capable of doing. An example cited is that similar to the 100 kg issue mentioned above. In multiple use applications some organisations offer HLLs on the basis that the “first” faller will apply a force of 6 kN to the lifeline, whereas the second and third fallers will only apply 1 kN to it (their weight). This offer is without recourse to analysis or testing, and in fact is a total misinterpretation and misapplication of clause 4.3.4 of BS EN 795 (1997). This clause refers to static test requirements for horizontal rail systems – not HLLs. Horizontal rails are the HLL’s rigid counterpart and behave very differently in fall-arrest situations. But because this clause is being misapplied, forces can be assumed to be much lower than indeed they could be, as a result specification can be lower, and hence the price.

In another case a scaffolding company had rigged a self-made, improvised HLL and had attached it to scaffolding. The ends of the wire were knotted around scaffold tubes, and three men were attached to it. The free space beneath the HLL was described as “minimal”. In a fall situation, the most likely outcome would be a fall to the ground, either as a result of failure of the end “attachments”, localised collapse of scaffold, or as a result of not allowing sufficient free space for the fall arrest equipment to extend in.

Another case described, involved the use of a retractable type fall arrester as an improvised HLL. These devices are designed and tested for use in overhead installations, i.e. where the arrester casing is anchored above the worker. In this particular case the fall arrester casing had been connected to a post secured to a roof, and the lifeline had been extracted horizontally and clipped to a second post. In effect a product intended for use in the vertical plane had been adopted for use in the horizontal plane. In such a case there is no way of knowing how such an arrangement will perform, whether a worker will be arrested should they fall, or whether the device and surrounding structure will resist the loads imposed in a fall.

4.3 INSTALLATION AND DESIGN APPROACH

4.3.1 Computer analysis

Computer-based analysis is a common approach taken to predict loadings and fall distances in enquiries pertaining to permanently-installed HLLs. It is seen as a vital part of the installation process. Customers who wish to install or receive an installation are invited to submit a pro forma which details the configuration of the proposed HLL. Details include:

· Span · Number of attached workers and their mass · The type of fall arrest equipment to be connected to the HLL · Worst case free fall possibility (after reviewing relative positions of walkway, HLL and

lanyard length) · Free space available beneath the HLL

These quantities are entered into a computer analysis program which has been validated by previous experimentation. Typically, a number of calculations are performed at different locations on the HLL, in order to determine the worst case scenario.

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A number of results are then obtained, in order to ascertain whether a particular configuration is viable or not, e.g:

· Forces in the fall arrest equipment connected to the HLL. If too high, a modification in the configuration will be needed or else another method of fall protection will have to be sought.

· Forces in the HLL itself. A limit is typically set, taking in to account a safety factor. If the force is too high, then again, a modification in the configuration will be needed or else another method of fall protection will have to be sought. Such a modification might be the introduction of an in-line energy absorber component.

· Forces at the end-anchors. A limit is typically set, taking in to account a safety factor. If the force is too high, then again, a modification in the configuration will be needed or else another method of fall protection will have to be sought. Such a modification might be the introduction of an in-line energy absorber component.

· Total fall distance (worst case). Typically, the maximum distance of the simulated fall, including free fall, “V” deflection of the HLL, braking distance of the arrest equipment, harness stretch and height of worker. If the distance is too great, (allowing for an additional safety clearance factor), indicating a possible collision with the ground, or a close miss, then again, a modification in the configuration will be needed or else another method of fall protection will have to be sought. Such a modification might entail installing the HLL at a greater height, or the introduction of an intermediate bracket.

· The position on the HLL where the worst case total fall distance occurs is usually indicated (mid-span for single span systems).

In determining worst case scenarios with multiple simultaneous users attached, consideration is given to the potential effects of a number of persons falling simultaneously or near-simultaneously.

In all cases, when a configuration or when the fall conditions are altered or additional components are introduced, then calculations have to be repeated in order to ensure that the alterations can ensure a safe system.

This approach works well, when installation companies and other professional organisations are using it as a design service in order to design and install permanently-installed HLLs; however it does not readily lend itself to be applied to the temporarily-installed versions. This is because the permanently-installed HLLs have to undergo a disciplined design approach before they can be installed, each system being tailor-made to the particular structure, with a variety of features, namely several intermediate anchors, corner arrangements and other special components. The anchors and fastenings which secure these HLLs to the structure are embedded within the host structure, using either mechanical or chemical bonding arrangements, and hence constitute a permanent installation39. Therefore a knowledge of the structure to which the system is being installed is paramount, in terms of strength and stability, and the ability to select the right type of fastening to anchor the HLL in place is crucial.

39 More information can be found in BS 7883 (1997)

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On the other hand, temporarily-installed systems are typically installed by the end-users themselves, i.e. installation is very much akin to other fall-arrest equipment, e.g. retractable arresters or energy-absorbing lanyards. They are also attached directly to features of the work place structure, e.g. around a beam or column. Being temporary, they can be easily removed and reinstalled somewhere else on a day to day basis.

This would make it very difficult to use a computer analysis program. First, the users would have to provide all the information for the purposes of calculation, including the measurements and potential fall conditions, and then would have to send this off in a particular format to the manufacturers. They would then have to wait for the reply, which might require several query and answer cycles, before commencing the installation. This would not work in some of the situations in which temporarily-installed HLLs are employed. Nevertheless, this approach can be used if the response can be rapid and if the education process is such that user organisations demand it.

4.3.2 Graphical and tabular approaches

In other approaches, a large number of configurations and fall conditions have been pre­calculated, based on a range of different spans and other features. The results of this work is expressed in a series of graphs, or tables, so that in theory a person installing a temporarily-installed HLL could refer to these graphs/tables in order to determine whether a particular installation was viable and safe. This approach depends upon the proposed configuration being covered by the parameters in the graphs/tables, and the ability of the user to interpret them. It also relies on the performance of the type of fall-arrest product intended to be attached to the HLL, being present in the table. If it is not, an incompatibility issue is then raised. For example, one manufacturer’s energy absorbing lanyard may not perform in the same manner as another’s, especially when connected to a HLL. This issue has led some suppliers to sell the fall arrest equipment and HLL as a complete system, so that there are no incompatibility issues.

4.3.3 Modelling multiple-fall scenarios

In some cases the approach to the modelling of falls involving multiple users was a bit vague, in others very clear. Some approaches assumed that it was possible for workers to fall and impact the HLL at around the same time, Figure 24, so that the worst case scenario could be addressed, (both in terms of loadings and fall distances), and safety factors applied accordingly.

As the permitted number of attached users increased, there was a tendency to relax the above approach, on the basis that the likelihood of simultaneous impacts in real life would decrease as the number of attached users increased. In one case a triple fall situation was modelled as a double simultaneous impact plus a load equivalent to a person’s weight. This modelled persons Nos. 2 and 3 falling simultaneously after No.1 had fallen and had come to rest. The same circumstance was modelled by assuming persons Nos. 1, 2 and 3 falling simultaneously which as expected, resulted in much higher end-anchor loadings.

This particular issue is not helped by the lack of guidance in standards and in other documents40.

40 in clause 5.7, a recommendation for future research is made to address this deficiency

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Figure 24 Simultaneous release of two torso dummies on HLL. Still from NEL archived U-matic tape footage (2004)

4.3.4 Controlling design changes

One of the great problems with designing particular configurations and designing for particular fall conditions is that if any quantity is changed during the installation process that would affect any computer calculation, then it must be disclosed so that a new analysis can be performed. One manufacturer’s approach is to cover and draw attention to this eventuality in their contractual agreements. In effect, if anyone in the supply chain does something different than that specified, they are deemed as having “broken the design specification” and they then become responsible for the “new” design. This is a clear concern for companies who provide these goods – where the configuration of the final installation is not as that understood at the time of analysis and calculation.

It was felt that any documentation used to describe the final design and configuration of the HLL must contain information about the use, limitations, and what other fall-arrest equipment it has been tested with.

4.4 SERVICING AND ANNUAL EXAMINATION

Concern was expressed by a number of manufacturers over methods of control. Some installation companies service other company’s products without their knowledge. Companies doing this servicing work tend not to have knowledge of the HLLs they are servicing, and would not have the necessary training and hence the necessary criteria to apply to decide whether a system was unserviceable or not. They certainly would not have reference to servicing manuals or access to the technical staff of the products that they are servicing. Hence a number of HLLs are being inadvertently damaged by tightening of components and tensioning of lines which in actual fact is not required.

Furthermore insurance companies are dispensing certificates which state that the installed systems are satisfactory after giving the system the simplest of visual examinations. This may not be enough in some cases. Some fall-arrest manufacturers refuse insurance companies permission to do this work.

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Pre-use, maintenance and annual examination information is extremely limited or non-existent.

Some HLLs had built-in wear indicators, because it was felt as the HLL would be installed/removed/reinstalled several times over in arduous environments, wear would be a concern. Exposure of an indicator would give a criterion for replacement of the lifeline.

With the permanently-installed version of HLLs, some companies provide an instruction plate which is mounted near the place to where the system is accessed, in conjunction with a handover file. The plate can contain information such as limitations of use, instructions, and when the next detailed examination is due. It was felt that this approach could not be readily adopted for temporarily-installed HLLs, but that a plate could be tagged to the lifeline, instead.

Some manufacturers mentioned that they encouraged maintenance and detailed examinations of their products on a regular basis, but customers did not always respond.

4.5 PRODUCT DESIGN

In appearance, temporarily-installed HLL products tend to be very simple, consisting of a HLL made from either textile rope, webbing or steel cable, with two anchor connections and a tensioning device.

Generally they have no corner arrangements or intermediate anchors, but there are exceptions. Some have a single intermediate anchor to reduce fall distance.

Some manufacturers limit the length of lifeline available, which simplifies any analysis because of the reduction in permutations.

In most cases temporarily-installed HLLs are supplied as kits, the differentiation between kits being different lengths of lifeline.

Some manufacturers have special connections at the HLL which slide along the lifeline and provide the attachment point for the user’s fall-arrest equipment; others permit the connection to be made with a simple karabiner.

Some temporarily-installed HLL products are attached via textile strops to uprights which are part of structure; some are attached to beams using special “A” frame assemblies; some are attached to a series of deadweight anchors and rely on the weight of the anchors to provide resistance to the fall motion.

Some companies employ large capacity in-line energy absorbers to allow for misuse situations, i.e. to prevent failure in overload situations. These typically limit the forces in the HLL (and hence at the end-anchors) to 12 kN, and have a safety factor of 2 plus a further misuse safety factor.

4.5.1 Terminations

The method of termination of the HLL was seen as a critical area. A loop or other method has to be provided at one end, to enable the HLL to be attached to the structure. It was discovered that, depending on lifeline structure and material, ordinary compression swages could reduce the minimum breaking strength by as much as 40%.

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At the other end, as mentioned under “tensioning”, a tension device is fitted to allow a single length of lifeline to be shortened to fit a number of different sized spans. This device grips the lifeline to maintain tension under normal and fall-arrest situations. The device itself is connected to the structure. It was discovered that in some cases, adoption of tensioning components from other industries may not necessarily be the best design solution. One example cited was the use of a conventional ratchet pulley. In order to be fed through the device, the lifeline had to be abruptly bent back on itself through 180º. This was found to reduce the lifeline’s minimum breaking strength by 40% at that point. There was also signs of the crushing effect of the jaws of the device upon the lifeline, which itself was felt could create a weakness. This weakening effect could become accumulative, with the repeated gripping of the lifeline during subsequent installations.

The dangers of bending failure were discussed, in situations where the articulation of end terminations was restrained. The opinion was that end terminations should be free to align in the direction that they would be pulled under fall-arrest loading.

An important issue was that of being able to provide the correct fitting to facilitate the attachment of the HLL to the structure chosen. It was envisaged that many different forms of structure could be used for installation – a range of fittings would therefore be necessary.

4.6 INSTALLATION AND USE

Manufacturers expressed concern about the control of products. Installers of temporarily-installed HLLs were the users themselves, i.e. these products are installed very much akin to other fall-arrest equipment, e.g. retractable arresters or energy absorbing lanyards; they are attached directly to the work place structure. They are “self-installed” products, but like retractable arresters or to a lesser extent, energy-absorbing lanyards, they have a great potential for being installed incorrectly and hence not operating correctly if called on to arrest a fall.

Hence there was concern that the user will not have the same levels of competency as those who install permanent FAS. Also with the fact that these self-installed situations could not be audited as with the permanently-installed versions.

Another area of concern was the problem of providing protection during installation and dismantling. Generally, temporarily-installed HLLs are needed in places where no anchoring method is available, so it is difficult to provide fall protection during installation and removal procedures.

Mention was also made of the danger of rearranging objects beneath the work area – they may become temporary obstacles in the path of a falling worker.

4.6.1 Attaching to structure

When asked about known problems of attaching to structures, there was little response. The problems which the author wished to discuss with manufacturers, included:

· Strength reduction of attachment loops that are knotted or hitched around columns or beams

· Slipping of attachment loops either down or off a structure

· Cutting through of attachment loops, caused by sharp or abrupt edges of structure

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Generally, there appeared to be little knowledge about these factors. However one manufacturer knew of the above problems and had conducted tests around channels of various sizes and had allowed strength reduction factors in their finished design. Attachment methods were also written into their instructions for installation to prevent slippage.

Some manufacturers took the interaction between end anchor and structure very seriously, having learnt from research and development testing, which has shown the unexpected failure mode of the surrounding structure rather than the product itself. This has led to subsequent testing being extended to cover substrates that systems will be installed to, so that reliance will not just depend on product integrity, but also on the structural interface. This is a simulation of actual in-field conditions, the environment in which the product will be expected to perform.

4.6.2 Multiple use situations

Some companies discouraged multiple use because of the following reasons:

· One worker can fall and pull the others off balance, (they can be knocked off balance or their connecting lanyard can be yanked by the deflecting lifeline).

· Workers falling simultaneously or near simultaneously can impact each other with considerable horizontal velocity, as a result of swinging into the centre of the “V” deflection together.

· Workers cannot pass each other when attached to lifeline unless they disconnect and then reconnect – a safety hazard.

Their solution was to have a HLL per user. This creates benefits in terms of rescue but can create anchoring issues; if end-anchors are in the same proximity then the structure will have to be capable of resisting the combined end loadings of each system.

4.6.3 Tensioning

Tensioning of the temporarily-installed HLL is a vital part of the installation process. It is generally achieved by threading the rope/cable/webbing through a tensioning component which grips it and acts as a kind of “non-return valve”. The rope/cable/webbing can be pulled through so as to increase the tension in the lifeline, but it cannot slip back through in the opposite direction, unless some kind of control is operated.

This approach is needed because of the nature of temporarily-installed HLLs. The span of the system has to be changed to adapt each different circumstance. On one day the HLL may have to span a 20 m gap, the next, a 8 m gap. Hence the tensioning mechanism allows the HLL to be lengthened or shortened to suit the gap that has to be bridged.

Setting of the correct tension in the lifeline can affect how the HLL operates and what level of loadings and distances are generated in falls, although perhaps not to such a great extent unless large amounts of tension are applied (5 – 10 kN). Some manufacturers have recognised this because over-tensioning can eat into the reserve of cable/rope/webbing strength, which can then be a significant risk in terms of potential HLL failure. And, as HLL spans get longer, more tension is needed to overcome the increased amount of weight. At some point an intermediate anchor is advisable.

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Some manufacturers have tensioning procedures in their installation instructions and/or a tension indicator on one of the HLL components. In either case the installer-user can determine the right tension setting.

Some tensioning components are designed to counter other known problems, namely:

· Interference - tensioning adjusting mechanisms have been known to be interfered with, perhaps by users who thought that “the line doesn’t seem tight enough” and have wound more tension into the system.

· Slackening off - tensioning components have also been known to slacken off in use, i.e. the rope/cable/webbing has crept back through the tensioning device over a period of time.

· Ratcheting – some tensioning devices are simply components adopted from other industries, e.g. cargo lashings in transport aircraft and road haulage. These are primarily designed to resist static loadings, not dynamic. The bouncing affect caused by a worker falling onto the HLL can cause these types of locking mechanism to repeatedly disengage and re-engage, allowing an incremental pay-out of lifeline during the fall, i.e. allowing the “V” deflection to increase. This subsides when the fall motion starts to be damped out. In one situation this phenomena was detected during testing, Feathers (1998).

In some cases there was no knowledge as to what tension should be initially set in the HLL, and nothing was contained with the instructions for use/installation which mentioned this. In one case the procedure was to tension the HLL during installation until it was “tight”.

4.6.4 Attachment of fall-arrest equipment

In some cases it is clear that there is no control of what equipment is attached to the HLL. In such cases if a fall occurs, there can be no knowledge as to what the arrest forces are, what the end-loadings are, and what the total fall distance will be.

In other cases manufacturers have rigid agreements in place as to what can be attached to the HLL and what cannot. Even in these instances however, evidence seemed unclear in regard to what fall distances are attributed to what equipment.

In yet other cases testing has been performed with specific types of equipment and the performance of these in combination with the HLL have been modelled in the company’s computer analysis program.

Some manufacturers had concerns about the compatibility of equipment, especially the issue of using retractable arresters. Some manufacturers see the use of retractable arresters in combination with HLLs as a problematic area.

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4.7 RESCUE

After a worker falls and is arrested by a HLL, they need to be recovered or rescued. At this point they will be suspended from the HLL, supported by their harness. They may be in shock and may have suffered some form of injury during the fall. Furthermore, they become subjected to “orthostatic shock”, a condition in which motionless suspension can induce a retention of blood volume in the venous system of the legs, which reduces the amount of oxygenated blood available to the brain and other vital organs. Loss of consciousness and death ensue, so an immediate method of rescue is vital, as part of any working at height safety plan. A thorough review of this subject can be found in Seddon (2002).

When considering a theoretical rescue of a person who has been arrested on a single-span temporarily-installed HLL, the first impression is that rescue would be extremely difficult.

When asked about rescue advice, and provision of equipment, some manufacturers remarked that no rescue methods were available, and comments were made along the line of: “this is a difficult area”.

The main reason for these remarks is that the deflected HLL cannot be easily accessed, even if it was intended to be used as a means of anchoring the Rescuer’s41 equipment, or even if it was intended to gain access to it, to haul in the worker. Rescue may be facilitated if there were substantial structure above the “V” deflection, as this would allow a Rescuer to descend to the Rescuee42 to effect a rescue. But such a structure may not always be in place, because one of the main applications of the HLL is to span significant gaps in structure.

Manufacturers’ comments were also made to the effect that users “were not asking for rescue equipment at the moment”.

Other manufacturers’ attitudes to rescue were different. At one time some manufacturers recommended that users should find their own equipment, but are now analysing the problem and are designing rescue methods and equipment to suit. One approach involves the redesign of intermediate anchors to allow the attachment and support of rescue equipment, even after having being stressed as a result of a fall-arrest loading.

In another approach being developed, the Rescuee is dragged back to a safe area using equipment mounted to an end-anchor.

In yet another approach, a second HLL running parallel and in close proximity to the first, is advocated as a rescue anchor line.

41 The person performing a rescue 42 The person being rescued

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4.8 APPLICATIONS

Manufacturers commented on the main areas of application. The concrete decking market was once one of the main areas of application, but now steel and wood erection is the main market, mainly for fall-arrest applications.

Temporarily-installed HLLs that are cable-based tend to be specified in heavy industrial conditions with arduous environments, where textile-based HLLs might be vulnerable. These systems have less of a “V” deflection in a fall, but tend to have higher end-loadings, so these are controlled by in-line energy absorbers.

There were recorded cases of tree surgeons using temporarily-installed HLLs attached to two trees.

In some cases manufacturers were dissatisfied with the minimalist approach taken by representatives and installers/distributors when it came to specifying the equipment that would be attached to the HLL, especially when considering other application types, e.g. systems for restraint. Some had a system for classifying applications and specifying equipment for each application.

4.9 TRAINING

In a number of cases manufacturers offer no training for temporarily-installed HLLs. One company did offer courses for temporarily-installed HLLs - they considered that end-user installation training was vital and have tried to get courses officially accredited.

Some companies take the responsibility for advising and educating external agencies who seek advice in regard to design and installation, e.g. civil, structural and consultant engineers. Most of these agencies who make these approaches whilst being very professional, do not initially understand the phenomenon of (i) the arrest force being greater than a falling person’s weight, and (ii) that this force is magnified at the end anchors. However most respond positively to the education process.

Some companies provide training vouchers to encourage the training of users.

Whereas there were cases where provision had been made to train and audit installers of permanently-installed HLLs, there seemed little in evidence to suggest the same provision had been made for the temporarily-installed versions. One of the factors in this was the fact that the installers would be the users of the product itself, and the link between users and manufacturers is not as strong as that between installers and manufacturers. Whereas it was felt that training should be provided to end-users, it was not clear whose responsibility it was to provide that training.

4.10 FALL INCIDENTS

Often there is little information available to document the circumstances when a FAS does its job and arrests a worker who has accidentally fallen. These situations may go unreported.

Three undocumented occurrences of arrested falls were divulged by one manufacturer; all were attributed to HLLs, and all in overhead installations above vehicle bays. In each case the HLL performed as expected. (All of these types had been thoroughly tested beforehand and all configurations had been subjected to computer analysis).

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In Johnson (1991), an Australian fall incident was described in which a worker fell whilst attached to a permanently-installed HLL, which had been installed “in the 1980’s”. The worker was taken to hospital and apparently had suffered no injury and was back to work the following day. The HLL was discarded and a new system was installed.

4.11 STANDARDS

Some manufacturers had the perception that BS EN 795 (1997) was not comprehensive enough in determining test requirements and criteria, so their testing is done to exceed these stipulations. The standard was still used for certifying purposes. Alternate test specifications were used for newly emerging developments which BS EN 795 (1997) did not cover, nor had anticipated. However alternate test methods were really dependant on the competency of testing institutions in deciding whether they could be applied to grant CE certification. This did not produce a level playing field as some manufacturers were being forced into testing to a greater extent than others, or saw a need to do this. In effect, standards were becoming obsolete.

4.12 PRODUCT ABUSE

Main areas of product abuse known about and disclosed by manufacturers, were:

· Not tensioning the HLL properly during installation

· Not locking the tensioner device properly after installation – allowing potential release of lifeline in fall situation

· Joining two HLLs together where one was insufficient in length to bridge the span in question

· Taking the HLL around (relatively sharp) corners

· Choke hitching the lifeline itself around the support structure (not using the anchor strap provided)

4.13 INSTRUCTIONS FOR INSTALLATION AND USE

A number of manufacturers’ instructions for installation and for use for temporarily-installed HLLs were reviewed. The following section represents a selection of the kind of information presented in these documents. Phrases contained in quotation marks are direct quotations.

4.13.1 Application

A common but important statement found in instructions, reflecting the application of these systems, is: “Temporarily–installed HLLs are for temporary use and should not be left installed for longer than is necessary”.

Some instructions referred to the possibility of using the HLL for restraint purposes as well as for fall-arrest.

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4.13.2 Restraint systems

The restraint system information found within the instructions was very limited. Restraint systems allow a worker to move horizontally within a defined area, whilst preventing the worker from reaching a position from which a fall could occur. They act as a tether. If restraint systems can prevent free fall, then there is no need to consider fall-arrest performance, neither is there any rescue requirement. Restraint systems are therefore the preferred means of protection over FAS, where they can be properly employed.

If a restraint system is unexpectedly called on to arrest a fall, the likelihood is that it will fail, leading to serious injury for the worker.

If it is discovered that a fall can occur when using a restraint system, use of that system should be stopped until it can be re-engineered for fall-arrest purposes.

One of the difficulties in determining whether a temporarily-installed HLL is a restraint system or not has to do with the amount of unsupported span. The “V” deflection in the lifeline which can be generated as a result of workers pulling at the extremes of their range of movement should not allow any free fall to take place.

There are currently no standards for restraint systems, but a new draft code of practice, BS 8437 (2003), is in the course of being edited (March 2004), which contains recommendations and advice for restraint systems.

4.13.3 Fall arrest systems

Limitations and rating

In one case three users are permitted to be attached to the HLL at any one time, each of a total mass of 136 kg. In another case up to five users are permitted in restricted circumstances. The total mass of each user is not stated.

Recommended free space beneath a worker

In one case: “Check that adequate clearance exists below the intended installation position for fall arrest purposes”, (graph included). However, the graph does not include any consideration of free fall or the type of fall-arrest equipment attached, nor does it make clear where the clearance should be measured from.

In another case two figures are given with no real information as to what the system configuration or fall conditions were, to generate those figures.

In another case more comprehensive design tables are utilised, which state the assumptions behind the calculations, so that the user is left in little doubt as to what is required. Diagrams are also used. However, little safety clearance seems to have been allowed between the feet of the person who has fallen and the nearest obstacle, at the point of maximum deflection of the system.

Anchor points

One case: “Check that anchorage points are of “adequate strength and stability””. (No reference to computer analysis made; no strength requirement stipulated). In another: “Structural end anchorage points must be able to withstand 20 kN load with an adequate factor of safety”.

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In another case: “It is important that anchor points are sufficiently strong enough. They should be capable of withstanding 15 kN”.

Installation

In one case padding is advised to be fitted between anchoring structure and HLL end loops to avoid damaging rope. In another case a series of drawings show how the anchor fitting should be disposed about the steel column with “correct” and “incorrect” designations. This a good example because it shows what can go wrong and alerts the installer-user to the problem.

In one case it is advised that the lifeline itself should be wrapped around the support structure twice, (presumably to generate friction), and secured with snap hooks through integral eyelets.

In one case, lifeline position is described as “it should be positioned as high as possible above user”. In another case the lifeline position is described as “it must be a minimum of 1.2 m above the walkway”. In another case there is no advice at all as to where the lifeline should be positioned.

One tensioning procedure is described as “operate tensioning handle until HLL is as taut as possible”, similarly: “use one hand to tension” (relying on the premise that one cannot over tension if the effort from just one hand is used). Another procedure is more comprehensive with diagrams, and utilises the product’s inbuilt tension indicator.

In one case “A” frame legs are described, which can be used to clamp the HLL to a girder flange; this includes a leg for providing an intermediate support. Clamping torque loadings are stipulated.

Attaching other fall-arrest equipment

In one case retractable arresters are allowed, providing that the rear full body harness attachment point is used and that the “maximum unextended webbing length is 1.0 m”.

In some cases, apart from a special link provided, no other connection to the HLL is permitted.

In one case the energy-absorbing lanyard length is specified as having to be 2.0 m maximum.

Marking

In one case a warning label is required to be attached at the point of access. Information is to include:

· The maximum number of attached workers · Only PPE supplied by Site Supervision to be attached · No unauthorised adjustments to systems, components or anchorages permitted

Maintenance and regular inspection

Instructions are generally very basic, being applied universally to a product range rather than specific equipment. Pre-use inspections are generally very basic with little or no pass/fail criteria. Some of this is attributable to the perceived simplicity of the equipment.

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Most require that the HLL to be removed from service, (although not all), following a fall-arrest loading having been applied.

In one case pre-use, regular and annual inspections are advocated, but no detail or defect pass/fail criteria is described.

In another case, reference is made to a wear indicator. When a certain colour becomes visible, this is the time for the HLL to be taken out of service.

Training

Training is generally required, but the onus is put on the installer-user to seek it out. In some cases it is presented as not being compulsory, but is simply a recommendation.

Rescue

In one case rescue is referred to; no methods are prescribed but it is advised that a fall victim should be rescued within 20 minutes of falling. In some cases there is no reference to rescue.

Rescue is generally not even alluded to in most of the instructions reviewed.

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5. CONCLUSIONS

The conclusions are compiled in such a way as to address the purposes of this research, by drawing on the findings of the review as detailed in Sections 2, 3 and 4. These sections are based on the study of nearly 60 references, which are detailed in Section 6.

A recommendation for further work is made in clause 5.7.

5.1 KEY FACTORS IN REGARD TO DESIGN AND PERFORMANCE

A number of important factors in regard to design and performance were identified in the research. These were highlighted in bold italics in Sections 2, 3 and 4, and are listed here in page order for reference.

· (Pages 23, 50, 56 and 57) In a fall arrest situation the lifeline is bent around certain points as a result of the “V” deflection, (e.g. where the lifeline runs over or through an intermediate anchor bracket, or where it runs through the travelling device at the bottom of a “V” deflection). These points can cause the lifeline to become more severely stressed than where the cable is in direct tension, which can significantly reduce its strength. These “stress concentrations” are particularly serious where the contact area between components is very small, and where friction is significant. Stress concentrations should be minimised or where possible, eliminated.

· (Pages 28, 32 and 33) Solvable mathematical equations cannot be obtained when modelling complex real time dynamics such as the trajectory of a falling man being decelerated by a HLL, due to the many factors involved. The equations can only be solved by using an iterative solution necessitating the use of computer modelling. The computer model, once created, has then to be verified against experimental results. This then enables predictive calculations to be made within a certain degree of accuracy, for subsequent analysis of different HLL configurations and fall conditions. Forces generated in the lifeline, at anchors, on workers, and displacements can be determined.

The degree of error should be identified and should be taken into account. It may be that the model may be improved upon to reduce the degree of error.

· (Page 29) Assessing the performance envelope for HLL configurations enables limits to be established such as:

o maximum allowable force in the lifeline; o maximum allowable load at the end-anchor; o maximum allowable arrest force on the worker o maximum allowable fall distance for the worker o minimum safety factors

· (Page 31) Fall-arrest performance should be assessed in conditioned atmospheres to replicate the ambient conditions in use, where these are likely to be severe (e.g. ambient temperature affects the impact properties of steel).

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· (Page 31) Fall-arrest performance can be assessed by using a range of sizes of test mass to represent different sizes of workers, where this has been identified as an issue. (e.g. Canadian research used an 80 kg mass, representing a worker’s weight in the 50th

percentile, and a 100 kg mass, representing a worker’s weight in the 95th percentile. A single 200 kg mass was used to simulate two workers falling simultaneously).

· (Page 31) Tests should be carried out to simulate the method by which any rescue is to be implemented, where additional loadings may be applied to the HLL after it has arrested a fall, in order to ascertain that these loadings can be sustained.

· (Pages 31 and 52) When retractable arresters are used in combination with HLLs there may be a tendency for them to be affected by “ratchet bounce” during a fall-arrest sequence. This effect, caused by the bouncing motion of the HLL during an arrest, can cause repeated unlocking and re-locking of the braking mechanism, which results in the worker being arrested several times, contributing to an excessive fall distance. This may be dangerous especially where the free space beneath a worker is at a minimum. This effect should be assessed for in testing. Preferably, retractable arresters for use with HLLs should be utilised, which have anti-ratchet bounce features.

· (Page 34) The reduction of forces on the person in a fall will result in lesser forces being transmitted to the HLL and hence through to the end-anchors.

· (Page 37) If a HLL is left in place after sustaining a fall-arrest loading, then the stiffness of the HLL will certainly be at a much higher level than it was when it was originally installed. Since stiffness has a significant effect on a HLL’s capability to absorb energy, and hence how much force is transmitted to end-anchors, it follows that in the event of a second fall-arrest loading being applied, sufficient loadings may be generated within the cable or at the end anchors to cause system failure, resulting in a worker falling to the ground or other substantial platform.

In other words, any calculation or analysis made when the system was originally installed, which was performed in order to assess loadings and system performance, will no longer be valid, because any increase in the value of stiffness will significantly increase the loadings transmitted through the system.

The above evidence establishes a very good reason to justify the replacement of HLLs after being subjected to fall-arrest loadings, (apart from other safety-critical reasons).

· (Page 38 and 45) The applied force in the interconnecting fall arrest equipment is multiplied by a factor by the time it has been transmitted to the end-anchor. This is mainly due to the fact that the sub-span in which the fall takes place is deflected into a characteristic “V” shape in an attempt to resist the downward motion of the test mass. This creates a proportionately higher tension within the HLL which, apart from the applied load in the lanyard and other factors, is dependent on the deflection angle.

· (Page 38) In research tests where the release of test mass was next to an intermediate support, the travelling device, (karabiner in the particular case), slid down the cable towards the centre of the “V” deflection during the first few rebounds. In test number SL9LM59, for example, the test mass is recorded as slipping a horizontal distance of 1700 mm in an internal sub-span of 7.0 m length. This emphasises that free space in the horizontal plane may be just as important as free space in the vertical plane.

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· (Page 41 and 43) When considering the simulated arrest of two or more workers by releasing the corresponding number of test masses at different time intervals, the dynamic response of the HLL based FAS becomes much more complex than when considering the arrest of a single worker.

When two test masses are released so as to fall simultaneously in the same sub-span, the maximum load recorded at end anchors may be significantly higher in comparison to that load which is recorded when a single test mass is released in identical conditions.

When two test masses are released with a time stagger of 200 – 300 ms, the lanyard load experienced by the test mass which reacts against the HLL first is similar to the lanyard force obtained for the release of a single test mass free falling through the same height. The second mass has to fall further than the first before reacting against the HLL, since the cable by that time will have been pulled downwards into the characteristic “V” shape, caused by the first test mass. Therefore, the second mass experiences a higher lanyard force than the first. (It should be understood that no energy absorbers were utilised in the tests concerned). Also at the moment of impact of the second mass, the level of tension in the HLL may be higher due to the load induced by the first mass.

When two test masses are released within 300 ms of each other in separate but adjacent sub-spans, lanyard loads and end-anchor loads are similar to those obtainable when under single test mass conditions. This is because when viewing the force-time graphs, the force being applied by the reaction of the first test mass against the HLL has virtually decayed by the time that the second mass starts to react.

· (Pages 41 and 44) Simulated arrest of four and six workers by releasing four or six test masses / anthropomorphic test dummies simultaneously, have been performed previously.

· (Pages 42 and 43) In-line energy absorbers can significantly reduce end-anchor loadings, which otherwise would be substantially higher in situations where the HLL is subjected to the simultaneous fall-arrest impact of four or six workers.

· (Page 42) In a test where four test masses were released so as to fall simultaneously on a single span HLL of 33 m span, of 12 mm 6 x 24 FC steel rope, the maximum “V” deflection was 3900 mm. This, (without even considering the length of lanyard, energy absorber extension, height of worker and safety clearance, page 58 refers), illustrates the disadvantage of not using intermediate anchor arrangements. In addition, significantly high loads can be generated at end-anchors of long single-span HLLs in comparison to those supported with intermediate anchors.

· (Page 43) In single span tests that simulated multiple-fall situations, it was noted that the travelling devices slid along the cable towards the bottom of the “V” deflection after the first impact, causing the masses to collide with each other.

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· (Page 43) For a given cable type and size, “V” deflection depends on:

o Span o In-line energy absorber extension o Position of falls o Free fall heights o Number of near simultaneous falls o Weight/type of test surrogate used

· (Page 43) “V” deflections in long, single-span HLLs, extension of in-line energy absorbers, and extension of personal energy absorbing lanyards in multiple fall situations requires special attention by designers and users of HLLs. The combinations of these displacements may become sufficiently large to pull other workers away from their position of work, (i.e. the first person who falls may pull others off-balance). Also, the excessive deflection of the HLL may cause second and subsequent workers to experience excessive free falls before being arrested by the HLL.

· (Page 44 and 45) When four anthropomorphic test dummies were released so as to fall simultaneously in the same sub-span of a HLL, simulating a four-person fall situation, they were not arrested by HLL at exactly the same time, (a time interval of 80 ms occurred between the first and last impact).

· (Page 45) In four-person fall simulation tests, forces transmitted to end-anchors are magnifications of the applied arrest forces, and applied arrest forces can be accumulative if they are applied within a short time frame, (4 arrest forces of an average 5 kN applied by the four dummies generated end-anchor loadings of 30-32 kN).

· (Page 48) In two-person fall simulation tests, in the case of staggered releases at 500 ms intervals in the same sub-span, at mid-sub-span, the first arrest was virtually complete before the second arrest started. Arrest forces were virtually identical, with end-loadings slightly higher and taking a longer time to decay with the second arrest than that of the first. This was probably due to the fact that the first dummy had deflected the HLL before the second dummy struck it. Hence the second dummy would impact the HLL with a higher velocity and with a greater amount of energy to be absorbed than that of the first, because of the extra distance through which it would have to fall.

· (Page 48) In the cases of simultaneous releases, lanyard forces were generally the same as in staggered releases at 500 ms, but were additive to produce approximately 50% higher end-anchor loads than those recorded in staggered releases.

· (Page 48) In the cases of the simultaneous releases in extremity sub-spans, end-anchor loads were approximately 80% higher than those recorded in staggered releases.

· (Pages 50 and 52) In static tests to destruction identical wire ropes were tested but with different travelling devices. In one test the travelling device was of good design for its intended function, but of poor design in how it interacted with the rope. It’s relatively abrupt edges effectively sliced through the rope at an applied load of only 12 kN. In comparison, another type of device, with its relatively smooth edges, did not cause the rope to fail below an applied loading of 18 kN. The results of these tests underline the absolute necessity to test for interaction and compatibility between device and rope in actual loading conditions.

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In another case, at an applied loading of 15 kN the travelling device cut completely through the rope, indicating that the interaction between device and rope constituted a serious weakness. The profile had been contributory to the cutting action. This test also showed that when individual components are combined together in a system, as would be the case in practice, the strength of the whole system may be different to the individual strengths of each component. Consequently, and especially with FAS based on HLLs, it is essential to assess how the whole system performs from a dynamic performance and strength viewpoint.

· (Page 51) Welding is often used as means to fabricate components for one-off installations. Welding and the necessary stress-relieving heat-treatment afterwards can be difficult processes to carry out, and poor welds can be prone to sudden brittle fracture. This is especially true when the welded area is within a load path which is likely to be dynamically stressed. Testing of such components can reveal these types of weaknesses, and in some cases has been shown to cause catastrophic system failure

· (Page 51) Springs are sometimes used to dissipate energy in component design, but do not really dissipate energy unless they permanently deform in some manner. They usually just store the energy and then release it back into the system at some stage.

· (Pages 54 and 56) Design for minimising degradation – due consideration should be given to those environmental factors which can cause degradation to the materials and manufacturing processes chosen in the make up of the product. Examples include: abrasion, wear, corrosion, sunlight. Water traps should be avoided; anti-icing features should be considered; performance should be considered in adverse conditions.

· (Page 56) Termination methods used to join cable to fitting to end-anchor should be as close as possible to 100% joint efficiency, (this is the situation where the minimum breaking strength of cable is the same before and after joining). Where joining methods reduce joint efficiency this needs to be taken into account when limiting loads in the lifeline.

· (Page 58) It is absolutely vital to know how much free space is required beneath a worker connected to a HLL, to ensure that, if a fall occurs, it will be arrested safely before a collision can occur, i.e. the free space must be greater to some degree than the distance the worker falls through.

· (Page 58) Mathematical calculations used to predict HLL fall-arrest performance should not rely on simple static analysis, because this method does not take into account dynamic factors which are present in real fall situations. In one case where such an analysis was relied on, subsequent dynamic testing resulted in the test masses striking the ground. This confirmed that the workers, had they fallen when connected to such an installation, would have been seriously injured or killed.

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· (Page 70) British Standards or British Standard equivalents of European Standards contain minimum requirements only; by just designing, testing, manufacturing and generally controlling products to the level required by the standard may not be enough. It is often thought that when marketing products, that if the product meets a standard’s requirements, then that will be sufficient, and that by gaining a CE mark in the case of PPE means that the PPE will be suitable for the particular task for which it is being sold. This is not necessarily the case as the testing in the relevant standard is often limited to checking standardised parameters under laboratory conditions and therefore may not cover the specific circumstances of use. A lot more may have to be done in excess of the standard to ensure that products are safe and satisfy legislation, e.g. the PPE Regulations (2002) and the Health and Safety at Work Act (1974).

It should be noted that all British Standards or British Standard equivalents of European Standards contain the following warning at the front of the standard: “Compliance with a British Standard does not of itself confer immunity from legal obligations”.

· (Page 87) End anchor terminations should be free to articulate and align in the direction that they would be pulled under fall-arrest loading to avoid bending failure.

· (Page 87) Potential strength reduction factors and slippage should be allowed for in the design of end-anchor attachments, due to method of attachment to structure, structure geometry and structure condition.

· (Page 88) Setting of the correct tension in the lifeline can affect how the HLL operates and what level of loadings and distances are generated in falls, although perhaps not to such a great extent unless large amounts of tension are applied (5 – 10 kN). Over-tensioning can eat into the reserve of cable/rope/webbing strength, which can then be a significant risk in terms of potential HLL failure. As HLL spans get longer, more tension is needed to overcome the increased amount of weight. At some point an intermediate anchor is advisable.

· (Page 89) Tensioning component design should take into account:

Interference - tensioning adjusting mechanisms have been known to be interfered with, perhaps by users who thought that “the line doesn’t seem tight enough” and have wound more tension into the system.

Slackening off - tensioning components have also been known to slacken off in use, i.e. the rope/cable/webbing has crept back through the tensioning device over a period of time.

Ratcheting – some tensioning devices are simply components adopted from other industries, e.g. cargo lashings in transport aircraft and road haulage. These are primarily designed to resist static loadings, not dynamic. The bouncing affect caused by a worker falling onto the HLL can cause these types of locking mechanism to repeatedly disengage and re-engage, allowing an incremental pay-out of lifeline during the fall, i.e. allowing the “V” deflection to increase. This subsides when the fall motion starts to be damped out. This has been detected during previous testing.

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· (Page 93) One of the difficulties in determining whether a temporarily-installed HLL is a restraint system or not has to do with the amount of unsupported span. The “V” deflection in the lifeline which can be generated as a result of workers pulling at the extremes of their range of movement should not allow any free fall to take place.

5.2 KEY FACTORS IN REGARD TO SELECTION

5.2.1 General considerations

Selection of the most appropriate equipment should result from a risk assessment and a PPE assessment43. Performing a task with inappropriate equipment can introduce additional and greater risks. If equipment is used outside its capability, its performance may not match up to expectations and so the degree of intended protection desired may not be achieved.

When planning a safe system of work an employer should consider:

· who the equipment is for

· what work is to be carried out

· how much space is needed

· where it will be carried out

· how long it will take

In particular, the following should be considered:

· the nature of the work place - its form, structure, geometry and materials

· the worker - size, ergonomics, movements to be made, postures to be adopted

· the task - any special risks attributable, range of movement required, space required, duration

· environment - adverse climate or atmosphere

· features and limitations of the equipment - materials, operation

· legal and standards requirements

These issues should be considered and taken account of as early on in the planning stage as is possible, i.e. from concept stage.

43 Required under the Management of Health and Safety at Work Regulations (1999) and PPE at Work Regulations (1992) in order for employers and self employed people to assess health and safety risks to workers and others who may be affected by their work or business. This enables them to identify the measures they need to take to comply with health and safety law. It should also be noted that the forthcoming Working at Height Regulations will prescribe a hierarchy of fall protection which will affect the choice of equipment selected.

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Field trials, with input from those workers who will use the FAS, are essential. Technical information, e.g. manufacturers' instructions for use and installation, together with research, test and performance information should be evaluated. Particular reference should be made to methods of test, the number of tests and the repeatability of results. Before purchase, discussions should be held between the purchaser and manufacturer/supplier on aspects of use, to determine the type of FAS to suit particular circumstances.

5.2.2 Product considerations

A temporarily-installed HLL is typically installed to stretch across any straight line horizontal access route and its length can be adjusted to suit the workplace. It can be used to bridge and therefore provide fall protection across gaps which have no intermediate supporting structure. HLLs typically provide fall protection solutions in the construction industry.

A temporarily-installed HLL is repeatedly installed, used, removed after use, transported to the next workplace or stored, and then reinstalled as necessary. They are not for permanent installation applications.

Primary factors

Factors that should be taken into account when selecting temporarily-installed HLL, include knowing:

· that there will be a sufficient length of lifeline to allow a worker to cover the extremes of travel in the intended work area(s);

· whether the HLL is for restraint or fall-arrest purposes;

· the maximum weight of workers that will be using the equipment and the number of workers that will be simultaneously attached is within the limitations of the equipment;

· what other fall-arrest equipment is intended for attachment to the HLL and whether or not this is (i) permissible and (ii) compatible44;

· the required strength of the structure to which the HLL will be attached, taking into account any factors of safety;

· whether any kind of support posts are required if no structure is available;

44 There are known and potential incompatibility problems when certain combinations of equipment are connected together (see clause 5.2). Most manufacturers limit what can be connected to the HLL because of this, i.e. they operate on the basis of what has been tested in conjunction with their HLL. Where uncertainty exists over compatibility between equipment it is recommended that full system testing is carried out in order to identify any undesirable characteristics.

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· the performance of the system in fall-arresting circumstances:

o end-anchor loadings (and intermediate anchor loadings, as appropriate) o fall arrest forces experienced by a worker or workers o the extension of the system and if there will be sufficient obstacle-free space

beneath the worker to arrest the fall safely o safety factors

for each configuration of system and each worst case fall condition. This includes the different types of fall-arrest equipment that is intended to attach to the HLL, and what will happen if all the attached workers fall simultaneously.

Secondary factors

Other factors that should be taken into account when selecting temporarily-installed HLL, are that they should:

· have interconnection component lengths (between travelling device and harness) as short as possible, commensurate with the work task;

· (in the case of multi-span HLLs) have preferably a travelling device which can pass through intermediate support brackets without undue resistance and without the need for removal and refitting of the device, or the unclipping of the lifeline;

· have suitable terminations to facilitate connections with anchor points. Terminations should be reinforced to prevent metal to fibre contact and to prevent wear from sliding movement and repeated connection / disconnection;

· have reinforced terminations to prevent wear where articulation occurs between parts, eg fall-arrest equipment attachment point on travelling device;

· have a tensioning unit that must not cause undue damage to lifeline even after repeated installation actions;

· be as light as possible but not at the expense of strength, durability, operation or reliability;

· have features incorporated to take into account specific risks or environment, eg: electrical resistivity, corrosion resistance, chemical resistance, ultraviolet resistance, wear/edge resistance, extreme heat/cold/dust/wet/oil contamination;

· have adequate protective covering for textile based energy absorbing elements;

· have preferably, in the case of tear-web energy absorbing lanyard designs, a parallel sewn in back-up strap. This prevents the worker falling to the ground in the event of energy absorbing element failure due to environmental degradation;

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· be energy-absorbing efficient, i.e. should offer the lowest arrest force over the shortest arrest distance. Tear-web type energy absorbers tend to give a very consistent arrest force characteristic, but since the energy is lost over a parted strip of material they produce an arrest distance equal to twice the torn distance. Other types tend to produce lower levels of arrest distance but may not have such a consistent arrest force as with the tear-web types;

· have travelling devices which should not be capable of inadvertent release from the lifeline, especially those designed to be removable at any point;

· have preferably a means of fall indication;

· have all ends of webbing, ropes and fittings properly finished off to prevent cuts and abrasions to hands;

· be manufactured under a recognised quality management system or other method of ensuring quality in production;

· if purchased as a proprietary system, be certified to the PPE Regulations 200245, 46.

5.3 KEY FACTORS IN REGARD TO INSTALLATION AND USE

5.3.1 Fundamental considerations

To look at, temporarily-installed HLLs are very simple. But in terms of the fall-arresting process, they are very complex. If not installed correctly, workers who fall whilst attached to these systems may be injured or killed.

The users of these FAS are likely also to be the installers, i.e. temporarily-installed HLL based FAS are user-installed like some other kinds of FAS, e.g FAS based on energy-absorbing lanyards or retractable arresters. However, the installation of HLL based FAS have more exacting requirements and performance is much more affected by error or negligence than with other types.

Some of the factors mentioned below are already mentioned in Section 5.2, but are repeated here again because they also apply to those carrying out installations. Factors that should be taken into account when installing temporarily-installed HLL, include:

45 A common misunderstanding often occurs in respect of CE certification marking which, under the PPE Regulations 2002, must be applied to all PPE sold since July 1995. The CE mark signifies that an independent Government- approved body (Notified Body) has established and certified that a pre-production model of the PPE in question satisfies the relevant provisions of the above regulations. This includes a technical assessment of the PPE, to ensure that it complies with the basic health and safety requirements of the aforementioned regulations, and examination and testing to a relevant European standard or other specification. It is often thought that this is sufficient in that the CE mark means that the PPE will be suitable for the particular task for which it is being purchased. This is not necessarily the case as the testing in the relevant European standard or other specification is often limited to checking the most important parameters under laboratory conditions and therefore may not cover the specific circumstances of use. Therefore ensuring that the PPE product possesses the PPE CE mark is only one of the factors involved in the selection process.

46 See also p.74

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Training

Installer-users need to be trained in theoretical and practical aspects and should demonstrate competence in how to install the particular kind of HLL. No attempt should be made to install before training is complete.

Instructions

Instructions for installation must be read and understood. Installation should not be attempted without this documentation.

Instructions should be explicit; generic statements should not be accepted.

If specific information is missing from instructions, or, if certain information is ambiguous or unclear, installation should not proceed until clarified by the respective design authority/manufacturer.

Fall-arrest performance

Temporarily-installed HLLs require dynamic predictive calculations to ensure that the particular configuration being installed, with the particular fall-conditions envisaged, will safely arrest the worker (s) attached to the lifeline. These calculations will usually either have to be performed by special computer software47, or may have been pre-calculated by a manufacturer at the onset, and will be contained in graphical or tabular format within the instructions.

No attempt should be made to install a HLL until in receipt of this information. Once in receipt, the contents should be carefully considered, and if not understandable, or if not complete, no work should commence until the matter is clarified.

If graphical or tabular information does not contain the specific configuration details or fall-conditions applicable to the situation in hand, then no attempt to extrapolate or interpolate48

information should be made, unless authorised to do so by the instructions. A common example of this is where the interconnecting fall arrest equipment to be attached cannot be found within the table. The table may refer to certain kinds of equipment, e.g. energy-absorbing lanyards of a certain type and length, and the conditions at the start of a potential fall. But they may not refer to the specific type of energy-absorbing lanyard to be attached, nor it’s specific length, nor the specific conditions at the start of a potential fall. Or, the instructions may allow types of interconnecting fall arrest equipment to be attached other than energy-absorbing lanyards, but may omit the performance information about this in the table.

Information should not be guessed at. Any omissions or uncertainties should be clarified with the design authority/manufacturer.

Factors that affect the performance of a FAS based on a HLL, in terms of how it is configured, and the fall conditions that are applicable at the beginning of any potential fall circumstance, are detailed in Section 2.

47 The numbers of factors in such calculations make the equations insolvable; multiple iterations are performed by computer to find the correct solution 48 To estimate a value beyond the values already known or to estimate a value between values already known.

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Particular attention should be given to the weight of workers, the number of workers to be attached at any one time, free fall, and the equipment they are planning to use to connect themselves to the HLL. Results from calculations should reflect the maximum weight of workers, the effects if they all fall simultaneously, actual free fall conditions and the type of interconnection equipment between HLL and harness.

Calculations should also consider, especially in the case of three or more attached workers, the case where one worker has fallen, and has stretched the HLL into the “V” shape, and the other two or more fall slightly later. The fall distances for these latter fallers will be greater than that for the first, and when they impact the HLL they will possess greater amounts of energy. This will require a greater extension of the connected fall-arrest equipment than that required of the first faller, and may apply greater end-anchor loadings, or both.

The degree of accuracy of any calculation should be given, as no calculation is expected to be 100% accurate.

Simple, static-load type calculations based on catenaries49 should not be used to predict performance of these systems. These types of calculations cannot give accurate answers as they omit key factors from the calculation. They are particularly prone to error in regard to calculating fall distances.

Anchor strength

Once the end-anchor loadings generated by the potential fall-conditions of the particular configuration of FAS are known, then the structure to which the HLL is going to be installed to can be assessed for strength. Consideration should be given to any recommended factor of safety that the manufacturer recommends. Assessment of the structure should be made by a competent person, e.g. a structural engineer, i.e. someone who through training and understanding of engineering, can assess, by calculation, test or other appropriate analysis, whether a particular structure is capable of withstanding the loads that will be imposed on it.

It is extremely dangerous simply to estimate or to guess whether a structure will support a load or not. Temporarily-installed HLLs are engineered safety systems and an engineering type approach must be taken in these circumstances, or else there will be no guarantee that the structure will support a worker during a fall-arrest incident.

Anchor height

Once the results of calculations generated by the potential fall-conditions of the particular configuration of FAS are known, then the area in which the HLL is going to be installed can be assessed to see if there is sufficient vertical free space underneath, in order to arrest the worker(s) safely in the case of a fall-arrest event, (Clause 3.5.7 refers).

Again, it is extremely dangerous to simply guess at or estimate this quantity. The test incident in clause 3.5.7 makes this clear. The quantity has to be determined by using a sound engineering basis.

Generally, the HLL should be installed in an overhead position to minimise free fall conditions which will in turn limit the amount of required free space.

49 Standard type formulas to determine static loads in cables hung between two points, e.g. along railway lines, for cable cars, or between electricity pylons.

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Long single-spans and pendulum-swing falls

As well as allowing sufficient vertical free space beneath the worker, in cases of long single-span systems, sufficient free space should be allowed in the horizontal plane. This is because the travelling device may be caused to slide downwards towards the centre of a “V” deflection during a fall, which may induce a large pendulum-swing fall component to the trajectory of the falling worker, (refer clauses 3.4.3 under “karabiner sliding” and 3.4.4). This may cause the worker to impact structure at significant velocity to cause serious injury.

Rescue

When considering installation and use, a method of immediate rescue will have to be considered alongside other requirements, (Clause 4.7 refers). Rescue of a worker whose fall has been arrested, is essential. Provision of anchors for rescue equipment may have to be considered.

Sharp edges

A fall which pulls part of a HLL or interconnecting fall-arrest equipment over a sharp edge can result in cutting through where it makes contact with the edge, with a resulting subsequent fall to the ground of the worker. This danger is greatly increased in swing fall circumstances, where energy absorbing lanyards or the lifeline of a retractable arrester is trailed across the edge in a slicing action. Anchoring positions should be avoided where the possibility exists of the lifeline/lanyard being pulled over an edge in a fall-arresting situation. Where such use cannot be avoided, a method of ensuring that the lifeline/lanyard cannot fail should be specified by a competent engineer 50.

Restraint systems

If the HLL is to be used for restraint purposes, it is vital to ensure that when the lanyard or other interconnection is made between the HLL and harness, at no point along the lifeline is there the possibility of a free fall. If a worker can free fall, the HLL must be reconfigured and reconsidered as a FAS, (Clause 4.13.2 refers).

Fall protection during installation/removal

Generally, temporarily-installed HLLs are needed in places where no method of anchoring is available, but it remains essential to provide some means of fall protection whilst the HLL is being installed or removed.

50 The manufacturer should be contacted in the first instance in regard to determining the resistance of the product to failure over edge conditions. The manufacturer may be unable to provide this information due to the large number and variety of edges that are possible. Also the current standards that control the design of fall-arrest equipment do not specify any fall-simulation testing over edges. However test methods can be devised to demonstrate the resistance to failure over edge conditions. Results of such tests should report test parameters: edge type, included edge angle, test surrogate, lifeline specification, free fall, swing fall angle, arrest force and distance, ultimate failure load. The test parameters should be for conditions that are at least as severe as the actual application.

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5.3.2 Product considerations

Anchor connections

The correct anchor connections should be made between the structure to which the HLL is to be anchored to and the termination of the HLL itself. In proprietary systems these fittings are usually supplied. Manufacturer’s instructions should be followed as it is likely that supplied fittings will have been tested in conjunction with the main components.

Fittings should not be substituted or modified without the manufacturer’s permission. Connections should not be improvised. The ends of the HLL itself should not be used to tie-off to the structure unless specifically allowed in manufacturer’s instructions.

Anchor connections should only be made on enclosed immovable structure, e.g. not cantilever beams where there is a possibility of any connecting loop slipping off, and not transportable, mobile objects, which may overturn if a fall-arrest loading is applied.

Anchor connections should only be made to surfaces where is no likelihood of connections slipping down structures.

Anchor connections, particularly those made from textile materials, should not be made to structures with sharp or very abrupt edges, without seeking further advice. If structures require connections which are larger than those supplied, further advice should be sought. It is dangerous to tie connections together or use improvised lashings. Fall-arrest loadings can be high and can easily cause failure of inadequate connections.

Anchor connections should permit the free articulation of components, especially so that in a fall-arrest occurrence, they can be pulled in the direction of the fall loading without being trapped. Otherwise in loading situations components may be deformed in bending, which can make them more vulnerable to mechanical failure.

In-line energy absorbers

These items should only be fitted where required by manufacturer’s instructions. Although they can lower end-anchor loadings, they add to fall-arrest distances, which increases the amount of space that is required to be underneath the worker to ensure a collision-free arrest.

Joints

Where there is insufficient length of lifeline to bridge a gap, lengths should not be increased by joining two lifelines together, or by adding improvised lashings. The performance and safety of such improvisations cannot be guaranteed.

Some manufacturers do produce joint fittings, but these are typically used to remove a damaged portion of the lifeline and re-join the gap so formed. They are not generally used to extend the lifeline.

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Longer span products should be sought from manufacturers as the first step to solving the problem. If this is not acceptable, joining by any method must not take place without the manufacturer’s permission, as this will affect product integrity51, fall-arrest performance and anchor strength requirements.

Tensioning

Only the supplied components and instructions should be used to perform the tensioning operation. If the instructions are inadequate or are not clear, points should be clarified before installation commences. HLLs should not be over tensioned, as this can lead to excessive end-anchor loadings.

Tensioning devices should be locked in some way, to prevent tampering.

Attaching fall-arrest equipment to the HLL

Attaching to the HLL should only be done via the travelling device (which may be a simple karabiner or other fitting). Attaching via any method other than stipulated by the manufacturer should not be used, as it could severely weaken the HLL in a fall incident, (refer to amateur fabrications sub-section in clause 3.5.4).

Fall-arrest equipment, whether it is energy absorbing lanyards, retractable arresters or rope-grabs, should only be attached to the HLL with the approval of the HLL manufacturer. This is vital because the attachment of such equipment has a direct and significant affect on:

· FAS performance, i.e. end-anchor load, system loads and fall distances. Such an attachment has to be taken account of in the calculations or else it will not be known whether a system is safe or not.

· Interaction/compatibility – some equipment can be incompatible with the HLL. For example, the performance of some manufacturer’s energy absorbing lanyards may not be suitable for connection to a particular HLL. Also, retractable arresters can have a locking/arresting problem when attached to HLLs (ratchet bounce - clauses 3.3.3, 3.5.4 and 3.7.2 refer).

· Functioning – in some circumstances when retractable arresters are attached to HLLs, it may be difficult for the travelling device to be pulled along the HLL in response to worker movement. This causes an excess amount of the arrester’s lifeline to be extracted, and can lead to excessive pendulum-swing falls.

Splicing of cable or rope, or sewing of webbing to produce joints in temporarily-installed HLLs is not recommended, due the vulnerability of the joint in the arduous conditions that these FAS are typically used in, and the degree of stress concentration imposed on a joint if fall arrest forces are applied in the immediate vicinity or directly over the joint.

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Some manufacturers limit52 the types of equipment that can be fitted to their HLL. If in doubt, the equipment should not be used. If retractable arresters are needed, and information about their use is not clear, systems tests should be performed to make sure that they can work properly in the configuration of HLL to be installed. Preferably, retractable arresters with special anti-ratchet bounce features should be used.

Generally, where energy absorbing lanyards are used, they should be as short as possible, to minimise free fall conditions.

Pre-use checks/action after fall

All pre-use checks should be carried out in accordance with manufacturer’s instructions. Equipment must be withdrawn from service if there is any doubt as to its condition for safe use.

Equipment must be withdrawn from use after having sustained a fall-arrest loading. Structure to which the HLL was attached should also be checked.

5.4 KEY FACTORS IN REGARD TO MAINTENANCE

5.4.1 General considerations

A product such as a temporary-installed HLL, which undergoes frequent repeated cycles of installation/de-installation/reinstallation, in all kinds of outdoor environments, and in heavy industrial conditions, and given it’s safety critical nature, would certainly need a regular planned preventative maintenance programme. This programme would probably be carried out at 3­monthly or even monthly intervals, depending on the durability of the design in question. Manufacturers’ maintenance schedules and instructions should be considered: any significant departure from them should be discussed with the manufacturers or their authorised agent, (refer clause 3.7.1 under “ongoing maintenance”).

5.4.2 Fundamental considerations

An effective system of maintenance is essential to make sure that equipment continues to provide the degree of protection for which it was designed. Key factors that should be addressed in regard to maintenance, include:

· the need for regular examinations, to different depths as appropriate. The safety of workers depends upon the continued efficiency and durability of the equipment (e.g Figure 21).

52 The performance-testing of FAS is a critical aspect of verifying whether a particular system design is capable of safely arresting a worker. During testing, the behaviour of the particular design is assessed for arresting capability under simulated fall conditions and for strength and other criteria in laboratory conditions. Each aspect of test behaviour has strict limits for the purposes of safeguarding life and preventing injury. Based on the results from testing, manufacturers impose limitations, apply criteria and make recommendations for the use of their equipment. It is essential that these limitations, criteria and recommendations are strictly adhered to. If FAS are used in potential fall conditions outside of manufacturer’s limitations or recommendations it is unlikely that performance will be known because those situations may have not been simulated by previous testing, or they may have been identified in previous testing as hazardous for workers.

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· frequency of regular examinations, taking account of such factors as legislation, equipment type, frequency of use, and environmental conditions. An in-depth examination should be made at least every 6 months as recommended in INDG 367 (2002), see page 67 of this report, although for the kind of use typically associated with temporarily installed HLLs this frequency should be increased to every three months or even every month, see INDG 367 (2002).

· examinations to be conducted by a competent person and strictly in accordance with the manufacturer’s procedures, covering such items as:

o visual and tactile checks of textile materials for defects such as: excessive wear, fraying, tears, cuts, burns, discolouration, powdered fibre, flattened fibre, loose strands and stitches, kinking;

o visual checks of metal and plastic parts for defects such as: cracks, splits, corrosion, distortion, sharp edges, excessive wear, loose fasteners, kinking of wires, fall-indicator operation, wear limit operation;

o functional checks/tests of trolley sliding ability and any special mechanisms, tensioner units, and connectors for correct operation.

These checks are especially vital on temporarily-installed HLLs, because of the repeated nature of installation, removal and reinstallation. Specific areas of vulnerability include:

o the part of the HLL cable/rope/webbing which passes through the tensioning device

o the terminations on the HLL and where it passes through intermediate anchors (if fitted)

o anchor connections

· making sure that the product markings remain legible

· repairs to be conducted by a competent person, who has been authorised by the manufacturer, and strictly in accordance with the manufacturer’s instructions

· cleaning and lubrication

· drying of wet equipment

· storage procedures, including all necessary preventative requirements where environmental or other factors could affect the condition of components, e. g. damp environment, sharp edges, vibration, ultra-violet degradation

5.5 RECOMMENDATIONS FOR NON-PROPRIETARY INSTALLATIONS

5.5.1 General considerations

There are organisations who from time to time consider the design, fabrication and installation of their own temporarily-installed HLL for their own workplaces. These are not proprietary systems that have been supplied by fall protection manufacturers, nor are they systems for sale.

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To look at, temporarily-installed HLLs seem very simple. But this perceived simplicity belies the complexity of the design and installation process required in order to verify that if and when a HLL is called on to arrest a fall, then it will do so in such a manner as:

· to apply an arresting force to the worker(s) who fall of a limited magnitude and in such a way as to not to kill or seriously injure the worker(s)

· to avoid causing failure of any part of the FAS or anchoring structure, thus causing the worker(s) to be forcibly disconnected from their protection and allowing a fall to the ground

· to ensure that the extension of the HLL, plus that of any connecting fall-arrest equipment, is less than the vertical space beneath the HLL on site, to prevent the worker(s) from colliding with the ground before the fall is stopped by the FAS

· to ensure that any horizontal swinging displacement of the worker that may occur during a fall is less than the available obstruction-free space in the horizontal plane

All of the factors mentioned in clauses 5.1, 5.2, 5.3 and 5.4 apply to this kind of design and installation, and so should be taken into account if it is wished to pursue such a project. The reader is also encouraged to read and thoroughly digest the technical information contained in Sections 2, 3 and 4 of this report. In the final analysis, it may be much easier, quicker and more economical to purchase one of the proprietary systems available in the market place.

5.5.2 Specific considerations

From the information contained within Sections 2, 3 and 4 of this report, it should be clear that design and installation of HLLs is not just a matter of stringing up some randomly chosen rope in an improvised manner, and in the process relying on a good degree of guesswork. HLLs are engineered systems and require engineering disciplines and approaches in order to ensure that they will perform as intended. This involves consideration of the following:

Legal aspects

There is a system of control for the design, testing, manufacture, installation and use of safety equipment in the UK, (see clause 3.7.1). Some of the information referred to may not be applicable if the HLL in question is not intended for sale, but nevertheless there is a great deal which does apply.

Standards and official guidance

British standards BS 7883, BS EN 795, BS EN 365, BS 8437 (a draft standard, currently) and HSG 33 have an important bearing on the design and installation of HLLs (refer to clauses 3.7.3 and 3.7.4).

Parameters that affect performance

There are several parameters which affect the performance of a FAS based on a HLL which need to be understood. A change to any single parameter affects the overall performance, and this is why HLL performance is so complex. Factors include:

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· Length of the HLL span

· Length of the interconnecting fall-arrest equipment

· Elastic properties of the HLL, interconnecting fall-arrest equipment, (whether energy-absorbing lanyard, or other) and harness

· Energy absorbing characteristics of any energy absorbing mechanism including in-line energy absorber (if fitted)

· Initial tension in the HLL

· Sub-spans between intermediate anchors (if installed)

· Amount of free fall (where the fall starts in relation to the level of the HLL)

· Position of fall (in relation from end-anchor)

· Weight of the worker(s)

· Friction at corner units and intermediate anchors

· End-anchor and anchor connection stiffness

· Arrest characteristics, compatibility and interaction between interconnecting fall-arrest equipment (e.g. retractable arresters) and the HLL

· Number of workers who fall, and whether they fall simultaneously or at staggered intervals (i.e. with an appreciable time difference)

Design criteria that affect safety

Design criteria and effects that have to be determined when designing a single-span HLL under fall-arrest conditions, include:

· Determining the magnitude of forces acting on end-anchors so that the required strength of the structure can be established (generally, this has to be at least two times any end-anchor loading)

· Determining the magnitude of forces acting in the system so that the required strength of the system can be established (generally, any component has to withstand at least two times any force transmitted through it, but in stress concentration areas, this may have to be higher, e.g clauses 3.2 and 3.5)

· Determining the magnitude of forces acting on the worker (this is limited to a maximum of 6 kN within Europe)

· Determining the total amount of vertical fall distance so that the required free space underneath the worker, before a fall occurs, can be established

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· Determining the total amount of horizontal displacement so that the required amount of obstruction free space, before a fall occurs, can be established

Fall simulation analysis to determine fall arrest loadings and arrest distances is usually performed by using specially written computer software, the accuracy of which has been determined by comparison with known test results. Static analyses, although relatively easy to perform, cannot be relied on to give accurate results. In fact they can produce dangerous misleading results, e.g clause 3.5.7.

Design detail

Special attention should be given to the choice of:

· Rope/cable/webbing construction

· Type and compatibility of fall-arrest equipment interconnecting HLL to harness

· Anchoring connection, termination and tensioning methods

· Travelling device and interaction with HLL

· Rescue methods / equipment that may affect the HLL

See especially but not exclusively clauses 3.2.2, 3.5.4, 3.5.5, 3.5.6, 3.5.7, 3.7.2, 3.7.3, 4.2, 4.3, 4.5.1, and 4.6.

The welding of components which will be subjected to dynamic loadings is not advised, unless particular attention is paid to them during their production. Proof loading may be required to verify successful heat treatment.

Testing

Various full scale testing needs to be carried out:

· Dynamic testing, to verify design, performance, calculations, compatibility issues and to detect any deficiency. The complete FAS should be tested, in all configurations for use and in the worst fall-arrest conditions. Components should not be tested in isolation.

· Static testing, and tests to destruction to verify reserves of strength, mode of failure and factors of safety. Attachment of rescue equipment and the loads imposed may have to be considered. Again, components should not be tested in isolation, e.g. clauses 3.2.2 and 3.5.4.

· Other miscellaneous testing such as effect of environment, corrosion resistance, etc

Testing can be used to verify individual configurations and fall condition arrangements. However tests results from one configuration cannot be used to automatically verify another configuration. Extrapolation and interpolation of results is not advised, since relationships between the quantities involved do not obey a linear law.

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5.6 RECOMMENDATIONS FOR THE TRAINING OF INSTALLER-USERS

Installer-users should be trained /instructed in the following areas:

· Legal requirements and advice in official guidance/standards

· The difference between restraint and fall-arrest applications

· The parameters that affect the performance of a HLL and how changing those parameters can change performance and alter risk

· Test results

· Aspects of compatibility between HLLs and other fall-arrest equipment

· Limitations, particularly but not exclusively: maximum weight and permitted number of attached workers, minimum and maximum span, maximum load allowed in HLL

· Selection techniques, to assess whether a product’s features meet the need of the particular application and environment in which the product is to be employed

· Analytical techniques to assess strength of structures (or strengths of common sections could be in a tabulated format)

· Interpretation of results of calculations that predict FAS performance or interpretation of table or graphical information containing calculation results

· Applying performance results in terms of whether installation is viable (eg: anchors of sufficient strength; knowing when to use in-line energy absorbers; enough free space beneath worker)

· Aspects of rescue and rescue techniques that will be used to rescue workers who fall

· Dangers of sharp edges

· Fall protection when installing/removing HLL

· The making of anchor connections and system connections and the dangers of not doing this correctly

· Manufacturer’s training in assembling/setting up system: including details of all components, tensioning procedure, pre-use checks, ongoing maintenance and examination pass/fail criteria

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5.7 RECOMMENDATIONS FOR FURTHER WORK

In the course of conducting the research, it became noticeable that the subject of simulating multiple falls on HLLs is in need of further investigation, since there appears to be a great deal of uncertainty in the market place as to how this factor affects fall-arrest performance and strength requirements.

As mentioned in the report, the situation is not helped by the lack of guidance in UK or European publications. This situation is virtually the same worldwide.

Some research has been conducted, as indicated in the report, but is either limited in scope or else complications have made the comparison of test results quite difficult.

Further investigation could be undertaken by carrying out a program of drop-testing on a standard HLL configuration, building on the research disclosed in this report. Parameters would be limited at the outset, so that the subject of multiple falls could be isolated and studied, without the complications of other factors.

Several drop test masses would be released simultaneously and at staggered time intervals.

Results and recommendations could be channelled into official guidance as well as standards.

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6. REFERENCES

ANSI A10.14 – American National Standard for Construction and Demolition Operations – Requirements for Safety Belts, Harnesses, Lanyards and Lifelines for Construction and Demolition Use (1991), American National Standards Institute, National Safety Council, Itasca IL 60143-3201.

Arteau, J. and Lan, A. (1992) “Use of Horizontal Lifelines in Structural Steel Erection”, Proceedings of the Conference on Protective Equipment, May 3-5 1992, Ottawa, Canadian Council on Protective Equipment.

Arteau, J. and Lan, A. (1994) “Use of Horizontal Lifelines in Structural Steel Erection”, Proceedings of the International Fall Protection Symposium, October 27-28 1994, San Diego, California, International Society for Fall Protection, Toronto.

AS/NSZ 1891.2 Australian/New Zealand Standard - Industrial Fall-Arrest Systems and Devices Part 2: Horizontal Lifeline and Rail Systems and Supplement 1: Prescribed Configurations for Horizontal Lifelines (2001), Standards Australia, Sydney Head Office, New South Wales, Australia.

BS 1397 - British Standard Specification for Safety Belts and Harness (1947), British Standards Institution, London.

BS EN 365 – Personal Protective Equipment Against Falls From a Height – General Requirements for Instructions for Use and for Marking (1993), British Standards Institution, London.

BS EN 795 – Protection Against Falls From a Height – Anchor Devices - Requirements and Testing (1997), British Standards Institution, London.

BS 7883 – Code of Practice for Application and Use of Anchor Devices Conforming to BS EN 795 (1997), British Standards Institution, London.

BS 8437 – Draft Code of Practice for the Selection, Use and Maintenance of Personal Fall Protection Systems and Equipment for Use in the Workplace (2003), DPC: 03/101170 DC, British Standards Institution, London.

Caisse Nationale de L’Assurance Maladie Note technique No 167 (1980) – Harnais de Securite – 2 – Note pour la Determination des cables de securite utilises en montage-levage. (National State Health Insurance Office Technical Note 167 (1980) – Safety Harnesses – 2 - Note to Determine Safety Cables used in Lifting-up/Raising). Caisse Nationale de L’Assurance Maladie, INRS Note No 1241-98-80, Paris.

CEBTP Test Report No. 672.6.166 (1984) Centre Experimental de Recherches et d’etudes du Batiment et des Travaux Publics, Paris

Code of Federal Regulations 29 CFR, Part 1910.66, Appendix C, Personal Fall Arrest Systems (1996), U. S. Government Printing Office, Washington D. C.

Code of Federal Regulations 29 CFR, Part 1926.500, Subpart M, Appendix E, Personal Fall Arrest Systems (1996), U. S. Government Printing Office, Washington D. C.

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Construction (Health, Safety and Welfare) Regulations (1996), Statutory Instrument 1996 No. 1592, The Stationery Office Ltd, London.

Council Directive 89/686/EEC (1989) on the Approximation of the Laws of the Member States Relating to PPE, Official Journal of the European Communities L 399 [32] 18-37.

Cloe, W. W. and Breslin, P. B. (1979) Occupational Fatalities related to Roofs, Ceilings and Floors as Found in Reports of OSHA Fatality/Catastrophe Investigations, Report No OSHA/RP-80/003, Office of Statistical Studies & Analysis, Directorate of Technical Support, U S Dept of Labor/OSHA, Washington D.C. 20210.

Corbeil, J. F., Arteau, J. and Lan, A. (1996) “Static and Dynamic Testing of Tubular Sections in Bending Collapse: Experimental Model”, Proceedings of the 8th International Congress on Experimental Mechanics, Society for Experimental Mechanics, Nashville, 10-13 June 1996.

CSA – Sixth Draft of Flexible Horizontal Lifeline Systems Standard (1999), Canadian Standards Association, Ontario, Canada.

Dayawansa, P. H., Goh, C. C. and Wilkie, R. (1989) Analysis and Testing of a Static Line System, Report No MRL/CN8/89/001, BHP Melbourne Research Laboratories, Victoria, Australia.

Dayawansa, P. H. and Ralph, R. (1996) Testing of Static Line Systems – Test Results, BHP Research Report No BHPR/SM/R/026, BHP Melbourne Research Laboratories, Victoria, Australia.

Dayawansa, P. H. and Ralph, R. (1997) “Tests on Static Line Systems”, Steel Construction, 31 [2] 2-26.

Dirscherl C. (2004) W-DOC 2004-04 Private e-mail between C Dirscherl, 89/686/EEC PPE Directive Manager of the European Commission and Safety Squared.

Drabble F. (1995) Report on Horizontal Lifeline Testing, Grange Dynamics, UK (unpublished).

Drabble F. and Brookfield, D. J. (1998), “Numerical Modelling of Fall Arresting Systems”, Proceedings of the 1998 International Conference on Mechanics in Design, The Nottingham Trent University, Nottingham, Great Britain, 6-9 July 1998.

Ellis J. N. (1993) “Which Fall Protection System Should be Used?” in Jaron, B. B. (ed.) (1993) Introduction to Fall Protection 2nd edn, pp 107-111, ASSE, Des Plaines, Illinois.

European Commission Communication 2000/C 40/05 – in the framework of the implementation of Council Directive 89/686/EEC of 21 December 1989 in relation to personal protective equipment (2000), Official Journal of the European Communities C40 p8, February 12, 2000.

Feathers L. J. (1998) Private communication between L J Feathers, independent consultant of L & G Associates and Safety Squared.

Finch A. (2003) Private communication between A Finch, DTI, and Safety Squared.

Fuller, G. A., Jackson C. M., Rice, R. C. and Jentgen, R. L. (1980) “Evaluation of Wire Alloys for Aircraft Carrier Arresting Gear”, Proceedings of the 50th Annual Convention of the Wire Association International Inc Cincinnati, Ohio, USA, Oct 1980.

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Health and Safety at Work Act (1974) (19th edn.), Controller and Chief Executive of Her Majesty’s Stationery Office and Queen’s Printer of Acts of Parliament, London.

Health and Safety Commission (2003) Consultation Document 192 – Proposals for Work at Height Regulations [online], Health and Safety Commission. Available from: http://www.hse.gov.uk/consult/condocs/cd192.htm [Accessed December 4 2003].

Health and Safety Executive (1985) Deadly Maintenance – A Study of Fatal Accidents at Work, HSE Books, Health and Safety Executive, Suffolk CO10 2WA.

HSG 33 – Health and Safety in Roofwork (1998), HSE Books, Health and Safety Executive, Suffolk.

Health and Safety Laboratory (2002) Assessment of Factors That Influence the Tensile Strength of Safety Harness and Lanyard Webbings – Part 1 - Main Report, Report No HSL/2002/16, Health and Safety Laboratory, Buxton, United Kingdom.

INDG 367 – Inspecting Fall Arrest Equipment made from Webbing or Rope (2002), HSE Books, Health and Safety Executive, Suffolk.

ISO/CD 16024 – Personal Protective Equipment for Protection Against Falls from a Height – Flexible Horizontal Lifeline Systems - Document Reference No. ISO/TC 94/SC4 N251 (1999), International Organisation for Standardization, Geneva, Switzerland.

Johnson B. (1991) Private communication between B Johnson, at the time Managing Director of P. A. Safety Systems Pty Ltd. and D Riches, Technical Director of Barrow Hepburn Sala Ltd.

Lobert H (2004) Results on drop tests – Energy absorber with lanyard, 12mm diameter, total length 2 m, fall factor 1. Deutsche Montan Technologie GmbH, Pruflaboratorium fir Bautreilsicherheit, D-44807 Bochum, Germany.

Management of Health and Safety at Work at Work Regulations (1999) & Guidance L21, HSE Books, Health and Safety Executive, Suffolk.

Monks K.E. (1990) A Report on Detail Tests on Horizontal Lifeline Sample Ropes, Nuclear Electric Report No TD/BNL/REP/341, September 1990, Structural Test Centre, Nuclear Electric plc, Cheddar, Somerset, UK.

Monks K.E. (1991) A Report on Horizontal Lifeline Testing, Nuclear Electric Report No TD/BNL/REP/386, August 1991, Structural Test Centre, Nuclear Electric plc, Cheddar, Somerset, UK.

National Engineering Laboratory (2004) Archived U-matic Tape Footage DVD No.3, TUV­NEL, East Kilbride, Glasgow, UK.

Occupational Health and Safety Administration (1999) OSHA Preambles – Fall Protection in the Construction Industry – III Summary and Explanations [online], OSHA. Available from: http://www.osha-slc.gov/Preamble/Fall_data/ [Accessed July 19 1999].

Personal Protective Equipment at Work Regulations (1992) & Guidance L25, HSE Books, Health and Safety Executive, Suffolk.

Personal Protective Equipment (EC Directive) Regulations (1992), Statutory Instrument 1992 No. 3139, The Stationery Office Ltd, London.

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Personal Protective Equipment Regulations (2002), Statutory Instrument 2002 No. 1144, The Stationery Office Ltd, London.

prEN 365 (2003) – Final Draft - Personal Protective Equipment Against Falls From a Height - General Requirements for Instructions for Use, Maintenance, Periodic Examination, Repair, Marking and Packaging European Committee for Standardization (CEN), Brussels.

Queensland Government – Workplace Health and Safety Queensland – Static Line Fall Arrest Systems (2002), Department of Industrial Relations, Queensland Government, Australia.

Riches D. (1992a) LIFE – Horizontal Lifeline Analysis Program – Instructions for Use, Barrow Hepburn Sala Ltd, Bristol, UK.

Riches D. (1992b) Sayfglida Lecture Notes, DBI Sala, February 12-13 1992, Barrow Hepburn Sala Ltd, Bristol, UK.

Riches D. (1997) “Some design principles of horizontal fall protection systems”, Safety and Health Practitioner, 15 [6] 17-21.

Riches D. (1998) “Fall Protection” in Tullet S. (ed) (1998) Health and Safety at Work, pp F2­F5, Croner Publications Ltd, Surrey.

Riches, D. and Feathers, L. J. (1998) “Research, Development and Testing of Multiple Span Multiple Use Horizontal Lifelines from the Designer’s Perspective” Proceedings of the International Fall Protection Symposium, Wuppertal, Germany, International Society for Fall Protection, Toronto.

Riches D. (2002) Analysis and evaluation of different types of test surrogate employed in the dynamic performance testing of fall arrest equipment, Contract Research Report No 411/2002, Health and Safety Executive, HSE Books, Suffolk, UK.

Riches D. (2003) Private e-mail between D Riches, CEN/TC 160 WG1 Convenor, and M-C Heloire, CEN PPE Standards.

Seddon P. (2002) Harness Suspension: Review and Evaluation of Existing Information, Contract Research Report No 451/2002, Health and Safety Executive, HSE Books, Suffolk, UK.

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Steinberg H. L. (1977) A Study of Personal Fall-Safety Equipment, Report No NBSIR 76-1146, National Bureau of Standards, Dept of Commerce, Washington D.C. 20234.

Sulowski, A. C. and Miura, N. (1983) Horizontal Lifelines, Report No 83-294-H, Mechanical Research Dept, Ontario Hydro Research Division, Toronto, Ontario, Canada.

Sulowski, A. C. (1991) “Fall Arresting Systems – Selection of Equipment” in Sulowski A. C. (ed.) (1991) Fundamentals of Fall Protection pp 303-320, International Society for Fall Protection, Toronto.

Wolner T. (1992) Private communication between T Wolner, at the time Senior Engineer of DBI Sala Inc. and D Riches, Technical Director of Barrow Hepburn Sala Ltd.

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7. APPENDIX:ARCHIVED NEL CINE FILM, U-MATIC TAPE AND VIDEO TAPE

In the course of the research, a number of cine films, “U-matic” tapes and video tapes were discovered in the National Engineering Laboratory (NEL) archives, which, from the title labels, were felt to be of importance to present and future research.

With permission from the NEL, a review of the material was made, and copies that were of relevance to HSE research were transferred onto DVD format. (Not every item was transferred).

The majority of the material relates to UK fall-arrest research dating back to the 1970’s, and a list giving brief details of each item can be found in Tables 11-13.

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Table 11 List of archived cine film

No. Date / title / details Contents / comments

1 4/2/83 Cine film: “Harness arrester drop tests”

Pre-NEL “Ministry of Technology” authorship; in-house test programme. Rope grab drop-testing with weights and with full dummy. Full dummy testing involves release of dummy on vertical ladder in various pre-release poses so as to fall backwards away from ladder. Some tests with full harness, some with waist belt. Some non-arrests. Very relevant to safety hoop / fall arrest system project. Transferred to DVD No 1.

2 16/6/72 & 27/4/73 Cine film: “Harness drops”

Pre-NEL “Ministry of Technology” authorship; in-house test programme. Drop tests of full dummies using fixed length lanyard. Accelerometer cable plugged into dummy’s head. Some tests with full harness, some with waist belt. Different harness attachment points used. Grid square back drop for measuring suspension angle. Very much of interest to HSE research. Transferred to DVD No 1.

3 10/5/78 Cine film: Simulations of falls away from wood pole with dummy wearing work “6A harness” positioning belt-sit harness and connected by strap. View is

perspective rather than elevation. Dummy is orange in colour with back skull cover; accelerometer cable is plugged into back of skull. Variation of pre-release posture. Of interest to HSE research. Transferred to DVD No 1.

4 17/11/72 Cine film: Short film of two or so drop tests of dummy with accelerometer cable “NEL 1335 ref 168/7 plugged into back of head. Gridline/box backdrop. Attachment at test No 1A00” both side D's. Of limited use. Not transferred.

5 17/11/72 Cine film: Short film of three or so drop tests. Dummy with accelerometer cable “Test Nos 5A A01, 6A plugged into back of head. Fixed length lanyard. Gridline/box A01” backdrop. Attachment at both side D’s. Also torso dummy drop

which fell to ground. Of limited use. Not transferred.

6 16/6/72 & 27/4/73 Pre-NEL “Ministry of Technology” authorship; in-house test Cine film “Tests 2D D01, 4C

programme. Long film made from 5 films spliced together. Drop tests of full dummies using fixed length lanyard. Accelerometer cable

D01” plugged into dummy’s head. Some tests with double waist attachment at side D’s. Trampoline present to catch dummy in case of lanyard failure. Some tests with full harness, some with chest harness, some with waist belt. Different harness attachment points used. Of interest to HSE research. Transferred to DVD No 1.

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8

9

Table 11 List of archived cine film

No. Date / title / details Contents / comments

7 Cine film: “Test Nos 1BB, 4CC, 4CA, 4CD”

Simulations of falls outside on yellow A-frame using blue dummy. Background is the inside corner of some office buildings – not any use from a scientific viewpoint. Perspective view rather than elevation. Trampoline is present to allow for test failures. White lanyard attached to various attachment points on harness. Some fall motion in some shots is lost (the pre-release shot suddenly transforms to the post-fall suspension shot). Of limited use. Not transferred.

Cine film: Various drop tests with Sierra Stan dummy. Martin Shelley in “Test Nos 8B A01 and background. Accelerometer cable plugged into dummy’s head. Of 8C A01” limited use. Not transferred.

Cine film: Film shows the winding of a weight up an electricity pylon. Weight “Inertia brake test on released and is allowed to fall at constant speed to ground. Looks like pylons” the test of a descender device although device not readily apparent.

Snow on ground. Of limited use. Not transferred.

10 Cine film: no title As before in item 7. Very short film shows simulations of falls outside on yellow A-frame but using Sierra Stan dummy. Background is the inside corner of some office buildings – not any use from a scientific viewpoint. Perspective view rather than elevation. The two or so drops shown involve two straps attached at front shoulder points, rather like parachute harness suspension. Trampoline present. Of limited use. Not transferred.

11 25/6/73 & 26/6/73 Graduated cross backdrop. Drop tests of full dummies using fixed Cine film: length lanyard. Accelerometer cable plugged into dummy’s head. “Tests 1A01, 2A01” Tests with double waist attachment at side D’s. Short film of limited

value. Not transferred.

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Table 12 List of archived U-matic tapes

No. Date / title / details Contents / comments

12 17/6/87 U-matic: “Drop tests”

Choke hitch tests performed over L section. Not high speed film, only video. Close up of karabiner failing on girder. Relevant to HSE edge research. Transferred to DVD No 2.

13 22/5/85 U-matic: “Comparison drops of safety belts & harnesses” Telecine

Produced by the Reliability of Safety Equipment Section, NEL. Circa 1975. Finished versions of item numbers 7 and 10 above, and has commentary. Educational video. Relevant to HSE research. Transferred to DVD No 2.

14 27/11/90 U-matic: “Harness testing in Stephenson building”

High speed filming of static test on parachute harness strap. Of no interest to HSE research. Not transferred.

15 U-matic: “Stockland hill slow motion sequences”

Film shows cage of weights being repeatedly arrested on inclined cable. Of no interest to HSE research.

16 17/6/82 U-matic: “Drop tests on ladder fall arrest systems and various harness / lanyard combinations”

Film shows the response of anthropometric dummy to simulated falls on ladder mounted fall arrest systems. Shows the typical problem of falling back away from ladder, the famous inverted fall to the ground, and drops whilst attached to the waist side D. Extremely relevant to safety hoop/fall arrest research. Transferred to DVD No 2.

17 26/4/84 U-matic: “Tower maintenance and inspection”

Promotional film of BT’s use of “Sureaccess system” and trouser harness and retractable arresters. Also some human falls whilst attached to arrest systems are shown (stumbles off towers). Relevant to HSE research. Transferred to DVD No 2.

18 17/6/82 & 14/7/82 U-matic: “Harness tests at Rugby radio station”

Drop tests simulating falls from a tower using retractable arresters, rope grabs and ladder systems. Relevant to HSE research. Transferred to DVD No 2.

19 15/12/82 U-matic: “Rugby dummy tests”

Drop tests simulating falls from a tower using ladder mounted fall arrest system and dummy. Shows leg interference problems with tower and effects of using waist side Dee on belt. Also shows tests using small inertia reel attached to harness. Very relevant to HSE research. Transferred to DVD No 2.

20 3/1/84 U-matic: “Rugby dummy tests re-edit”

As per item 19 but promotional video with full commentary interspersed with actual use of product. Very relevant to HSE research. Transferred to DVD No 2.

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Table 12 List of archived U-matic tapes

No. Date / title / details Contents / comments

21 28/8/87 U-matic: “Construction Steel Tests” three tapes

Testing of falls onto anchors formed by steel angles using choke hitches and other anchor devices. Very relevant to HSE research. Transferred to DVD No 3.

22 Oct 1985 U-matic: “horizontal line tests” two tapes

Testing of horizontal lines. Relevant to HSE research. Transferred to DVD No 3.

Table 13 List of archived video tapes

No. Date / title / details Contents / comments

23 1989 Video: Relevant to HSE research. Transferred to DVD No 4. “Lanyard tests”

24 29/3/90 Video: Previous HSE research showing swing falls simulated with full “Tree climbers sit belts dummy. Relevant to HSE research. Transferred to DVD No 4. & harnesses”.

25 Video Inverted falls. Relevant to HSE research. Transferred to DVD No 4. “Secam harness tests”

26 Video Promotional video about harness suspension. Relevant to HSE “Hanging in harness – research. Transferred to DVD No 4. Dr Amphoux”

127

Printed and published by the Health and Safety ExecutiveC30 1/98

Printed and published by the Health and Safety Executive C1.10 11/04

ISBN 0-7176-2892-2

RR 266

78071 7 628926£20.00 9