Introduction to Ergonomics PDF

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Introduction to Ergonomics Essential Reading Ergonomics for Beginners, 2nd edition Jan Dul, Erasmus University, The Netherlands and B. A. Weerdmeester, TNO Institute, The Netherlands Taylor & Francis Pbk 0-7484-0825-8 A Guide to Methodology in Ergonomics: Designing for Human Use Neville Stanton...

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Introduction to Ergonomics

Essential Reading

Ergonomics for Beginners, 2nd edition Jan Dul, Erasmus University, The Netherlands and B. A. Weerdmeester, TNO Institute, The Netherlands Taylor & Francis Pbk 0-7484-0825-8 A Guide to Methodology in Ergonomics: Designing for Human Use Neville Stanton and Mark Young, Brunel University, UK Taylor & Francis Pbk 0-7484-0703-0 Fitting the Task to the Human, 5th edition K. Kroemer and E. Grandjean Taylor & Francis Hbk 0-7484-0664-6; Pbk 0-7484-0665-4 Evaluation of Human Work, 2nd edition John Wilson and Nigel Corlett, The University of Nottingham, UK Taylor & Francis Hbk 0-7484-0083-4; Pbk 0-7484-0084-2

For price availability and ordering visit our website www.ergonomicsarena.com Alternatively our books are available from all good bookshops.

Introduction to Ergonomics

R.S. Bridger

First edition published 1995 by McGraw-Hill, Inc. This edition published 2003 by Taylor & Francis 11 New Fetter Lane, London EC4P 4EE Simultaneously published in the USA and Canada by Taylor & Francis Inc, 29 West 35th Street, New York, NY 10001 Taylor & Francis is an imprint of the Taylor & Francis Group This edition published in the Taylor & Francis e-Library, 2003. © 2003 Robert Bridger All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. Every effort has been made to ensure that the advice and information in this book is true and accurate at the time of going to press. However, neither the publisher nor the authors can accept any legal responsibility or liability for any errors or omissions that may be made. In the case of drug administration, any medical procedure or the use of technical equipment mentioned within this book, you are strongly advised to consult the manufacturer’s guidelines. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data A catalogue record has been requested ISBN 0-203-42613-4 Master e-book ISBN

ISBN 0-203-44054-4 (Adobe eReader Format) ISBN 0-415-27378-1 (pbk) 0-415-27377-3 (hbk)

Para Barbara, Daniella y Angelo

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Contents

Preface to the second edition 1 Introduction

xii 1

The focus of ergonomics 2 Ergonomics and its areas of application in the work system 10 A brief history of ergonomics 11 Attempts to ‘humanise’ work 19 Modern ergonomics 21 Effectiveness and cost effectiveness 26 Future directions for ergonomics 31 Summary 31 Essays and exercises 32 2 Anatomy, posture and body mechanics

33

Some basic body mechanics 34 Anatomy of the spine and pelvis related to posture 36 Postural stability and postural adaptation 42 Low back pain 44 Risk factors for musculoskeletal disorders in the workplace 48 Behavioural aspects of posture 53 Effectiveness and cost-effectiveness 55 Research directions 56 Summary 56 Essays and exercises 57 3 Anthropometric principles in workspace and equipment design Designing for a population of users 58 Sources of human variability 58 Anthropometry and its uses in ergonomics 60 Principles of applied anthropometry in ergonomics 69 Application of anthropometry in design 76 Design for everyone 79

58

viii Contents Anthropometry and personal space 83 Effectiveness and cost-effectivness 84 Research directions 86 Summary 86 Essays and exercises 87 4 Static work: Design for standing and seated workers

89

Fundamental aspects of standing and sitting 90 An ergonomic approach to workstation design 96 Design for standing workers 103 Design for seated workers 107 Worksurface design 110 Visual display units 112 Guidelines for the design of static work 113 Effectiveness and cost-effectivness 116 Research directions 118 Summary 119 Essays and exercises 120 5 Design of repetitive tasks

121

Introduction to work-related musculoskeltal disorders 121 Injuries to the upper body at work 128 Review of tissue pathomechanics and WMSDs 129 Disorders of the neck 134 Carpal tunnel syndrome 137 Tennis elbow (epicondylitis) 139 Disorders of the shoulder 140 Lower limbs 142 Ergonomic interventions 143 Trends in work-related musculoskeltal disorders 151 Effectiveness and cost-effectivness 153 Research directions 156 Summary 156 Essays and exercises 157 6 Design of manual handling tasks Anatomy and biomechanics of manual handling 158 Prevention of manual handling injuries in the workplace 161 Design of manual handling tasks 171 Carrying 178 Effectiveness and cost-effectiveness 184 Research issues 186

158

Contents ix Summary 186 Essays and exercises 186 7 Work capacity, stress and fatigue

187

Stress and fatigue 187 Muscles, structure, function and capacity 188 The cardiovascular system 199 The respiratory system 200 Physical work capacity 200 Factors affecting work capacity 205 Effectiveness and cost-effectiveness 210 Research issues 212 Summary 212 Essays and exercises 213 8 Industrial applications of physiology

214

Measurement of the physiological cost of work 215 Applied physiology in the workplace 218 Fitness for work 223 Effectiveness and cost-effectiveness 228 Research issues 230 Summary 230 Essays and exercises 231 9 Heat, cold and the design of the physical environment

233

Fundamentals of human thermoregulation 233 Measuring the thermal environment 235 Thermoregulatory mechanisms 237 Work in hot climates 239 Work in cold climates 242 Skin temperature 246 Protection against extreme climates 247 Comfort and the indoor climate 250 ISO standards 256 Effectiveness and cost-effectiveness 256 Research directions 260 Summary 260 Essays and exercises 261 10 Vision, light and lighting Vision and the eye 262 Measurement of light 274

262

x Contents Lighting design considerations 278 Visual fatigue, eyestrain and near work 286 Psychological aspects of indoor lighting 288 Effectiveness and cost-effectiveness 289 Research issues 293 Summary 293 Essays and exercises 293 11 Hearing, sound, noise and vibration

295

Terminology 296 The ear 296 Measurement of sound 303 Ear protection 309 Design of the acoustic environment 311 Industrial noise control 314 Noise and communication 317 The auditory environment outdoors 317 Effects of noise on task performance 318 Non-auditory effects of noise on health 319 Noise and satisfaction 320 Vibration 321 Effectiveness and cost effectiveness 323 Research issues 327 Summary 327 Essays and exercises 328 12 Human information processing, skill and performance

329

A general information processing model of the user 329 Cognitive systems 351 Problem solving 352 Effectiveness and cost-effectiveness 357 Research issues 358 Summary 358 Essays and exercises 358 13 Displays, controls and virtual environments Principles for the design of visual displays 360 Auditory displays 375 Design of controls 379 Combining displays and controls 386 Virtual (‘synthetic’) environments 392 Effectiveness and cost-effectiveness 396 Research issues 399

360

Contents xi Summary 399 Essays and exercises 400 14 Human–computer interaction, memory and language

401

Human-centred design processes for interactive systems 402 Designing information in external memory stores 407 Human-computer dialogues 413 Memory and language in everyday life 418 Effectiveness and cost-effectiveness 427 Research issues 433 Summary 434 Essays and exercises 434 15 Human–machine interaction, human error and safety

436

Human error and equipment design 436 Mental workload in human machine interaction 442 Psychological aspects of human error 445 Characterising human–machine interaction 454 GOMS 459 Prevention of error in human–machine interaction 460 Accidents and safety 467 Effectiveness and cost-effectiveness 471 Research issues 475 Summary 476 Essays and exercises 476 16 System design: organisational and social aspects

477

Systems design methods for ergonomics 477 Organisational aspects: some macroergonomic examples 481 Psychosocial factors 495 Litigation 503 Cross-cultural considerations 504 Effectiveness and cost-effectiveness 505 Research directions 507 Summary 507 Essays and exercises 508 Further reading References Index

509 511 543

Preface to the second edition

Can it work, does it work, is it worth it?1 These three questions have been foremost in my mind throughout the revision of ‘Introduction to Ergonomics’. In revising and updating the text, I have tried to attain three goals. First, to update the scientific content of the book to reflect the state of our knowledge at the beginning of the twenty-first century. Second, to maintain the book’s essential character as a general introductory text that teaches the basic science that ergonomists use at work. Third, to add new material at the end of every chapter to answer the three questions above. There is a great deal of evidence that ergonomics does work. It really does improve the interactions between people and machines and it really can make systems work better. How to demonstrate this has been one of the challenges in the process of revision. Several criteria have influenced the selection of supporting evidence. It would be ideal if evidence for the benefits of all of the diverse practices and subdisciplines of ergonomics came in the form of randomised controlled trials with double-blind application of treatments to satisfy even the most sceptical reviewer. This is not the case, and it never can be, so I have tried to present a variety of evidence that best exemplifies what each particular area has to offer. The evidence comes in the form of field trials, field experiments, longitudinal studies and even a few laboratory experiments. Such a variety of research methods will never please everyone – what satisfies the university academic may seem dry and other-worldly to the production manager. Uncontrolled trials in real factories may not impress the academic, but practitioners may find therein much useful ammunition for arguing their cause. Another theme that is pursued throughout the book is that engineering and design are increasingly driven by standards. Probably the best evidence that the value of ergonomics is now recognised is the publication of international standards for ergonomics. These standards are paving the way for a new, quantitative and much more precise form of practice. With this in mind, I have tried to inform the reader about these standards, wherever possible (with the rider that this is a textbook, not a design manual). The reader is encouraged to use these standards in practice and, with due deference to national bodies, the International Organization for Standardization (IOS) is recommended as the first port of call. In keeping with these modern trends, some new essays and exercises have been added to encourage the learning of quantitative skills. Some of the older, perhaps 1

Haynes. 1999. Can it work? Does it work? Is it worth it? British Medical Journal, 319 (Sep. 11): 652– 653.

Preface to the second edition xiii more frivolous, illustrations have been replaced by new drawings illustrating modern research in ergonomics. These have been rendered, in her customary ‘estilo cuadradito’, by Rina Araya, my graphic artist in Chile. Restrictions on the length of the book have led to some fairly ruthless editing to make way for new material. It is hoped that lecturers will continue to find much useful material to structure their courses and to illustrate the concepts of ergonomics and, at the end of their courses, that students will be able to give the following correct answers to the three opening questions: ‘Yes, it can, Yes, it does, Yes it is!’ R. S. Bridger Lee-on-the-Solent Hants, UK 2002

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Introduction 1

1

Introduction

In the past, the man has been first; in the future, the system must be first. (Frederick Winslow Taylor, The Principles of Scientific Management, 1911, p. 7)

Ergonomics is the study of the interaction between people and machines and the factors that affect the interaction. Its purpose is to improve the performance of systems by improving human machine interaction. This can be done by ‘designing-in’ a better interface or by ‘designing-out’ factors in the work environment, in the task or in the organisation of work that degrade human–machine performance. Systems can be improved by •

• • •

Designing the user-interface to make it more compatible with the task and the user. This makes it easier to use and more resistant to errors that people are known to make. Changing the work environment to make it safer and more appropriate for the task. Changing the task to make it more compatible with user characteristics. Changing the way work is organised to accommodate people’s psychological, and social needs.

In an information processing task, we might redesign the interface so as to reduce the load on the user’s memory (e.g. shift more of the memory load of the task onto the computer system or redesign the information to make it more distinctive and easier to recall). In a manual handling task, we might redesign the interface by adding handles or using lighter or smaller containers to reduce the load on the musculoskeletal system. Work environments can be improved by eliminating vibration and noise and providing better seating, desking, ventilation or lighting, for example. New tasks can be made easier to learn and to perform by designing them so that they resemble tasks or procedures that people are already familiar with. Work organisation can be improved by enabling workers to work at their own pace, so as to reduce the psychophysical stresses of being ‘tied to the machine’ or by introducing subsidiary tasks to increase the range of physical activity at work and provide contact with others. The implementation of ergonomics in system design should make the system work better by eliminating aspects of system functioning that are undesireable, uncontrolled or unaccounted for, such as

2 Introduction to ergonomics • • • • •

Inefficiency – when worker effort produces sub-optimal output. Fatigue – in badly designed jobs people tire unnecessarily. Accidents, injuries and errors – due to badly designed interfaces and/or excess stress either mental or physical. User difficulties – due to inappropriate combinations of subtasks making the dialogue/interaction cumbersome and unnatural. Low morale and apathy.

In ergonomics, absenteeism, injury, poor quality and unacceptably high levels of human error are seen as system problems rather than ‘people’ problems, and their solution is seen to lie in designing a better system of work rather than in better ‘man management’ or incentives, by ‘motivating’ workers or by introducing safety slogans and other propaganda. The name ‘ergonomics’ comes from the Greek words ‘ergon’, which means work and ‘nomos’ which means law.

The focus of ergonomics The focus is on the interaction between the person and the machine and the design of the interface between the two (Figure 1.1). Every time we use a tool or a machine we interact with it via an interface (a handle, a steering wheel, a computer keyboard and mouse, etc.). We get feedback via an interface (the dashboard instrumentation in a car, the computer screen, etc.) The way this interface is designed dertermines how easily and safely we can use the machine.

Recycling Waste products Rejects Accidents

BY-PRODUCTS

E Products H M

Energy

Energy (transformation) Knowledge

OUTPUTS

Matter

Information Injuries Absenteeism

BY-PRODUCTS

Heat Recycling

Figure 1.1 A simple work system. People interact with machines to turn inputs into outputs. System capacity refers to amount of input that can be processed over time. Productivity refers to the ratio of outputs to inputs. Efficient systems minimise by-products of all kinds (E = local environment, M = machine, H = human operator).

Introduction 3 When faced with productivity problems, engineers might call for better machines, personnel management might call for better-trained people. Ergonomists call for a better interface and better interaction between the user and the machine – better task design. Human–machine systems A system is a set of elements, the relations between these elements and the boundary around them. Most systems consist of people and machines and perform a function to produce some form of output. Inputs are received in the form of matter, energy and information. For ergonomics, the human is part of the system and must be fully integrated into it at the design stage. Human requirements are therefore system requirements, rather than secondary considerations and can be stated in general terms as requirements for • • • •

Equipment that is usable and safe Tasks that are compatible with people’s expectations, limitations and training An environment that is comfortable and appropriate for the task A system of work organisation that recognises people’s social and economic needs.

Compatibility – matching demands to capabilities Compatibility between the user and the rest of the system can be achieved at a number of levels. Throughout this book we will encounter compatibility at the biomechanical, anatomical, physiological, behavioural and cognitive levels. It is a concept that is common to the application of ergonomics across a wide range of settings and disciplines. In order to achieve compatibility, we need to assess the demands placed by the technological and environmental constraints and weigh them against the capabilities of the users. The database of modern ergonomics contains much information on the capabilities and characteristics of people and one of the main purposes of this book is to introduce the reader to this information and show how it can be used in practice. Ergonomic entropy (Karwowski et al., 1994) is disorder in system functioning that occurs owing to a lack of compatibility in some or all of the interactions involving the human operator. This incompatibility can occur for a variety of reasons, for example: •

•

•

Human requirements for optimum system functioning were never considered at the design stage (e.g. there was a failure to consult appropriate standards, guidelines or textbooks). Inappropriate task design (e.g. new devices introduce unexpected changes in the way tasks are carried out and these are incompatible with user knowledge, habits or capacity, or they are incompatible with other tasks). Lack of prototyping (e.g. modern software development is successful because it is highly iterative; users are consulted from the conceptual stage right through to pre-production protoypes).

Disorder in the way systems function usually costs money and examples of the economic benefits of ergonomics are given throughout the book.

4 Introduction to ergonomics Table 1.1 Basic interactions in a work system and their evaluationa Interaction

Evaluation

H > M: The basic control actions performed by the human on the machine. Application of large forces, ‘fine tuning’ of controls, stocking raw materials, maintenance, etc.

Anatomical: Body and limb posture and movement, size of forces, cycle time and frequency of movement, muscular fatigue. Physiological: Work rate (oxygen consumption, heart rate), fitness of workforce, physiological fatigue. Psychological: Skill requirements, mental workload, parallel/sequential processing of info...