IEC_61508_CRR373_2001_HSE_Human_Factors_in.pdf

HSEHealth&SafetyExecutiveProposed framework for addressinghuman factors in IEC 61508 Prepared byAmey VECTRA Limitedfor the Health and Safety ExecutiveCONTRACT RESEARCH REPORT373/2001HSEHealth&SafetyExecutiveProposed framework for addressinghuman factors in IEC 61508 Michael Carey BSc,MErgSAmey VECTRA LimitedEuropa House301 Europa BoulevardGemini Business ParkWestbrookWarringtonWA5 7YQUnited KingdomIEC 61508 is an international standard developed to provide a basis for conformity assessment on theapplication of electrical,electronic and programmable electronic(E/E/PE)safety-related systems.Thestandard recognises the need to address human factors,but provides minimal guidance as to whatthis entails.This report explores various issues that are involved in addressing human factors underIEC 61508.Firstly,existing human factors requirements within IEC 61508 are reviewed.Considerationis then given to a range of applications of E/E/PE systems in safety-related application to drawconclusions concerning the relationship between Safety Integrity Levels and required human factorseffort.A proposed framework is introduced with the purpose of relating required human factorsactivities and assurance processes to types of safety-related applications.The framework addressesways in which requirements for human factors may vary according to the integrity levels of thefunctions provided by a safety-related system.Finally,questions raised by the framework arehighlighted and discussed to stimulate debate prior to further development and application.This report and the work it describes were funded by the Health and Safety Executive(HSE).Itscontents,including any opinions and/or conclusions expressed,are those of the author alone and donot necessarily reflect HSE policy.HSE BOOKSii Crown copyright 2001Applications for reproduction should be made in writing to:Copyright Unit,Her Majestys Stationery Office,St Clements House,2-16 Colegate,Norwich NR3 1BQFirst published 2001ISBN 0 7176 2114 6All rights reserved.No part of this publication may bereproduced,stored in a retrieval system,or transmittedin any form or by any means(electronic,mechanical,photocopying,recording or otherwise)without the priorwritten permission of the copyright owner.iii ACKNOWLEDGEMENTS In developing the ideas in this report,valuable assistance has been provided by the HSE project officers,Mr Simon Brown and Mr Sarabjit Purewal.They have provided the author with assistance in keeping the framework simple and avoiding allowing the complexities of IEC 61508 to obscure some of the more obvious results of this research.Further thanks are due to the organising committee of the annual IEE Vacation School on Safety-Critical Systems and particularly Mr Ron Bell.They have continued to tolerate the authors regular lectures on human factors and have been prepared to debate some of the issues touched upon within this report,often into the early hours.Finally,much encouragement was provided by the late Dr Matthew Bransby during the progress of this research.He would have enthusiastically reviewed this report and no doubt had some valuable and incisive views on its content.iv v FOREWORD This report is a result of recently commissioned research into the development of a framework for addressing human factors in electrical,electronic and programmable electronic(E/E/PE)safety-related systems in the context of IEC 61508.The report is the opinion of the author alone and does not necessarily represent HSE policy.However,in situations where the human has an impact on the safety integrity of the E/E/PE safety-related system,the framework proposed in this report is intended to be the basis for further development work in this area.HSE invites comments on the practicability and effectiveness of the recommended approach and on any other aspect of human factor issues impacting on E/E/PE safety-related systems that is not considered to be addressed in this report.Please send your comments by 16 November 2001 to:Sarabjit Purewal Technology Division Electrical and Control Systems Unit Magdalen House Stanley Precinct Bootle Merseyside L20 3QZ vi vii CONTENTS Acknowledgements iii Foreword v Contents vii Executive Summary ix 1 Introduction 1 2 Objectives 3 3 Scope 5 4 Approach 7 4.1 Task 1:Identify Human Factors Requirements in IEC 61508 7 4.2 Task 2:Outline Current Human Factors Techniques 7 4.3 Task 3:Construct Outline Framework 7 4.4 Task 4:Apply to Sample Application Areas and Develop Framework 7 5 Human Factors in IEC 61508 9 5.1 Overview of the Standard 9 5.2 References to Human Factors in IEC 61508 9 5.3 Coverage of Human Factors Issues in the Standard 10 5.4 System Architectures Addressed by IEC 61508 11 5.5 Implications for Human Factors in Applying IEC 61508 14 6 Overview of Human Factors Methods 17 6.1 Background to Human Factors Methods 17 6.2 Key Elements of Human Factors Approaches 18 6.3 Human Factors Activities in the Context of the Safety Lifecycle 20 6.4 Human Factors Standar