Guide to safety analysis for accident prevention

348 Pages·2013·1.94 MB·English

Guide to safety analysis
for accident prevention
Lars Harms-Ringdahl
www.irisk.se
IRS Riskhantering AB
Guide to safety analysis for accident prevention

Copyright © 2013 Lars Harms-Ringdahl
All rights reserved. This is a non-commercial work; no content may be sold
for profit or distributed without the written permission of the copyright
holder.

The electronic version is subject to revision; it is not permitted to put copies
on the internet without the prior permission of the copyright holder.

Drawings by Nils Peterson
Diagrams and photos by the author

Published by IRS Riskhantering AB,
Bergsprängargränd 2A, Stockholm, Sweden
www.irisk.se

ISBN 978-91-637-3164-8

The updated electronic version can be found www.irisk.se/sabook

Paperback

Also available as paperback: www.shopmybooks.com
In the Nordic countries: www.gmlforlag.se
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Contents

Preface 7
1 Accidents in a systems perspective 12
1.1 The accident concept 12
1.2 The size of the accident problem 16
1.3 Critical accidents 19
2 Safety work and accident prevention 20
2.1 Safety work 20
2.2 Elements in safety work 21
2.3 Theories and principles 25
2.4 Assumptions and priorities 32
2.5 A challenge 34
3 A framework for safety analysis 35
3.1 A starting point 35
3.2 Safety analysis procedure 38
3.3 Safety analysis in context 41
3.4 The probabilistic tradition 44
3.5 An accident investigation framework 47
3.6 Relationships 51
3.7 In conclusion 53
4 A brief summary of methods 54
4.1 Selection of methods 54
4.2 Types of methods 55
4.3 Examples of methods 57
4.4 Do we need more than one method? 59
5 Evaluation of risks and systems 61
5.1 Basics of evaluation 61
5.2 Direct Risk Evaluation 68
5.3 Quantitative evaluations 73
5.4 The Risk Matrix 76
5.5 Other evaluation approaches 84
5.6 Critical issues 86
6 Energy Analysis 91
6.1 Principles 91
6.2 Energy Analysis procedure 92
6.3 Example 97
6.4 Comments 100
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7 Direct Hazard Analysis 104
7.1 Principles 104
7.2 Job Safety Analysis 107
7.3 Example of a Job Safety Analysis 111
8 Deviation Analysis 116
8.1 On deviations 116
8.2 Principles of Deviation Analysis 118
8.3 Deviation Analysis procedure 126
8.4. Examples 130
8.5 Comments 136
9 Hazop 140
9.1 Principles 140
9.2 Hazop procedure 142
9.3 Hazop example 144
9.4 Hazop comments 148
10 Fault Tree Analysis 151
10.1 Introduction 151
10.2 Principles and symbols 152
10.3 Fault Tree Analysis procedure 154
10.4 More on Fault Tree Analysis 159
10.5 Strict and informal fault trees 165
10.6 Example of a fault tree 168
10.7 Comments 173
11 Barriers and safety functions 176
11.1 The analysis of safety 176
11.2 Barrier concepts and methods 177
11.3 Concept of safety function 181
11.4 Safety Function Analysis 185
11.5 Evaluation of SFs 189
11.6 Improvements to safety functions 196
11.7 Example 198
12 Some further methods 204
12.1 Introduction 204
12.2 Failure Mode and Effects Analysis 206
12.3 Event Tree Analysis 208
12.4 Cause-Consequence Diagrams 211
12.5 Human error methods 213
12.6 Task Analysis 217
12.7 Management-oriented methods 219
12.8 Coarse analyses 224
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13 Methods for event analysis 228
13.1 Introduction 228
13.2 STEP 232
13.3 Simple Event Mapping 235
13.4 The AEB method 239
13.5 Events and Causal Factors Analysis 242
13.6 MTO Analysis 244
13.7 AcciMap 247
13.8 Change Analysis 254
13.9 Deviation Analysis of events 255
13.10 Safety Function Analysis of events 259
13.11 Tree analysis of events 262
14 Planning and implementation 264
14.1 Decisions before the analysis 264
14.2 Performing the analysis 268
14.3 Improvements and conclusions 270
14.4 Reporting and decisions 273
14.5 Quality aspects 274
15 Choice and summary of methods 277
15.1 Basic considerations 277
15.2 Methods of system analysis 278
15.3 Methods of event analysis 283
15.4 Methods of evaluation 288
15.5 Choosing method 291
16 Examples of safety analysis 295
16.1 Introduction 295
16.2 Analysis of incidents in hospital care 296
16.3 Household gas fire 301
16.4 Accident investigation at a workshop 306
16.5 Safety analysis at a workshop 309
16.6 Safety analysis of a school kitchen 314
16.7 Safety analysis at a medical care centre 319
16.8 Safety analysis of an outdoor convention 323
16.9 Analysis at a pharmaceutical company 326
17 Concluding remarks 332
18 References 333
19 Index 345
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Preface
This book is about safety analysis as a tool for accident prevention. The
methods can be used to analyse systems and to investigate accidents, and
thereby generate knowledge for systematic improvements.
The prevention of accidents is an extensive and complex subject. In the
accident prevention arena, many practices and theories exist side by side.
There are different traditions involved in explaining accidents, and
investigating, and preventing them. The variations are not necessarily
problematic, but they suggest that accident prevention in practice is not as
efficient as it could be.
The variety is fascinating in many ways, and I have had the opportunity
to see it from different perspectives and in various roles. Over the years, I
have had the privilege to work with safety in a number of fields. At the
beginning, it was in the industrial sector, including paper mills, and the
engineering, chemical, and pharmaceutical industries, where the focus was
on occupational accidents. In stages, my scope has widened to encompass
other areas, and it has been interesting to test the arsenal of industry-based
methods in new settings. Examples are:
• Power production
• Railway and other transportation
• Hospital care
• Emergency services
• Safety work at societal level
There are many similarities between safety analyses and accident
investigations, and often similar methods can be applied. It is also possible
to apply a general methodology that can be efficiently applied in many
different sectors. This has been one of my motives in attempting to write a
generalised description of safety analysis and how it can be applied.

Safety analysis
Safety analysis is a central concept in this book, and it is here defined as a
procedure for analysing systems in order to identify and evaluate hazards
and safety characteristics. The definition is wide, and covers many ways of
analysing. It includes quantitative and qualitative risk analyses, accident
investigations, and also some other applications. The rationale for this wide
scope will be discussed further on.
8 Guide to safety analysis

Safety analysis can be used to:
• Support efficient accident prevention.
• Contribute to an understanding of how accidents can occur at the
specific workplace under examination.
• Increase awareness and communication.
• Demonstrate systematic safety work.

About this book
The aim of this book is to explain general methods of safety analysis, which
can be used for accident prevention in different fields. The idea is to give
simple straightforward descriptions, and relate them to practical
experiences. The ambition is to promote wider use of the methodology,
which offers a potential for better accident prevention.
The book builds further on earlier publications (Harms-Ringdahl, 1987,
1993, 2001), which had a focus on occupational accidents. The material has
been developed from the specialised literature, and from the author’s own
work on the analysis and prevention of accidents. Many important lessons
have been learned from teaching on training courses in safety analysis and
accident investigation.
The most obvious feature of the new book is that it will be published as
an electronic book that is free to download. The reason for this is that it will
make for a larger circulation, which will spread the methodology more
widely. There will be no economic obstacles to looking at the book, and if it
is found useful, it can be applied directly.
There are other advantages to having an electronic version, since you
can easily search and jump between pages. The use of links makes it easy to
look at other references. But some people prefer paper versions, and it is
possible to obtain a print-on-demand version.

General comments
The ambition has been to be general in descriptions, since the principles of
many methods can be applied to different types of systems. This might
make the descriptions harder to follow, but, on the other hand, it makes the
methodology more general applicable.
The book suggests a general framework for accident prevention and
safety analysis. Several methods of analysis will be described. Some
selected methods are thoroughly described and practical suggestions given –
almost like in a cookbook. The intention is that the reader should get
sufficient advice to perform a fairly good analysis on the basis of the
description.
Preface 9

The general perspective means that the methodology can be applied to a
variety of systems and situations where safety is an important issue. They
may concern a mechanical workshop, a ward at a hospital, or children in a
school. They all have it in common that some kind of organised activity is
involved. The word company comes up throughout the book, and this
should usually be interpreted in a wide sense. It refers to any type of
organised activity in the public or private sector.
Safety analyses and accident investigations have many common
features, which will be further explained in the framework discussion
(Chapter 2). Both approaches can be applied:
• To identify problems and hazards in a given situation, e.g., in a
workplace
• To understand how a situation can be made safer
• To develop safety improvements
• To be important tools for safety management within the organisation

The basic idea underlying the book is to show how safety analysis can be
practically applied. Its emphasis lies on explaining how different methods
work. It is important to consider theories of accident causation, system
behaviour, management, human error, and so on. However, they are kept to
a minimum in order to limit the number of pages. The reason for this is that
the book is mainly intended as a guide for people who would like to employ
the methodology. For this reason, there is no stress on theory. A
bibliography is provided for those who want to go further theoretically.
Looking in the literature, you will find a large number of different
methods, which are more or less thoroughly documented. The book presents
a set of methods that are described in detail, and a selection of others that
are more cursorily explained. Chapter 4 gives a short overview, and a more
extensive one can be found in Chapter 15. The main focus is on qualitative
methods, which can be beneficial in large application areas. Quantitative
and probabilistic methods are only briefly presented. One reason for this is
that there is already a large literature available, which is more directed at
technical and/or hierarchical systems.

Sections in the book
The book is built up in four major sections:
1) Background to and framework for analysis
2) Methods of analysis
3) Planning and accomplishment
4) Examples
10 Guide to safety analysis
The framework section concerns the analytic procedure, i.e., the various
stages that make up an analysis and how these are related to one another.
This section also aims to give a perspective on how you can get an
integrated and consistent framework for how different methodologies can
be applied.

The method section presents a number of methods. It starts with techniques
for risk evaluation, such as the risk matrix. The book describes methods for
both analyses of systems and accident investigations. The number of
existing methods is large, and a limited selection has therefore been made.

The planning section discusses the practical aspects of an analysis. One
basic step is to define the aim of the analysis and the type of results desired.
In order to achieve this, careful planning is essential. An analysis should be
seen as a supplement to a company’s own safety activities. The section also
considers quality aspects, as well as arguments for and against specific
methods of safety analysis.

The examples section presents case studies of accident investigations and
analyses of systems from different application areas.

Use and practical reading
This book is primarily intended for practitioners, but may also be useful for
researchers. Persons most interested in practical applications can skip over
several of the chapters. An important readership consists of those who
intend to do some kind of a safety analysis themselves, such as:
• Safety professionals
• Fire engineers
• Designers
• Consultants in different specialities

Another important group consists of persons who, in one way or another,
have an interest in the results of an analysis:
• The customer, who is to commission an analysis and get a sufficiently
good result
• The manager, who can use safety analysis to support the planning of a
new system
• Other stakeholders, such as employees, whose safety is concerned
• Safety committee members, who want to be able to question
management on what methods have been used to assess risks
• Officials from a supervising authority, who need to know if an
analysis is accurate enough