The Blame Machine: Why Human Error Causes Accidents

Robert Whittingham

• Publisher: Routledge
• Year: 2004
• ISBN:
  9781136359576
• Edition: 1
• Topic: Technik & Maschinenbau
• Subtopic: Maschinen- und Anlagebau

The Blame Machine describes how disasters and serious accidents result from recurring, but potentially avoidable, human errors. It shows how such errors are preventable because they result from defective systems within a company. From real incidents, you will be able to identify common causes of human error and typical system deficiencies that have led to these errors. On a larger scale, you will be able to see where, in the organisational or management systems, failure occurred so that you can avoid them.The book also describes the existence of a 'blame culture' in many organisations, which focuses on individual human error whilst ignoring the system failures that caused it. The book shows how this 'blame culture' has, in the case of a number of past accidents, dominated the accident enquiry process hampering a proper investigation of the underlying causes.Suggestions are made about how progress can be made to develop a more open culture in organisations, both through better understanding of human error by managers and through increased public awareness of the issues. The book brings together documentary evidence from recent major incidents from all around the world and within the Rail, Water, Aviation, Shipping, Chemical and Nuclear industries. Barry Whittingham has worked as a senior manager, design engineer and consultant for the chemical, nuclear, offshore oil and gas, railway and aviation sectors. He developed a career as a safety consultant specializing in the human factors aspects of accident causation. He is a member of the Human Factors in Reliability Group, and a Fellow of the Safety and Reliability Society.

I

Understanding Human Error

1

To Err is Human

1.1 Defining Human Error

1.1.1 Introduction

Everyone makes mistakes. Human errors are a part of our everyday experience. A human error could therefore be defined quite simply as ‘someone making a mistake’. The reality is much more complex and before this book can proceed much further, it is necessary to produce some clear definition of human error and the way it is manifested. Many have tried and some have succeeded in defining human error. Some examples from various sources follow and are listed under the name of the author. In studying these definitions, it should be noted that each author has a distinct purpose in mind when formulating his definition and that the definition will be useful within that context. The objective here is to produce a final definition which will be suitable within the context of this book.

1.1.2 Swain and Guttman 1983

An error is an out of tolerance action, where the limits of tolerable performance are defined by the system.

Swain and Guttman 1983

This is an interesting definition because it allows the system response to determine whether an error has occurred. Thus a human error is a deviation from normal or expected performance, the deviation being defined by the consequence. The consequence is some measurable characteristic of the system whose tolerable limits have been exceeded, rather than the human action that contains the error. However, after the error has been made, the human action within which the error occurred can be examined to determine the cause of the deviation. Also useful here is the concept of an out of tolerance action, indicating that there are limitations to human performance which can be accepted without a human error having necessarily occurred.

1.1.3 Reason 1990

A generic term to encompass all those occasions in which a planned sequence of mental or physical activities fails to achieve its intended outcome, and when these failures cannot be attributed to some chance agency.

Reason 1990

Again, this definition focuses on the outcome or consequence of the action rather than on the action itself in order to determine if an error has occurred. In this definition it is recognized that the desired end result may follow a pre-planned sequence of human actions, which has to take place successfully before the result is achieved. Any one or more of the actions in the sequence may contain an error that causes the intended outcome not to be achieved. This closely reflects the reality of many industrial situations. The definition is also interesting in that it excludes random or chance events from the category of human error. This is discussed in more detail below.

1.1.4 Hollnagel 1993

An erroneous action can be defined as an action which fails to produce the expected result and/or which produces an unwanted consequence.

Hollnagel 1993

Hollnagel prefers to use the term ‘erroneous action’ rather than ‘human error’. The problem, according to Hollnagel, is that human error can be understood in different ways. Firstly, it can refer to the cause of an event, so that after an accident occurs, it is often reported that it was due to human error. Human error can also be a failure of the cognitive (or thinking) processes that went into planning an action or sequence of actions, a failure in execution of the action or a failure to carry out the action at all. Erroneous action defines what happened without saying anything about why it happened.

1.1.5 Meister 1966

A failure of a common sequence of psychological functions that are basic to human behaviour: stimulus, organism and response. When any element of the chain is broken, a perfect execution cannot be achieved due to failure of perceived stimulus, inability to discriminate among various stimuli, misinterpretation of meaning of stimuli, not knowing what response to make to a particular stimulus, physical inability to make the required response and responding out of sequence.

Meister 1966

This quite detailed definition perceives human actions as comprising three elements:

• Stimulus – the perception by the senses of external cues which carry the information that an action should be carried out.

• Organism – the way these stimuli are interpreted, the formulation of an appropriate action and the planning of how that action should be carried out.

• Response – the execution of the planned actions.

As with Reason’s definition, this emphasizes the reality that no single human action stands alone, but is part of a sequential process and that human error must be understood in the context of this. This principle will become abundantly clear as human error is examined in the light of accident case studies. When the events that precede a human error are found to have an influence on the probability of the error occurring, the error is referred to as a human dependent failure. In addition, although a human error may represent a deviation from an intended action, not every error necessarily leads to a consequence because of the possibility of error recovery. In fact many errors are recoverable, if they were not, then the world would be a much more chaotic place than it actually is. Error recovery is an extremely important aspect of the study of human error and will be dealt with in more detail later in this book, as will human error dependency.

1.1.6 Characterizing an Error

1.1.6.1 Intention to Achieve a Desired Result

A common element in all the above definitions is that for a human error to occur within an action, the action must be accompanied by an intention to achieve a desired result or outcome. This eliminates spontaneous and involuntary actions (having no prior conscious thought or intent and including the random errors which are discussed in more detail below) from the category of human errors to be considered in this book. To fully understand spontaneous and involuntary errors it is necessary to draw upon expertise in the fields of psychology, physiology and neurology, disciplines which are beyond the scope of this book which offers, as far as possible, a pragmatic and engineering approach to human error. Readers interested in delving further into these topics can refer to more specialist volumes.

1.1.6.2 Deciding if an Error has Occurred

One way of deciding whether or not an error has occurred is to focus on the actual outcome and compare this with the intended outcome. Then, it could be said, if the intended outcome was not achieved within certain limits of tolerability, an error has occurred. Such a definition would, however, exclude the important class of recovered errors mentioned above. If an error occurs but its effects are nullified by some subsequent recovery action, it would be incorrect to say that this was not a human error and need not be investigated. It is possible that on a subsequent occasion, the same error might occur and the recovery action not take place or be too late or ineffective, in which case the actual outcome would differ from the intended outcome. It must be true to say that the initiating error was always an error even if the final outcome was as intended, if it was necessary to carry out an intervening action successfully for the intended outcome to be achieved. The subject of error recovery is considered in detail in a later chapter.

1.1.6.3 The Significance of an Error

An important principle to be established in the study of human error is that the significance or severity of a human error is measured in terms of its consequence. A human error is of little or no interest apart from its consequence. In one sense, a human error that has no consequence is not an error assuming that recovery has not taken place as discussed above. There is nothing to register the occurrence of an error with no consequence except for the perception of the person making the error assuming the person was aware of an error being made. At the same time, an error does not have to be special or unique to cause an accident of immense proportions. The error itself may be completely trivial, the most insignificant slip made in a moment of absentmindedness or an off-the-cuff management decision. The seriousness of the error or the decision depends entirely on the consequences. This principle makes the study of human error not only important but also challenging. If any trivial human error is potentially capable of causing such disproportionate consequences, then how can the significant error that will cause a major accident be identified from the millions of human errors which could possibly occur. Significant error identification will be discussed later in this book.

1.1.6.4 Intention

An extremely important aspect of ‘what characterizes an error’ is the degree of intention involved when an ‘out of tolerance action’ is committed. It is important because later in the book a distinction is made between errors and violations. The violation of a rule is considered as a separate category to that of an error. A violation of a rule is always an intentional action, carried out in full knowledge that a rule is being disobeyed, but not necessarily in full knowledge of the consequences. If a violation is not intentional then it is an error. It is important to make the distinction because the method of analysis of violations (proposed later in this book) differs from the normal methods of human error analysis which are also described. The difficulty is that some classes of violations verge on error and are quite difficult to differentiate. The best method of making the distinction is to assess whether the action was intentional or not. For the purposes of this book, a human error is by definition always considered to be unintentional.

1.1.6.5 A Final Definition

A final definition of human error which suits the purposes of this book yet which takes into account the above characteristics and some of the other definitions given above, is proposed as follows:

A human error is an unintended failure of a purposeful action, either singly or as part of a planned sequence of actions, to achieve an intended outcome within set limits of tolerability pertaining to either the action or the outcome.

With this definition, a human error occurs if:

(a) there was no intention to commit an error when carrying out the action,

(b) the action was purposeful,

(c) the intended outcome of the action was not achieved within set limits of tolerability.

With this definition in place, it is now possible to examine how human error can be classified using a number of error types and taxonomies. First of all, however, it is necessary to make an important distinction between random errors, which are not considered in this book, and systemic errors which are considered.

1.2 Random and Systemic Errors

1.2.1 Introduction

Although random errors are not the main subject of this book, it is necessary to examine them briefly here in order to be able to distinguish them from systemic errors. The characteristics of a random error (adopted for the purposes of this book) are that it is unintentional, unpredictable and does not have a systemic cause (an external factor which caused the error or made it more likely). The source of a random error will be found within the mental process and will therefore be difficult to identify with any certainty and e...

Table of contents

• Cover Page
• Half Title Page
• Title Page
• Copyright Page
• Contents
• Preface
• Acknowledgements
• Part I Understanding Human Error
• 1 To Err is Human
• 2 Errors in Practice
• 3 Latent Errors and Violations
• 4 Human Reliability Analysis
• 5 Human Error Modelling
• 6 Human Error in Event Sequences
• Part II Accident Case Studies
• 7 Organizational and Management Errors
• 8 Design Errors
• 9 Maintenance Errors
• 10 Active Errors in Railway Operations
• 11 Active Errors in Aviation
• 12 Violations
• 13 Incident Response Errors
• 14 Conclusions
• Appendix: Train Protection Systems
• Index