Accident causation

This model of accident causation is described further in Figure 1.3. This represents the defenses against accidents as a series of shutters (engineered safety systems, safety procedures, emergency training, etc.) When the gaps in these shutters come into coincidence then the results of earlier hardware or human failures will not be recovered and the consequences will occur. Inap-... 

From the organizational view of accident causation presented in the previous section, it will be apparent that the traditional approach to human error, which assumes that errors are primarily the result of inadequate knowledge or motivation, is inadequate to represent the various levels of causation involved. These contrasting views of error and accident causation have major implications for the way in which human error is assessed and the preventative measures that are adopted. 

The system-induced error approach can be restated in an alternative form as an accident causation model (see Figure 1.4). This shows how error-inducing conditions in the form of inadequate PIFs interact with error tendencies to... 

In the shorter case studies, only the immediate causes of the errors are described. However, the more extended examples in the latter part of the appendix illustrate two important points about accident causation. First, the precondihons for errors are often created by incorrect policies in areas such as training, procedures, systems of work, communications, or design. These "root causes" underlie many of the direct causes of errors which are described in this section. Second, the more comprehensive examples illustrate the fact that incidents almost always involve more than one cause. These issues will... 

The traditional safety engineering approach to accident causation focuses on the individual rather than the system causes of error. Errors are primarily seen as being due to causes such as lack of motivation to behave safely, lack of discipline or lack of knowledge of what constitutes safe behavior. These are assumed to give rise to "unsafe acts." These unsafe acts, in combination with "unsafe situations" (e.g., imguarded plant, toxic substances) are seen as the major causes of accidents. 

One of the origins of this view of error and accident causation is the theory of accident proneness, which tried to show that a small number of individuals were responsible for the majority of accidents. Despite a number of studies that have shown that there is little statistical evidence for this idea (see, e.g., Shaw and Sichel, 1971) the belief remains, particularly in traditional industries, that a relatively small number of individuals accoimt for the majority of accidents. Another element in the emphasis on individual responsibility has been the legal dimension in many major accident investigations, which has often been concerned with attributing blame to individuals from the point of view of determining compensation, rather than in identifying the possible system causes of error. 

The type of data collected on human error and the ways in which these data are used for accident prevention will vary depending upon the model of error and accident causation held by the management of an organization. This model will also influence the culture in the plant and the willingness of personnel to participate in data collection activities. In Chapters 1 and 2 a number of alternative viewpoints or models of human error were described. These models will now be briefly reviewed and their implications for the treatment of human error in the process industry will be discussed. 

FIGURE 6.2. Accident Causation Model (From Chapter 2). 

Because of the emphasis on modeling accident causation, data collection systems based on the system-induced error approach are likely to modify their data collection strategies over time. Thus, as evidence accumulates that the existing causal categories are inadequate to accoimt for the accidents and near misses that are reported, the data collection philosophy will be modified, and a new accident causation model developed. This, in turn, will be modified on the basis of subsequent evidence. 

Such examples illustrate the fundamental need to provide guarantees of anonymity and freedom from sanctions in any data collection system which relies on volimtary reporting. Such guarantees will not be forthcoming in organizations which hold a traditional view of accident causation. 

This is accomplished using the ECFC and the Critical Human Achon Profile (CHAP), a fask analysis-based method used to identify the most critical actions necessary for the performance of the task. Change Analysis is a technique for investigating the role of change in accident causation. It will be described in Section 6.8.6. 

Management and Policy Influences on Error and Accident Causation As has been emphasized in Chapters 1,2, and 3, the system-induced error view states that it is insufficient to consider only the direct causes of errors. The underlying organizational influences also need to be taken into accoimt. However, most of the available techniques stop when an immediate cause has been identified, such as less than adequate procedures or poor equipment design. The questions of why the procedures were poor, or why the equipment was badly designed, are rarely addressed at the level of policy. Kletz (1994a)... 

A very important contribution in this socio-technical era is made by Reason (Reason, 1990). He made a distinction between active failures, and latent conditions. The active failures are in general failures made by those at the sharp end of the accident causation (e.g. technical and human failures). Effects are felt almost immediately. Latent conditions are removed in time and space from the sharp end of the accident causation (e.g. organizational and technical failures) creating conditions for active failures to be made. A strict boundary between both concepts cannot be made and in reality can be seen as a sort of sliding transition. Here, the two concepts are separated... 

Figure 3 Latent condition - active failure model of accident causation passing through...

Similar remarks can be made about accident reports, it was observed that the focus of the majority is on the direct safety related deviations in the accident causation path, and almost no attention is given to the indirect safety related deviations. Indirect safety related deviations were mentioned but no attention was given to the fact that these deviations were in the causal path, re-occurring, and often present for a long time prior to the accident. Korvers (Korvers et al., 2002) gave some good examples by showing ten cases in which identical indirect safety related deviations present prior to accidents repeatedly caused similar accidents. 

I, Chapters 2 and 3 deal with the general backgrounds of industrial safety (e,g, models of accident causation and of human behaviour) and with the contributions that near miss reporting could make in understanding and controlling accidents and incidents, Also theoretical criticisms of the near miss reporting efforts are discussed here,... 

The Swiss cheese model of accident causation was originally proposed by British psychologist James T. Reason and has since gained widespread acceptance in many risk-analysis and management fields including process safety. 

In this section, a real case is presented so that the accident causation model can be applied to identify the root cause of the errors (BBC News, 1999a-g). 

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