25
Human Factors in Accident Investigation
Focussing on the hazard is more likely to lead to effective safety recommendations than focussing on the ‘ situation awareness’ of the drivers or their ability to
‘ make sense’ of the situation they were in.
Auto-detection of Error: How do people become aware that they or their colleagues have made an error? Sellen ( 1994) described three mechanisms by which
people detected their own errors and also identified situations in which the errors
were detected by others. The main mechanisms of self-detection are action-based,
outcome-based and process-based ( in which the constraints in the external world
prevent further action). Action-based detection involves ‘ catching oneself in the act’
and depends on whether people are monitoring their actions in relation to their intentions ( paying attention to what they are doing). It also depends on feedback from the
task and therefore on the design of the task and the equipment. An operator who fails
to open a pressure relief valve when required may not detect the error if there is no
indication that it has not been done or if the feedback is misleading or the system
state is not explicitly displayed. Action-based detection can be a form of ‘ just in
time’ error detection allowing remedial action. There are several requirements for
successful detection of error on the basis of outcome. Firstly, the person must have
expectations about what the outcome of the behaviour is likely to be; secondly, the
effects of the actions must be perceptible; thirdly, the behaviour and the system must
be monitored throughout the action sequence; and fourthly, the person must attribute any mismatches between desired and actual outcomes to their own actions and
not to the hardware or to extraneous factors. Process-based detection occurs when
constraints in the world ‘ short circuit’ the sequence of actions. For example, word
processors usually prevent users from closing a working file until it has been saved.
In summary, whether people are able to detect the errors they have made depends
to a large extent on the design of the task; the design of the objects used to perform
the task; the feedback given during the sequence of actions needed to complete the
tasks; and their level of knowledge and training – all of which are in accordance with
the approach of HF described in Figure 2.1.
VIOLATIONS AND ADAPTATIONS TO
UNDERSTAND WORK AS DONE
Whereas errors are unintentional, violations are intentional actions or decisions
not to follow procedures, rules or instructions. Violations are classed as ‘ routine’ or
‘ exceptional’. Routine violations are sometimes ubiquitous. Many years ago, trade
unions used ‘ working to rule’ as a form of industrial action – by explicitly following every rule to the letter, productivity was lower. Routine violations can happen
in highly bureaucratic organisations where new rules are introduced without proper
integration, resulting in a plethora of minor rules and procedures. In these cases, violations may even be tolerated by management. This theme has appeared more recently
in the safety literature as ‘ work as imagined’ as opposed to ‘ work as done’, which
sees violations as simply a way of getting the job done. People may break the rules
for organisational gain ( so that the organisation benefits) or for personal gain ( e.g. to
finish work early) or due to recklessness ( ignoring the risk) or for intentional sabotage. Exceptional violations are isolated departures from authorised procedures due
Human Factors in Accident Investigation
Focussing on the hazard is more likely to lead to effective safety recommendations than focussing on the ‘ situation awareness’ of the drivers or their ability to
‘ make sense’ of the situation they were in.
Auto-detection of Error: How do people become aware that they or their colleagues have made an error? Sellen ( 1994) described three mechanisms by which
people detected their own errors and also identified situations in which the errors
were detected by others. The main mechanisms of self-detection are action-based,
outcome-based and process-based ( in which the constraints in the external world
prevent further action). Action-based detection involves ‘ catching oneself in the act’
and depends on whether people are monitoring their actions in relation to their intentions ( paying attention to what they are doing). It also depends on feedback from the
task and therefore on the design of the task and the equipment. An operator who fails
to open a pressure relief valve when required may not detect the error if there is no
indication that it has not been done or if the feedback is misleading or the system
state is not explicitly displayed. Action-based detection can be a form of ‘ just in
time’ error detection allowing remedial action. There are several requirements for
successful detection of error on the basis of outcome. Firstly, the person must have
expectations about what the outcome of the behaviour is likely to be; secondly, the
effects of the actions must be perceptible; thirdly, the behaviour and the system must
be monitored throughout the action sequence; and fourthly, the person must attribute any mismatches between desired and actual outcomes to their own actions and
not to the hardware or to extraneous factors. Process-based detection occurs when
constraints in the world ‘ short circuit’ the sequence of actions. For example, word
processors usually prevent users from closing a working file until it has been saved.
In summary, whether people are able to detect the errors they have made depends
to a large extent on the design of the task; the design of the objects used to perform
the task; the feedback given during the sequence of actions needed to complete the
tasks; and their level of knowledge and training – all of which are in accordance with
the approach of HF described in Figure 2.1.
VIOLATIONS AND ADAPTATIONS TO
UNDERSTAND WORK AS DONE
Whereas errors are unintentional, violations are intentional actions or decisions
not to follow procedures, rules or instructions. Violations are classed as ‘ routine’ or
‘ exceptional’. Routine violations are sometimes ubiquitous. Many years ago, trade
unions used ‘ working to rule’ as a form of industrial action – by explicitly following every rule to the letter, productivity was lower. Routine violations can happen
in highly bureaucratic organisations where new rules are introduced without proper
integration, resulting in a plethora of minor rules and procedures. In these cases, violations may even be tolerated by management. This theme has appeared more recently
in the safety literature as ‘ work as imagined’ as opposed to ‘ work as done’, which
sees violations as simply a way of getting the job done. People may break the rules
for organisational gain ( so that the organisation benefits) or for personal gain ( e.g. to
finish work early) or due to recklessness ( ignoring the risk) or for intentional sabotage. Exceptional violations are isolated departures from authorised procedures due