23
Human Factors in Accident Investigation
thing before and whether anything unusual was happening at the time. As Dekker
( 2006) has argued, the identification of human error should be the starting point of
an investigation, not the end point. Designers and managers often have the erroneous
assumption that human error is rare, whereas most of us are ‘ accident prone’ to a
greater or lesser extent as is explained below. Coupled with simplistic notions about
cause and effect, these misconceptions may engender undue focus on those involved
at the time rather than focussing on the rest of the system where deeper PSFs and
causal factors may be found. For example, the probability of a car fatality in the
US is twice the probability of a fatality in N orway – this is due to the totality of the
system – not that drivers in the US are so much worse.
SITUATION AWARENESS
Endsley ( 1995) defines three levels of situation awareness:
Level 1, the perception of task relevant elements in the environment
Level 2, the comprehension of their meaning in relation to task goals
Level 3, the prediction of future events
To be ‘ situationally aware’ means having a mental model of the task, ‘ running’ the mental model and updating it as the task progresses. When you imagine yourself carrying
out a task, you are ‘ running’ your mental model of that task ( imagine yourself reversing
your car into a parking space, for example). ‘ Running’ the model requires monitoring
one’s actions in relation to one’s intentions and the state of relevant features of the task
environment. Loss of ‘ situation awareness’ is nothing more than a mismatch between
one’s model of the task status at a particular point and the actual status of the task.
These ideas about situation awareness are useful when systems are being developed. User trials can be conducted using prototype systems and a variety of techniques can be used to assess operator situation awareness. The task can be stopped
at critical points and the operator can be asked probe questions to assess his or her
understanding of the current state of the system. This can be used to assess the design
of the task, identify latent hazards or design faults if critical information is not properly displayed or easy to interpret. Operators can be asked to give a running commentary as they perform the task to assess their level of understanding and identify
knowledge gaps for further investigation.
Accidents are often said to have occurred because individuals lacked ‘ situation
awareness’ or failed to make the right sense of the situation. It is in the retrospective
use of the concept that problems can arise. Terms like ‘ situation awareness’ are only
descriptive and they do not describe much. They should not be used as a final explanation for what happened, as they do not explain why individuals did what they did or
why the accident occurred. What is important is to understand the actual awareness
operators had at the time, and why this may have differed from what they should
have been aware of, with the benefit of hindsight. We can never be fully aware of
everything that is happening around us all the time.
The purpose of conducting safety investigations is to generate safety recommendations to improve the safety of a system. One of the problems that can arise when
Human Factors in Accident Investigation
thing before and whether anything unusual was happening at the time. As Dekker
( 2006) has argued, the identification of human error should be the starting point of
an investigation, not the end point. Designers and managers often have the erroneous
assumption that human error is rare, whereas most of us are ‘ accident prone’ to a
greater or lesser extent as is explained below. Coupled with simplistic notions about
cause and effect, these misconceptions may engender undue focus on those involved
at the time rather than focussing on the rest of the system where deeper PSFs and
causal factors may be found. For example, the probability of a car fatality in the
US is twice the probability of a fatality in N orway – this is due to the totality of the
system – not that drivers in the US are so much worse.
SITUATION AWARENESS
Endsley ( 1995) defines three levels of situation awareness:
Level 1, the perception of task relevant elements in the environment
Level 2, the comprehension of their meaning in relation to task goals
Level 3, the prediction of future events
To be ‘ situationally aware’ means having a mental model of the task, ‘ running’ the mental model and updating it as the task progresses. When you imagine yourself carrying
out a task, you are ‘ running’ your mental model of that task ( imagine yourself reversing
your car into a parking space, for example). ‘ Running’ the model requires monitoring
one’s actions in relation to one’s intentions and the state of relevant features of the task
environment. Loss of ‘ situation awareness’ is nothing more than a mismatch between
one’s model of the task status at a particular point and the actual status of the task.
These ideas about situation awareness are useful when systems are being developed. User trials can be conducted using prototype systems and a variety of techniques can be used to assess operator situation awareness. The task can be stopped
at critical points and the operator can be asked probe questions to assess his or her
understanding of the current state of the system. This can be used to assess the design
of the task, identify latent hazards or design faults if critical information is not properly displayed or easy to interpret. Operators can be asked to give a running commentary as they perform the task to assess their level of understanding and identify
knowledge gaps for further investigation.
Accidents are often said to have occurred because individuals lacked ‘ situation
awareness’ or failed to make the right sense of the situation. It is in the retrospective
use of the concept that problems can arise. Terms like ‘ situation awareness’ are only
descriptive and they do not describe much. They should not be used as a final explanation for what happened, as they do not explain why individuals did what they did or
why the accident occurred. What is important is to understand the actual awareness
operators had at the time, and why this may have differed from what they should
have been aware of, with the benefit of hindsight. We can never be fully aware of
everything that is happening around us all the time.
The purpose of conducting safety investigations is to generate safety recommendations to improve the safety of a system. One of the problems that can arise when