Accident sequence 53-7 display

Human errors may be dependent on the specific accident sequence displayed in the event tree, and, for that reason, may be included in the event tree. This requires the human-factors specialist to consider the context of the error in terms of stress, operator training in response to the accident, di.tgnosiic paiierns, environmental, and other performance-shaping factors. 

We here recommend using graphical techniques in the display of accident sequences on an exceptional basis only. A cost-benefit consideration must be made, where the time and attention needed to establish and analyse the diagram are considered as well. Experience shows that the establishment of, for example, a STEP diagram, is merited in the investigation of accidents involving complex interaction and communication between different actors. 

The Multi-linear Events Chartering Method is based on the view that an accident is a process involving interacting events and conditions (Benner, 1975). An accident begins when a system is transformed by a disturbance and ends with the last injurious or damaging event. An event is described in terms of an actor (animate or inanimate) and an action. The sequence of actions of each actor and the interrelations between the actions are displayed in a diagram. Also, conditions that influence the different actions are displayed. This method is a central part of the so-called STEP method for accident investigations that we will come back to in Part III. 

A typical example is the so-called Finnish model for accident analysis. Figure 13.6. It displays accidents in a standard format in terms of two separate event sequences. One of these considers the build-up of hazardous energy and the second the movements of the victim in relation to this energy source. The accident occurs when the person and the released hazard come in contact. We recognise the energy model presented in Section 5.4 in this accident-analysis model. 

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