Task analysis and critical incidents.

The tasks of the watchkeeper was investigated using Hierarchical Task Analysis (HTA). This technique yields a description of the task in terms of the goal-directed behaviour of the human rather, than, for example, in terms of the functions of the system components. Descriptions of critical incidents were also collected from a number of watchkeepers independently of the HTA. The critical incidents were then mapped onto the task analysis. This operation thus formed a validation of the analysis and also placed the incidents within a common explanatory structure. (A)