Most of the human error probability (HEP) data that can be Used in human reliability analysis are nominal values. Nominal HEP is the probability of a given human error when the effects of performance shaping factors (PSFs) have not been considered. In order to yield more realistic human reliability analysis, the nominal HEPs of task elements must be modified according to the task situation. This paper presents a modification model of the nominal HEP based on the rationale that the likelihood of human error depends on the combined effects of a relatively small set of PSFs. The quality scores of individual PSFs are used in conjunction with the relative importance weights of PSFs on a task to compute a composite quality score. Finally, a new mapping method of the composite quality score of PSFs into a situation-specific basic HEP is proposed with a numerical example. Relevance to industry Human error probabilities are the essential ingredients of human reliability analysis for complex systems such as process industries or nuclear power plants, This paper proposes an approach to incorporate performance shaping factors in situation-specific human error probabilities. The model has implications for the design and management of such systems, and the training and measurement of their personnel performance.
