An approach to human reliability in man-machine systems using error possibility

This paper is concerned with proposing the concept ‘error possibility’ instead of the error rate and presenting a method of fault tree analysis of human errors based on this concept. The dependence between consecutive human tasks is considered as a fuzzy causal relation. Human reliability is defined as the evaluation of the error possibility from several points of view: (1) the likelihood of error which gives the maximal grade of membership, (2) potentiality for error, (3) fuzziness of error possibility, and (4) importance of a basic event. As an illustrative example, the emergency tasks in blackout at a PWR plant are shown and the fault tree concerning the error of these tasks is analyzed. It is shown that the proposed method gives us information as well.