Fuzzy Fault Tree analysis in modern γ-ray industrial irradiator: use of fuzzy version of HEART and CREAM techniques for human error evaluation

As well known, the lack of accurate quantitative human reliability data is a serious limitation and source of uncertainty in risk assessment. Therefore, in the last years, many Authors suggested that the use of the fuzzy sets theory can fill up this gap, performing as useful tool when dealing with qualitative or vague information. In such a framework, the present paper refers to the obtained results by using Fuzzy Fault Tree analyses of accidental scenarios which entail the potential exposure of operators working in γ-ray irradiation industrial plant. For these analyses the HEART methodology, a first generation HRA (Human Reliability Analysis) method, has been employed to evaluate the probability of human erroneous actions. This technique has been modified by us on the basis of fuzzy set concept to more directly take into account the uncertainties of the so called error-promoting factors, on which the methodology is grounded. The obtained results have been compared with the ones produced by using a new approach of the CREAM methodology, a second generation technique modified by other Authors on the basis of the fuzzy logic modeling architecture. The comparison shows that the occurrence probabilities of the examined potential exposure accidental event are quite coherent to each other.