Fault Tree Analysis to Compute the Probability of an Event: A Case Study in Oil and Gas Industry

The aim of this study is establishing Fault Tree Analysis (FTA) with using experts’ opinions to compute the probability of an event (as a main factor of risk value). Thus, in order to find the probability of top event, all of the basic event’s probability should be available when FTA is drawn for an event. In this case, several experts will be employed to express their opinions in qualitative terms for all basic events instead of using probabilities from handbooks. In real life, participated experts have subjective weights based on their background and experiences. Therefore, they should be weighted by a standard method like as AHP. Then the experts’ opinions will be collected. In this case, fuzzy set theory will be employed. All experts’ opinion which is expressed in qualitative terms (crisp value) is transferred to fuzzy set number (triangular or trapezoidal). Accordingly, in fuzzy environment their opinions will be aggregated in a set of fuzzy number form. So, the fuzzy number requires to be defuzzified to crisp value. Finally probability of basic events will be computed, and subsequently the probability of top event will be calculated using Boolean algebra. Keywords: Fault tree analysis, Fuzzy logic, Chemical complex plant, Expert judgment