Uncertainty Handling in the Safety Risk Analysis: An Integrated Approach Based on Fuzzy Fault Tree Analysis

Chemical process plants, especially the oil and gas plants operating under severe processing conditions and dealing with hazardous materials, are susceptible to catastrophic accidents. Thus safety risk assessment is vital in designing effective strategies for preventing and mitigating potential accidents. Fault tree analysis (FTA) is a well-known technique to analyze the risks related to a specific system. In the conventional FTA, the ambiguities and uncertainties of basic events (BEs) cannot be handled effectively. Therefore, employing fuzzy set theory helps probabilistic estimation of BEs and subsequently the top event (TE). This study presents an integrated approach to fuzzy set theory and FTA for handling uncertainty in the risk analysis of chemical process plants. In this context, the worst case scenario based on a qualitative risk analysis is selected first and then the fuzzy FTA is established. Finally, different fuzzy aggregation and defuzzification approaches are employed to obtain the probability of each BE and TE, the output of each approach is compared to the occurrence probability of TE, and the critical BEs are ranked. The proposed methodology is applied to the fuzzy probabilistic analysis of hydrocarbon release in the BP tragic accident of March 2005. The results indicate that the proposed approach is very effective in risk analysis considering uncertainty reduction or handling.