Fuzzy Risk Assessment and Categorization , based on Event Tree Analysis ( ETA ) and Layer of Protection Analysis ( LOPA ) : Case Study in Gas Transport System

Process safety and risk assessment are vital demands for any industry to characterize hazards and their risks for personnel, environment and loss of money. Risk matrix is a very useful tool to estimate risk of process or equipment that helps decision-making processes. Thus fuzzy logic method for risk assessment is selected as a new and efficient way to industry resource management. This study generally includes quantitative reviews of possible accidents, based on previous accident experiences that may occur in a typical natural gas transport system. For current risk assessment study the possibility exists to limit failure in case definition and risk modeling to only accidents that may include fire, explosion and toxic effect risks. Consequently a fuzzy risk matrix is extracted based on Layer of Protection Analysis (LOPA) and Event Tree Analysis (ETA) procedures for analyzing 3 leakage scenarios based on the size of leakage, then classical risk indexes are compared with those obtained from the fuzzy approach. Results of case study showed that risk indexes of fuzzy risk assessment in small and medium leakage differ 30% and 8% to classical risk indexes respectively, and shown that fuzzy risk assessment overcomes uncertainties and imprecision of classical risk assessment.