Oil storage tanks are identified as the major hazard installations because of the hazard of huge fire & explosion. Evaluating the risk and controlling the danger is the advancement of accident prevention and the compulsory requirement of laws. HAZOP (Hazard and Operability Analysis), is a simple but intensive, systematic, qualitative risk analytical method, is an important technique for the identification of hidden hazards in operation of tank facility. It can only qualitatively account for potential risks, but cannot quantify their possibility and severity. Thus, research involving HAZOP quantitative analysis has become an area of focus. Due to uncertainty of deviation probability in the traditional HAZOP analysis, this paper discusses a new approach of HAZOP quantitative analysis, combining HAZOP with fuzzy set theory to calculate the possibilities of deviation and consequence quantitatively. The evaluation process and technique route of risk analysis is also brought forward in this paper.

Based on the traditional HAZOP analysis, the typical outputs of a HAZOP analysis can be achieved, including identification of possible deviation states, identification of the possible causes for deviations and probable worst case consequence. Next, according to fuzzy evaluation of some HAZOP experts on deviation by means of their knowledge, the triangular fuzzy-number is introduced in this paper to conduct quantitative calculation. Based on the fuzzy set theory, combining Delphi method and judging matrix method, the linguistic values are transformed into triangular fuzzy numbers. The probability of deviation is evaluated by fuzzy cut and raking method of fuzzy numbers. Finally, the probability of consequence caused by deviation is evaluated.

A complete quantitative risk analysis example for oil tank is conducted, the probabilities of deviations and incident consequence are computed, the quantitative risk is determined and reasonable mitigations of the storage tanks are given. It is shown that the proposed approach is advanced and practicable to make a quantitative assessment on the risk of existing deviation, which is helpful for risk managers to bring forward the suggested measure and regulate the hidden hazards.

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