Abstract
An advanced layers of protection analysis (LOPA) method is proposed in this study for assessing the risk associated with a chemical process. It is difficult to determine the values of the acceptable risk for accident scenarios and the probability of failure on demand (PFD) for emergency protection using the traditional LOPA method. Thus, based on an analysis of chemical accident statistics between 2001 and 2013 in China, we first established an acceptable risk function for chemical processes. We then demonstrated that the acceptable risk value for an accident scenario can be calculated by combining the acceptable risk function with the accident consequences evaluation method. The assessment index for an emergency system was developed to assess the protective function of emergency protection based on the analytic hierarchy process, and the PFD of emergency protection was obtained using a fuzzy comprehensive assessment method with fuzzy settheory, which completed the LOPA. The proposed method was applied to a methanol distillation installation. The acceptable risk value for an explosion scenario was 6.08×10–7 and the PFD for emergency protection was 1 × 10–2. The efficiency of each type of independent protection was analyzed in the explosion scenario and the probability of mitigating the scenario was obtained by multiplying the PFDs for all of the independent protective layers. The result showed that the protection was sufficiently effective because the probability of mitigation bythe different types of independent protection (1×10–8), including emergency protection, was less than the acceptable risk value (6.08×10–7). Thus, this advanced LOPA method is a powerful tool, which could improve the integrity and accuracy of traditional LOPA.
