Hazard Identification and Risk Assessment in Two Gas Refinery Units

Background: The analysis of causes and consequences of past accidents in gas refinery plants has indicated that the consequences of accidents in these plants may be catastrophic and irreversible, influencing human health, environment, and the economy. This study aimed at assessing risks using layer of protection analysis (LOPA) in gas sweetening units of 2 different gas refinery plants and determining the probability of initiating events with application of protection layers, using the event tree analysis (ETA) method. Methods: Hazard and operability (HAZOP) analysis was used in hazard identification. Data obtained from HAZOP analysis was applied to assess risks using the LOPA technique. The most likely scenarios were selected and the probability and consequences of initial events were determined using the ETA method. Results: Results of the HAZOP method led to identification of 52 risks and their levels in processes of both gas sweetening units, considering the control equipment. The results of LOPA showed that the levels of risk with different scenarios of both gas sweetening towers were similar. The probability of the total near misses in plant 1 and 2 were 0.00214753 and 0.00214149, respectively. The probabilities of incidents according to the top events in refinery 1 and 2 were 0.0000011 and 0.000005, respectively. Conclusions: The LOPA is a useful tool for the assessment of effectiveness of independent protection layers in reducing risk in both studied refinery plants. The results indicated that event tree analysis is an effective tool for quantitative analysis of consequences and probabilities of accidents in the studied gas refinery units.