Quantitative risk analysis of fire and explosion on the top-side LNG-liquefaction process of LNG-FPSO

•We suggested a simplified procedure of QRA for the top-side process of off-shore platforms.•We conducted the proposed QRA for the LNG-liquefaction process of LNG-FPSO.•From the results, we showed additional protection is not required under ALARP criteria.•For safer design and operation, we recommended the selection of IPL to meet the SIL 3. Since the massive use and production of fuel oil and natural gas, the excavating locations of buried energy-carrying material are moving further away from onshore, eventually requiring floating production systems like floating production, storage and offloading (FPSO). Among those platforms, LNG-FPSO will play a leading role to satisfy the global demands for the natural gas in near future; the LNG-FPSO system is designed to deal with all the LNG processing activities, near the gas field. However, even a single disaster on an offshore plant would put the whole business into danger. In this research, the risk of fire and explosion in the LNG-FPSO is assessed by quantitative risk analysis, including frequency and consequence analyses, focusing on the LNG liquefaction process (DMR cycle). The consequence analysis is modeled by using a popular analysis tool PHAST. To assess the risk of this system, 5 release model scenarios are set for the LNG and refrigerant leakages from valves, selected as the most probable scenarios causing fire and explosion. From the results, it is found that the introduction of additional protection methods to reduce the effect of fire and explosion under ALARP criteria is not required, and two cases of the selection of independent protection layers are recommended to meet the SIL level of failure rate for safer design and operation in the offshore environment.