Fire risk comparison of fuel gas supply systems for LNG fuelled ships

As regulations on pollutant and greenhouse gas emissions of ships are gradually being strengthened, using liquefied natural gas (LNG) as fuel for ships is being recognized as an important alternative solution. In this study, we compared the fire risk assessments of the two types of LNG fuel gas supply (FGS) systems generally used in marine vessels. Actual navigation data of a vessel were collected to determine its fuel consumption, and an LNG fuel tank was designed based on the data. To observe the FGS system's thermodynamic state and condition according to its operation, a dynamic process simulation was conducted. Fire risk assessments were made through fire frequency analysis and consequence analysis on the FGS system's operating conditions. An event tree for a fire accident was compiled, and the leak frequency and ignition probability for each system were obtained. The release rates due to leakage were obtained, and computational fluid dynamics (CFD) simulations were used for consequence analysis. Fire exceedance curves for heat doses were generated by combining the results of frequency and consequence analyses. The cumulative frequency was found to be higher in the Pump FGS for the same heat dose. Required heat dose resistance would be higher in the Pump FGS than in the Build-up FGS for the same fire risk acceptance criteria.