Assessment of LNG fire scenarios on board of LNG-fuelled ships

Decarbonization represent one of the main challenges of the maritime transport sector for the near future. As recent international environmental regulations have set more stringent emission limits, the use of liquefied natural gas (LNG) as alternative ship fuel has proven to be a viable and less-polluting solution, compared to conventional oil-based fuels. However, LNG is a highly flammable substance and safety aspects need to be assessed thoroughly, especially for its use on board passenger ships. Two different gas engine concepts are typically used for ship propulsion: Low-Pressure Dual Fuel (LPDF) and High-Pressure Dual Fuel (HPDF) engines. Regardless of the gas engine technology, the fuel gas supply system process equipment is located inside a specific enclosed space, the fuel preparation room (FPR), that can be sited below deck. Given this background, this study aims to investigate the consequences of LNG pool fires occurring inside a confined space, assessing the influence of different operating conditions. Credible loss of containment events were identified to define the characteristics of LNG pools. Furthermore, LNG pool fires were simulated using the fire dynamic simulator (FDS) to estimate the radiation heat flux received by the process equipment installed inside the FPR and to assess the possibility of experiencing accident escalation on board. To evaluate the effect of forced mechanical ventilation of the FPR, two different cases were modelled: one assuming the standard functioning of the ventilation system, while the other one considered a halted air supply inside the FPR with a working exhaust system only. The outcomes of this study provide useful data for the consequence estimation of small-scale LNG pool fires occurring inside enclosed spaces, also addressing the possibility of accident escalation on board LNG-fuelled ships