LNG has significant advantages in regard to environmental aspects comparing with conventional oil. In case of using LNG, it is estimated that NOx and SOx emission can be reduced by about 90% and 100%, respectively. Therefore, LNG enables us to comply with stricter emission requirements for ships under the MARPOL Convention combined with regionally enforced Emission Control Areas (ECA) and GHG emission reduction initiated by IMO. LNG-fuelled ship have been considered to be the best option both from an environmental and an economic point of view. Along with these trends, some major shipyards and Classification Societies have started to carry out the risk-based system design for LNG-fuelled ship.
However, new conceptual gas fuelled ship has high risk level compared with vessels using traditional oil especially in view of gas explosion accident. Therefore safety area which is installed fuel gas supply system is required risk based system design with special considerations. First of all, in order to control the risk level, hazards should be identified by experts in various fields and risks should be ranked by semi-quantitative way. Nevertheless, in case of ship design requirements are not satisfied with general safety level, to obtain quantitative risk data, reanalysis is required to meet the available safety level. Quantitative risk analysis has various ways, such as investigating the accident case, opinion collection from experts etc. However quantitative risk analysis using computational fluid dynamics(CFD) is widely used for decisions of risk-based design according to the general advantages of the computational fluid dynamics.
Since the engine room with fuel gas supply system is highly confined, it can be congested highly enough to be damaged at partial hull structure and risk sensitive auxiliary equipment by explosion overpressure. For this reason, explosion analysis needs to be performed to prepare the data required to assess the structural resistance or to mitigate the explosion overpressure in the developing new code of safety for ships using gases or other Low flashpoint fuels(IGF Code). In order to obtain quantitative risk data by explosion analysis, gas leak analysis and gas cloud analysis under the strict boundary conditions by conventional regulations should be carried out. According to the results of explosion simulations conducted based on the forecast the size and the position of the gas cloud made available through the gas leak analysis and gas cloud analysis, show the explosion overpressure contours and quantitative graphs in the engine room with fuel gas supply system. Quantitative risk analysis can be carried out various ways however especially explosion analysis should be conducted by quantitative calculation of gas cloud and gas release. Also in order to obtain the information of the characteristics of gas leaks, the use of general purpose chemical process simulator is essential.
On this paper, the entire process necessary for the quantitative risk analysis was explained to meet the satisfactory safety level of gas fuelled ship. And the results of this study can further be used to carry out structural analysis or assess the impact on the auxiliary equipment for the similar stage of risk level with traditional vessels using general crude oil.