Application of integrated risk-based approach to safety design of high speed LNG powered vessels

The increasing demand to comply with new environmental regulations has caused liquefied natural gas (LNG) to be considered as an emerging potential fuel in high speed vessels. According to the SOLAS convention, damage stability calculations indicated that no damage should extend inside the line of breadth divided by five (B/5) of a vessel. To this end, the location of the LNG tanks on a high speed ferry is a key aspect; hence, the potential consequences due to an unintentional LNG release must be carefully addressed and their associated adverse impacts are to be fully assessed. This study aims at developing a risk-based approach through which the locations of LNG tanks are determined, considering the potential consequences associated with the accidental release of LNG, i.e. overpressure due to vapour cloud explosion and/or thermal radiation due to fire. The explosion overpressure is modelled by implementing the empirical approach multi-energy (ME) method. The fire heat radiation is simulated by the application of both empirical (solid-flames model) and computational fluid dynamic (CFD) code, fire dynamic simulator (FDS). Probit functions are used to define the human hazards caused by either explosion overpressure or fire heat radiation. Introducing a score scheme for different hazards and risks due to different impacts is defined. The final risk is estimated by the summation of each impact. The decision making on the optimum location of the LNG tank is performed based on the final risk profile on the vessel. Implementing the proposed methodology on a typical high speed LNG vessel proved the LNG tank located on the roof of a vessel has the minimum cumulative risk; hence, it is confirmed as the optimum location. It should be noted that this is the location based on the risk of the accidents; however, other factors affecting the operation of a vessel does not consider which may affect the final decision.