Sustainability and risk management of LNG as a fuel for marine transportation

The use of liquefied natural gas (LNG) as an alternative ship fuel marks a fundamental step towards the reduction of emissions linked to maritime transportation of goods and passengers. Despite the positive safety record of the LNG shipping industry, natural gas is a hazardous substance and safety concerns for its use onboard passenger ships demand a thorough evaluation. This study aims at a comprehensive safety and sustainability assessment of marine LNG technologies, focusing on small-scale applications, seeking to fill the current knowledge gap in this field. An in-depth evaluation of the safety of existing technologies for LNG bunkering and onboard fuel gas supply systems is performed, providing key information about the credible accident scenarios and their expected consequences. The safety criticalities are identified based on the application of specifically developed models for the evaluation of the inherent safety performance of LNG bunkering and propulsion technologies. Another part of the work is dedicated to the development of a computational fluid dynamic (CFD) setup to model the behaviour of cryogenic tanks exposed to accidental hydrocarbon fires, overcoming the limitations of the previous modelling approaches, and providing precise data for further analysis of the tank structural integrity under extreme conditions. Furthermore, a preliminary CFD modelling of LNG fire scenario consequences occurring inside the fuel preparation room of gas-fuelled ships is carried out to evaluate the heat flux received by the ship structure. The obtained results represent a first step towards a wider approach aimed at enhancing the safety of the entire LNG supply for maritime propulsion. Furthermore, these results can make a valuable contribution to support the decision-making process for shipowners and port authorities in the design and safety assessment of such systems, both in port areas and onboard ships, also providing guidance for emergency responders.