An integrated qualitative–quantitative risk assessment for defining toxic and hazardous zones on hydrogen-fuelled ships with ammonia cracking systems

This paper proposes a novel quantitative risk assessment model aimed at determining toxic zones in response to a critical design challenge in ammonia-powered vessels. The developed model was applied to a hydrogen-fuelled ship equipped with an ammonia cracking system. This vessel is currently under design and construction and is scheduled to be dispatched to service in 2025 in the coastal area of Busan, South Korea. A qualitative risk assessment, HAZID, identified five high-potential gas leak points across the entire system. These points include critical areas where gas leaks could occur, posing severe risks to the crew and environment. The analysis results suggest the following toxic zones: bunkering connection (less than 1m radius), ammonia storage tank connection (7m radius), ammonia cracking system (5m radius), ammonia tank vent master (less than 1m radius), and fuel cell room ventilation (less than 1m radius). The model effectively determines practical toxic and safety zones for the utilization of hydrogen and ammonia as marine fuels, demonstrating that the proposed risk assessment model can serve as a new solution or standard to address one of the most challenging design issues in using ammonia as marine fuel. This research finally underscores the importance of integrating advanced risk assessment methodologies into the design and operational planning of maritime vessels.