From Flammability to Toxicity: A Comparative Regulatory Analysis of Safety Frameworks for LNG and Ammonia as Marine Fuels

The decarbonization of international shipping has accelerated interest in ammonia as a zero-carbon marine fuel. However, its acute toxicity poses safety challenges fundamentally different from those associated with LNG. This study presents a structured comparative regulatory analysis of the IGF Code and the IMO Interim Guidelines for Ships Using Ammonia as Fuel through a chapter-by-chapter review of key safety domains. The results show that, despite structural similarities, the two frameworks diverge significantly in their underlying safety logic: LNG regulation is primarily oriented toward flammability and explosion prevention, whereas ammonia regulation adopts a toxicity-driven safety architecture. This shift is reflected in ppm-level gas detection thresholds, ammonia release mitigation systems (ARMS), toxic area and Safe Haven concepts, broader secondary containment measures, and enhanced personnel protection requirements. These findings suggest that ammonia safety cannot be adequately addressed through incremental extensions of LNG-based rules alone. Instead, it requires a dedicated regulatory approach that explicitly incorporates toxic exposure management into ship design and operation.