Comparative risk assessment of gaseous and liquid hydrogen fuel gas supply systems for hydrogen-fueled vessels

• Comparative risk assessment for gaseous and liquid hydrogen fuel gas supply systems. • Gaseous hydrogen requires enhanced protection against high-pressure leaks. • Liquid hydrogen emphasizes management of thermal contraction and pipe damage risks. • Provides safety guidelines for eco-friendly hydrogen adoption in maritime industry. This study compares qualitative risk analyses of compressed hydrogen gas (GH 2 ) and liquid hydrogen (LH 2 ) fuel gas supply systems (FGSSs) for eco-friendly marine vessels. Using hazard identification (HAZID) and hazard and operability (HAZOP) methodologies, the study systematically identifies and compares the unique risks and safety strategies for GH 2 and LH 2 FGSS. For GH 2 -FGSS, HAZID identifies 22 hazards, with one unacceptable risk related to potential explosions from high-pressure hydrogen accumulation due to ventilation failure. HAZOP identifies 27 hazards, all categorized as acceptable or ALARP. Recommended safety measures include pressure protection devices, real-time alarms, and enhanced piping durability. For LH 2 -FGSS, HAZID identifies 38 hazards without any unacceptable risks, though cryogenic icing and overpressure remain significant concerns. HAZOP reveals 43 hazards, with one unacceptable risk involving thermal contraction and piping damage from repeated operations, posing fire hazards. Suggested mitigations include improved cooling and purge gas procedures, along with rigorous insulation management. Primary differences in safety management focus on high explosion risk of GH 2 -FGSS from high-pressure storage and the piping damage risk of LH 2 -FGSS from icing and thermal contraction. To enhance risk management for each system, future research implements an operational simulation-based quantitative risk assessment. This study provides foundational safety strategies and guidelines for future vessels, supporting the adoption of eco-friendly fuels in the maritime industry.