Effectiveness of mechanical ventilation in mitigating ammonia leaks: A safety assessment for ammonia-fuelled ships

This study assesses the effectiveness of mechanical ventilation systems in mitigating ammonia leaks onboard ships, with a focus on crew safety. Numerical simulations are conducted for two case vessels – a container ship and a RoPax ship – under various leak scenarios in storage spaces. The analysis evaluates ammonia concentration levels against the occupational safety threshold of 30 ppm and the lower flammability limit. Sensitivity analysis considers vent position, number of vents, ventilation rate, and ambient temperature. Results show that optimal vent configurations and higher air-change rates (ACH) significantly reduce ammonia concentrations and decay times, thereby enhancing ventilation efficiency. The minimum ventilation durations for safe crew access to the storage areas following a leak were determined as 20 min for the Container ship and 15 min for the RoPax ship. These findings provide practical guidance for ship designers and operators, supporting the safe adoption of ammonia as a marine fuel while addressing the risk associated with its toxicity and handling. • Peak leaks decay below 30 ppm within 12–18 min under 30 ACH. • Clearance is strongly influenced by ventilation strategy and spatial layouts. • RoPax spaces reach safe levels quicker than container holds.