Numerical environmental impact assessment of accidental release of ammonia during bunkering in the Singapore Strait.

Ammonia is a promising maritime fuel for decarbonization, but its impact on marine environments is less understood. This study uses a high-resolution numerical model to examine the short-term (from hours to days) effects of ammonia releases during bunkering in Singapore - one of the world's busiest ports. Results show that nearshore shallow-water jetties experience more localized but longer-lasting impacts than open seas due to limited mixing. High discharge volumes exacerbate toxicity, highlighting the need for rapid containment; multi-hose systems with low flow rates are recommended. A dimensionless number and a regression model are developed to estimate the extent and duration of lethal ammonia plumes across varying discharge volumes. The study also highlights the role of tidal dynamics: spring tides enhance rapid but widespread dispersion, while ebb-flood cycles dictate the directional transport of ammonia. Beyond toxicity, ammonia contributes to the local nitrogen cycle, stimulating algal growth in semi-enclosed waters but posing lower risks in open seas due to stronger mixing. The presence of sensitive marine species, such as coral reefs, should be considered in bunkering strategies. These findings provide scientific ground for safer ammonia bunkering practices and support the development of effective emergency response frameworks in coastal port environments.