Risk-Based Analysis of Safeguards for Ammonia Tank Trucks Used in Bunkering

Ammonia bunkering is becoming increasingly important in the maritime industry as ammonia is recognized as a viable alternative fuel for reducing carbon emissions in shipping. Bunkering by tank truck plays a crucial role in the early stages of ammonia-fueled ship development. It involves the efficient transportation of ammonia from production facilities to bunkering stations, offering flexibility in refueling vessels at ports, including those lacking extensive infrastructures like pipelines or large storage tanks. However, the safety and regulations surrounding ammonia use in bunkering are paramount to its adoption. This study focuses on analyzing the effectiveness of safeguards designed to reduce the frequency of ammonia releases and mitigate potential leak damage during bunkering operations. We examine how safeguards, such as breakaway couplings and dry disconnect couplings (DDC), can reduce leak occurrences, while excess flow valves (EFVs) and automatic emergency shut-off valves (ESVs) can limit the consequences of such incidents. If the breakaway coupling and DDC are implemented as safeguards in the flexible hose, and maintenance is performed in accordance with ANSI/CGA G-2.1, the probability of hose failure per bunkering operation will be reduced from approximately 10−5 to 10−7. Under the worst weather conditions during the day, the probit value (Pr) depends on both the amount of ammonia released and the distance from the release point, with the distance having a greater effect on fatality than the amount of ammonia. The individual risk is analyzed to determine whether the bunkering process using tank trucks is acceptable. The analysis concludes that, with these safeguards in place, the individual risk at a location 20 m from the bunker site can be reduced to the lower limit of the As Low As Reasonably Practicable (ALARP) zone, ensuring a safe and acceptable level of risk for ammonia bunkering operations. The safety integrity level (SIL) of the automatic ESV should be at least 2 or higher, and it should be activated within a few seconds after a gas leak begins.