HAZID-based quantitative framework for design-stage risk evaluations of ship-to-ship ammonia bunkering

Ammonia is a promising alternative fuel for maritime decarbonization. This research addresses the first step of risk management for ammonia ship-to-ship (STS) bunkering through a structured risk assessment procedure that complies with IMO MSC.1/Circ.1455 and ISO 17776. Thirty-four hazard scenarios were mapped from a multidisciplinary Hazard Identification (HAZID) workshop. Risk levels were evaluated using a 5 × 5 risk matrix with four priority tiers (Low, Moderate, High, Critical), and they highlighted uncontrolled vessel movement, vaporization, and venting. Critical hazards accounted for 8.8% of the total hazards and were dominated by equipment failures and malfunctions. To provide greater reliability than ordinal ranking, an expected risk score (ERS) was utilized to perform continuous hazard prioritization, and the robustness was verified through sensitivity and Monte Carlo analyzes. Based on the ERS results, preventive and response measures, such as emergency shutdown, hose pressure control, and crew training, were developed as additional safeguards. The combination of HAZID with regulatory guidance and ERS offers a reproducible template for design-stage decision-making in ammonia bunkering and a transferable tool for other emerging alternative fuels.