An integrated HAZOP-FTA-FMECA framework for ammonia leakage in a high-pressure ship fuel supply system

Ammonia has recently gained attention as a viable zero-carbon alternative fuel for maritime transport. However, despite its environmental advantages, ammonia presents significant safety challenges due to its high toxicity, flammability, and corrosive characteristics. Although ammonia-fueled vessels are expected to increase their commercial service in the near future, there is currently a lack of comprehensive studies addressing the safety and risk management of high-pressure ammonia fuel supply systems. This study aims to identify potential ammonia leakage failure modes within high-pressure ammonia fuel supply systems and to propose improvement actions to support preventive safety measures. An integrated HAZOP (Hazard and Operability), FTA (Fault Tree Analysis), and FMECA (Failure Mode, Effects, and Criticality Analysis) methodology was implemented with an expert group to systematically evaluate the critical components and potential failure modes. The HAZOP analysis identified hazardous areas and possible incident scenarios, which were subsequently modeled in FTA to reveal underlying events contributing to ammonia leakage. The FMECA evaluation provided quantitative risk prioritization by assessing the severity, occurrence, and detection of identified failure modes. According to the evaluation, there are 1 extreme criticality, 34 high criticality, 24 medium criticality, and 3 low criticality sub-events in the system. The results indicate that human factors, control system failures, and material incompatibility are the most critical contributors to ammonia leakage. The most critical sub-event is BE-36 Failure to detect wear or damage, with the risk priority number (RPN) of 168. The control system equipment-related sub-events (BE-24, BE-26, BE-27) and IE-2 Piping and valve leakage are the second and third most critical sub-events with the RPN of 144 and 135, respectively. Proposed improvement actions, including enhanced training, upgraded detection and alarm systems, and the selection of ammonia-resistant materials, effectively reduced the risk priority numbers for the identified failure modes. After the improvement actions, the sub-event numbers are 17 and 45 for medium criticality and low criticality, respectively. The RPN of the most critical event, BE-36, is reduced to 60 (medium criticality) from 168 (extreme criticality) after the proposed improvement actions. This study is the first to apply the integrated HAZOP-FTA-FMECA framework to a high-pressure ammonia fuel supply system. The study demonstrates that a structured, multi-method approach can provide actionable insights for risk mitigation in ammonia fuel supply systems.