Integrated Human–Equipment Reliability Assessment of Ammonia Loss of Containment During Shore-to-Ship Bunkering

Current studies on ammonia bunkering safety have largely focused on release scenarios, dispersion modelling and equipment-related hazards, while human error, equipment failure and emergency response are often assessed separately. This creates an important gap because the safety of ammonia bunkering depends on how operators and engineered systems work together during both routine and abnormal conditions. This study therefore develops an integrated human–equipment reliability framework for shore-to-ship ammonia bunkering, with emphasis on loss-of-containment scenarios. The study combines Hierarchical Task Analysis, Bow-tie analysis and the HEART to identify critical human actions, estimate human error probabilities and map the equipment associated with preventive and mitigative safety functions. Rather than assuming that all equipment simply reduces human error, the framework distinguishes between equipment that supports human tasks, alarm systems that require a subsequent human response, human-initiated engineered functions, and independent protective barriers. Appropriate reliability relationships are then applied according to the role of each barrier. The HEART results identified tank-capacity verification and hose-connection verification as critical preventive activities, with bounded human error probabilities of 1.00000 under the adopted assessment assumptions. The integrated reliability assessment also showed that an independent valve interlock increased the estimated reliability of the valve-line-up safety function to 0.91360, whereas the gas-alarm and evacuation function achieved 0.791946 because successful mitigation depended on both equipment operation and human response. Sensitivity analysis further demonstrated that these estimates were influenced by the adopted equipment probability of failure on demand (PFD) values and HEART input assumptions. The study provides a function-based way of representing human–equipment interaction in ammonia bunkering safety assessment. The framework is intended as a semi-quantitative screening approach for identifying vulnerable tasks and strengthening preventive and mitigative barriers where installation-specific reliability data remain limited.