Phase 2: Vessel-, location-, and operations-specific safety assessments for a ship-to-ship ammonia transfer

To use ship-to-ship transfers as a proxy to understand ammonia bunkering

• Conduct risk assessment studies for vessels

• Evaluate impact of spill through quantitative risk assessment (QRA) and computational fluid dynamics (CFD) studies

• Develop emergency response plans (ERP)

• Develop plans for trials

Conducted with industry partners, the safety assessments evaluated the feasibility of ammonia transfers between two handysize liquid ammonia carriers at Raffles Reserve Anchorage.

Key highlights from the safety studies include:

• Navigational risk assessment (NRA) confirmed that the transit and side-by-side mooring of two gas carriers can be safely managed under local weather and sea-state conditions, capped at a conservative abort criteria with significant wave height of 1.5 m-2.0 m and wind speeds of 23 knots (12 m/s), and continuous pilotage support for emergency separation and manoeuvring when needed.

• Hazard identification (HAZID) and hazard and operability study (HAZOP) workshops each identified 11 medium-level risks, primarily related to vessel interface, mooring integrity, equipment reliability, and procedural adherence. These risks were deemed tolerable with proper mitigation measures, including clearer emergency response planning and strict adherence to procedures and checklists.

• QRA demonstrated that safety zones can be established, with deterministic modelling recommending a conservative safety zone having a radius of 547 m for once-a-year transfers.

• CFD plume dispersion modelling revealed the formation of toxic clouds that could compromise escape routes and accommodation intakes in the most credible worst-case scenario of pipe rupture, resulting in a release of 12 m³ of ammonia on deck. These findings reinforce the importance of robust detection systems, rapid isolation measures and effective crew protection.

• ERP outlined a tiered response strategy and emphasised the need for strong shipboard readiness in the initial minutes of a release incident, supported by coordinated shore-based and agency resources for any progressive escalation.