Ammonia-fuelled vessel design and operation: Key recommendations


A joint study into ammonia safety onboard ships undertaken by Lloyd’s Register (LR) Maritime Decarbonisation Hub and the Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping, has found that a range of mitigation methods are required to keep toxicity risks to crew within published tolerable limits.


Using Quantitative Risk Assessment analysis, a data-driven method that allows users to assess risk in a quantitative and granular manner, the joint study has been able to identify vessel design and operational measures that would reduce ammonia risks to a tolerable level.


Key findings: - Secondary containment mechanisms, such as double-walled piping, used for ammonia-related equipment outside of already-restricted areas have been proven to significantly reduce risk.


- Ventilated gas-tight enclosures installed around any gas valve units in engine rooms also reduce risk.


- Ventilation of spaces containing ammonia equipment provides mitigation of toxic effects for many smaller, but not all, potential ammonia leaks. This mitigation is particularly efficient for smaller leaks. Consideration of additional precautions is required for personnel entering these spaces.


- Ventilation of spaces containing ammonia equipment reduces the risk of ammonia concentrations reaching a flammable level. - Although ammonia is much less flammable than some other fuels, the flammability hazard should not be ignored.


- Ammonia leak alarms should be installed both in controlled areas (for example, the fuel preparation room) and near potential leak sources.


- The fuel system should be subject to rapid and reliable manual and automated shutdown in the event of an ammonia leak.


Leaking gasket caused cargo damage


The Swedish Club has published a monthly safety scenario to draw lessons learned from an incident where a leaking gasket caused cargo damage.


The crew were washing down the main deck on the containership. Both fire pumps in the engine room were running and the valves were closed to increase the water pressure to the anchor hawser. The water pressure increased when the valves on the main fire line were closed. When the washing down was completed, all valves were closed, leaving the pumps in operation.


The vessel entered port the next day. During cargo operations the stevedores noticed water in cargo hold 1. The Master immediately sent the crew to investigate the other holds as well. It was noted that there was about 20cm of water in cargo hold 2.


The Master asked the Chief Engineer to locate the leak. The Chief Engineer discovered that the high-level bilge alarm had been activated repeatedly, but the duty engineer had only acknowledged the alarms without investigating the cause. The duty engineer had assumed that the alarms were triggered by rain. The crew found that water was leaking from the fire lines (port and starboard side) to the void spaces adjacent to all cargo holds and then through openings in longitudinal bulkheads, to cargo hold 1 and 2.


Water from the void spaces adjacent to holds 1 and 2 would flood the cargo holds through openings in the longitudinal bulkheads. It was found that the rubber gaskets on the main fire line had started to leak and so water had filled the port side void space adjacent to hold 2 and the starboard side void space adjacent to hold 1.


Once water reached the level of the lower edge of the openings in the longitudinal bulkheads, it started to flood the holds.


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