ClassNK to approve machine room safety for an ammonia-fuelled vessel

Japanese classification society ClassNK is set to approve the machine room safety design of a 40,000-cbm ammonia-fuelled ammonia gas carrier.

PHOTO: Concept of 40,000-cbm ammonia-fuelled ammonia gas carrier. NYK

The vessel, designed by Japanese shipping major Nippon Yusen Kabushiki Kaisha (NYK) and currently under construction at Japan's Nihon Shipyard, is scheduled for delivery in November 2026.

The machinery room safety notation “shall be granted only to ships that meet the functional requirements and ensure the highest level of safety,” NYK said.

This means the vessel will receive certification once the shipyard demonstrates that the machinery room complies with the requirements to minimise exposure to ammonia leaks. A machinery room typically houses engines, generators, pumps and other equipment required for a ship's operation.

Ammonia can be lethal if its exposure is severe and prolonged. Ammonia concentrations of 2,500-4,500 parts per million (ppm) can be fatal within 30 minutes, according to the US National Institutes of Health. Levels above 5,000 ppm typically cause rapid respiratory arrest, while concentrations over 10,000 ppm can result in skin damage. These dangerous levels usually occur during large-scale ammonia releases or leaks, often in enclosed or poorly ventilated spaces.

As a result, shipping classification societies have developed their own guidelines for safe handling and storage of ammonia on ships.

ClassNK recommends that gas alarms and gas evacuation systems should be triggered when the ammonia concentration in the machinery space exceeds 25 ppm. Ammonia concentrations above 300 ppm should trigger an emergency shutdown of master valves and other ammonia supply systems on the ship, the classification society added in its ammonia guidelines.

Other classification societies have suggested an alarm threshold between 30–220 ppm of ammonia concentration in the ship's machinery room.

These class recommendations could be considered in the IMO’s interim guidelines for using ammonia as fuel on ships. The final draft of ammonia guidelines is expected to be reviewed and approved by the Maritime Safety Committee (MSC) in December.

By Konica Bhatt

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