IACS Withdraws UR H1 for Ammonia-Fuelled Vessels in Response to IMO Guidelines

The International Association of Classification Societies (IACS) has made the decision to withdraw Unified Requirement UR H1, “Control of Ammonia Releases in Ammonia Fuelled Vessels,” in response to the evolving regulatory landscape for ammonia as a maritime fuel. This move comes ahead of the scheduled implementation date of January 1, 2025, and is based on discrepancies between IACS safety parameters and the IMO Interim Guidelines on ammonia. The IMO Sub-Committee on Carriage of Cargoes and Containers recently finalized draft guidelines for the safety of ships using ammonia as fuel, with approval expected at MSC 109.

The IMO Interim Guidelines for ammonia as a maritime fuel introduce several key differences from IACS’s original UR H1 requirements. These guidelines set a 220ppm threshold for acute exposure without specifying a hazardous concentration, and mandate the prevention of direct ammonia release during normal and controllable abnormal scenarios. Toxic areas are defined, requiring gas dispersion analysis to ensure concentrations do not exceed 220ppm in critical locations. An ammonia release mitigation system is also required to maintain outlet concentrations below 110ppm, with alarms for exceedances.

In order to promote consistency and avoid conflicting interpretations, IACS has chosen to withdraw UR H1 and plans to release a revised version aligned with the IMO guidelines in 2025. The revised UR will incorporate the safety measures outlined in the IMO Interim Guidelines for ships using ammonia as fuel. This decision reflects IACS’s commitment to ensuring the safe and compliant use of ammonia in the maritime industry, in accordance with international standards and regulations.

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