The International Association of Classification Societies (IACS) has introduced a new Unified Requirement setting out a common safety framework for ammonia release mitigation systems (ARMS) on ammonia-fuelled vessels.

Unified Requirement H2 (UR H2) establishes harmonised expectations for the design, testing and certification of ARMS, covering both routine operations and credible abnormal scenarios. The framework is intended to support the safe adoption of ammonia as a marine fuel as alternative fuel uptake accelerates.

IACS said the requirement aligns with IMO guidance under MSC.1/Circ.1687 and clarifies how mitigation systems should be assessed and approved by classification societies. The approach focuses on identifying potential ammonia release scenarios and defining appropriate mitigation measures, while allowing flexibility in how those measures are engineered.

UR H2 recognises multiple technical solutions, including dissolution tanks, scrubbers, combustion units and dilution systems, provided they meet defined safety objectives and exposure limits. The requirement avoids prescribing specific technologies, instead setting consistent safety outcomes across different design approaches.

The framework also establishes expectations for workshop testing, onboard trials, certification and operational readiness, with the aim of ensuring mitigation systems remain effective throughout a vessel’s service life.

Eva Peno Jimenez, chair of IACS's Safe Decarbonisation Panel, noted: "This publication represents an important step towards harmonised global standards for ammonia-fuelled ships. By providing a common technical reference, the UR supports designers, shipowners, equipment manufacturers and regulators, and facilitates consistent implementation across the IACS membership."

IACS represents twelve classification societies whose rules and standards cover the majority of the world’s cargo-carrying fleet.