The International Association of Classification Societies (IACS) has announced a landmark revision to its Unified Requirement UR M78, introducing comprehensive safety requirements for marine engines fuelled by ammonia. This update marks a pivotal step toward achieving the maritime industry’s decarbonization goals and supporting the transition to zero-carbon fuels.

The newly published Rev.4 of UR M78 expands its scope to include ammonia as an approved fuel for reciprocating internal combustion engines. This development reflects IACS’s commitment to enabling innovative propulsion technologies while maintaining the highest safety standards.

The highlights of this revision to UR M78 include:

• Ammonia added to scope
  UR M78 now covers ammonia-fuelled engines (specifically anhydrous ammonia), alongside natural gas, ethane, LPG, methanol and ethanol, ensuring regulatory clarity for emerging zero-carbon fuels.
• Enhanced Risk Analysis and Mitigation Systems
  New requirements mandate gas return/recovery systems and Ammonia Release Mitigation Systems (ARMS) to prevent leaks and manage toxic releases effectively.
• Addressing Toxic Hazards and Explosion Risks
  The revision introduces measures to mitigate hazards from crankcase leakage, vent systems, explosion relief devices, and flexible hoses, ensuring crew safety.
• Updated Engine Safety Concept
  A comprehensive safety philosophy now addresses gaps not covered by IMO regulations, integrating advanced monitoring and emergency response protocols.
• Design Requirements for Gas Piping and Components
  Revised standards for double-walled piping, expansion bellows, and flexible hoses include mandatory leak detection and type testing for ammonia expansion bellows, and flexible hoses.
• Crankcase Ventilation and Monitoring
  Underpressure ventilation and continuous monitoring are required to defined concentration limits, with automatic safety actions triggered at specified conditions.
• Technical Documentation and Compliance
  Manufacturers must submit detailed schematics, safety concepts, and risk analysis reports for ammonia-fuelled engines.

Rev.4 will be uniformly applied by IACS Member Societies for engines with type approval applications dated on or after 1 July 2027.

Commenting on the UR M78 revision, Dr. Ajay Asok Kumar, IACS GPG (General Policy Group) Chair, said:

“The inclusion of ammonia in UR M78 represents a major milestone in our journey toward decarbonization. IACS is committed to supporting the industry with robust safety standards that enable innovation without compromise.”

This revision provides a clear regulatory framework for ammonia-fuelled engines, enabling shipowners, designers, and engine manufacturers to advance toward zero-carbon shipping with confidence. By addressing both technical and safety challenges, IACS reinforces its role as a global leader and trusted partner in maritime innovation and sustainability.

The IACS Machinery Panel Project Team 43 worked in close collaboration with industry stakeholders to ensure that the inclusion of ammonia as an alternative fuel aligns with global decarbonization objectives. This achievement represents significant progress not only for IACS but for the entire maritime industry.

For more information and access to UR M78 Rev.4, visit here.