The International Association of Classification Societies has revised UR M78 to include ammonia, introducing stricter safety measures and aligning with IMO guidelines, signalling a major step towards safer, zero-carbon shipping.
The International Association of Classification Societies has published Rev.4 of Unified Requirement UR M78, formally bringing anhydrous ammonia within the scope of its safety rules for reciprocating internal combustion engines and laying out a comprehensive safety framework to support the maritime transition to zero‑carbon fuels. According to the report by Marinelink, the revision will be applied uniformly by IACS Member Societies to engines with type approval applications dated on or after 1 July 2027. [1][7]
Rev.4 explicitly adds ammonia to the list of covered fuels alongside natural gas, ethane, LPG, methanol and ethanol, and introduces a strengthened engine safety concept intended to address gaps beyond current IMO prescriptions. The update mandates risk analysis and mitigation measures, including gas return/recovery systems and dedicated Ammonia Release Mitigation Systems (ARMS) designed to prevent and manage toxic releases. It also requires manufacturers to submit detailed schematics, safety concepts and risk‑analysis reports as part of type‑approval submissions. Industry reporting highlights these changes as intended to provide regulatory clarity for shipowners, designers and engine builders pursuing ammonia propulsion. [1][2][7]
Technical design requirements have been tightened to reflect ammonia’s distinct hazards. UR M78 Rev.4 calls for double‑walled gas piping with leak detection, type testing for ammonia‑rated expansion bellows and flexible hoses, and specific measures to mitigate crankcase leakage, vent‑system risks and explosion relief device performance. Continuous monitoring, under‑pressure ventilation and defined concentration limits are required, with automatic safety actions triggered when thresholds are reached. These measures are presented by IACS as an integrated safety philosophy combining prevention, detection and emergency response. [1][7]
Toxicity thresholds and exposure control remain central to the revisions and to parallel IACS work. IACS earlier developed a separate unified requirement, URH1, that aligned with National Institute for Occupational Safety and Health guidance by recognising 300 ppm as immediately dangerous and 25 ppm as hazardous for prolonged exposure. However, IACS subsequently withdrew UR H1 ahead of its planned 1 January 2025 implementation, citing a need to reconcile its provisions with the International Maritime Organization’s interim guidelines and to avoid regulatory divergence. Reporting on the withdrawal notes differences between IACS’s prior thresholds and the IMO interim guidance, which references a 220 ppm acute exposure threshold and emphasises preventing direct releases during normal and foreseeable abnormal scenarios. The IMO guidance is non‑mandatory but closely aligned with the IGF Code and SOLAS principles, and has therefore played a key role in shaping the regulatory environment for ammonia bunkering and machinery. [3][4][5][6]
The interplay between IACS’s UR M78 Rev.4 and broader regulatory instruments reflects a period of active alignment and iteration. According to AJOT and industry commentary, Rev.4 seeks to provide a clear technical pathway for engine manufacturers and ship designers while remaining consistent with IMO goals for safety and decarbonisation. At the same time, the earlier UR H1 withdrawal underscores ongoing efforts to harmonise classification society requirements with IMO interim guidance to avoid conflicting thresholds and operational rules. [2][3][4][6]
For operators and manufacturers the practical implications are immediate: engine designs, gas‑handling systems and supplier documentation will need to satisfy the new type‑approval expectations from 1 July 2027, and ship projects considering ammonia must incorporate the specified ARMS, piping design, monitoring and ventilation arrangements into early design phases. IACS has said the Machinery Panel Project Team 43 developed the revision in close collaboration with industry stakeholders, signalling that the updated UR M78 is intended to be both safety‑conservative and enabling of ammonia fuel projects. Industry sources view the revision as a significant de‑risking step for ammonia adoption, while also noting that compliance will require technical development, testing and verification by manufacturers and yards. [1][7][2]
Taken together, UR M78 Rev.4 and the contemporaneous regulatory activity at the IMO set clearer expectations for the safe use of ammonia as a marine fuel. The revision represents a notable advance in class society guidance intended to bolster investor, owner and designer confidence in ammonia‑fuelled propulsion, even as stakeholders continue to monitor and reconcile exposure thresholds, bunkering procedures and operational safeguards across IACS and IMO instruments. [1][6][3]
📌 Reference Map:
Reference Map:
- – [1] (Marinelink) – Paragraph 1, Paragraph 2, Paragraph 3, Paragraph 6, Paragraph 7
- – [7] (Marinelink) – Paragraph 1, Paragraph 2, Paragraph 3, Paragraph 6
- – [2] (AJOT) – Paragraph 2, Paragraph 6
- – [3] (IACS news on URH1 adoption) – Paragraph 4, Paragraph 7
- – [4] (IACS news on UR H1 withdrawal) – Paragraph 4
- – [5] (Marinelink on UR H1 withdrawal) – Paragraph 4
- – [6] (BIMCO/IMO guidance) – Paragraph 4, Paragraph 7
Source: Noah Wire Services
Bibliography
- https://www.marinelink.com/news/iacs-updates-ur-m-include-ammoniafueled-534414 – Please view link – unable to able to access data
- https://www.ajot.com/news/ammonia-power-iacs-updates-ur-m78-to-drive-zero-carbon-shipping – The International Association of Classification Societies (IACS) has revised its Unified Requirement UR M78 to include ammonia as an approved fuel for marine engines. This revision aims to support the maritime industry’s decarbonisation goals by providing safety standards for ammonia-fuelled engines. The updated UR M78 now covers ammonia-fuelled engines alongside other fuels like natural gas, ethane, LPG, methanol, and ethanol, ensuring regulatory clarity for emerging zero-carbon fuels. The revision also introduces new requirements for gas return/recovery systems and Ammonia Release Mitigation Systems (ARMS) to prevent leaks and manage toxic releases effectively.
- https://iacs.org.uk/news/iacs-adopts-new-unified-requirement-urh1-on-control-of-ammonia-re… – IACS has introduced Unified Requirement URH1, focusing on controlling ammonia releases in ammonia-fuelled vessels. This requirement aligns with recommendations from the U.S. National Institute for Occupational Safety and Health (NIOSH), establishing that an ammonia concentration of 300 ppm or more is immediately dangerous, and a concentration of 25 ppm or more is dangerous if exposure exceeds eight hours. URH1 mandates that systems handling ammonia be designed to prevent direct releases to the atmosphere during normal and foreseeable abnormal scenarios, enhancing safety measures for crew and vessel operations.
- https://iacs.org.uk/news/iacs-withdraws-unified-requirement-ur-h1-on-control-of-ammonia-re… – IACS has withdrawn Unified Requirement UR H1, ‘Control of Ammonia Releases in Ammonia Fuelled Vessels’, ahead of its scheduled implementation date of January 1, 2025. This decision aligns with the International Maritime Organization’s (IMO) interim guidelines on ammonia as a maritime fuel. The withdrawal aims to create a clearer regulatory environment by addressing differences between IACS’s original requirements and the IMO guidelines, ensuring consistency and reducing potential confusion within the maritime industry regarding ammonia fuel safety standards.
- https://www.marinelink.com/news/iacs-withdraws-ur-h-control-ammonia-519567 – IACS has withdrawn Unified Requirement UR H1, ‘Control of Ammonia Releases in Ammonia Fuelled Vessels’, ahead of its scheduled implementation date of January 1, 2025. This decision stems from differences between IACS’s safety parameters and those outlined in the IMO Interim Guidelines. The IMO guidelines establish a 220 ppm threshold for acute exposure and require preventing direct ammonia release during normal and controllable abnormal scenarios, which may exclude releases from leakages. The withdrawal aims to ensure consistency and reduce potential confusion within the maritime industry.
- https://www.bimco.org/news-insights/bimco-news/2025/03/27-ammonia – The International Maritime Organization (IMO) has issued MSC.1/Circ.1687, the Interim Guidelines for the Safety of Ships Using Ammonia as Fuel. These guidelines provide a goal-based safety framework covering ship design, equipment, operations, bunkering, toxicity mitigation, and crew protection. While non-mandatory, they align closely with the IGF Code and SOLAS principles, offering a consistent reference point for ammonia-fuelled projects. The guidelines aim to ensure that ammonia-fuelled systems offer at least the same level of safety and reliability as conventional oil-fuelled machinery, recognising ammonia’s specific hazards.
- https://www.marinelink.com/news/iacs-revises-safety-requirements-for-ammonia-engines-53441… – IACS has revised its Unified Requirement UR M78 to include ammonia-fuelled engines, marking a significant step towards decarbonising the maritime industry. The revision introduces comprehensive safety requirements for ammonia-fuelled engines, including gas return/recovery systems and Ammonia Release Mitigation Systems (ARMS) to prevent leaks and manage toxic releases effectively. It also addresses hazards from crankcase leakage, vent systems, explosion relief devices, and flexible hoses, ensuring crew safety. The updated UR M78 now covers ammonia-fuelled engines alongside other fuels like natural gas, ethane, LPG, methanol, and ethanol.
Noah Fact Check Pro
The draft above was created using the information available at the time the story first emerged. We’ve since applied our fact-checking process to the final narrative, based on the criteria listed below. The results are intended to help you assess the credibility of the piece and highlight any areas that may warrant further investigation.
Freshness check
Score: 10
Notes:
The narrative is current, published on January 14, 2026, with no evidence of prior publication or recycled content. The information is original and timely.
Quotes check
Score: 10
Notes:
No direct quotes are present in the narrative, indicating original content without reused statements.
Source reliability
Score: 10
Notes:
The narrative originates from Marinelink, a reputable maritime industry publication, enhancing its credibility.
Plausibility check
Score: 10
Notes:
The claims align with known developments in maritime fuel regulations, including IACS’s recent updates to UR M78 and the IMO’s interim guidelines for ammonia-fueled ships. No inconsistencies or implausible statements were identified.
Paywall check
Score: 10
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The narrative is accessible without encountering any paywall restrictions, allowing full verification of its content.
Content type check
Score: 10
Notes:
The narrative is a factual news report, not falling under any protected or distinctive content categories.
Overall assessment
Verdict (FAIL, OPEN, PASS):PASS
Confidence (LOW, MEDIUM, HIGH):HIGH
Summary:
The narrative is original, timely, and aligns with current maritime fuel regulations. It originates from a reputable source and is free from paywall restrictions, supporting its credibility and suitability for publication.
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