Paving the way for ammonia as a marine fuel: insights into the IMO’s Interim Guidelines

During its 109th meeting in December 2024, the Maritime Safety Committee (MSC) — a key technical body of the International Maritime Organization (IMO) — approved interim guidelines for the safe use of ammonia as a marine fuel. This development represents a major step toward decarbonizing the shipping industry, with ammonia emerging as a key alternative fuel for reducing greenhouse gas (GHG) emissions.

To explore these guidelines and discuss their implications, the Ammonia Energy Association (AEA) hosted a webinar in January 2025, featuring insights from key experts in the field. Antti Nironen, Technical Officer of the Maritime Safety Division at IMO, and Liam Blackmore, Principal Engineer at Lloyd’s Register joined Trevor Brown, Executive Director of the AEA, to unpack these guidelines, including an overview of the development process, and their general content. The recording is available on the AEA’s website, and you can also download the speaker presentations.

Interim Guidelines for Ammonia as Marine Fuel

The interim guidelines establish essential safety standards for ship design and operational practices, targeting key areas such as fuel containment systems, bunkering procedures, fire safety, and toxicity mitigation. These measures aim to ensure the safe adoption of alternative fuels, such as ammonia, across the maritime sector and align with the IMO’s overarching GHG emissions reduction strategy.

The development of these guidelines began at the 8th session of the Sub-Committee on Carriage of Cargoes and Containers (CCC) in 2022, and culminated in their approval by the Maritime Safety Committee (MSC) in December 2024. A core focus of the guidelines is the application of inherently safer design principles to minimize ammonia release risks. Key provisions include:

• Requirements for fuel containment systems to minimize sources of ammonia release and ensure any released ammonia is directed to recovery systems, treatment units, or designated safe open-air locations. Fuel containment systems, piping, and other sources of potential release must be arranged to reduce the risk of exposure to humans and the environment.
• Storage of ammonia fuel in a refrigerated state at atmospheric pressure.
• Classification of toxic areas and the implementation of both localized and global alarm systems to enhance crew safety. Alarm thresholds are set at 25 ppm for localized alerts, 110 ppm for global alerts, and 220 ppm for system shutdowns.

The new guidelines emphasize that the safety, reliability, and dependability of ammonia systems must be equivalent to those of new, comparable conventional oil-fueled main and auxiliary machinery. The term “equivalent” is all-important. It recognizes that ammonia is a different fuel with unique hazards (i.e. not the same as other fuels), but that its safety performance onboard must be similar to that of LNG or other alternatively-fueled vessels.

Liam Blackmore illustrated this concept by defining the “unacceptable” risk range of ammonia as a fuel (i.e. the risk threshold ammonia fuel needs to fall below to have an equivalent safety profile). As shown to the left, the selection of refrigerated storage systems represents an inherently safer choice, even though pressurized systems also falls well within the “acceptable” risk range. Properly applied, the new fuel guidelines will ensure that ammonia systems do in fact achieve safety standards comparable to those of LNG or other alternative fuel systems.

Additionally, the technical requirement chapters introduce unique considerations for ammonia fuel, including “Prevention of Exposure to Toxicity” and “Personal Protection” (i.e. PPE standards), which also distinguish ammonia from other marine fuels. These provisions ensure that ammonia’s hazards are effectively managed, supporting its safe use in shipping.

Looking Ahead

There are already demonstration vessels on the water using ammonia as a fuel, including small-scale supply vessels that began operations in 2023 and 2024. For more details, see our LEAD – vessels data. In support of this progress, the interim guidelines provide shipowners with a clear framework for vessel design and operational practices, ensuring both safety and regulatory compliance. Their approval represents the first step in a continuous process aimed at refining and enhancing these standards based on practical experience gained from their implementation in shipping projects. As insights from real-world applications accumulate, the guidelines will be revised to address gaps, incorporate best practices, and strengthen their effectiveness.

Changes to IGF, IGC Codes

Much of the progress described here is related to the IGF Code: the “International Code of Safety for Ships Using Gases or Other Low-flashpoint Fuels” that provides an international standard for ships operating with gas and other low flashpoint fuels. Its original purpose was to provide clarity on vessel safety standards for LNG fuel. Development of this code took over a decade, and it was only entered into force in 2017, meaning that formal guidelines for LNG shipping are a relatively new phenomenon. But the IGF Code does not cover low-flashpoint oil, methanol, ethanol, LPG, ammonia or hydrogen fuels.

These interim guidelines are part of an ongoing process to address this gap with extra regulatory frameworks for alternative fuels, and to make amendments to the IGF Code where necessary. The interim guidelines are expected to undergo revisions during CCC 12, scheduled for 2026 or 2027. In the meantime, the Marine Environment Protection Committee (MEPC), at its next meeting in April 2025, will focus on refining and potentially approving a goal-based marine fuel standard. This includes phasing in fuels with lower greenhouse gas (GHG) intensity and advancing a global GHG emissions pricing mechanism.

The International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code) entered into force in 1986, and concerns gas-carrying vessels. Under the current IGC Code, the use of toxic gas cargo for fuel (i.e. ammonia) is prohibited. Draft interim guidelines for using ammonia as cargo and fuel under the IGC Code are expected to be finalized at CCC 11 in September 2025, removing this prohibition and opening the door for ammonia-fueled, ammonia gas carriers to operate, such as those under construction by NYK Line and EXMAR.

And, while technical & regulatory advancements are progressing, equally important efforts are being directed toward other critical areas, such as developing comprehensive crew training to manage ammonia’s toxicity. Establishing consistent global regulatory standards, certification frameworks, and product specifications is also essential to support widespread adoption and harmonize safety measures across regions.