Practical Guide for Approval of Ammonia- or Hydrogen-Fuelled Ships

April 29, 2025

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by Linda Sigrid Hammer (DNV) As the maritime industry moves towards zero-emission operations, ammonia and hydrogen are gradually emerging as suitable ship fuels due to their carbon-free emissions. These new fuels require a change of mindset in terms of design, operations and crew competence, all addressed in a new DNV paper. With no specific IMO regulation available, IMO's alternative design approval (ADA) process is essential for approval, and the paper outlines how DNV rules provide structured, prescriptive requirements to simplify the procedure.

The paper – Safe introduction of alternative fuels: Focus on ammonia and hydrogen as ship fuels – offers a structured pathway for shipowners to achieve approval through IMO’s alternative design approval (ADA) process.

Seven steps to obtain approval for ammonia- and hydrogen-fuelled ships

“We outline seven steps to assist shipowners and other stakeholders in obtaining approval and safely deploying ammonia- and hydrogen-fuelled ships in today’s immature regulatory environment,” says Linda Hammer, Principal Consultant, Environment Advisory at DNV and lead author of the white paper. “The regulatory path is certainly complex, but the steps and safety measures in the paper add up to a clear, achievable pathway to ship approval and safe operations. It also explains how DNV’s support can significantly ease this process through its tailored rule sets and learnings from pilot projects.”

Understanding ADA phases: From initial design to final approval

IMO’s IGF Code (International Code of Safety for Ship Using Gases or Other Low-flashpoint Fuels) currently covers natural gas but not ammonia or hydrogen. Without detailed regulations, IMO’s risk-based ADA process (MSC.1/Circ.1455) is used. It involves demonstrating that the ship’s safety level is equivalent to that of conventional oil-fuelled vessels.

ADA has two main phases. A preliminary design approval requires a hazard identification (HAZID) study, developing a preliminary risk assessment, and defining preliminary risk-control measures and safety strategies.

Phase two, final design approval, starts with refining the design with detailed technical and safety documentation, then making a final risk assessment, addressing integration and operation-specific concerns. Then come complete system integration testing and submitting findings to the flag administration.

Role of class and flag administrations in approval process

As the IMO regulatory framework progresses towards eventually amending the IGF Code, classification societies like DNV can give shipowners a head start in designing vessels by issuing class certificates and providing prescriptive rule frameworks to support ADA.

Flag administrations enforce statutory regulations and have the final say on approvals. Early and active engagement with the relevant flag administration is therefore the key to clarifying approval expectations and streamlining ADA.

Subject to flag administration acceptance, the DNV rules can be applied as the flag administration’s approval basis or to significantly reduce the complexity of ADA.

Simplifying ship approval: DNV’s rules for ammonia and hydrogen fuels

DNV’s classification rules for ammonia and hydrogen (i.e. the “Gas fuelled ammonia” notation published in 2021 and the 2024 “Gas fuelled hydrogen” notation) provide structured, prescriptive requirements as far as possible to simplify ADA. Applying them helps reduce uncertainty in flag administration approval, streamlines design focus by aligning with expected risk assessments, and provides predictability to shipowners, ship designers and shipyards.

The paper describes step-by-step actions for obtaining approval. First, engage DNV and the flag administration early to clarify the approval basis. “DNV can help owners and yards in the initial contact with the flag administration to obtain necessary clarification regarding the approval scope and process,” says Hammer.

Second, align the design with DNV rules to ensure it provides a strong technical basis for risk evaluation. Third, tap into DNV’s extensive and growing experience from prior projects to anticipate what risk studies and documentation may be needed.

The paper also discusses measures to manage the new technical, human and organizational risks that both fuels bring compared to conventional fuels. DNV’s dedicated ship rules for each fuel type outline technical requirements and mitigation systems to integrate during design and operation.

Addressing hydrogen safety challenges in design and operations

Hydrogen is highly flammable, with wide explosive limits and low ignition energy.

Hydrogen storage involves cryogenic systems (−253°C) or high-pressure tanks (up to 700 bar).

Safety focus areas include preventing leaks through robust designs and secondary enclosures, ignition prevention, controlled gas dispersion from leakages and personnel protection from frostbite and asphyxiation.

Addressing ammonia safety challenges in ship design

Ammonia is corrosive, toxic to inhale even in small concentrations, and can cause severe tissue damage upon contact.

Safety focus areas discussed in the paper include preventing and detecting leaks, especially near accommodation areas, using ventilation as well as toxic release mitigation strategies, designing safe bunkering systems and containment spaces, and providing personnel protection, including safe havens.

Preparing for safe operations and crew competency

The safety challenges with hydrogen and ammonia also require changes in ship operation, crew training and possibly the organizational set-up.

Safety management system updates must include fuel-specific operating procedures, maintenance protocols and emergency preparedness and drills.

Training and competency development is hampered by the fact that there are currently no courses for ammonia or hydrogen under the STCW (International Convention on Standards of Training, Certification and Watchkeeping for Seafarers).

Developing safety training for handling ammonia

The paper recommends that training should be developed in consultation with the flag administration, and that courses should cover fuel properties, normal operation, safety barrier management and emergency response.

DNV Recommended Practice DNV-RP-0699 “Competence related to the use of ammonia as fuel” enables the assessment and verification of individuals’ knowledge and skills to ensure they can operate and maintain systems and equipment safely.

Guidelines from the Maritime Technologies Forum (MTF) on alternative fuel safety management systems can also help in updating the safety management system.

“Organizations must also adapt their safety management systems to ensure continuous oversight of fuel system integrity and safety,” Hammer explains.

Coordinating safe bunkering and port approvals

Safety concerns extend beyond individual ships to the maritime industrial ecosystem within which they operate.

Unlike on-board fuel systems (regulated by the IGF Code), bunkering operations are governed by port, local and national authorities. Each bunkering site requires site-specific risk assessments and dispersion analyses as well as harmonized procedures between ship and shore teams.

The paper suggests adopting harmonized regional practices as developed in studies by the European Maritime Safety Agency (EMSA) and the Maritime Technologies Forum. This could be realized through the development of a network of bunkering locations and green shipping corridors.

Collaborating to accelerate regulatory maturity

Industry-wide collaboration is essential, says Hammer. “As the paper stresses, the maritime industry cannot wait decades to mature these fuel systems as it did with liquefied natural gas. Rapid learning, pilot projects and knowledge sharing are critical.”

DNV supports this through the Nordic Roadmap for Future Fuels, the MarHySafe hydrogen handbook, the Ammonia Safety Handbook published by the Green Shipping Programme and engagements with EMSA to develop hydrogen guidance and training programmes for hydrogen and ammonia. READ MORE