NOVEMBER 2026 · SAFETY GUIDANCE FOR ALTERNATIVE MARINE FUELS
Position as at the Sub-Committee on Carriage of Cargoes and Containers (CCC) 12th session, 14-18 September 2026. Given the evolving nature of safety guidance, there will be future iterations of this note.
Published November 2026
Safety guidance for the selected fuels – methanol, hydrogen and ammonia – is progressing. Interim guidelines are now in place for all three fuels and classification societies have introduced requirements to help fill gaps while international regulations are still being developed. Together, IMO instruments, IACS resolutions and interpretations, and class rules provide a structured framework for demonstrating an acceptable level of safety.
These guidelines are being developed with less operational experience than was available when Liquefied Natural Gas (LNG) regulations were established. The instruments acknowledge this, each committing to review as experience accumulates.
Some dimensions of hazard control sit largely outside the instruments. These include how risk assessments are scoped and conducted, competency and training, and disciplines such as process safety management and human and organisational factors (HOF). For conventional fuels, decades of service experience shape how these dimensions are handled in practice. For methanol, ammonia and hydrogen, whose hazards and failure modes differ, that experience is still limited and cannot yet play the same role.
The Decarb Lens is a series of short notes summarising the progress of maritime decarbonisation, linked to the systemic barriers we track in our Theory of Change. Each note takes a specific topic and presents where the industry stands currently, adding commentary from our experts on where further progress can be made.
This note shows where safety guidance for methanol, ammonia, and hydrogen as marine fuels stands today. It tracks how far guidance for each fuel has progressed along the regulatory pathway, from the first approvals under the alternative-design route to binding international requirements. Liquefied Natural Gas (LNG) is included as a comparator, showing what progression through the regulatory stages looks like.
The note focuses on current regulatory progress, drawing on published instruments from the International Maritime Organization (IMO) and the International Association of Classification Societies (IACS). Relevant regulatory instruments referenced are listed in the register published alongside this note. Future notes will examine other parts of the transition, and this one will be updated as the position develops.
Ships using LNG as a fuel have been covered by detailed, fuel-specific mandatory requirements under the International Code of Safety for Ships Using Gases or Other Low-flashpoint Fuels (IGF Code) since 2017. Equivalent requirements are not yet in place for methanol, ammonia or hydrogen. Methanol- and hydrogen-fuelled ships are currently covered by the Code’s general requirements, while ammonia sits outside its scope. This is set to change: amendments approved at the 111th session of the Maritime Safety Committee (MSC 111) would bring ammonia and other gaseous fuels within the scope of the IGF Code. They are expected to be adopted at MSC 112 and enter into force on 1 July 2028. Until more specific requirements are in place, ships using methanol, ammonia or hydrogen are approved on a case-by-case basis by the flag Administration under the alternative-design route in the International Convention for the Safety of Life at Sea (SOLAS) regulation II-1/55. To gain approval, the design must meet the intent of the relevant requirements and provide an equivalent level of safety.
As experience develops, interim guidelines approved by MSC provide a common technical basis for these approvals. Guidelines were approved for methanol in 2020, ammonia in 2024 and hydrogen in 2026. These guidelines are not mandatory and do not replace case-by-case approval: vessels must still be approved under SOLAS regulation II-1/55. Instead, they give regulators, designers and classification societies a shared technical reference for demonstrating an equivalent level of safety.
The next step in the regulatory pathway is mandatory requirements. So far, only LNG has reached this stage. Its 2009 interim guidelines were superseded by the IGF Code, adopted in 2015 and in force from 2017. There is no fixed timeframe for moving from interim guidelines to mandatory requirements. For methanol, ammonia, and hydrogen no timeline has been set.
Where four marine fuels sit on the IMO regulatory safety pathway
Included: IMO instruments only — fuel-specific safety guidance for ships using the fuel, and the general alternative design route (SOLAS II-1/55), shown separately. Node date is the MSC approval (or, for resolutions, adoption) date for interim guidelines and the MSC adoption date for mandatory instruments (entry into force shown as annotation); month and year only.
Not included: IACS unified interpretations and class society rules; gas carriers using their own cargo as fuel (IGC Code track); fuel cell guidelines (fuel-agnostic).
The "today" marker reflects the September 2026 analysis date, not the publication date. Dotted lines show an unscheduled future pathway, not a delivery date.
Alternative design, SOLAS regulation II-1/55
The flag Administration approves each ship individually. The design must meet the intent of the relevant requirements and provide an equivalent level of safety. Applied using MSC.1/Circ.1455 and MSC.1/Circ.1212/Rev.2.
No fuel-specific requirements exist, so each ship is approved case by case.
Ships are still approved case by case. The guidelines give regulators, designers and classification societies a shared technical reference for the assessment.
Ships comply with the fuel-specific requirements in the IGF Code. The route stays open for designs that depart from them.
Instead, all vessels must be approved individually through the alternative-design process under SOLAS regulation II-1/55, using the IMO’s approval guidelines (MSC.1/Circ.1455 and MSC.1/Circ.1212/Rev.2 for the engineering analysis). This allows vessels to be approved and to operate while international requirements for the fuel are still being developed.
A fuel-specific standard issued through an MSC circular. These guidelines are recommendations only – they do not bind flag States unless adopted by an Administration through national requirements or approval processes. They give Administrations, designers and classification societies a common reference where previously each project had to develop its approach from first principles.
A fuel reaches this stage when binding fuel-specific requirements for it are adopted into the relevant mandatory framework. For the fuels considered here, this is the IGF Code, given force through SOLAS Chapter II-1. The Code was designed to evolve in this way, with requirements for additional gases or other low-flashpoint fuels added as they are developed. There is no set timeline for interim guidelines to be developed into mandatory requirements. Each fuel’s guidelines must be reviewed and the resulting requirements formally adopted by MSC before they become mandatory.
So far, only LNG has completed this transition, and the IGF Code itself was the result of that process. Reaching this stage means that the requirements become binding. These requirements draw on the best available knowledge from operational experience, field data, and research and development. As experience grows and technology evolves, they are reviewed and updated.
Alternative design under SOLAS regulation II-1/55, applied using the IMO's approval guidelines (MSC.1/Circ.1455, with MSC.1/Circ.1212/Rev.2 for the engineering analysis). This is how the first vessels are approved and how the interim guidelines are applied. This route also remains available once a mandatory code is in place. Approval is granted vessel by vessel by the flag Administration, typically supported by a classification society acting as a Recognised Organisation. Where an IACS member classification society is involved, IACS Unified Requirements, Unified Interpretations, and technical guidance may promote consistency in the assessment. However, approval authority remains with the flag Administration and there is no central register of approvals; consequently, differences in interpretation and acceptance can still occur between Administrations.
Requirements are introduced in stages. Each instrument has an adoption or approval date, followed by a later date when it takes effect. For IMO instruments, this is the entry-into-force date; for IACS instruments, it is the implementation date. Requirements generally apply based on a vessel’s contract or construction date, rather than retrospectively. This means that a vessel operating today may legally predate requirements that are now mandatory for new designs.
When this note shows where a fuel sits on the pathway, it refers to the requirements that apply to new designs. The public evidence register provides the adoption and effective dates for each instrument.
The code that applies depends on how the substance is used on board, because different uses bring different safety risks. Ships using gases or other low-flashpoint fuels as fuel fall under the IGF Code framework. Where the IGF Code does not yet include requirements for a particular fuel, fuel-specific interim guidelines apply. For example, the methyl/ethyl alcohol guidelines (MSC.1/Circ.1621) were introduced because the IGF Code did not contain relevant provisions for methanol. They are applied through the alternative-design route under SOLAS regulation II-1/55, within the same framework.
A gas carrier burning its own cargo falls under the International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code), which was amended to allow ammonia cargo to be used as fuel. Chemical tankers using their methanol cargo as fuel are instead given special consideration within the interim guidelines themselves (MSC.1/Circ.1621, 5.3.6).
The requirements for each fuel reflect its specific hazards.
Methanol
MSC.1/Circ.1621
The methanol guidelines require toxicity to be specially considered when designing detection systems and planning maintenance (MSC.1/Circ.1621, 15.7.4, 17.3.1).
Ammonia
MSC.1/Circ.1687
The ammonia guidelines go much further: toxic areas and toxic spaces are treated as specific classification categories (MSC.1/Circ.1687, 2.2.5–2.2.6), and toxicity hazards must be explicitly considered in the risk assessment (4.2.2). A dedicated chapter on preventing exposure requires dispersion analysis against a 220 parts per million (ppm) criterion, safe havens that can shelter everyone on board in the event of a release (12bis.5) and escape respiratory protection for each person on board (20.4.5).
Hydrogen
MSC.1/Circ.1701
Hydrogen presents a different set of risks. Because it is not toxic, its guidelines contain no toxicity provisions. Instead, they address hazards that do not appear in the other instruments, including self-ignition, hydrogen embrittlement, condensation of air and oxygen enrichment at cryogenic temperatures, and fire detection designed to detect flames that are invisible (MSC.1/Circ.1701, 4.2.2, 11.2.4).
When the IGF Code was adopted in 2015, LNG-fuelled vessels had operated for years and numbered in the hundreds1. In contrast, when the interim guidelines for ammonia were approved in December 2024, operational experience with ammonia as a marine fuel was limited to a handful of vessels2. Vessel numbers also do not necessarily reflect the amount of operating experience available: most of these vessels are dual-fuel, and limited fuel availability and higher prices mean they may operate using conventional fuel rather than alternative fuels. Having an alternative-fuel-capable vessel on the water therefore does not necessarily mean it is gaining experience using that fuel.
This matters because operational experience takes time to accumulate and informs the further development of the rules. Yet vessels entering service today need to be safe to operate on the alternative fuel from the outset.
IMO instruments recognise this challenge: the interim guidelines are intended to be reviewed as experience with their application accumulates, providing an important input to future rule development and supporting decarbonisation trajectories. Building this experience will require investments of time, thought and financial resources from across the maritime ecosystem.
Classification societies are independent, non-governmental bodies that establish technical rules for the design, construction, and through-life maintenance of ships, and verify compliance with those rules through survey and other assurance processes. The International Association of Classification Societies (IACS) is the association of the major societies: it establishes, develops, reviews, and promotes minimum technical requirements for ship design, construction, maintenance and survey; assists international regulatory bodies in developing, amending and interpreting regulations and standards, including by contributing technical expertise to IMO rule development and committee activities; and operates a quality certification scheme with which its members must comply.3
IACS issues two kinds of instrument relevant here. Unified Interpretations (UIs) resolve ambiguity in an IMO instrument: where a provision sets a goal but does not explain how to meet it, a UI provides the criteria, so all member societies interpret the requirement in the same way. Unified Requirements (URs) set minimum technical requirements that member societies incorporate into their own rules. A UR can be developed even where no IMO instrument exists, giving classification societies a common technical basis when a new fuel has moved ahead of the international regulatory framework. Both carry an adoption date and a separate implementation date, applied by contract or construction date.
Three series cover the requirements and interpretations relevant to new fuels.
Gas and low-flashpoint fuels
GF SERIES
Contains UIs covering the IGF Code and fuel-specific interim guidelines. This includes the body of interpretations developed for LNG, as well as the methanol UIs linked to MSC.1/Circ.1621.
Ammonia-fuelled ships
H SERIES
Contains URs setting requirements where no binding IMO instrument yet exists. This includes UR H2 on mitigating ammonia releases.
Gas carriers
GC SERIES
Covers gas carriers, including interpretations for using cargo as fuel.
Classification societies set technical rules for ships and assign class when those rules are met. Their rules incorporate IACS Unified Requirements, which set common minimum requirements across IACS members.
Organisations which are classification societies may also act as Recognised Organisations, carrying out surveys and certification on behalf of a flag Administration under delegated authority. In doing so, they apply IMO requirements, where these exist, together with any additional domestic legislation in force for that flag Administration. IACS Unified Interpretations may also clarify how IMO requirements should be applied where the flag Administration has not issued its own instruction.
Classification rules can be particularly important for newer fuels. Where there is no mandatory code, a design can be approved through the alternative-design route under SOLAS regulation II-1/55 by the flag Administration with support from a Recognised Organisation acting on its behalf. The classification society’s own rules, together with a risk assessment, provide much of the technical basis needed to assess the design.
Class is not a parallel authority to the IMO, but it plays a key role in making the alternative-design route work in practice. Ongoing class surveys also help ensure that the ship continues to meet the relevant technical requirements while in service.
These sections have described what is covered by the compliance safety regime today: the technical requirements that must be met by the vessel design, the interpretations that ensure these requirements are applied consistently, and the verification process that confirms that the installed equipment meets them. The discussion now turns to the issues that are not yet fully captured within existing regulatory and assurance frameworks, including human and organisational factors (HOF) and other operational considerations that remain essential to safety.
This note describes primarily technical requirements for vessels. Crew certification and competency standards sit under the Standards of Training, Certification and Watchkeeping for Seafarers (the STCW Convention), and safety management in the International Safety Management (ISM) Code, though the fuel codes themselves contain onboard drill and operational requirements.
The guidelines call for each project to carry out its own risk assessment, for ammonia and hydrogen, explicitly a holistic one (MSC.1/Circ.1687 and MSC.1/Circ.1701, paragraph 4.2.1 in each), but leave its scope to those who conduct it. For fuels with almost no operating history, the quality of that assessment carries more weight than usual, because there is no service experience to ground it.
Current regulations do not consistently provide detailed guidance on how human performance should be considered in hazard analysis and control design4. Yet alternative fuels and other emerging technologies are changing both the risk profile of ships and their operational demands, meaning that technical compliance alone provides only partial assurance of safe operation. Human factors engineering is one approach used to address this gap, by considering the entire socio-technical system it can serve as a validation mechanism for novel ship designs, providing evidence that they can be operated safely and effectively, particularly where operational experience is limited.
This note records where the rules stand today. How to track the parts of safety that sit outside them, including HOF, is what the next editions of this series will address.
Conclusion: what this note shows
Safety guidance for the new fuels exists and is progressing. Interim guidelines are in place for ammonia, methanol and hydrogen, while class rules and interpretations help fill gaps as international requirements develop. Together, these instruments provide a framework for demonstrating and maintaining an acceptable level of safety, but some aspects of managing risk sit outside them. With limited operational experience of these fuels, requirements and practices will continue to evolve as experience grows.
1. Clarksons World Fleet Register data, July 2026 ↩
2. Ammonia Energy Association (2024). Global Project List: Ammonia-fueled
Vessels – Executive Summary, December 2024. ↩
3. IACS. Role of Class. Available at: Role of Class - Safer and Cleaner Shipping - IACS (September 2026); IACS. Classification Societies – What, Why and How? Available at: About us - Safer and Cleaner Shipping - IACS (September 2026). ↩
4. MSC.1/Circ.1455 lists human factors experts among those who may join the design team and includes human behaviour among the techniques a risk assessment may use, but no method is specified; for interim guidelines, MSC.1/Circ.1621, MSC.1/Circ.1687, MSC.1/Circ.1701 do not refer to human factors. ↩
LNG is included as an example of a fuel that has already reached mandatory requirements. The focus is on ammonia, methanol and hydrogen, where the Decarb Hub’s Human Safety and Risk programme has been most actively focused to date.
The IMO interim guidelines cover methyl/ethyl alcohol as fuel (MSC.1/Circ.1621). This note focuses on methanol. We use “methyl/ethyl alcohol” only when referring to the guidelines by their official name.
The framework does not distinguish between production pathways or conversion technologies, since neither changes the hazards of the fuel itself.
This note draws on publicly available documents from the IMO and IACS websites, as well as Lloyd’s Register summary reports of sessions of the IMO’s Sub-Committee on Carriage of Cargoes and Containers (CCC) and of the IMO’s Maritime Safety Committee (MSC).
A public version of the regulatory register (instrument, adoption date, entry-into-force date) is published alongside this note.
A glossary of key terms is provided.
(SOLAS regulation II-1/55, applied using IMO guidelines MSC.1/Circ.1455 and MSC.1/Circ.1212/Rev.2). The established route for approving a design that does not follow prescriptive requirements, by showing the flag Administration that it provides an equivalent level of safety.
The date from which an instrument’s requirements apply.
The flag State of a ship (the State with which the ship is registered). It approves alternative designs and delegates survey and certification, via Recognised Organisations.
The science of understanding and designing the interactions between people and the wider socio-technical system. It ensures that safety and performance emerge from resilient systems that enable successful human performance under both routine and unexpected conditions, from concept design through commissioning and operations.
The International Association of Classification Societies: the association of the major classification societies.
The International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk: the mandatory code which provides safety regulations for gas carriers, including how they can use their own cargo as fuel.
The International Code of Safety for Ships Using Gases or Other Low-flashpoint Fuels: the mandatory code for ships using low-flashpoint fuels. Detailed requirements currently exist for natural gas, with other fuels due to be added as their safety standards are finalised.
The International Maritime Organization: the United Nations agency responsible for the safety and security of shipping and the prevention of pollution from ships. Its Maritime Safety Committee (MSC) approves the instruments this note describes.
The International Safety Management Code: the mandatory instrument governing safety management systems for the operation of ships.
Liquefied natural gas, included in this note as the reference case of a new fuel that has completed the regulatory pathway.
A document approved by the IMO’s Maritime Safety Committee and circulated to Member States. Interim guidelines are issued in this form: they are recommendatory, not binding.
Parts per million: the unit in which ammonia exposure thresholds are set
An organisation, often also a classification society, authorised by a flag Administration to carry out statutory survey and certification on its behalf.
An enclosed refuge required by the ammonia interim guidelines, with capacity for all persons on board, designed to minimise exposure in the event of an ammonia release.
The International Convention for the Safety of Life at Sea: the principal international treaty on ship safety. Its regulation II-1/55 provides the alternative-design route described in this note, applied using IMO guidelines MSC.1/Circ.1455 and MSC.1/Circ.1212/Rev.2.
The International Convention on Standards of Training, Certification and Watchkeeping for Seafarers: the instrument governing crew training, competency and certification.
An IACS instrument that clarifies how requirements in IMO Conventions or Recommendations should be interpreted and applied in practice, so that all member societies apply it the same way.
A requirement covering matters directly linked to classification societies’ rules and practices, as well as the broader principles on which those rules and practices are based. It can exist where no IMO instrument yet does.
A public version of the regulatory register (instrument, adoption date, entry-into-force date) is published alongside this note.
