IGF Code: Low-Flashpoint Fuel Ship Safety

What the IGF Code is and what it governs

The IGF Code is the IMO’s mandatory, SOLAS-linked safety standard governing the design, construction, and operation of ships that burn low-flashpoint fuels (fuels with a flashpoint below 60 degrees Celsius) such as LNG, methanol, and, in future, ammonia and hydrogen. Its full title is the International Code of Safety for Ships Using Gases or Other Low-Flashpoint Fuels, and it is the foundation document of the gas-fuelled and alternative-fuel maritime sector.

The Code is distinct from the IGC Code , which governs ships that carry liquefied gas as cargo. The same substance, LNG or ammonia, is regulated under one regime when it is used as fuel and a different regime when it is shipped as cargo, even if it sits in similar pressure vessels. Adopted by Resolution MSC.391(95) on 11 June 2015 and in force from 1 January 2017, the IGF Code today provides detailed prescriptive requirements for the natural-gas pathway and a goal-based, risk-assessment route for newer fuels. It governs the rapidly growing fleet of LNG-fuelled container ships, ferries, and cruise ships (the LNG as Marine Fuel article covers the trade context), the first generation of methanol-fuelled vessels , and the early ammonia-fuelled and hydrogen-fuelled prototypes now entering service.

A vessel can be subject to both codes at once. A modern LNG carrier with dual-fuel propulsion burns some of its own cargo as fuel, complying with the IGC Code for the cargo function and, where it applies, the IGF Code for the fuel function. For a non-gas-cargo ship using gas as fuel, only the IGF Code applies, and the fuel is bunkered into dedicated tanks distinct from any cargo system.

Why the IGF Code exists

By the late 2000s several trends were converging to make a dedicated regulatory framework for gas-fuelled ships necessary. Tightening sulphur limits under MARPOL Annex VI Chapter 3 and the Emission Control Areas made low-sulphur compliance economically attractive, and natural gas, methanol, and ammonia all burn with substantially lower sulphur oxides than residual fuel oil. The Norwegian short-sea industry had run LNG-fuelled ferries since the early 2000s under flag-state-specific approvals and was pushing for an internationally harmonised regime so that gas-fuelled ships could trade worldwide. And container-shipping fleet renewal for the 2020s required a stable framework before the commitment of multi-billion-dollar newbuilding programmes.

The IMO’s Maritime Safety Committee began work on a unified gas-as-fuel code in 2009. After six years of drafting, drawing on class societies, gas-industry stakeholders, the maritime authorities of importing and exporting nations, and the established European LNG-ferry operators, the IGF Code was adopted on 11 June 2015 by Resolution MSC.391(95) and entered into force on 1 January 2017.

Legal status: SOLAS Chapter II-1 Part G

The IGF Code derives its mandatory force from a new part of SOLAS, Chapter II-1 Part G (“Ships using low-flashpoint fuels”), added at the same 2015 conference by Resolution MSC.392(95). Two regulations carry the obligation:

• Regulation II-1/56 sets the application: which ships, and from what date, must meet Part G.
• Regulation II-1/57 is the operative provision, requiring that any ship within scope comply with the IGF Code.

The definition of a low-flashpoint fuel sits in Regulation II-1/2.29: a fuel with a flashpoint lower than otherwise permitted for fuel oil under Regulation II-2/4.2.1.1, in effect below 60 degrees Celsius. The IGF Code is therefore not a stand-alone instrument but is incorporated by reference into the binding SOLAS framework, and its amendments take effect through the SOLAS tacit-acceptance procedure. Because the Code hangs off SOLAS Chapter II-1, it applies principally to new-build and converted ships to which that chapter applies.

Scope: what counts as a low-flashpoint fuel

The IGF Code defines low-flashpoint fuel as any fuel with a flashpoint below 60 degrees Celsius, distinguishing it from conventional residual marine fuels (heavy fuel oil, flashpoint typically 60 to 110 degrees Celsius) and distillate fuels (marine gas oil and marine diesel oil, flashpoint 60 to 65 degrees Celsius). Methane has no practical liquid-phase flashpoint (it is gaseous at all relevant marine conditions), but the Code categorises it as low-flashpoint by convention because of its overall fire-and-explosion hazard profile.

The Code provides detailed prescriptive requirements for natural gas in Part A-1 and Chapter 6. Every other fuel (methanol, ethanol, LPG, ammonia, hydrogen, and fuel cells running on any of them) is addressed through the Code’s risk-based design provisions together with the relevant IMO interim guidelines, where the designer demonstrates that the proposed fuel system meets the same safety goals as the prescriptive natural-gas requirements. There is, at present, no adopted IGF Code chapter for any fuel other than natural gas.

IGF versus IGC: a crucial distinction

A common source of confusion is the relationship between the IGF and IGC Codes. They cover different regulatory subjects:

• The IGC Code governs ships carrying gas as cargo: LNG carriers, LPG carriers, ammonia carriers, ethylene carriers, and chemical-gas carriers. The gas is the commodity being transported.
• The IGF Code governs ships using gas as fuel: any ship type whose propulsion or auxiliary power runs on LNG, methanol, ammonia, hydrogen, or another low-flashpoint fuel. The fuel is consumed during the voyage, not delivered to a customer.

A vessel can be subject to both at once. A modern LNG carrier with dual-fuel propulsion draws fuel gas via a vapour-return line from its cargo system, complying with the IGC Code for the cargo and, where applicable, the IGF Code for the fuel. Most LNG carriers built since 2010 are dual-fuel. Older steam-turbine LNG carriers built before 2010 pre-date the IGF Code and were governed entirely by the IGC Code with extensions for the fuel application.

For non-gas-cargo vessels using gas as fuel, LNG-fuelled container ships, LNG-fuelled cruise ships, methanol-fuelled tankers, only the IGF Code applies. The fuel is bunkered like marine diesel, from a bunker barge, truck, or shore terminal, into dedicated fuel storage tanks distinct from any cargo system.

Goal-based design and the alternative-design route

Why goal-based

The drafters faced a fundamental difficulty: the universe of potential low-flashpoint fuels is large (natural gas, LPG, methanol, ethanol, di-methyl ether, ammonia, hydrogen, biofuels, and dual-fuel arrangements running several of them), and each has distinct hazard properties, toxicity, flammable range, flame speed, ignition energy, vapour density, low-temperature behaviour, and water reactivity. Writing prescriptive requirements for every combination would have produced an unmanageable Code.

The chosen structure is goal-based: Part A articulates safety functional requirements that any fuel system must satisfy, supplemented by detailed prescriptive provisions for natural gas (Part A-1 and Chapter 6) where industry experience allowed prescriptive specification. The goal-based route gives a flexible pathway for novel fuels while holding every installation to the same safety targets.

Functional requirements

Chapter 4 establishes the functional requirements any low-flashpoint fuel system must meet: safety at least equivalent to a conventional oil-fuelled ship; containment of any fuel leakage so that it cannot reach manned spaces or ignition sources; detection of any leakage through continuous gas monitoring; mitigation of a leak through shutdown, ventilation, and isolation; limitation of damage so that a leak does not cascade to multiple failures; crew protection through appropriate equipment and procedures; and asset protection through fire and explosion safeguards equivalent to conventional fuels. These are demonstrated through a Chapter 4 risk assessment, a HAZID or HAZOP-style hazard study for the specific fuel system, presented to the flag-state administration and the classification society acting on its behalf.

The alternative-design route (SOLAS Regulation II-1/55)

Where a fuel or arrangement falls outside the prescriptive natural-gas provisions, approval runs through the alternative-design and arrangements provision of SOLAS Regulation II-1/55. The designer produces a documented engineering analysis and risk assessment showing that the arrangement provides a level of safety equivalent to the prescriptive requirements, and the administration approves it on that basis. This is the mechanism through which methanol, ammonia, hydrogen, and fuel-cell installations are currently certified, in combination with the relevant IMO interim guidelines. The prescriptive natural-gas provisions of Chapter 6, by contrast, can be followed directly without invoking the alternative-design process, which is why the majority of LNG-fuelled newbuildings take the prescriptive path.

How the Code is structured

The IGF Code is organised so that the general and the fuel-specific parts stay separable. Part A carries the general requirements and the functional-requirement framework, including the goal-based philosophy and the risk-assessment obligation. Part A-1 carries the specific requirements for ships using natural gas as fuel, the prescriptive engineering detail (Chapter 6 and the surrounding chapters) covering fuel containment, material selection for cryogenic service, bunkering systems, fuel-supply systems, power generation with gas-fuelled main and auxiliary engines, fire safety, explosion prevention, ventilation, electrical installations, and control, monitoring, and safety systems. Part B carries additional requirements for particular arrangements. This division means a future mandatory chapter for methanol or ammonia can be added as a new specific part without reopening the general framework, which is exactly how the IMO’s current amendment work is structured.

Fuel containment systems

Type C pressure vessels

The dominant containment arrangement for LNG-fuelled ships is the Type C pressure vessel, the same containment type used extensively in LPG carriers and small LNG carriers under the IGC Code . Type C tanks are pressure vessels designed to recognised boiler-and-pressure-vessel standards, with meaningful gauge-pressure capability (typically 5 to 10 bar gauge for fuel applications) that allows passive boil-off-gas accumulation without immediate pressure-relief activation. Because they hold pressure, a Type C tank paired with a tank connection space may have its connections below the highest liquid level, which simplifies installation.

Type C tanks for LNG fuel service are typically cylindrical or bilobe in cross-section, of 50 to 1,500 cubic metres capacity (far smaller than cargo tanks), built in 9% nickel steel or equivalent cryogenic material with internal and external insulation delivering a boil-off rate of roughly 0.10 to 0.20 percent per day. Where fuel capacity is large enough that pressure-vessel construction becomes uneconomical, on very large container ships or large cruise ships, Type A prismatic tanks are used instead, requiring full secondary barriers and additional protection that parallel the IGC Code arrangements. The LNG cargo containment systems article covers the membrane and independent-tank types in the cargo context.

Boil-off gas and pressure management

Because LNG is stored cryogenically, heat ingress continuously boils off a fraction of the liquid, raising tank pressure. A Type C tank absorbs this by allowing pressure to rise within its design margin, giving a holding time, the interval a closed tank can sit before pressure reaches the relief setting, that must exceed defined minimums so a ship can wait out a delay without venting. In service, boil-off gas is consumed by the engines, warmed and recompressed by a boil-off-gas compressor, or, as a last resort on some designs, disposed of in a gas-combustion unit. Venting fuel gas to atmosphere is avoided both for safety and because methane is a potent greenhouse gas.

Tank connection space and fuel storage hold space

The IGF Code requires a tank connection space (TCS), a gas-tight enclosed space surrounding all fuel-tank connections (fill lines, vapour lines, instrumentation penetrations, and safety-valve outlets). The TCS is mechanically ventilated at a high air-change rate, continuously gas-detected, and arranged so that leakage from a tank connection vents to a safe area rather than into the ship. The tanks themselves usually sit within a fuel storage hold space, an enclosed compartment with gas-tight bulkheads, water-tight subdivision to the applicable SOLAS damage-stability standard, and cofferdams separating the fuel space from adjacent machinery and accommodation. Both spaces are treated as gas-hazardous areas and follow the Code’s electrical-installation rules.

Fuel piping

Double-walled and ducted piping

The IGF Code requires double-walled fuel piping (or a ventilated duct) for any part of the fuel-gas system passing through manned spaces or unprotected machinery spaces. The inner pipe carries the fuel; the outer pipe or duct is a continuous secondary barrier with continuous gas detection in the annular space and ventilation sufficient to dilute any inner-pipe leak. Gas detection in the annular space initiates automatic safety action. Because the barrier is ventilated and monitored, the piping is not treated as a release source for hazardous-area classification.

The outer specification depends on the fuel state. Cryogenic liquid LNG requires a cryogenic-rated outer pipe (9% nickel or stainless steel), because a leak rapidly chills the outer wall. Vaporised gas at moderate temperature allows a standard structural-steel outer pipe. Methanol, being liquid at ambient temperature, relaxes the low-temperature requirements while adding toxicity and material-compatibility considerations.

Ventilated trunk and the fuel valve unit

A permitted alternative to a double wall is the ventilated trunk, a continuously ventilated enclosure around single-wall piping that extracts any leakage to a safe outboard location, functionally equivalent to the outer pipe. At each engine, the fuel valve unit (FVU) provides a double block-and-bleed valve arrangement isolating the engine from the supply, pressure regulation and metering, and a connection to the engine’s shutdown chain. A single FVU per engine is standard; multi-engine plants share a fuel manifold with an FVU at each engine.

Machinery-space concepts and hazardous-area zoning

Two machinery-space concepts

The Code offers two ways to arrange a space that contains gas-consuming machinery. An inherently gas-safe machinery space is designed so that a single failure cannot release fuel gas into the space, achieved with fully double-walled (ducted) piping and gas-safe equipment; in normal operation the space is treated as non-hazardous. An ESD-protected machinery space tolerates single-wall piping but is fitted so that, on gas detection, all non-safe electrical equipment and the gas supply are automatically shut down and the space is made safe. The inherently gas-safe concept is generally regarded as the safer of the two and is the more common choice on modern LNG-fuelled newbuildings.

Hazardous-area classification

Spaces where fuel gas or vapour may be present are classified into hazardous zones on the same principle used across the industry, with the most stringent controls where an explosive atmosphere is continuously or frequently present and progressively lighter controls further out. Electrical equipment in these zones must be of a certified-safe (explosion-protected) type, cable penetrations must be gas-tight, and ignition sources are excluded. The tank connection space, the fuel preparation room, the annular space of fuel piping, and the bunkering-manifold area are the principal zoned locations, and the zoning drives the selection of every electrical fitting placed in or near them.

Fuel preparation room

The fuel preparation room houses the equipment that takes stored cryogenic LNG and delivers it to the engines in the required form: warm gas at pressure for the engine type in use, or vaporised gas at lower pressure for boilers. Typical equipment includes in-tank or separate fuel pumps, a fuel vaporiser (commonly a glycol-water or seawater-heated exchanger), fuel-pressure regulation and metering, the boil-off-gas compressor where fitted, and pressure-relief equipment. The engine side, the low-pressure versus high-pressure gas-admission concepts of the main LNG fuel system , determines the delivery pressure the room must produce.

The room is treated as a hazardous area. The Code requires a gas-tight enclosure with vapour-tight closures on doors and ventilation openings, mechanical ventilation at high air-change rate, continuous gas detection with read-out at the control station, hazardous-area-rated electrical equipment, automatic shutdown on gas detection above the set threshold, and a dedicated bilge system isolated from the conventional engine-room bilge. It must be located on an open deck or, if below deck, arranged with the containment and airlock provisions of a tank connection space.

Bunkering procedures

Three principal bunkering modes

LNG and methanol fuel can be delivered to a ship in three principal ways. Truck-to-ship (TTS) uses a road tanker on the quay discharging through flexible cryogenic hoses, at the smallest delivery rate, for small volumes or where terminal infrastructure is absent; it is currently the most widespread mode for methanol and for small LNG-fuelled vessels. Ship-to-ship (STS) uses a dedicated bunker barge or small bunker ship alongside, at medium-to-high delivery rate, common at major hubs; the barge itself is an IGC Code vessel carrying LNG as cargo to deliver it as fuel. Shore-to-ship uses a permanent dock-side terminal with cryogenic loading arms or hoses, at the highest delivery rate, where a permanent installation justifies the capital cost.

Bunkering plan, safety zone, and ship-shore link

The Code, supported by ISO 20519 for LNG bunkering and the wider bunkering-safety guidance in ISO 18683, requires a bunkering plan prepared jointly by the ship and the bunker provider for each operation. The plan documents the quantity and quality (LNG specifications such as methane number and calorific value), the transfer rate and pressure, tank fill levels and high-level alarms, the communications protocol, and the emergency-shutdown procedures. Around the manifold a bunkering safety zone is established, an exclusion zone within which ignition sources and non-essential activity are prohibited during transfer. The ship-shore link, a fibre-optic or pneumatic emergency-shutdown signal connection made up at the manifold, ties the two sides together so that an ESD on either side propagates immediately to the other.

Emergency shutdown during transfer

Fuel-transfer operations use a two-stage emergency-shutdown sequence defined in ISO 20519 and industry guidance. ESD-1 stops the pumps and closes the ship and shore emergency-shutdown valves to halt flow. ESD-2 escalates to activate the emergency release coupling (ERC), safely parting the transfer hose or loading arm and isolating the receiving ship from the supply. Either party can trigger the sequence through the ship-shore link. These bunkering-specific ESD stages are separate from the Code’s own gas-detection safety actions described below.

SIMOPS

Simultaneous operations (SIMOPS), performing bunkering at the same time as cargo operations, passenger embarkation, or other dock-side activity, are a particularly sensitive area. The Code requires a documented SIMOPS risk assessment, with defined exclusion zones around the manifold, suspension of hot work and ignition-source activity in the zone, coordinated communication between the bunkering, cargo, and embarkation teams, and any port-state and flag-state approvals required. Many ports still restrict or prohibit SIMOPS during LNG bunkering, though the trend at major hubs has been gradual relaxation as operational experience accumulates.

Bunker custody transfer measurement

Custody-transfer measurement for LNG fuel is more complex than for fuel oil, because LNG is a low-density, low-temperature, multi-component liquid whose volume varies with temperature, pressure, and composition. Practice combines tank gauging by independent radar and float-type gauges, mass-flow metering at the manifold (typically Coriolis meters), composition measurement by gas chromatograph, and calorific-value correction to ISO 6976. The result is documented in a bunker delivery note stating both volume and energy content, since LNG quality varies between sources and the customer is buying energy, not volume.

Leak detection and automatic safety action

Detection coverage and thresholds

The IGF Code (Regulation 15) requires continuous gas detection at every location where leakage could plausibly occur: the tank connection space of every fuel tank, the fuel preparation room, the annular space of double-walled piping, the fuel valve units, machinery spaces where any single-wall piping is permitted, accommodation and machinery air intakes, and the bunkering-manifold area. Detection is referenced to the lower explosive limit (LEL). The core logic for tank and fuel spaces is an alarm at 20% LEL and automatic isolation and safety action when 40% LEL is reached at two detectors, closing the tank valve and cutting the gas supply to the machinery space. For ventilation ducts and hoods a separate pair applies: alarm at 30% LEL and safety action at 60% LEL. Detection is typically by infrared point sensors for hydrocarbons, with catalytic or dedicated sensors for hydrogen and toxic-gas sensors for ammonia.

These automatic safety actions are the Code’s own mechanism, and they are distinct from the bunkering ESD-1 and ESD-2 stages: the informal “ESD-1/ESD-2” labels belong to fuel-transfer operations, not to the gas-detection response. On a dual-fuel ship, gas-supply isolation transitions the engines to their backup oil fuel (typically marine gas oil), so that a fuel-gas fault does not by itself remove propulsion, which could be hazardous while entering port or in heavy weather. A full shutdown of the fuel system cleanly stops gas supply, and the engines accept it and shut down in a controlled way without damage.

Crew training: STCW Section A-V/3

The STCW Convention , through Section A-V/3 introduced by the 2015 STCW amendments (Convention amendments in Resolution MSC.396(95) and Code Part A amendments in Resolution MSC.397(95), both adopted 11 June 2015 and in force 1 January 2017), sets training requirements for seafarers on IGF-Code ships. There are two levels: Basic Training (Table A-V/3-1) for all crew with designated safety duties related to the fuel or fuel systems, and Advanced Training (Table A-V/3-2) for masters, chief engineers, officers, and anyone with immediate responsibility for the fuel and fuel systems. Advanced training combines approved training with a period of approved seagoing service that includes a set of bunkering operations, part of which may be met by approved simulator training.

The IGC and IGF training regimes are related but each carries its own certificate. There is cross-recognition: a seafarer holding the relevant liquefied-gas-tanker certificate of proficiency is generally deemed to meet the equivalent IGF-Code training requirement, subject to specified service conditions, because both regimes address low-flashpoint fuel hazards. Many seafarers in the gas-fuel sector hold both. The broader engine-department and special-training context sits in the STCW Convention article.

Fuel-specific provisions

Natural gas (LNG and CNG)

LNG and CNG are governed in prescriptive detail by Part A-1 and Chapter 6, the deepest body of operational experience and the most mature regulatory framework in the Code. The great majority of IGF-Code vessels in service today are LNG-fuelled, and a natural-gas ship can comply by following Chapter 6 prescriptively without invoking the alternative-design route.

Methanol and ethanol

Methanol and ethanol are within the Code’s low-flashpoint scope, but there is no adopted IGF Code chapter for them: Part A-1 remains natural-gas-specific. A methanol-fuelled ship is instead approved through the alternative-design provision of SOLAS Regulation II-1/55 combined with the IMO Interim Guidelines for the Safety of Ships Using Methyl/Ethyl Alcohol as Fuel, MSC.1/Circ.1621, approved by the Maritime Safety Committee at its 102nd session in November 2020. These interim guidelines adapt the Code’s functional requirements to methanol’s properties: it is liquid at ambient temperature (no cryogenic handling), has a low flashpoint near 12 degrees Celsius, is toxic on acute exposure, burns with a nearly invisible flame, and is corrosive to some common materials. Mandatory provisions are in development at the IMO Sub-Committee on Carriage of Cargoes and Containers (CCC), with draft amendments progressing toward a 2026 session and entry into force not expected before roughly 2028. Until then, the interim-guidelines-plus-alternative-design route governs the growing methanol fleet. See Methanol as Marine Fuel for the trade context.

Ammonia

Ammonia is within scope but has no dedicated IGF chapter; ammonia-fuelled ships are approved through interim guidelines and project-specific risk assessment under the alternative-design route. The dominant hazard is toxicity: ammonia is acutely dangerous at low concentrations, with a NIOSH immediately-dangerous-to-life-or-health (IDLH) value of about 300 ppm (workplace exposure limits are far lower, in the tens of ppm). This drives toxic-gas detection, dedicated alarms, stringent leak containment and ventilation, and crew-protection provisions distinct from the flammability focus of natural gas. First-generation ammonia-fuelled bulk carriers and tankers are being delivered from the mid-2020s under this regime.

Hydrogen

Hydrogen’s hazards are dominated by flammability and storage. It has a very wide flammable range, roughly 4 to 75 percent in air, against methane’s 5 to 15 percent, a very low minimum ignition energy, an extremely low boiling point requiring deep-cryogenic storage (or high-pressure gaseous storage), low density that speeds leak dispersion but also produces rapid pressure changes in containment, and a tendency to embrittle metals. Commercial deep-sea hydrogen-fuelled ships are not yet in service, but prototype passenger and offshore-supply vessels are operating and feasibility studies are advanced.

Fuel cells

The Code addresses fuel cells through its general framework with cross-reference to the underlying fuel, supported by IMO interim guidelines for fuel-cell power installations. A fuel cell running on natural gas via on-board reforming follows the natural-gas provisions for the fuel side and the fuel-cell module’s own safety case for the electrochemical side; methanol and hydrogen fuel cells run through the alternative-design route.

Class-society LNG-ready and gas-fuelled notations

To support investment before bunkering infrastructure was widely available, classification societies developed gas-ready and LNG-ready notations allowing a ship to be built and certified except for the actual fuel installation, with provisions for retrofitting the IGF system later when bunkering becomes economical on the vessel’s routes. Examples include the ABS LNG Bunker Ready notation, the Lloyd’s Register LNG-Ready notation, and the DNV Gas Fuelled and Gas Ready notations, with counterparts from Bureau Veritas and ClassNK.

These notations are typically tiered. A first level reserves notional space and makes structural and piping-run reservations for a later retrofit. A second level completes the detailed design of the retrofit and pre-engineers key bulkhead penetrations and foundations. A third level actually fits substantial portions of the installation, leaving only the cryogenic tank and final commissioning for activation. The tiered approach lets owners commit to the gas-ready position with varying capital exposure and convert to active gas fuel when bunkering economics justify it. A gas-ready notation does not mean the ship yet meets the full IGF-Code operational requirements; it means the design is prepared for the conversion that would bring it into IGF compliance.

Retrofit and conversion to low-flashpoint fuel

Converting a conventionally fuelled ship, or activating a gas-ready design, is a substantial drydock project. The scope typically includes installing the fuel tank and its tank connection space, the fuel preparation room and its equipment, double-walled or ducted fuel piping to the engines, the fuel valve units, the gas-detection and safety-action systems, and the bunkering station, together with the engine modifications needed to run dual-fuel. Because the ship must then meet Part A-1 (or the alternative-design case for a non-gas fuel), the conversion is approved on the same basis as a newbuilding, and the crew must gain the STCW A-V/3 certification before the ship trades on the new fuel. The gas-ready notations exist precisely to reduce the cost and downtime of this conversion by making the reservations in advance.

Bunkering infrastructure

The principal LNG-fuel bunkering hubs of the mid-2020s are Rotterdam and Antwerp-Zeebrugge in northwest Europe, Singapore (expanding rapidly since its first bunker barges in 2017), the mature Norwegian coastal network that supports the short-sea fleet, the major Japanese and Korean ports, several US Gulf ports, and the fast-growing Chinese ports led by Shanghai. Methanol bunkering is at an earlier stage, with truck-to-ship from chemical terminals the current norm and permanent-terminal investment in early planning at Rotterdam, Singapore, and the US Gulf. Bunkering infrastructure availability on a ship’s trading routes remains the decisive practical constraint on adopting any low-flashpoint fuel, which is why so many owners hold a gas-ready notation rather than an active gas installation.

The IGF Code in the decarbonisation framework

Connection to MARPOL Annex VI

The IGF Code is enabling for compliance with MARPOL Annex VI and the IMO greenhouse-gas work. Using the IMO carbon-conversion factors, residual fuel oil produces about 3.114 tonnes of CO2 per tonne of fuel burned; LNG about 2.750 (though methane slip from incomplete combustion offsets part of the benefit); methanol about 1.375 (lower because the molecule already contains oxygen); and ammonia and hydrogen produce no direct combustion CO2, though their lifecycle emissions depend entirely on the production pathway. These Cf values are set out in the IMO guidelines under Resolution MEPC.281(70). By making these fuels operationally practical, the IGF Code is a principal pathway toward lower carbon intensity.

The Energy Efficiency Existing Ship Index (EEXI) and Carbon Intensity Indicator (CII), introduced by the 2021 revised MARPOL Annex VI adopted as Resolution MEPC.328(76) (in force 1 November 2022), measure efficiency and operational carbon intensity; the CII calculation methods sit in the associated guidelines Resolution MEPC.336(76). LNG-fuelled ships typically show a meaningful reduction in attained EEXI and CII against oil-fuelled equivalents, the magnitude depending on the engine’s methane-slip characteristics and the fuel’s actual lifecycle CO2.

EU MRV, EU ETS, and FuelEU Maritime

The European Union has layered its own regime on top of the IMO framework: EU MRV monitoring and reporting since 2018, the extension of the EU Emissions Trading System to shipping from 1 January 2024, and FuelEU Maritime, which sets tightening per-ship greenhouse-gas-intensity limits from 1 January 2025 with explicit recognition of bio-LNG, e-methanol, e-ammonia, and other low-carbon pathways. The IGF Code and the interim guidelines for alternative fuels provide the safety framework that lets ships use gas, methanol, ammonia, or hydrogen to comply, and the gas-ready notations are expected to convert progressively to active use as the EU regime tightens toward 2030.

The proposed IMO Net-Zero Framework

The IMO’s mid-term greenhouse-gas measure, informally the Net-Zero Framework, would add a new Chapter 5 to MARPOL Annex VI: a two-tier goal-based marine fuel greenhouse-gas-intensity (GFI) standard and an associated emissions-pricing mechanism applying to ships above 5,000 gross tonnage. The framework was approved by vote at MEPC 83 in April 2025, but the extraordinary session convened to adopt it, MEPC/ES.2 in October 2025, adjourned for one year without adopting it. It is therefore approved but not adopted; the session is expected to reconvene around October 2026, and the earliest entry into force is now 1 March 2028. Because the framework would credit well-to-wake emissions, bio-LNG and e-methanol from renewable energy would receive lower GFI values than fossil-derived equivalents, making the fuel-production pathway, not only the fuel chemistry, a compliance variable. The IGF Code and its companion interim guidelines remain safety instruments and set no emissions limit themselves.

Operational experience and lessons

The IGF era is young: the Code has been in force since 2017, and the major deliveries of large LNG-fuelled container ships, cruise ships, and tankers are concentrated in the first half of the 2020s. Casualty experience is therefore limited but growing, and the multiple barriers built into the Code have so far contained the minor leakage events that have been reported. The principal operational lessons from the first generation of IGF-Code vessels are consistent across operators: bunkering is slower than fuel-oil bunkering because the Code’s safety provisions extend the operation, so voyages must be planned accordingly; gas-detection false alarms are common and demand routine cleaning, calibration, and inspection of detector heads; crew training is the load-bearing element, because IGF systems differ enough from oil-fuel systems that hands-on simulator and on-the-job experience is critical; fuel quality varies between bunker sources, with methane number, composition, and trace contaminants affecting engine performance; and material compatibility, particularly for methanol service, is an emerging concern as the alternative-fuel fleet grows.

Limitations

This article states the IGF Code’s structure and the load-bearing figures as they stand in early 2026, but several caveats apply. The regulatory position for fuels other than natural gas is actively moving: methanol, ammonia, hydrogen, and fuel cells are governed today by interim guidelines and the alternative-design route, and the mandatory IGF chapters now in development at the CCC Sub-Committee will change the detailed requirements when adopted. The greenhouse-gas landscape is likewise unsettled, the IMO Net-Zero Framework is approved but not adopted, and the EU instruments continue to tighten, so any emissions-related statement here is a snapshot. Specific numerical thresholds (gas-detection setpoints, tank pressures, boil-off rates, holding times) are quoted as the Code’s core values and typical practice; a particular ship’s approved arrangement, flag-state interpretation, and class rules govern the actual figures, and this article is not a substitute for the Code text, the applicable SOLAS regulations, or classification-society rules. Readers acting on a specific design or operation should consult the current instruments and their administration.

Related Articles

• IGC Code (carriage of liquefied gases as cargo)
• LNG as Marine Fuel
• LNG Fuel System
• Methanol as Marine Fuel
• LNG Cargo Containment Systems
• LNG Carrier
• STCW Convention
• SOLAS Chapter VII: Carriage of Dangerous Goods
• MARPOL Annex VI: Prevention of Air Pollution
• Marine Inert Gas Systems