IGF Code

The International Code of Safety for Ships using Gases or other Low-flashpoint Fuels (IGF Code) is a mandatory IMO instrument adopted under SOLAS Chapter II-1, Part G. It entered into force on 1 January 2017 and applies to ships using fuels with a flashpoint below 60°C that are not covered by the IGC Code (LNG carriers as cargo ships) or the IBC Code.

The IGF Code was developed primarily for LNG-fuelled vessels but is written as a goal-based framework intended to accommodate current and future alternative fuels — methanol, ethanol, ethane, liquefied petroleum gas (LPG, under a separate regulatory track), ammonia, and hydrogen. Where prescriptive rules do not exist for a given fuel, Chapter 3 provides the risk-assessment pathway.

Scope and application

Applies to ships using low-flashpoint fuels for propulsion, power generation, or auxiliary machinery — not to LNG carriers (which carry LNG as cargo and use it as fuel under the IGC Code + SOLAS Ch II-G overlap).
Does not apply to ships using fuel oil with flashpoint ≥ 60°C (conventional HFO, VLSFO, ULSFO) or to LPG carriers using cargo as fuel under the IGC/IBC regimes.
New ships of 500 GT and above on international voyages must comply in full. Existing ships are subject to a phased-in survey schedule per SOLAS regulation II-1/57.

Chapter structure

Ch 1–2General provisions & definitions
Application, definitions, goals. Applies to ships using fuels with flashpoint below 60°C (and any alternative fuel approved under the goal-based framework of Ch 3).
Ch 3Goal-based design and risk assessment
Sets the safety goals and functional requirements. Where no prescriptive rule exists, a formal safety assessment (FSA) — including HAZID and HAZOP — is mandatory. This is the pathway for novel fuels such as ammonia and hydrogen where prescriptive chapters do not yet exist.
Ch 4Fuel containment (storage tanks)
Type A (gravity, max fill 98%), Type B (pressurised, with partial secondary barrier), and Type C (vacuum-jacketed pressure vessel) tanks for liquefied gas fuels. Design temperature, relief valve settings, and secondary barrier requirements are specified per tank type.
Ch 5Fuel supply systems
Bunkering manifold design, hose specifications, Emergency Shutdown (ESD) integration, and overfill protection. Fuel supply piping must be double-walled or in a dedicated duct with ventilation.
Ch 6Fuel preparation room
A dedicated space for fuel treatment (vaporisation, pressure regulation, filtration). Minimum 30 air changes per hour (ACH) mechanical ventilation; gas detection mandatory; classified as hazardous zone.
Ch 7Bunker manifold and fuel supply systems
Manifold location (open deck, accessible), connection standards (ISO 21593 for LNG), drip tray, vapour return line where required, and emergency release coupling (ERC) at the manifold.
Ch 8Power generation and propulsion
Dual-fuel engine requirements: automatic changeover to backup fuel; safe failure mode. Boil-off gas (BOG) utilisation or management. Provisions for fuel cells (goal-based).
Ch 9Fire safety
Additional fire zones (Z-Z boundaries) around fuel spaces. Dry powder or CO₂ systems in fuel preparation rooms. Water-spray deluge on bunkering manifold. Foam systems not appropriate for LNG due to cryogenic temperatures.
Ch 10Explosion prevention
Classification of hazardous zones (Ex zones) per IEC 60079 / IEC 60092-502. No ignition sources within hazardous zones. Inert gas purging procedures before maintenance.
Ch 11Ventilation
Double-wall supply pipes or enclosed in a ventilated trunk (30 ACH minimum in enclosed fuel spaces). Ventilation failure alarm interlock with fuel supply shutdown.
Ch 12Electrical installations
All electrical equipment in hazardous zones must be certified Ex-rated (explosion-proof or intrinsically safe) per applicable IEC standards. Cable routes must avoid hazardous zones where practicable.
Ch 13Control, monitoring and alarm systems
Continuous gas detection mandatory in all enclosed fuel spaces, engine rooms, and machinery spaces where fuel may leak. Two-level alarm: low alarm (warning), high alarm (automatic shutdown ESD-2). Gas detection head response time ≤ 30 seconds.
Ch 14Manufacture, workmanship and materials testing
Weld inspection, pressure testing, and material certification requirements for fuel system components. Cryogenic materials for LNG must meet ductility requirements at design temperature.
Ch 15Operational requirements and maintenance
Procedures for bunkering, cool-down, warm-up, gas freeing, and maintenance of fuel systems. Planned maintenance system (PMS) entries for all fuel system components. Procedures to be included in the Safety Management System (SMS).
Ch 16Crew training
STCW V/3 basic and advanced training. Master and designated officers with direct fuel system duties must hold advanced certificate. All crew must have basic familiarisation.
Ch 17–20Specific provisions for individual fuels
Chapter 17: LNG-specific requirements. Chapter 18: Methanol and ethanol. Chapter 19: Ethane. Chapter 20: Reserved for future fuels (ammonia and hydrogen expected in next round of amendments).

Fuel-specific provisions

LNG (Liquefied Natural Gas)Flashpoint −188°C (methane)
Stored at cryogenic temperature (−163°C at atmospheric pressure). Type C pressure tanks or membrane tanks. Boil-off gas (BOG) must be managed — burned in dual-fuel engines or re-liquefied. No visible flame in daylight. Asphyxiation risk in confined spaces.
Key hazards: Rapid Phase Transition (RPT) if LNG contacts water. Cryogenic burn. Explosion from vapour cloud ignition. Rollover risk in large shore tanks (less relevant shipboard).
Methanol (CH₃OH)Flashpoint 11°C
Liquid at ambient temperature and pressure — simpler storage than LNG. High fire risk: burns with an almost invisible flame (no luminosity), making daylight fires extremely dangerous. Corrosive to certain seal materials and coatings. Water-miscible, making spill cleanup easier.
Key hazards: Invisible flame — foam/dry powder detection required. Acute toxicity (skin absorption, ingestion): IDLH 6,000 ppm, TLV-TWA 200 ppm. Cofferdam separation between methanol tanks and other spaces. Eye and respiratory protection mandatory during bunkering.
Ammonia (NH₃)Flashpoint Not flammable at ambient in standard conditions (autoignition 651°C)
Zero-carbon fuel with high energy density per unit volume as a liquid (−33°C at atmospheric pressure, or pressurised at ambient temperature). Being developed under IGF Ch 3 goal-based pathway. Positive-pressure accommodation design required to prevent gas ingress. IACS UR M91 under development.
Key hazards: Extreme toxicity: IDLH 300 ppm, PEL 25 ppm, LC50 (rat, 1hr) ~7,300 ppm. All fuel system seals and gaskets must be ammonia-resistant. Self-contained breathing apparatus (SCBA) mandatory for all bunkering personnel. Medical facility to treat chemical burns and inhalation casualties onboard.
Hydrogen (H₂)Flashpoint −253°C (liquid); gas is flammable 4–75% in air
Extremely wide flammability range; low ignition energy. Stored as compressed gas (700 bar) or cryogenic liquid (−253°C). Very low volumetric energy density requires large storage. Currently limited to fuel-cell vessels; used under IGF Ch 3 goal-based approval. IACS guidelines in development.
Key hazards: Invisible flame, no radiant heat from flame. Hydrogen embrittlement of steel. Cryogenic hazard (liquid hydrogen). Deflagration-to-detonation transition possible in confined spaces.

Bunkering operations and ESD

LNG and other low-flashpoint fuel bunkering operations require a pre-transfer Declaration of Inspection (DoI) between ship and terminal/bunker vessel, agreed communication protocol, and a designated safety zone (typically 25 m radius, no ignition sources). Emergency shutdown is provided at two levels:

ESD-1 (Warning)
Triggers: High gas alarm (first threshold), minor hose pull, manual trip at bunker station
Action: Alert alarms; close bunker manifold valve; inform ship and terminal. Transfer may be paused; investigation before resuming.
ESD-2 (Emergency)
Triggers: High-high gas alarm, large hose pull / breakaway coupling activation, fire detection in bunker area, loss of communications, manual emergency trip
Action: Immediate closure of all manifold and ship-side fuel valves; automatic disconnection via Emergency Release Coupling (ERC) or Dry Break Coupling (DBC); all bunkering transfer ceases. Alarm sounds on ship and terminal simultaneously.

STCW V/3 — crew training

Basic training (STCW V/3-1) — All crew serving on ships subject to the IGF Code must complete basic familiarisation: fuel properties and hazards, safety precautions, personal protective equipment (PPE) requirements, emergency procedures, and environmental protection. Typically a 1–2 day course.
Advanced training (STCW V/3-2) — Officers and ratings with direct fuel system duties (including bunkering, fuel system maintenance, and operational control) must hold the advanced certificate. Additional competencies: fuel system operation, gas detection systems, ESD operation, bunkering procedures, maintenance of fuel systems, and emergency response. Typically 3–5 days including simulator exercises. Revalidation every 5 years.

IGF Code amendments and future fuels

2018 amendments — Consequential amendments to SOLAS and STCW following initial experience with LNG vessels.
2022 amendments — Provisions for low-pressure dual-fuel engines (lower pressure fuel injection systems for retrofit and newbuild applications).
Ammonia and hydrogen — Interim guidelines (MSC-MEPC.2/Circ.25, 2023) provide guidance pending prescriptive IGF chapters. Full prescriptive chapters anticipated in future amendments; IACS unified requirements UR M91 (ammonia) under development.
Class notations — IACS Unified Requirement UR M89 covers LNG as fuel; class societies issue notation such as LNG Fuelled, Methanol Fuelled, etc. Surveys are conducted at initial, annual, intermediate, and renewal intervals aligned with SOLAS survey cycles.

Risk-based design pathway (Chapter 3)

Where the prescriptive requirements of the IGF Code do not address a specific fuel, arrangement, or technology, Chapter 3 provides a formal safety approval pathway. The process requires:

Hazard Identification (HAZID) — structured identification of all hazards associated with the fuel system design, conducted by a multidisciplinary team.
Hazard and Operability study (HAZOP) — systematic examination of deviations from design intent in the fuel system; used to identify credible failure scenarios.
Quantitative Risk Assessment (QRA) or equivalent — establishes that the residual risk of the proposed design is equivalent to or lower than a prescriptive IGF Code design.
Flag state approval — the Administration must approve the alternative design; major classification societies act as recognised organisations. IMO MSC Circulars may be issued for widely applicable solutions (e.g., ammonia interim guidelines).