Operational Guide · Registers & Logbooks

# Liquefied Gases and Operational Notes on the IGC Code

The IGC Code governs the construction and equipment of gas carriers (LNG, LPG and other liquefied gases in bulk): cryogenic temperatures, containment systems and boil-off gas require specific operational competence.

IGC Code liquefied gases LNG LPG gas carrier

## Operational Explanation

The IGC Code (International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk) sets construction and operational standards for ships carrying liquefied gases in bulk, such as LNG (liquefied natural gas) and LPG (liquefied petroleum gas), often at cryogenic temperatures (down to -163°C for LNG).

Unlike chemical tankers, gas carriers manage the phenomenon of boil-off gas (natural evaporation of the cargo during transport due to heat exchange), which must be managed through reliquefaction systems, combustion in the engines (on gas-fuelled ships) or controlled release, according to the ship's specific procedures.

2026 update: Res. MSC.523(106) replaced Table 6.3 of the IGC Code, approving high-manganese austenitic steel as an approved material for cargo tanks, secondary barriers and process pressure vessels down to -165°C, with staggered entry into force during 2026. In parallel, the Maritime Safety Committee approved at MSC 111 a broader package of amendments, with formal adoption expected in December 2026 and entry into force from 1 July 2028: clarifications on the "one ship, one code" principle for gas carriers using alternative fuels, new provisions for the carriage of CO2 as cargo, for the use of LPG, ethane and toxic cargoes as fuel, finite-element analysis requirements for Type C tanks, cargo tank filling limits and cause-and-effect matrices for emergency shutdown (ESD). The International Certificate of Fitness will be revised with a new three-date system, and only products explicitly listed in Chapter 19 of the Code will be able to appear in the certificate's table as cargo or fuel.

Liquefied hydrogen as cargo (MSC 111, May 2026): distinct from hydrogen used as fuel (governed by separately approved Interim Guidelines), the carriage of liquefied hydrogen in bulk as cargo follows the "Interim recommendations for the carriage of liquefied hydrogen in bulk", whose revision (Resolution MSC.565(108)), finalised at CCC 11 (September 2025), was adopted at MSC 111 itself. The revision introduces a new Part D dedicated to membrane cargo containment systems with insulation spaces kept under vacuum, with definitions for the primary and secondary insulation space, and specific requirements on structural integrity, barrier tightness, insulation performance, vacuum monitoring, leak detection, pressure control, material compatibility and emergency procedures — a direct response to the specific safety challenges posed by the carriage of liquefied hydrogen, a cargo still in its early stages compared with LNG and LPG.

## Regulatory Reference

SOLAS Chapter VII, Part C makes the IGC Code mandatory for gas carriers built after 1 July 1986. The Code has been periodically revised to keep pace with new containment technologies and gas-fuelled propulsion systems. Res. MSC.523(106) (Table 6.3, high-manganese steel, in force during 2026); a broader package of amendments approved at MSC 111, adoption expected December 2026, in force from 1 July 2028 (CO2 cargo, alternative fuels, FEA for Type C tanks, new three-date Certificate of Fitness). Res. MSC.565(108), adopted at MSC 111 (May 2026): revision of the Interim recommendations for the carriage of liquefied hydrogen in bulk, with a new Part D on membrane containment systems with vacuum insulation.

## Scope of Application

Tank ships dedicated to carrying liquefied gases in bulk, with the crew specialised in managing cryogenic temperatures, membrane or independent-tank containment systems, and boil-off gas management.

## Procedure / How to Complete It

1. Check the integrity of the cargo containment systems and cryogenic insulation before every loading operation.
2. Continuously monitor tank pressure and temperature during the voyage, managing boil-off gas according to the prescribed procedure (reliquefaction, combustion or controlled release).
3. Carry out gradual tank cooldown before loading, to avoid thermal shock to the structures.
4. Check the operation of the gas detection systems and the emergency plants specific to cryogenic gases.
5. Apply gas-freeing and inerting procedures to tanks before entry for maintenance or survey.
6. Monitor the development of the package of amendments approved at MSC 111, in particular for gas carriers that carry or use as fuel CO2, LPG, ethane or toxic cargoes, ahead of the entry into force on 1 July 2028.
7. For units intended to carry liquefied hydrogen as cargo, check the membrane containment system's compliance with the requirements of the new Part D (Res. MSC.565(108)), including continuous vacuum monitoring in the insulation spaces.

## Practical Example

Example: before loading LNG, the crew carries out gradual tank cooldown according to the cooling curve set out in the ship-specific operating manual, checking that the cooling rate does not exceed the structural limits set to avoid thermal-shock fractures.

## Real Cases

Managing boil-off gas is one of the distinctive operational challenges of gas carriers: incorrect management can lead to tank overpressure or, conversely, to excessive cargo loss through unnecessary release, with economic and safety impact; this is why specific training for personnel on board gas carriers is markedly more specialised than for other types of tank ship.

## Common Mistakes Mistake Library

Mistake | Consequence | How to avoid it
--- | --- | ---
Tank cooldown carried out too quickly relative to the prescribed cooling curve | Risk of thermal shock and structural damage to the containment system | Strictly follow the gradual cooling curve specified in the ship-specific operating manual
Boil-off gas management not continuously monitored during the voyage | Risk of tank overpressure or unnecessary cargo loss | Continuously monitor tank pressure and temperature, not only at scheduled intervals
Personnel not specifically trained on the cryogenic characteristics of the cargo carried | Incorrect management of specific emergencies (freezing, cryogenic material embrittlement) | Ensure specialist training for personnel serving on gas carriers, distinct from generic tank-ship training
Gas detection systems not periodically calibrated according to manufacturer specifications | False negatives in the event of an actual gas leak, delaying detection of a hazardous condition | Calibrate gas detection systems according to the manufacturer's required schedule, not only after an obvious malfunction
Tank gas-freeing and inerting procedure not correctly completed before entry for maintenance or survey | Residual hazardous atmosphere in the tank when personnel enter | Instrumentally verify the tank atmosphere according to the full procedure before any entry, regardless of the expected gas-freeing time
Loss of cryogenic insulation not detected promptly, exposing ordinary steel structures to very low temperatures | Risk of brittle fracture of the exposed structure, not designed for cryogenic temperatures | Systematically monitor the integrity of the cryogenic insulation and the temperature of structures adjacent to the containment systems

## PSC Observations

PSCOs on gas carriers check the crew's specialist training, the operation of the gas detection and containment systems, and the consistency between the Certificate of Fitness and the type of gas actually being carried.

## Operational Tips

- Do not generalise chemical tanker procedures to gas carriers: cryogenic temperatures introduce specific risks (material embrittlement, thermal shock) not present when carrying chemical products at ambient temperature.
- Monitor boil-off gas as a continuous operational parameter, not as an occasional check.
- Check that crew training includes specific cryogenic emergency scenarios, distinct from generic firefighting scenarios.

## Checklist

- Containment and cryogenic insulation systems checked before loading
- Gradual cooldown procedure followed according to the ship-specific manual
- Boil-off gas continuously monitored during the voyage
- Gas detection systems and cryogenic emergency plants tested
- Specialist crew training on cryogenic risks documented
- Tank and secondary barrier materials checked against the updated Table 6.3 (Res. MSC.523(106))
- For the carriage of liquefied hydrogen: membrane containment system compliant with the new Part D (Res. MSC.565(108)), vacuum monitoring in the insulation spaces operational

## FAQ

What changes with the IGC package of amendments approved at MSC 111?
Formal adoption is expected in December 2026, in force from 1 July 2028: it clarifies the 'one ship, one code' principle for gas carriers using alternative fuels, introduces provisions for carrying CO2 as cargo and for using LPG/ethane/toxic cargoes as fuel, finite-element analysis requirements for Type C tanks, and a new three-date Certificate of Fitness.
What does the new Part D of the Interim recommendations for liquefied hydrogen introduce?
Adopted at MSC 111 (May 2026) through Resolution MSC.565(108), it governs membrane cargo containment systems with insulation spaces kept under vacuum, with requirements on structural integrity, barrier tightness, vacuum monitoring, leak detection and emergency procedures specific to liquefied hydrogen as cargo.
What is boil-off gas?
It is the gas that naturally evaporates from the liquefied cargo during transport through heat exchange with the external environment, and which must be managed through reliquefaction, combustion in the engines or controlled release according to the ship's procedure.
Why must tank cooldown be gradual?
Cooling too quickly can generate thermal shock in the structures and materials of the containment system, with a risk of fractures or structural damage that is not immediately visible.
Does the IGC Code also apply to gas-fuelled ships?
The IGC Code specifically governs ships that carry liquefied gases as cargo; gas-fuelled ships (which use gas as fuel) are governed by specific regulation (the IGF Code), conceptually related but distinct.
What is the difference between membrane and independent-tank containment systems?
Membrane systems use a thin metal barrier supported by the hull's insulated structure; independent-tank systems are self-supporting structures separate from the hull, with different construction and inspection requirements under the IGC Code.
What happens if boil-off gas cannot be managed, for example due to a failure of the reliquefaction system?
The ship-specific emergency procedure typically provides for controlled release of the excess gas through dedicated safety valves, to avoid tank overpressure, according to the limits and methods set out in the operating manual.
Which materials are prohibited for structures exposed to cryogenic temperatures?
Ordinary carbon steel and other materials not specifically qualified for low temperatures are prohibited in structures in direct contact with cryogenic gases, since they become brittle and prone to sudden fracture; the IGC Code requires specific materials (e.g. nickel steels, aluminium) for these applications.
🎬 Additional photos, videos and interactive diagrams for this topic will be available in a future version of the platform.

## Related Topics

IBC Code and Operations on Chemical Tankers Cargo Record Book (Record Book for Noxious Liquid Substances)

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