Fixed CO₂ systems: what is checked monthly, every two, five, ten and twenty years

The guideline that applies

Fixed CO₂ systems are maintained to MSC.1/Circ.1318/Rev.1, approved by IMO’s Maritime Safety Committee in May 2021. It supports SOLAS regulation II-2/14 and replaced the 2009 version of the circular. The general fire protection guideline, MSC.1/Circ.1432, covers other systems but leaves CO₂ out.

Compared with the 2009 text, Rev.1:

• requires all high-pressure cylinders to be hydrostatically tested by their twentieth year and every ten years after that;
• requires cylinders sent away for testing to be replaced, so the required quantity of CO₂ stays on board;
• adds a five-yearly internal inspection of the control valves;
• refers to ISO 18119:2018 for cylinder testing instead of ISO 6406.

The monthly and annual lists, the 90 % refill threshold and the ten-year limit for flexible hoses did not change.

The schedule

When	What	Basis
Monthly	Valves, release controls, piping, cylinders and alarms checked; on low-pressure systems the tank gauges and valves	Circ.1318/Rev.1
Every year	Openings in the protected space, damaged cylinders retested or replaced, nozzles clear, hoses tight, signs and instructions in place	Circ.1318/Rev.1
Every 2 years ± 3 months (passenger ships); each intermediate, periodical or renewal survey (cargo ships)	Content of high-pressure and pilot cylinders measured by weighing or liquid level, refilled below 90 %; low-pressure tank quantity checked; dry air or nitrogen blown through the piping	Circ.1318/Rev.1, HSSC
Same interval (passenger ships); renewal survey (cargo ships)	Pilot lines, release cables, alarms and time delay tested by trained technicians	Circ.1318/Rev.1
Every 5 years	Internal inspection of the control valves	Circ.1318/Rev.1
Within 10 years	Flexible hoses renewed at the maker’s interval	Circ.1318/Rev.1
At 10 years	At least 10 % of the high-pressure cylinders hydrostatically tested, pilot cylinders included; one failure means 50 %, a further failure means all	Circ.1318/Rev.1
By year 20, then every 10 years	All high-pressure cylinders hydrostatically tested	Circ.1318/Rev.1

Some flags add to this: Liberia, for example, adds weekly checks.

The Dutch flag deadline

The Dutch administration (ILT) applies Rev.1 from 1 January 2023. All cylinders must comply by the next scheduled dry-docking and by 1 January 2028 at the latest. Due dates follow the date stamped on each cylinder, not the ship’s age. Low-pressure tanks follow IACS Recommendation 53.

Where the guidance is still moving

• The twenty-year step. IRClass reads it as testing the roughly 90 % of cylinders not tested at ten years; DNV reads it as all cylinders.
• A pending revision. In March 2026 IMO’s SSE 12 sub-committee drafted clarifications: the anniversary date is the cylinders’ date of manufacture, and a simulated functional test is required after any modification or change of components. They go to the Maritime Safety Committee in December 2026 and would apply no earlier than twelve months after approval.

Who may do the work

Competent crew can carry out the monthly and annual checks; the maintenance plan should say which items need trained personnel. Release tests need technicians trained to standards the flag accepts. The Marshall Islands, for example, leaves the monthly and annual items to the ship’s officers and requires a facility accepted by the recognised organisation for the two-, five- and ten-year work. Liberia only accepts hydrostatic tests from an authorised facility.

Class approval of fire-extinguishing service firms follows IACS UR Z17 (Rev.21 in force from 1 July 2026), which refers to Circ.1318/Rev.1, requires weighing, level-gauging and hydrostatic test equipment, and requires reports to carry the firm’s approval certificate. Keep the records in the maintenance plan of the safety management system, with corrective actions and the service reports.

Working safely on a CO₂ system

Unintended CO₂ releases caused 72 deaths between 1975 and 2000. Before any work:

• make a safety plan and do a headcount;
• lock or remove the operating arms of the directional valves, or lock the block valve, so the system cannot be released;
• only ever simulate a discharge during a test;
• ventilate the CO₂ room for 15 minutes before entering. The room must be used for nothing else, and when below deck it needs exhaust from the bottom with at least six air changes an hour.

After renewing pilot hoses, prove the pilot lines are clear. On the Finnmaster in 2021 only 21 of 42 cylinders fired because newly fitted pilot hoses were blocked, and more than 33,000 hose assemblies came from the same supply chain.

What PSC finds

In the Paris MoU’s 2023 fire safety campaign, inspectors recorded 156 deficiencies on fixed fire-extinguishing installations of all types, 23 of them grounds for detention. On ships classed by ClassNK, 55 detainable deficiencies on fixed systems were recorded in 2025, mainly corroded lines and malfunctions. Inspectors compare the records with the installed system and check connections and labels.

Checklist

1. Put the Rev.1 schedule into the safety management system and split it into crew tasks and technician tasks.
2. Before any test: safety plan, headcount, release locked out, ventilation running.
3. Book the content check and blow-through for the survey window.
4. Track the stamp date of every cylinder, the hose dates and your flag’s deadlines.
5. After renewing hoses, prove the pilot lines are clear.
6. Use an approved service firm and keep its reports and certificates on board.

How we help

We plan the Rev.1 schedule with you, measure cylinder contents without discharging, blow through the piping, inspect the control valves, renew hoses and organise cylinder testing so the required quantity of CO₂ stays on board. See Fixed fire-fighting systems.