A fixed carbon dioxide system is the only firefighting equipment on board that nobody ever tests by using it. Everything anyone knows about whether it works comes from a maintenance regime that is written down in detail and followed in outline.
The System That Is Never Exercised
Most firefighting equipment gets used, or at least operated. Hoses are run out at drills. Extinguishers are discharged in training. Pumps are started. A fixed carbon dioxide system is different: discharging it costs a recharge, a space full of an asphyxiant and a vessel out of service, so it is released once in its life or never.
That makes the maintenance regime the entire basis of confidence. IMO sets it out in MSC.1/Circ.1318/Rev.1, the Revised Guidelines for the Maintenance and Inspections of Fixed Carbon Dioxide Fire-Extinguishing Systems, approved at the Committee’s 103rd session and issued on 25 May 2021, superseding the original circular.
The structure of those guidelines is the first thing worth reading, because it sorts the work by who may do it. Section 1 states that some procedures may be carried out by competent crewmembers and others require specially trained persons, with the onboard maintenance plan indicating which is which. That is not a formality. It means the plan has to allocate every task, and a plan that does not is incomplete before any inspection starts.
The guidelines do not just say what to check. They say that the onboard plan must say who checks it, which is the requirement most plans quietly fail.
Records sit in the same place. Section 3 requires the maintenance plan to include records of inspections and maintenance, corrective actions among them, and says the plan should form part of the safety management system. A system in good order with no record of how it got there is, for audit purposes, a system of unknown condition.
What the Intervals Actually Say
The intervals are more specific than the generic “annual service” most operators have in mind, and the biennial checks are where the substantive work sits.
Monthly. Visual checks, including releasing controls and alarm devices.
Annual. Inspection in accordance with the system manufacturer’s instructions and safety precautions. Entrance doors are to close properly and display their warning signs.
Biennial. At least every two years, within a window of plus or minus three months, on passenger ships; on cargo ships, at each intermediate, periodical or renewal survey. This is where cylinder contents, hydrostatic test dates, pipework and the release train are all addressed.
Five-yearly. Internal inspection of all control valves.
Ten-yearly. Periodic testing of high-pressure cylinders, at intervals not exceeding ten years, with the escalating sample described below. Flexible hoses are replaced at the manufacturer’s intervals, not exceeding ten years.
The practical point: the cargo ship biennial is tied to the survey cycle rather than to a date, so it moves with the surveys. An operator tracking it as a calendar item will drift out of step with the regime it is meant to satisfy.
The biennial also splits by competence. The contents, test dates and pipework work falls in one clause; the activating heads, pilot lines, release controls and warning devices fall in another, and that second clause requires service technicians or specialists trained to standards accepted by the Administration. That phrase is the one to read before engaging a contractor, because it is a qualification requirement rather than a preference.
The Three Checks That Catch Real Problems
Three biennial items between them account for most of what goes wrong on a system nobody has exercised.
Contents. Cylinders are weighed, or verified by other reliable means, and the available charge must be above 90 per cent of the nominal charge. Any cylinder below that is refilled. On a low-pressure installation the tank liquid level has to confirm sufficient carbon dioxide for the largest hazard the system protects. Slow leakage over years is invisible without this check, and a bank that has quietly lost charge will not reach design concentration in the space it was sized for.
Pipework. The discharge piping is isolated from the system and dry air or nitrogen is flowed through it to verify that nothing is blocked, at the biennial interval. This is the check that finds a line obstructed by debris, corrosion product or, occasionally, something stowed in a space during a refit. A full bank discharging into a blocked line protects nothing.
The release train. All controls and warning devices must function normally, and where a time delay is fitted it must prevent discharge for the required period. The delay exists so people can leave; a delay that has drifted or failed is both a life safety defect and a reason the system may not be released when it is needed.
A system can hold a full charge, have perfect paperwork, and still deliver nothing, because the line between the bank and the space was never blown through.
The Hydrostatic Rule and the Exemption That Does Not Apply
Cylinder testing is where the guidelines are most precise, and where the most expensive misunderstanding sits.
At the ten-year inspection, at least 10 per cent of cylinders receive an internal inspection and hydrostatic test. If one or more of that sample fails, a total of 50 per cent are tested. If further failures appear, all of them are tested. And regardless of sampling, all cylinders are hydrostatically tested before the twentieth anniversary and every ten years thereafter.
That escalation is worth understanding before a budget is set. A ten-year docking priced on a 10 per cent sample can become a 50 per cent or a 100 per cent job on the strength of one failed cylinder, and the yard time that follows is not recoverable from the schedule. The twenty-year rule then removes sampling entirely, so an older vessel has a known, unavoidable cost arriving on a known date.
Now the misunderstanding. Operators sometimes expect to substitute visual inspection and non-destructive testing for hydrostatic testing, having heard that the option exists. It does exist, in the separate IMO guidelines on maintenance and inspection of fire protection systems and appliances, where visual inspection and non-destructive examination may be accepted in lieu of hydrostatic testing for halon cylinders where the Administration permits. That provision is for halon, and the circular containing it states that it does not address carbon dioxide systems. Carrying the concession across to a carbon dioxide bank is not a reading the instruments support.
Preparing for the Check Rather Than Reacting to It
The operators who come through this cleanly treat the regime as a planning input instead of a periodic surprise.
The safety plan the guidelines require before work starts deserves its own mention, because the hazard is real. Section 2 calls for a plan accounting for all personnel, with communications established with the on-duty crew, before any work on the system begins. Carbon dioxide displaces oxygen without warning, and the people most at risk during maintenance are the ones doing it.
None of the above is onerous relative to what the system is for. It is the price of a protection measure that will be released, if ever, on the worst day the vessel has, with no opportunity to discover then that a cylinder was at 80 per cent or a line was blocked. Our firefighting solutions work covers the servicing and record side of fixed installations, which is the part that determines whether the system will do what the drawing says.
Frequently Asked Questions
What governs maintenance of a fixed CO2 system?
MSC.1/Circ.1318/Rev.1, the Revised Guidelines for the Maintenance and Inspections of Fixed Carbon Dioxide Fire-Extinguishing Systems, approved at the Committee’s 103rd session and issued on 25 May 2021, superseding the original MSC.1/Circ.1318. It sets monthly, annual, biennial, five-yearly and ten-yearly requirements, and requires the onboard maintenance plan to indicate which procedures competent crew may perform and which need specially trained persons.
How much charge can a cylinder lose before it has to be refilled?
The available charge must be above 90 per cent of the nominal charge, checked at the biennial interval by weighing or other reliable means, and any cylinder below that is refilled. On a low-pressure installation the tank liquid level must confirm sufficient carbon dioxide for the largest hazard protected. Slow leakage is otherwise undetectable until the system is called on.
How does the ten-year cylinder testing work?
High-pressure cylinders are tested at intervals not exceeding ten years. At the ten-year inspection at least 10 per cent receive internal inspection and hydrostatic testing; if one or more fail, 50 per cent are tested, and on further failures all of them. Every cylinder is hydrostatically tested before the twentieth anniversary and every ten years after. Flexible hoses are replaced at the manufacturer’s intervals, not exceeding ten years.
Can non-destructive testing replace hydrostatic testing?
Not for carbon dioxide. The provision allowing visual inspection and non-destructive examination in lieu of hydrostatic testing, where the Administration permits, sits in the separate IMO guidelines on maintenance and inspection of fire protection systems and appliances and applies to halon cylinders; that circular states it does not address carbon dioxide systems. Confirm any proposed alternative with the Administration or class before relying on it.
Sources: IMO MSC.1/Circ.1318/Rev.1, Revised Guidelines for the Maintenance and Inspections of Fixed Carbon Dioxide Fire-Extinguishing Systems, approved at the Committee’s 103rd session and issued 25 May 2021, superseding MSC.1/Circ.1318, covering in section 1 the division of procedures between competent crewmembers and specially trained persons as indicated by the onboard maintenance plan, in section 2 the safety plan accounting for all personnel and communications with the on-duty crew before work begins, in section 3 the maintenance plan requirement to include records of inspections and maintenance including corrective actions and to form part of the safety management system, in section 4 the monthly visual checks including releasing controls and alarm devices, in section 5 the annual inspection in accordance with the manufacturer’s instructions and safety precautions together with the requirement for entrance doors to close properly and display warning signs, in section 6 the biennial regime at two years plus or minus three months for passenger ships and at each intermediate, periodical or renewal survey for cargo ships, with 6.1.1 requiring cylinders to be weighed or verified by other reliable means with available charge above 90 per cent of nominal and refilling below that, and low-pressure tank levels confirming sufficient carbon dioxide for the largest hazard, 6.1.2 requiring high-pressure cylinder testing at intervals not exceeding ten years with internal inspection and hydrostatic testing of at least 10 per cent escalating to 50 per cent on a failure and to all cylinders on further failures, hydrostatic testing of all cylinders before the twentieth anniversary and every ten years thereafter, and replacement of flexible hoses at manufacturer’s intervals not exceeding ten years, 6.1.3 requiring isolation of discharge piping and the flow of dry air or nitrogen to verify absence of blockage, and 6.2 requiring the activating heads, pilot lines, release controls and warning devices to be addressed by service technicians or specialists trained to standards accepted by the Administration with 6.2.2 requiring normal function of all controls and warning devices and a time delay that prevents discharge for the required period, and in section 7 the five-yearly internal inspection of all control valves · IMO MSC.1/Circ.1432, Revised Guidelines for the Maintenance and Inspections of Fire Protection Systems and Appliances, as amended by MSC.1/Circ.1516, which at paragraph 10.1.3 permits visual inspection and non-destructive testing in lieu of hydrostatic testing for halon cylinders where the Administration permits and which states in its section 1 that it does not address carbon dioxide systems · SOLAS chapter II-2 regulation 14, maintenance, testing and inspections of fire protection systems and appliances and the onboard maintenance plan
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