Fixed Firefighting Systems: CO2 and Water Mist
Checking a fixed system includes its charge, controls, alarms, distribution and periodic tests. CO2, water mist and water monitors have different maintenance programmes and operating conditions.
Operational Explanation
CO2 systems extinguish by reducing oxygen concentration in the protected space and present a lethal risk to anyone remaining inside. Water mist and water spray apply according to their approval, protected hazard and manual; they are not automatically interchangeable CO2 substitutes. Vehicle-deck water monitors are a distinct arrangement from water mist.
MSC.555(108), FSS 7/2.5: for relevant new ro-ro passenger ships from 1 January 2026, combined monitor capacity is at least 2.0 L/min/m² of protected area and at least 1,250 L/min per monitor, not per nozzle. Areas not reached by monitors require nozzles delivering 5.0 L/min/m². SOLAS II-2/20.6.2.3, introduced by MSC.550(108), also requires upgrades on relevant existing passenger ships by the first survey on or after 1 January 2028, under its own conditions; do not automatically apply all newbuilding specifications to them. MSC.555(108) · MSC.550(108).
Regulatory Reference
FSS Code, with amendments Res. MSC.555(108) to Chapter 7 (water-spraying/water mist) and Chapter 9 (fire detection), with distinct scopes: FSS 7/2.5 and 9/2.5.1.2–4 for ro-ro passenger ships constructed from 1 January 2026; FSS 9/2.3.1.5 and 9/2.4.2.2 for all ships constructed from that date. CO2 maintenance (MSC.1/Circ.1318/Rev.1): general visual inspection at least every 30 days; at each periodical service — two-yearly with a ±3-month tolerance on passenger ships, at each intermediate, periodical or renewal survey on cargo ships — all main and pilot cylinders must be weighed or their contents verified by other reliable means: cylinders below 90% of the nominal charge must be refilled. Internal inspection of all control valves at least every 5 years; replacement of hoses at the manufacturer's recommended intervals and in any case within 10 years.
Periodical testing of the cylinders: at intervals not exceeding 10 years. At the ten-year inspection at least 10% of the cylinders must undergo internal inspection and hydrostatic test; if one or more fail, testing extends to 50%, and to all cylinders if further failures occur. Before the twentieth anniversary, and at every ten-year anniversary thereafter, all cylinders must be hydrostatically tested. Cylinders removed for testing must be replaced so that the available quantity of extinguishing medium remains as designed. Some Administrations impose stricter regimes: always check your flag State.
The formula of 100% of the first ten and 50% of the remainder, up to 60 charges, concerns portable extinguishers rechargeable on board (SOLAS II-2/10.3.3.1). Do not transfer it to fixed CO2 or infer that every fixed system is exempt from reserves: check the system, approval, flag and equipment required by its manual.
The programme must also include annual inspections, alarms and controls, pipes and nozzles, in addition to charge measurement and cylinder tests. For water mist check pumps and supply, valve positions, filters, nozzles, water quality and functional tests under the system-specific programme. Work requires appropriately competent personnel and documented restoration to service. IMO maintenance circulars, flag compilation.
Scope of Application
Ships fitted with the respective approved systems. CO2 and water-mist/water-spray programmes must be read separately by system, approval, Administration, class, manual and PMS.
Procedure / How to Complete It
- For CO2 apply MSC.1/Circ.1318/Rev.1 as implemented by the Administration, together with the manual, PMS and class requirements.
- For water mist/water spray apply the system-specific programme under MSC.1/Circ.1432 and applicable revisions, manual, approval, flag and class.
- Do not transfer CO2 tasks and intervals automatically to water mist.
- Check new ro-ro passenger requirements and, separately, MSC.550(108) retrofits for relevant existing passenger ships by the first survey on or after 1 January 2028.
Practical Example
Example: before a periodic CO2 service check each cylinder’s dates and deadlines, charge by weighing or another reliable method, alarms and test programme. Ship age does not replace cylinder dates. Plan samples and extensions under MSC.1/Circ.1318/Rev.1 as implemented by the flag.
What Typically Goes Wrong
Common Mistakes Mistake Library
| Mistake | Consequence | How to avoid it |
|---|---|---|
| CO2 system dosing not re-verified after structural modifications to the protected space | Insufficient CO2 concentration for effective extinguishing in the modified space | Always re-verify dosing per the FSS Code tables after any relevant structural modification |
| Believing that a fixed system requires a recharge stock equal to 100% of the charges | Application of a quantity criterion that does not belong to the system, and false confidence about a “second intervention” | The 100% / 50% requirement is SOLAS II-2/10.3.3.1 and applies to portable extinguishers (100% of the first ten, 50% of the remainder capable of being recharged on board, maximum 60 charges). For the fixed system check approval and specific requirements |
| Cylinders not weighed at the required periodical interval | A system charged below 90% of nominal, i.e. unable to deliver the designed quantity | Weigh or verify the contents of all cylinders, main and pilot, at each periodical service, and refill those below 90% |
| Planning “the ten-year hydrostatic test of all cylinders” | Unnecessary cost at year ten and, conversely, a surprise at year twenty, when testing all cylinders does become mandatory | At year ten a sample of at least 10%, extending to 50% and then 100% on failure; test every cylinder before the twentieth anniversary |
What the PSCO Checks
PSC may check system maintenance, charge, controls and tests. For MSC.550(108) and MSC.555(108), identify ship category, construction and spaces; distinguish new arrangements from existing-passenger-ship requirements and their applicable survey deadline from 2028.
Operational Tips
- Check reserves under the system approval, flag requirements and manual; the portable-extinguisher 100%/50% formula does not determine a fixed system’s equipment.
- Always re-verify the CO2 system's dosing after any structural modification to the protected space, even an apparently minor one.
- Put two different deadlines in the plan, not one: the ten-year sample inspection and the test on all cylinders before the twentieth anniversary. It is the second that catches out anyone who planned only the first.
Preparation checklist
- System and applicable programme identified
- CO2 maintained under implemented regime and manual
- Water mist/water spray maintained under its system-specific programme
- Intervals not automatically unified
- MSC.555(108) checked where applicable
FAQ
Related Topics
Last substantive revision of this page: 16 September 2026 · page fingerprint 62645f93fc69