Fixed Firefighting Systems: CO2 and Water Mist
A fixed CO2 system is not verified by eye: it is verified by weighing the cylinders and following a testing regime that changes at the tenth and twentieth year. That is where the deficiencies are.
Operational Explanation
Fixed CO2 firefighting systems (typically used in engine rooms and holds) work by injecting carbon dioxide into the protected space to displace oxygen and extinguish the fire, with dosing calculated by the FSS Code based on the volume of the protected space and the cylinder arrangement. Water mist systems (pressurised, atomised water) offer an alternative with lower environmental impact and reduced risk to personnel, increasingly common also on exposed vehicle decks of ro-ro passenger ships.
Resolution MSC.555(108) introduced amendments to Chapter 7 (pressure water-spraying and water mist fixed systems) and Chapter 9 (fire detection) of the FSS Code: the new Section 2.5 of Chapter 7 requires fixed water systems on exposed ro-ro passenger vehicle decks, with minimum flow rate requirements (2.0 L/min per m² protected, with individual outlets not less than 1,250 L/min), applicable to ships with keels laid from 1 January 2026.
Regulatory Reference
FSS Code, with amendments Res. MSC.555(108) to Chapter 7 (water-spraying/water mist) and Chapter 9 (fire detection), applicable to ro-ro passenger ships with keels laid from 1 January 2026. 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.
No recharge stock is required for fixed systems, either by SOLAS II-2 or by the FSS Code, which in Chapter 5 requires only that spare parts for the system be kept on board.
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 the specific requirements for relevant new ro-ro passenger ships.
Practical Example
Example: during the annual inspection of the engine room CO2 system, the qualified technician verifies the dosing against the actual volume of the space (unchanged by recent structural modifications), weighs the cylinders and confirms that none has fallen below 90% of the nominal charge, and checks where the system stands in the testing cycle: the ship is in its ninth year, so the ten-year inspection with a 10% sample goes into the programme now, and the test on all cylinders before the twentieth anniversary goes into the long-term maintenance plan.
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 | Purchase and stowage of a reserve that no regulation requires, 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). Fixed systems have no stock requirement |
| 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
Operational Tips
- Don't apply the spare-charge requirement to fixed systems: it belongs to portable extinguishers. If you find it written into a shipboard procedure, trace it back to source before buying cylinders nobody is asking for.
- 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: 15 August 2026 · page fingerprint cb148a47e6b3