Operational Guide · Registers & Logbooks

# Fixed Firefighting Systems: CO2 and Water Mist

A CO2 system requires recharging 100% of the reserve cylinders, while other extinguishing agents only require 50%: a detail that clearly distinguishes these systems in maintenance planning.

FSS Code CO2 water mist fixed firefighting systems

## 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: monthly visual inspection, annual servicing by qualified personnel, hydrostatic test every 10 years; onboard recharge stock equal to 100% of total CO2 charges and 50% for other types of extinguishing agent.

## Scope of Application

Every ship fitted with fixed CO2 firefighting systems (engine room, holds) or water mist/water-spraying systems (exposed ro-ro passenger vehicle decks and other protected spaces), with the crew responsible for the maintenance and periodic testing of these systems.

## Procedure / How to Complete It

1. Verify the CO2 system's dosing against the volume of the protected space per the FSS Code tables, particularly after structural modifications to the space.
2. Carry out the monthly visual inspection and annual servicing by qualified personnel for both types of system (CO2 and water mist).
3. Verify the onboard recharge stock: 100% of total charges for CO2, 50% for other extinguishing agents.
4. For ro-ro passenger ships with keels laid from 2026, verify the compliance of the fixed water system on exposed decks with the new flow rate requirements of Section 2.5.
5. Carry out the hydrostatic test of the cylinders every 10 years to verify their structural integrity.

## 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), checks cylinder pressure, and confirms the availability of the recharge stock equal to 100% of the required total charges.

## Real Cases

The distinction in stock requirements (100% for CO2, 50% for other agents) reflects the particular criticality of CO2 systems in the engine room, where a second use of the system after an initial fire intervention must be guaranteed without waiting for replenishment: managing stock inconsistent with this distinction exposes the ship to a real operational risk in the event of a fire recurrence.

## 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
CO2 recharge stock maintained at 50% instead of the required 100%, by analogy with other extinguishing agents | Inability to carry out a complete second intervention in the event of a fire recurrence | Always maintain the CO2 recharge stock at 100% of total charges, distinct from the 50% requirement for other agents
Ten-year hydrostatic test of the cylinders not planned in time, with the deadline exceeded before verification | Non-compliant cylinders used beyond the required structural verification window | Plan the ten-year hydrostatic test with adequate lead time, integrating it into the planned maintenance programme

## PSC Observations

PSCOs verify the maintenance status of fixed firefighting systems (monthly/annual inspection records, recharge stocks, validity of the ten-year hydrostatic test) and, for more recent ro-ro passenger ships, compliance with the new requirements on exposed deck systems.

## Operational Tips

- Don't treat CO2 and other extinguishing agents the same way for recharge stock: the 100% requirement for CO2 is specific and distinct.
- Always re-verify the CO2 system's dosing after any structural modification to the protected space, even an apparently minor one.
- Plan the ten-year hydrostatic test of the cylinders well in advance in the maintenance programme, to avoid overdue deadlines.

## Checklist

- CO2 system dosing verified against the actual volume of the protected space
- Monthly visual inspection and annual servicing carried out for all fixed systems
- Compliant recharge stock (100% CO2, 50% other agents) maintained on board
- Ten-year hydrostatic test of the cylinders planned and carried out on time
- Compliance with the new MSC.555(108) requirements verified for affected ro-ro passenger ships

## FAQ

Why must the CO2 recharge stock be 100% and not 50% like other agents?
Because CO2 systems, typically installed in engine rooms, must guarantee the possibility of a complete second intervention in the event of a fire recurrence, without waiting for replenishment; for other extinguishing agents the requirement is 50%.
What does Resolution MSC.555(108) introduce?
Amendments to Chapter 7 (water-spraying/water mist) and Chapter 9 (fire detection) of the FSS Code, including the new requirement for fixed water systems on exposed decks of ro-ro passenger ships with keels laid from 1 January 2026.
How often must the hydrostatic test of fixed system cylinders be carried out?
Every 10 years, to verify their structural integrity, in addition to the monthly visual inspection and annual servicing by qualified personnel.
🎬 Additional photos, videos and interactive diagrams for this topic will be available in a future version of the platform.

## Related Topics

Fire Drill and Fire Safety Helicopter Operations and Helideck Safety

### Leave feedback

Help us improve the platform during the beta -- it takes thirty seconds.

How useful do you find the platform so far?
Comment (optional)
Sign me up for the newsletter
Role