CO2 Fixed Fire-Fighting System on Ships

1. Principle, Regulation & CO2 Bottles

This is the most important section in the Safety oral — surveyors ask at least one main question from CO2, and a weak answer here fails the sitting. For "what is the principle of CO2 flooding?" — smothering plus cooling, reducing the oxygen content to below 15 percent so combustion cannot sustain. The system works only inside enclosed spaces — in open space it does not work at all — so it protects machinery spaces, engine rooms, purifier rooms and cargo holds.

• Regulation: SOLAS requires that a ship with a category-A machinery space of 500 cu m and above volume be fitted with an additional fixed fire-fighting system.
• Discharge rule: 85 percent of the required CO2 quantity must be released into the space within 2 minutes of actuating the system — and of evacuating the fire-affected space.
• Operation authority: the system must be operated by the Chief Engineer or Second Engineer — those two are responsible for the whole release operation.

CO2 bottles — construction and fittings:

• Bottles are solid drawn steel, hydraulically tested to 228 bar.
• Bottles must not be stored where the temperature exceeds 55 °C; bottle pressure is normally about 52 bar and varies with temperature.
• Contents are checked by level indicator, radio-active isotope gun, or weighing.
• In each bottle head assembly the bursting disc is designed to rupture at 177 bar produced by a temperature of about 63 °C.
• Each bottle has a syphon tube so that liquid CO2 is discharged from the bottle.

Why the syphon tube matters — say this line:

• Without the syphon tube the CO2 would evaporate from the surface, giving a very slow discharge rate and, by taking its latent heat, would cause the remaining CO2 in the bottle to freeze.
• Liquid discharge at the nozzle flashes to gas — that flash gives the cooling half of the principle alongside smothering.

2. CO2 Room, Safeties & Leak Hunting

For "describe your CO2 room" (Q21c), give the room first, then the safety chain, then the leak drill:

CO2 room regulation (Q21c):

• The storage room shall be used for no other purposes.
• If below deck, it shall be no more than one deck below the open deck and directly accessible by stairway or ladder from the open deck.
• Spaces below deck, or without open-deck access, shall have mechanical ventilation taking exhaust from the bottom of the space, sized for at least 6 air changes per hour.
• Access doors open outwards, and bulkheads, decks, doors and every closing means forming boundaries with adjacent enclosed spaces shall be gas tight.
• Room temperature maintained below 55 °C.
• Minimum clear height 2.4 m for manifold mounting and cylinder weighing.
• If the fixed medium is stored outside a protected space, it shall sit in a room behind (aft of) the forward collision bulkhead.

System safeties (Q21b) — walk the chain in order:

• Trip switch: the control cabinet has a special trip switch for ventilation trip and CO2 alarm — as soon as you open the cabinet it trips ventilation and sounds the alarm.
• Master valve (Q21d): fitted on the main manifold line going to machinery or cargo spaces — it prevents CO2 reaching any space on an accidental release; open it only as part of the ordered release sequence.
• Relief valve: located at the end of the manifold — if manifold pressure exceeds the set point it lifts to atmosphere at 180 bar.
• Safety pin: provided in each bottle head assembly — it locks the operating lever against accidental operation; pull it out for manual operation.
• Bursting disc: also in each bottle head assembly — bursts when bottle pressure exceeds 177 bar with about 63 °C around the bottle.
• Non-return check valve: located between each bottle and the manifold — acts as a non-return so that blow-through service air cannot pass back, and on a partial release (a few bottles for a cargo hold) the pressurised manifold cannot force open the unoperated bottles after the pilot cylinder fires.
• CO2 leak alarm: located on the manifold, working as a pressure switch at 4 bar. Any leaking bottle feeds gas into the manifold; at 4 bar it trips the alarm. Since even a small leak off a 52-bar bottle pressurises the manifold fast, the alarm tells you a bottle leaks — but never which one. Finding it: two persons go together with communication equipment, ventilate the room and wait outside until gas-free, then enter and hand-touch bottles in turn — the leaking bottle is markedly cooler than its neighbours. Mark every cooler bottle, check all of them, and report the count.
• Pipework: solid drawn mild steel, galvanised against corrosion.

3. Quantity Calculation & the Worked Vessel

For "how much CO2 does your ship carry?" (Q21e), give the percentages, the formula, then your ship's worked example:

SOLAS quantity regulations & formulas:

4. Weighing & the Maintenance Schedule

For "how do you weigh a bottle?" (Q21f) and "what maintenance?" (Q21g), give the tool, the steps, then the full interval table:

SOLAS CO2 System Maintenance Ladder:

5. Engine-Room & Purifier-Room Fire Actions

Knowledge of the system is only half the question — the surveyor then gives you a fire: "E/R on fire — your actions?" Note first that the engine room also has a hypermist system — if you are sure it will extinguish the fire you may operate it with no shutdowns needed; but if the surveyor asks for CO2, explain CO2.

Fire in the engine room — actions in order:

• On seeing fire anywhere in the engine room, immediately raise the fire alarm from the nearest point by breaking the glass — and if the hammer is missing, remove a safety shoe and strike with its steel toe plate.
• If the fire type is recognisable and not too big, attack with the proper portable extinguisher.
• If it cannot be extinguished, immediately run to inform the Chief Engineer and the deck officer or bridge — report location and type of fire.
• If the main engine is running, slow down and stop it.
• Before leaving the engine room on orders to release CO2, make sure all accesses are closed properly.
• Stop the running auxiliary engines and start the emergency generator on load — stopping the auxiliaries also stops ventilation; then close the flaps.
• All crew except the bridge watchkeeper (or officer/master) muster for headcount, then follow muster-list duties — closing vents, doors, flaps, dampers and quick-closing fuel valves.
• Start the emergency fire pump for boundary cooling of the engine-room bulkheads, continuously.
• Operate CO2 from the fire control station; confirm every crew member present, nobody missing.
• Open the release cabinet with the key — opening it cuts ventilation power and sounds the CO2 release alarm in the engine room.
• Operate the pilot-cylinder valve and the master valve to release the gas.
• Continue boundary cooling and check the bulkhead temperatures from time to time.

Fire in the purifier room — actions in order:

• The purifier room also has hypermist — use it if it will help, with no shutdowns; explain CO2 when the surveyor asks for CO2.
• Immediately raise the fire alarm by breaking the glass (shoe-steel-toe fall-back as above).
• Stop the purifier from outside the room with the emergency stop.
• If the fire type is recognisable and not too big, use the proper portable extinguisher.
• Close the purifier-room door — do not forget to close it.
• Immediately run to inform the Chief Engineer and the deck officer or bridge — location and type of fire.
• Shut purifier-room ventilation from the MSB and shut the flaps.
• Shut the quick-closing fuel valve for the purifier line only.
• Carry out boundary cooling for the purifier room.
• The Chief Engineer releases CO2 from outside the purifier room or from the fire control station; keep up boundary cooling.

6. Purifier Fire Prevention & Closing Drill

The surveyor's last move is "how do you prevent a purifier fire?" — give the six fitted defences, then close with the number drill:

Prevention of purifier fires — six points:

• All pipes leading to the separator are double-sheathed — an inner-pipe leak drains into the outer pipe instead of spraying over the room.
• Drip trays below the purifier/separator catch spilled oil so it cannot flow, spread and touch hot material.
• All pipe flanges and connections are wrapped with anti-spill tape to contain flange leakage.
• Fixed protection fitted: water-mist and CO2 systems installed in the space.
• Quick-closing valves and remote stopping of pumps and purifier provided.
• Fire detection and alarm system provided so quick action can be taken.

Closing number drill — recite cold:

• Principle: smothering + cooling, O2 below 15%; cat-A ≥ 500 cu m; 85% in 2 min.
• Bottles: drawn steel, hydro 228 bar, stow ≤ 55 °C at ~52 bar, disc 177 bar at 63 °C, syphon tube against freezing.
• Room: sole use, ≤ 1 deck down with stair/ladder, 6 changes, outward gas-tight doors, 2.4 m, aft of collision bulkhead.
• Quantities: 30 / 40 / 35% through V × factor / 0.56 / 45.4; ship carries 212 at 58 bar, 107 s vs 120 s.
• Upkeep: beam 0–220 kg ± 5°, recharge at 10%; ladder 25 – weigh – 180 – 250 – 170/80/6-7.