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.

Why the Syphon Tube? Liquid CO2 sits at the bottom and flashes to gas at the nozzle — that flash gives the cooling half of the principle. A bottle without its dip tube blows vapour only, so always confirm syphon tube + bursting disc 177 bar at 63 °C in one breath.

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.

1. Cabinet Access & Automatic Safety Interlock. Break glass, unlock remote release cabinet door. The integrated microswitch trips mechanical ventilation fans, closes fire dampers automatically, and activates pre-discharge audio-visual alarms in protected spaces.
2. Personnel Evacuation & Space Sealing. Verify all crew members evacuated via headcount. Confirm quick-closing valves (QCV) tripped, fuel pumps stopped, and all skylights/doors sealed gas-tight.
3. Open Master Valve First. Open the designated master distribution valve to the space requiring extinction (Engine Room or Cargo Hold). This ensures the discharge line to nozzles is open before high-pressure gas is released into the manifold.
4. Actuate Pilot Release Cylinder. Pull the pilot bottle release lever. High-pressure pilot gas travels down the pilot line to pneumatically open the cutter heads across the required cylinder bank, discharging 85% of CO2 within 2 minutes.

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:

• 30% — Largest Cargo Space Volume
• 40% — Machinery Space (Excl. Casing)
• 35% — Machinery Space (Incl. Casing)
• 85% / 2 min — Discharge Rate Requirement

SOLAS quantity regulations & formulas:

Cargo Holds (30%)

30% Gross Volume Formula:

• Sized for the largest single protected cargo hold
• Gas delivered selectively via 3-way distribution manifold
• 0.56 m³/kg is free CO2 volume at 21.1 °C, 1 bar

Machinery Space (40% / 35%)

Casing Area Rule:

• Use 40% if casing area ≤ 40% of horizontal floor area
• Use 35% if casing is included in total volume
• Must discharge ≥ 85% of total required gas in ≤ 2 minutes

Worked Vessel Bank (212 Bottles)

Shipboard Installation:

• 201 Cylinders: Main Engine Room total flood
• 7 Cylinders: Dedicated Purifier Room flood
• 4 Cylinders: Uncommitted spare inventory
• Actual Test: 107 s total discharge (within 120 s design)
• Storage: 58 bar @ 21 °C; tare 72–80 kg; gross ~120 kg

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.

Stop — seal — flood: Stop fuel + fans; Seal vents + doors; Flood release CO2.

Fixed CO₂ Deployment Sequence, Alarms & Automatic Trips:

In oral exams, surveyors rigorously test the exact sequence of events from the moment fire is confirmed until CO₂ gas discharges into the machinery space. Every automatic safety trip, interlock, and operational verification must be recited without omissions:

1. Command Authorization & Space Sealing. CO₂ flooding is the ultimate firefighting measure and is executed only under the direct command of the Master (in close consultation with the Chief Engineer). The space is completely sealed: all watertight and fire doors battened down, skylights closed, funnel dampers and emergency ventilation fire flaps tripped shut manually and pneumatically.
2. Headcount & Complete Evacuation. Muster the entire ship's crew. A 100% headcount verification is conducted by the Chief Officer and Second Engineer. Absolute certainty that no personnel remain inside the machinery space is mandatory before opening the release cabinet.
3. Cabinet Door Opened — Immediate Automatic Trips & Pre-Discharge Alarms. The CO₂ release cabinet (located in the Fire Control Station outside the machinery space) is unlocked. Opening the cabinet door activates a mechanical/electrical microswitch (limit switch) that automatically:
   • Trips all Machinery Space Ventilation Fans: Power to supply and exhaust fans is instantaneously cut off via the emergency trip contactors in the main and emergency switchboards, preventing fresh air ingress and gas dilution.
   • Trips Fuel & Booster Pumps: Emergency trips de-energize fuel oil supply pumps, booster pumps, purifier feed pumps, and boiler oil firing units.
   • Sounds the Pre-Discharge Alarm: Triggers distinctive audible alarms (pneumatic sirens / high-decibel electric horns) and rotating visual warning beacons (xenon strobes) throughout all levels of the engine room, warning any straggler of imminent discharge.
4. Pilot Bottle Actuation & Distribution Master Valve. The operator pulls the release handle of the starting pilot bottles inside the control cabinet:
   • High-pressure pilot CO₂ gas travels through the pilot line to open the engine-room master distribution stop valve, establishing the path to the machinery space overhead manifold.
   • Pilot gas simultaneously charges the pneumatic time delay unit (a calibrated reservoir and orifice assembly providing a 30 to 60-second mechanical delay to grant a final window of escape for personnel).
   • Pilot line pressure transducers and pressure switches activate, transmitting confirmed gas-arming signals to the navigation bridge and safety management consoles.
5. Pneumatic Gang Release of Main CO₂ Battery. Once the time delay expires, pilot gas acts on the pneumatic release cylinder with piston. The advancing piston rod pulls the steel multi-cylinder release wire cables (or trips pilot-operated gang release manifolds). This physically trips the individual quick-release levers of all designated CO₂ cylinders simultaneously.
6. Gas Flooding Criteria & Rapid Smothering. High-pressure liquid CO₂ ascends through internal siphon dip tubes, passes individual non-return check valves into the main header, rushes through the open master stop valve, and flashes into heavy vapour across the nozzle array. SOLAS Chapter II-2 mandates that at least 85% of the total required CO₂ quantity must be discharged into the machinery space within 2 minutes, dropping the oxygen concentration to below 15% to suffocate the fire.
7. Boundary Cooling & Post-Extinction Protocols. The Emergency Fire Pump is started from outside the engine room to supply continuous boundary cooling water to adjacent bulkheads and decks. Bulkhead temperatures are monitored using thermal imaging cameras or surface contact pyrometers. Space must remain sealed for at least 24–48 hours to prevent flashover re-ignition. Re-entry is strictly prohibited until extensive cooling is verified and full Enclosed Space Entry protocols with positive-pressure SCBA, lifelines, and multi-gas detection (O₂ ≥ 21%, CO₂ < 0.5%, CO = 0 ppm) are enforced.

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.

Say It in Order. Alarm → muster → headcount → stops → dampers → cooling → evacuate → release. Actions out of order — cooling before stops, release before headcount — fail the question even when every item is named.

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:

Clean — cool — contain: Clean oil mist out; Cool bearings fed; Drain no hot pool.

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.

Favourite Trap. "Why not release CO2 immediately?" — because men, ventilation and fuel come first: evacuate, headcount, stop air and fuel, seal, cool boundaries — then release. CO2 in a breathing, ventilated space kills men and wastes gas.