Fixed Fire Fighting - CO2 — Most Asked Questions
34 questions asked about fixed fire fighting - co2 across the General and Fn 3 papers, heaviest first. 1 of them are must-master.
Learn the system first
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1 Co2 system safeties ?
Answer
CO2 kills by suffocation, so the system buys escape time first: alarms the instant the cabinet opens and holds the gas back 60–90 seconds.
- Opening the release cabinet immediately sounds the alarm in the protected space.
- A time-delay unit holds pilot CO2 from the bottle head assembly for 60–90 seconds so anyone inside can escape even after both cabinet valves are operated.
- The delay also guarantees the master (section) valve opens positively before bottle pressure hits it — dumping bottles first could pin the master valve shut.
- Fitted per the FSS Code with separate release cabinets where engine room and pump room share main bottles, plus lock-outs, warning notices and ventilation stops before release.
Surveyor follow-up: fire reported in the engine room and the cabinet is already open — list your release sequence including what you shut down first.
Full theory: CO2 Fixed Fire-Fighting System on Ships -
2 Co2 periodic maintenance
Also asked: “Co2 all maintenance”, “Co2 system maintainace”, “Co2 routine maintenance”
Answer
CO2 upkeep is movement, pipework and contents: keep releases free, blow the lines clear, and weigh the bottles — a light bottle is an empty promise.
- Keep every moving part clean, free and lubricated; wires tight, toggles and pulleys greased.
- Blow distribution pipes through with compressed air periodically so a nozzle is never the thing that discovers a blockage.
- Weigh bottles on schedule or check liquid level by ultrasonic or isotope detector — seals double as bursting discs, and a slow leak shows only on the scale.
- Pressure milestones: cylinders to 250 bar with internal and siphon-tube inspection; after 20 years every 5 years; HP lines 190 bar and MP lines 80 bar hydraulically, LP lines 7 bar air, then dry-air blow-through.
Surveyor follow-up: one bottle is 10% light with pressure normal — leak or temperature, and what is your next step?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
3 Fixed CO2 system
Answer
Fixed CO2 kills fire by smothering the whole space: flood it past 30% by volume after the crew is out, machinery stopped and openings shut.
- Release only on the master’s order, by the chief or second engineer — cabinet key from the break-glass box, local cabinet preferred.
- Opening the cabinet sounds audio-visual alarms and trips ventilation; count all crew out before touching a valve.
- Shut skylights, dampers and openings; stop machinery; close quick-closing fuel valves and lube/fuel pump emergency stops.
- Open pilot cylinder valve, then master valve, then release valve — gas arrives after the 60–90 second delay; prove release by the roar, cold bottles and manifold pressure.
Surveyor follow-up: cabinet open, alarms sounding, one man unaccounted for — release or hold, and what do you do with the delay time?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
4 Fuel leak off
Answer
Leak-off lines catch the fuel that slips past injector needles and return it — a rising leak-off alarm means an injector is passing.
- Normal leak-off is a trickle to the return; a leaking needle or cracked nozzle floods the line and lifts the alarm.
- First action: identify the unit by exhaust temperature and leak-off sight flow, then cut fuel to it.
- A passing injector also shows as black smoke, high exhaust temperature on that unit and fuel in the leak-off tank gaining fast.
- Change and pressure-test the injector, re-check timing — never blank a leak-off alarm to finish the watch.
Surveyor follow-up: leak-off high on all units at once — injectors or fuel viscosity, and what single check decides?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
5 Co2 10 year maintenance
Also asked: “Co2 maintenance- weekly;5yrly;10 yrly”, “Co2 10 yr maintenance”
Answer
At ten years a tenth of the bottles go for internal inspection and hydrostatic test — one failure doubles the sample, two failures take the whole bank.
- Test at least 10% of bottles internally and hydraulically at 250 bar; discard any with permanent volume change.
- One failure means 50% of bottles tested; further failure means every bottle tested.
- Flexible hoses renewed by maker interval and never beyond ten years; HP lines to 190 bar, MP to 80 bar, LP to 7 bar air, then dry-air blow-through.
- After 20 years the cycle repeats every 5 years; siphon tubes checked and logged each time.
Surveyor follow-up: one bottle fails hydro at year ten with the rest passing — how many more do you test?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
6 location of i) time delay unit. ii) relief valve iii) master valve
Also asked: “Location where following are fitted Time delay unit, Relief valve, Master valve”
Answer
Delay lives in the cabinet pilot line, master on the manifold, relief on the protected-space line — each where its job happens.
- Time-delay unit sits between pilot bottles and bottle heads inside the release cabinet, holding gas 60–90 seconds.
- Master valve stands on the common manifold where one wheel isolates or floods the whole protected space.
- Relief and section valves ride the distribution lines to each space with pressure gauges and alarms on the manifold.
- Pilot bottles, both valves and the delay all live duplicated across local and remote cabinets in parallel.
Surveyor follow-up: point at the cabinet and trace pilot gas to the bottle heads — which fitting does it meet first?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
7 Ows discharge criteria
Answer
Bilge water goes overboard only en route through working filtering gear at 15 ppm or less — five conditions, all met.
- Ship proceeding en route outside 12 miles with the mixture through compliant filtering equipment.
- Oil content 15 ppm or less without dilution, proved by the monitor with automatic stop.
- Never from cargo pump-room bilges on tankers nor mixed with cargo residues.
- Special areas add the same bar with tighter watch — log time, position and quantity every discharge.
Surveyor follow-up: 15-ppm alarm sounds mid-discharge — what stops, what is logged, and can you restart on the spare unit?
Full theory: When You May Discharge — MARPOL Annex I Limits, Distances and Special Areas -
8 Sewage discharge criteria
Also asked: “Sewage holding tank discharge criteria”
Answer
Sewage goes overboard by treatment or distance: approved plant effluent near shore, held sewage only far offshore en route.
- Comminuted and disinfected sewage through an approved system past 3 miles from land.
- Untreated held sewage only past 12 miles en route at moderate speed, never instant-slugged overboard.
- Holding tanks keep every litre inside special areas and ports for reception facilities.
- Log every discharge with time, position and treatment state — the surveyor reads the sewage book next.
Surveyor follow-up: holding tank full 11 miles out with reception closed — discharge, hold or treat, and under which rule?
Full theory: MARPOL Annex IV — Prevention of Pollution by Sewage from Ships -
9 Co2 10 year routine
Answer
At ten years a tenth of the bottles go for internal and hydrostatic test at 250 bar — one failure doubles the sample.
- Test at least 10% internally and hydraulically; discard any with permanent volume change.
- One failure means 50% tested; further failure means every bottle tested.
- Pipes prove alongside: high-pressure lines 190 bar, medium 80 bar, low 7 bar air with dry-air blow-through.
- After 20 years the cycle repeats every 5 years with siphon tubes checked each time.
Surveyor follow-up: one bottle fails hydro at year ten with the rest passing — how many more do you test?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
10 Co2 bulk system
Answer
Bulk CO2 stores refrigerated liquid in one tank, not banks of bottles: compressors hold minus 17 with a standby twin.
- Pressure vessel with twin refrigeration compressors on separate inside coils — one runs, one stands by.
- Water or air cooled with temperature holding the liquid ready at low pressure.
- Distribution by insulated lines to protected spaces on master-valve release like bottle banks.
- Survey points are refrigeration duty, insulation, relief sizing and level against the flooding calculation.
Surveyor follow-up: one compressor down with temperature holding — sail, repair or inhibit release, and why?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
11 Co2 bulk system co2 carriage in what form in pipe ?
Answer
CO2 travels as liquid in bottles and bulk tanks by siphon tubes, flashing to cold gas-snow at the nozzles.
- Dip tubes deliver liquid from the bottle bottom; without them vapour alone leaves and liquid freezes inside.
- Bottles ride upright so liquid covers the tube foot at every heel and trim.
- Pipes carry liquid under bottle pressure until nozzles expand it to smothering gas with dry-ice snow.
- Prove by upright stowage, tube checks and discharge tests — inverted bottles fail the flood.
Surveyor follow-up: discharge weak with pressure normal — dip tube, nozzle or distribution, and what proves it?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
12 Co2 system arrangment
Also asked: “Co2 system arrangement”
Answer
CO2 layout is bottles to manifold to spaces: banked cylinders, master valve, delay and distribution with two cabinets.
- Bottle bank with siphon tubes feeding a common manifold through non-return cylinder valves.
- Master valve plus 60–90 second delay holding pilot gas for crew escape and positive valve opening.
- Distribution lines with stop valves to each space sized for design concentration.
- Local cabinet in the CO2 room with remote cabinet at fire control in parallel — pilot bottles in each.
Surveyor follow-up: draw the release path from pilot bottle to nozzle — which valve opens first?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
13 Co2 system full
Answer
A full CO2 answer names quantity, release and proof: design concentration per space, timed release, roar-and-cold proof.
- Quantity sized per protected volume to design concentration with bottles shared across engine and pump rooms.
- Release on master’s order with crew counted, stops shut and cabinet sequence run pilot, master then flood.
- Delay 60–90 seconds guards escape and valve opening with alarms and ventilation trips from the cabinet door.
- Monthly leak and valve checks with annual controls and 10-year bottle testing behind every release.
Surveyor follow-up: cabinet open with one man missing — release or hold?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
14 What was it high pressure or low pressure
Answer
CO₂ ships high or low pressure: bottles at 56 bar for small plants, a refrigerated 21-bar bulk tank for big ones.
- High-pressure banks hold liquid CO₂ near 56 bar at 20°C, rising past 70 bar hot — keep the room cool with bursting discs near 200 bar.
- Pilot bottles in the release cabinet fire the mains with alarms and ventilation shut on door opening.
- Low-pressure bulk holds tonnes near 21 bar at −20°C insulated, replacing rooms full of bottles.
- Choose by protected volume: holds and machinery with many bottles earn the bulk tank and its refrigeration watch.
Surveyor follow-up: bottle room hot with pressure past 70 bar and one disc weeping — cool, release or evacuate first?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
15 Carbon dioxide type extinguishers
Also asked: “Co2 fire extinguisher”
Answer
CO₂ portables smother with cold gas: 4.5 kg liquid charge, dip tube delivery, horn of insulating material, pin-pulled lever valve.
- Solid-drawn steel body near 53 bar charge pressure, hydraulically tested toward 227 bar with zinc coating inside and out.
- Dip tube delivers liquid from the bottom so discharge stays liquid-to-gas — operate upright or the tube sucks vapour and freezes.
- Swivelling non-conducting horn spreads the cloud safely on electrical fires; bursting disc guards overpressure.
- Attack upwind at the flame base with no frostbite grip on the horn, back off before the cloud thins — reflash watches follow.
Surveyor follow-up: extinguisher laid sideways during discharge with sputtering flow — empty, frozen or wrong attitude, and what next?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
16 (i had no idea thta co2 system have two pressure system
Answer
CO₂ ships two pressure systems: the high-pressure bank feeding the engine room, and a low-pressure bulk tank for the large spaces.
- High-pressure: cylinders of liquid CO₂ near 56 bar at 20°C, rising to 64 and 71 bar at 25 and 30°C, fed by pipe at design pressure.
- Low-pressure: a single refrigerated tank holding tonnes at about 21 bar, which replaces rooms full of bottles.
- The choice is driven by protected volume — a bulk tank earns its refrigeration once a space is beyond a bank of cylinders.
- A ship with both runs them independently, with separate release cabinets, because the pressures and pipe ratings are not the same.
Surveyor follow-up: engine room on low-pressure feed with HP lines still in the ship — which arrangement, and what pipe rating applies?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
17 CO2 10 year chcks
Also asked: “Co2 10 years checks”
Answer
After twenty years the CO₂ plant goes to five-yearly testing: cylinders, piping and seals are re-proved, not just looked at.
- Cylinders are pressure tested at high pressure and inspected internally, with dip tubes and siphon tubes checked.
- Any permanent change in volume condemns the cylinder — it is discarded, not repaired.
- High-pressure pipes are hydraulically tested, medium and low-pressure lines tested to their own ratings.
- After twenty years of installation these tests are carried out every five years thereafter.
Surveyor follow-up: plant 22 years old with the last cylinder test 11 years ago — overdue how many years, and what follows?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
18 Co2 cheacks all(from weekly to 15 yearly
Answer
The CO₂ schedule runs from a weekly look at the system to a 10% cylinder hydrostatic test, with a 5-year step after twenty years.
- Weekly and monthly: alarm indication and control valve settings proved, and the whole system checked for condition.
- Yearly: cylinders and control valves inspected, discharge piping and nozzles tested to prove the flow.
- At intervals, at least 10% of cylinders go to internal inspection and hydrostatic test — 50% if one fails, all if more fail.
- After twenty years, pressure testing moves to every five years, and lines are blown through with dry air after hydraulic testing.
Surveyor follow-up: one cylinder failed the 10% test last month with the 50% batch not yet tested — what is the ship’s status?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
19 Co2 full detail regulations
Answer
CO₂ is governed end to end: design quantity, alarm and delay, 85% in two minutes, sealed space after, tested system before.
- The design quantity is calculated from the protected volume so the space is flooded to the required concentration.
- Alarm and a 60-to-90-second time delay precede discharge, and the micro switch cuts ventilation on release.
- At least 85% of the required quantity must be delivered within two minutes, proved by timed tests.
- After release the space stays sealed and gas-light to the next port, with no entry until tested and ventilated.
Surveyor follow-up: 85% delivered but no two-minute trace and the delay unit bypassed — compliant release or a lucky flood?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
20 Co2 high pr and low pr
Answer
High-pressure banks hold liquid at around 56 bar; low-pressure bulk holds tonnes at about 21 bar, and the two feed different spaces.
- High-pressure cylinders are charged with liquid CO₂; pressure climbs with temperature — about 64 bar at 25°C and 71 bar at 30°C.
- Keeping the CO₂ room cool is therefore a pressure-control measure, not just a comfort measure.
- Low-pressure bulk storage runs near 21 bar and is kept liquid by refrigeration instead of by pressure alone.
- The pipework differs to match: HP, medium and low-pressure lines are each tested to their own rating, not one common figure.
Surveyor follow-up: cylinder pressure above 71 bar in a hot CO₂ room — cool, vent, or is the plant still safe?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
21 Co2 how to operate and why 85% regulation for releasing?
Answer
The system releases on alarm after a time delay, and the 85% rule is the proof that the space is flooded before anyone enters.
- Open the release cabinet, which alarms, cuts ventilation and starts the time delay before the pilot gas reaches the bottles.
- The master valve and pilot valves then open and CO₂ floods the space at the design rate through the distribution lines.
- At least 85% of the required quantity must reach the space within two minutes, proved by test traces and weights.
- Leaking openings or a partial bank is why the rule exists — a flood that only partly arrives leaves the space unsmothered.
Surveyor follow-up: release traced at 80% in two minutes with one damper leaking — flood, reseal, or open the space?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
22 Co2 release procedure
Answer
Release is a sequence: secure the boundary, start boundary cooling, account for the crew, then operate the cabinet — in that order.
- Close vents, doors, flaps and dampers, and shut the fuel-line quick-closing valves for the space.
- Start the emergency fire pump and keep boundary cooling running, checking bulkhead temperatures as you go.
- Account for every crew member, then open the cabinet with the key — alarms sound and ventilation fans cut immediately.
- Operate the pilot and master valves to release the gas, and keep boundary cooling until the fire is proved out.
Surveyor follow-up: release ordered with one crew member unaccounted for — flood, search first, or hold the cabinet?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
23 Co2 system full plus regulations. Wanted to hear microswitch
Answer
The micro switch is the safety interlock: opening the release cabinet alarms the ship, shuts ventilation and starts the time delay.
- As soon as the release cabinet door is opened, the micro switch activates the CO₂ warning alarms and the ventilation shutoff.
- The cabinet holds two pilot cylinders, which supply the gas to open the master valve and the bottle head assemblies.
- A time-delay unit passes that pilot gas on after 60 to 90 seconds, giving personnel time to escape the protected space.
- The whole arrangement is required by the FSS Code, which sets the alarm, delay, capacity and discharge-time rules.
Surveyor follow-up: micro switch found welded shut so the alarm cannot sound — was it a repair, and what does the code require?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
24 Describe the causes for the following in the domestic refrigeration system: (8) i) Frequent cut-in and cut-out of the compressor ii) lub oil low pressure cut out of the compressor ii) High pressure cut out of the compres
Also asked: “Describe the causes for the following in the domestic refrigeration system: (8) i) Frequent cut-in and cut-out of the compressor ii) lub oil low pressure cut out of the compressor ii) High pressure cut out of the compressor iv) Frosting in the compressor suction side”
Answer
Three trips, three stories: short-cycling, oil starvation and a blocked or overcharged condenser all stop the compressor.
- Frequent cut-in and cut-out: low refrigerant charge, a thermostat hunting, or a system with too little thermal mass.
- Lube oil low pressure cut-out: low oil level, a clogged oil filter, a failing pump or a leaking suction line.
- High pressure cut-out: blocked condenser tubes or fouling, overcharge, non-condensable gas, or a stopped condenser fan.
- Check pressures, sight glass and condenser approach temperature before changing any part — the symptom names the side, not the fault.
Surveyor follow-up: compressor tripping on high pressure with a clean condenser and a full sight glass — charge, air or airflow?
Full theory: Refrigeration Principles and the Vapour Compression Cycle -
25 Dip tube in co2 reason
Answer
The dip tube delivers liquid CO₂ out of the bottle: without it the vapour leaves, the liquid freezes and the discharge fails.
- CO₂ evaporates from the surface, taking latent heat and freezing the liquid that remains inside the bottle.
- A siphon or dip tube inside the bottle draws liquid to the valve instead of vapour, so the full charge is delivered.
- Without it the bottle empties of vapour and stops discharging — a failure that looks like an empty bottle.
- This is why CO₂ extinguishers must be operated upright, and why dip tubes are checked at every survey.
Surveyor follow-up: extinguisher discharging weakly and found on its side — dip tube, pressure or level first?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
26 Is there orifice in leakoff line nd where
Answer
The manifold relief does vent to atmosphere, and a restriction in the line is deliberate — it stops a full discharge of the bank.
- CO₂ accumulates in the manifold when bottles release with the master valve closed, and its pressure rises with temperature.
- Since the piping is tested to a much lower figure, a relief valve in the manifold is necessary to bring the pressure down safely.
- Accumulated pressure can also trip intact bottles if the non-return valve between bottle and manifold has failed.
- The leak-off is therefore a controlled vent — restricted so it relieves pressure without discharging the whole bank into the ship.
Surveyor follow-up: manifold relief lifted repeatedly with the master valve proved shut — is the vent, the valve or the non-return at fault?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
27 Regulation for the co2 discharge
Answer
The regulations govern the whole sequence: alarm, delay, capacity, discharge time, and what is allowed after the flood.
- At least 85% of the required quantity must be discharged within two minutes of the system being released.
- Alarm and a time delay of 60 to 90 seconds must precede discharge so the space can be cleared of people.
- The space is kept sealed after release and gas-light maintained to the next port, with no entry until tested.
- The FSS Code sets the design, and the surveyor checks the test trace, the sealing and the drill record together.
Surveyor follow-up: flood released and the hatch opened after twenty minutes because it was clear outside — inside or outside rule?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
28 Release the smothering gases (Steam or CO2) to extinguish fire
Also asked: “Release the smothering gas (COZor steam) to extinguish fire la”
Answer
Smothering gases kill by cutting oxygen, not heat: CO₂ displaces the air, steam does the same with a vapour blanket.
- CO₂ floods the space and reduces the oxygen below the level that supports combustion, extinguishing without cooling.
- Steam smothering works the same way through a vapour blanket, and is used where CO₂ is unsuitable for the space.
- Both are useless on a fire that keeps its own air supply — so all vents and openings are sealed before release.
- They need the detection and delay system working, because release into a manned space is what kills rather than the fire.
Surveyor follow-up: release into a space with one vent still open — does the smothering still work, and what proves it?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
29 Role of trip switch in co2 system
Answer
The trip switch is the proof of release: it confirms the system has actually operated so the alarm and the shut-down can be trusted.
- It signals that the release cabinet has been opened and the gas is on its way, closing the alarm and ventilation circuit.
- It interlocks the ventilation shutoff so the fans cannot restart and dilute the gas being released.
- It also starts the time delay, which is what makes the manual release survivable for anyone still in the space.
- Test it on the routine: a system that releases silently is a system nobody will dare to use.
Surveyor follow-up: trip switch proven on test but the ventilation restarted on power failure — which circuit should hold?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
30 Time delay unit
Answer
The time delay holds the pilot gas 60 to 90 seconds so the space empties of people before any CO₂ is discharged.
- Pilot CO₂ from the release cabinet passes through the time-delay unit before reaching the bottle head assemblies.
- Opening valve 2 therefore does not release the bank at once — discharge follows 60 to 90 seconds later.
- It also guarantees the master valve is positively open before gas flows, avoiding the pressure-lock problem.
- The delay is required by the FSS Code and is the difference between a system and a fatality.
Surveyor follow-up: delay set to five seconds by a previous repair — restore it, or is the escape time still adequate?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
31 Wht is ur action after co2 flooding?
Answer
After flooding: seal the space, keep boundary cooling, keep the gas light and let nobody in until it is tested and ventilated.
- Keep the space sealed and ventilate from outside — gas holds fire down, and opening it can restart the fire.
- Maintain boundary cooling on the surrounding steel and keep watching bulkhead temperatures for the whole period.
- The compartment stays closed until the fire is extinguished, cooled and the atmosphere tested and ventilated.
- Re-entry is only with breathing apparatus, an entry permit and an attendant at the hatch — the gas kills long after the fire does.
Surveyor follow-up: space opened after 20 minutes because the alarm stopped — safe re-entry, or has the fire simply gone quiet?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
32 Why time delay in co2 system
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33 Why time delay is provided
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34 high pressure pipes between fuel injection pump and injector are double skinned
Answer
Every external high-pressure fuel line is double-walled: a spray of pressurised oil across hot surfaces is the engine’s worst fire hazard.
- The line between the fuel pump and injector carries pressure shock waves and heavy vibration of its own.
- Pressurised oil leaking from it sprays across hot engine surfaces and can start a fire in seconds.
- Double-walling gives a second barrier so a fracture is contained and the leak is seen before it reaches a hot surface.
- Keep the lines clear of steam, exhaust manifolds and silencers, all of which are insulated or shielded for the same reason.
Surveyor follow-up: one line found single-walled on an engine with a weeping union beside an exhaust manifold — what first?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors
Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.