Gas Cylinder & CO2 Room Safety — Most Asked Questions
25 questions asked about gas cylinder & co2 room safety across the General and Fn 3 and Fn 4b and Fn 6 papers, heaviest first. 1 of them are must-master.
Learn the system first
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1 Acetylene bottle safety
Also asked: “Oxy acetylene safety”, “Oxy-Acetylene safety”, “Acetelene bottle safety”
Answer
Acetylene is dissolved in acetone inside a honeycomb mass — treat the bottle upright, cool, secured and backfire-proof.
- Acetylene gas is dissolved in acetone within a perforated honeycomb structure — never lay the bottle down or use it below minimum pressure, or acetone carries over.
- Stow upright, secured, cool and ventilated, caps on, oxygen and acetylene stored apart and away from heat, oil and grease.
- Fit flashback arrestors and non-return valves at the regulator/torch; leak-test joints with soapy water, never a flame.
- Oxygen fittings stay oil-free — oxygen plus hydrocarbon grease detonates — and empty bottles are marked, valved shut and landed separately.
Surveyor follow-up: flashback pops in the hose — which cylinder do you shut first, and what do you check before relighting?
Full theory: Safety on Oxygen & Acetylene Bottles -
2 How to weight co2 bottle
Also asked: “How to weight co2 bottel”, “How to weight the co2 bottle, what precautions you will take”
Answer
CO2 bottles are weighed hanging free on a scale beam: lift clear, read at 90 degrees, recharge at 10% loss.
- Pull the scale handle down to lift the cylinder clear of its bottom contact.
- Ease the beam to 90 degrees against the hook and read the scale — 5 degrees of beam angle either way is allowed.
- A 10% weight loss means recharge, no debate — leaking contents cannot be topped up by pressure reading.
- Precautions: isolate the bank, keep the room ventilated, protect valve and siphon tube, log every bottle.
Surveyor follow-up: pressure gauge reads normal but weight is 12% light — in service or for recharge?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
3 A) sketch and describe the operating principle of an OWS. State the regulatory requirements including ORB
Also asked: “Sketch and describe the operating principles of an OWS”
Answer
Sketch gravity chamber to coalescer to monitor: oily water in, oil up, clean water out under 15 ppm with every drop logged.
- First-stage gravity with baffles drops big oil to the top collection space with air vented on fill.
- Second-stage coalescer joins fine mist into drainable drops with polishing filter behind it.
- Monitor with auto-stop guards the overboard line; failure stops discharge and goes in the book.
- Regulatory side: 400 gross tons and up carry the book, discharge only en route through working gear, entries by code.
Surveyor follow-up: draw the flow from inlet to overboard — where do monitor, stop valve and sampling point sit?
Full theory: How Oily Water Separation Works — Gravity, Coalescence and Why Turbulence Ruins It -
4 So that the correct mass of air is allowed into the cylinder for combustion of the fuel. (the higher the temperature the greater the specific volume
Also asked: “• So that the correct mass of air is allowed into the cylinder for combustion of the fuel. (the higher the temperature the greater the specific volume”
Answer
Hot air is thin air: cool dense charge packs more oxygen mass per stroke for the same swept volume.
- Specific volume grows with temperature — hot scavenge air carries less oxygen per litre.
- Cooling charge air toward 60–70 degrees after the blower packs more mass into every stroke.
- Dense air burns more fuel cleanly at lower thermal stress with longer component life.
- Watch cooler outlet temperature and pressure together — thin air shows first on the pyrometers.
Surveyor follow-up: power down with scavenge temperature up and pressure normal — cooler, filter or load?
Full theory: Cooling, Lubrication and Fuel — Systems and the Tanks Checked Before Starting -
5 Air Bottle Pressure Test
Answer
Air bottles are tested by the maker or an approved place, hydrostatically to a stated multiple of the working pressure, never in the ship.
- A service air bottle carries a safety valve, a gauge and the drain, and its pressure is the compressor’s working pressure.
- When that pressure is reached the bottle pushes the service valve down against its spring and the bottle unloads.
- As pressure falls the spring dominates and the valve closes again, so the compressor cycles to hold the receiver pressure.
- Test the bottle itself ashore, hydrostatically to the required multiple, and discard on any permanent set — a bottle that has been worked is a bomb.
Surveyor follow-up: bottle with no current test stamp and permanent set on its gauge — service, retest or scrap?
Full theory: Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution -
6 Air bottle safties
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7 As per solas how much co2 is required of e/r in fire (don't tell formula to calculate no. Of cylinders
Answer
For a typical engine room the calculation gives about 4.6 tonnes of CO₂ in roughly 102 cylinders of 45 kg — check your ship’s own figure.
- An engine room including casing at about 7 324 m³ gross volume, at 40% for the usable free volume, gives the basis of the calculation.
- Quantity of CO₂ in kg is that volume multiplied by the mixing ratio, then divided by 0.56 for the volume each kilogram occupies.
- For that volume the worked example gives about 4 577 kg, which divides into roughly 102 cylinders of 45 kg.
- Answer with your own ship’s volume and cylinder size — the formula proves you, the number proves you know the ship.
Surveyor follow-up: surveyor accepts the formula but your cylinder count differs from the book — which figure governs, and where is the error?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
8 Co2 bottle pr
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9 Co2 system explain, safety, why bursting disc provided? Why door opens outwards?
Answer
CO₂ smothers by displacing air, and the system is designed so a release cannot trap a man: bursting discs, outward doors, remote release.
- The bursting disc on each bottle head protects against overpressure from heat or fire in the CO₂ room.
- Doors open outwards so a person collapsing against one can still be pulled out, and so the door never traps an escapee.
- Release is operated from a remote station with an alarm and a 60-to-90-second delay, so nobody is inside when it happens.
- The room itself is ventilated, gas-tight, flameproof lit and kept free of anything else — the store serves no other purpose.
Surveyor follow-up: CO₂ room door found closing inwards — is it a fitment defect, an entry hazard or both?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
10 How will you identify the co2 bottle is fully released or not
Answer
Weighing is the answer: a full bottle loses about 10% of its charge before it is recharged, and that is the yardstick.
- Every bottle is weighed on discharge and on the routine check, and the reading is logged against the certificate weight.
- A drop beyond the maker’s permitted loss, commonly 10% or more, means the bottle is condemned for recharge or scrap.
- A gauge on the manifold tells you the system is live, but it cannot tell you which bottle is spent.
- Weighing is the only method that answers the question — so the scale and the certificates are part of the system.
Surveyor follow-up: bottle reading 12% down with the manifold gauge at normal — is the leak, the valve or the scale?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
11 It is defined as the maximum volume of the combustion chamber (with the piston farthest out, or bottom dead centre) divided by the volume with the piston in the full-compression position (with the piston nearest the head
Also asked: “It is defined as the maximum volume of the combustion chamber (with the piston farthest out, or bottom dead centre) divided by the volume with the piston in the full-compression position (with the piston nearest the head of the cylinder, or top dead centre”
Answer
That is the compression ratio: swept volume plus clearance over clearance alone — the space the piston cannot get rid of.
- Maximum volume is the volume with the piston at bottom dead centre; the clear volume is taken with the piston nearest the head.
- Compression ratio equals (Va + Vs) divided by Va, where Va is the clearance and Vs the swept volume.
- It sets the pressure ratio the machine can reach, which is why the clearance and the valves dominate compressor performance.
- More clearance means less ratio and less efficiency, but it is needed to allow the gas to expand before the suction valve opens.
Surveyor follow-up: compression ratio down with the valves proven good — is it the clearance, the rings or the air in the charge?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
12 Scba how to fill bottle
Also asked: “SCBA how to fill bottel”
Answer
SCBA cylinders are filled with a dedicated charging set — cool, dry, hand-tight connection, and never by pouring.
- Use the charging unit with a yoke and a hand-tight connection, with the cylinder valve closed and cool.
- Fill to the maker’s full pressure, typically 200 to 250 bar, watching the gauge rather than judging by feel.
- Close the cylinder, bleed the connection and yoke, then record the pressure and date against the set’s register.
- A cylinder that will not come to full pressure goes for hydrostatic test, not back into the battery.
Surveyor follow-up: set charged to 180 bar with the compressor rated 300 — usable, or recharge to the maker’s figure?
Full theory: LSA Chapter 3: Line Throwing, EEBD & SCABA -
13 Steps for removal of cylinder cover and overhaul of safety/ indicator valve
Answer
Isolate the gas first, then strip in order, clean and lap, and prove the valve on the rig before it goes back.
- Close the relevant valves, blank the lines, vent the system and confirm it is gas free before removing the cover.
- Remove the valve cover, unscrew or slacken the seat, and withdraw the valve, spring, disc and guide in that order.
- Clean and lap the seat and valve, check the spring for set, and renew any O-rings or gaskets rather than reusing them.
- Reassemble, test the valve on a rig for lift pressure and tightness, then refit and pressure-test the line before it is in service.
Surveyor follow-up: safety valve reassembled with old seals and proved only on the bench — is the line test still required?
Full theory: Deck Foam & Inert Gas (IG) Systems on Tankers -
14 The indicator diagram is very important to know the combustion in the cylinder and
Answer
The indicator diagram is the combustion portrait: compression, peak, expansion and exhaust on one sheet, once per watch.
- The card gives the indicated work, and the compression and peak pressures show the state of the cylinder.
- The position of the peak relative to TDC is the injection timing and the pressure rise, which is the combustion quality.
- The tail of the curve shows the exhaust and scavenging, so a bad tail means the exhaust valve or the scavenging.
- Comparing cards at the same load across the units is what finds the one cylinder that is different.
Surveyor follow-up: one card with a late peak and a long tail — is it the injector, the exhaust valve or the scavenging?
Full theory: Marine Fuel Testing, ISO 8217 & Combustion Analysis -
15 This results in loss of compression pressure in the cylinder
Also asked: “• This results in loss of compression pressure in the cylinder”
Answer
The loss of compression pressure is the working of a compression ratio: the ratio is set by the clearance and the delivered volume.
- Compression ratio is the maximum volume of the combustion chamber, piston farthest out, divided by the volume at full compression.
- That ratio is what converts the swept volume into pressure, so losing it means losing power as well as economy.
- A worn machine with excessive clearance, leaking valves or a weak charge shows the loss as low compression pressure on the card.
- So the card is the proof: compression line, peak pressure and the tail together tell the surveyor which of the three has gone.
Surveyor follow-up: compression pressure down on every unit with the peak normal — mixture, clearance or charge condition?
Full theory: Marine Fuel Testing, ISO 8217 & Combustion Analysis -
16 To drain the water and surplus oil in the air bottle
Answer
Drain the bottle while it is out of service: isolate, depressurise, open the drain and clear the moisture trap as well.
- Isolate the bottle from the compressor and receiver and depressurise it, then open the drain at the bottom.
- Water and oil separate on the drain, and both are cleared until only air comes out at the drain.
- Clear the moisture trap and the strainer in the line at the same time, or the water simply collects again.
- Refill, pressurise and log it — a wet bottle corrodes its inside and carries water into the starting air.
Surveyor follow-up: water found in the bottle with the receiver valve shut and the trap clear — where else is the water coming from?
Full theory: Air Compressor Maintenance — Lapping, Clearances & Overhaul -
17 Total number of bearings in one cylinder unit
Answer
Count them by function: the main bearings carry the shaft, the bottom end takes the rod load, and the thrust bearing locates it.
- Main bearings, one per frame, carry the weight of the shaft and the firing forces along the whole length.
- The bottom-end bearing takes the connecting rod at the crankpin, and the crosshead bearing takes it at the crosshead.
- The thrust bearing locates the shaft axially, and there is a further thrust face at the coupling or the block.
- So the total follows the count by function — the surveyor is testing whether you know the load path, not a number.
Surveyor follow-up: bearing count wrong on a two-stroke with a crosshead — which bearing was missed?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
18 Ventilation in co2 room
Answer
The CO₂ room ventilates from the bottom: exhaust takes suction low where leaked gas ponds, at six air changes an hour.
- Below-deck stores get mechanical ventilation drawing exhaust air from the bottom of the space.
- The rate is at least six air changes per hour, sized to clear the room after a release.
- Inlets go low and outlets high, because carbon dioxide is heavier than air and settles before it rises.
- The fan is independent of other ventilation, with non-sparking blades and the motor outside the gas path.
Surveyor follow-up: CO₂ room vent drawing from the top with the fan running — will it clear a leak, and what is the first fix?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
19 When acetylene is mixed with oxygen in correct proportions and ignited, then a flame will be produced at the tip of the torch which is sufficient enough to join the parent metal. The fuel gas mostly used is Acetylene, be
Also asked: “When acetylene is mixed with oxygen in correct proportions and ignited, then a flame will be produced at the tip of the torch which is sufficient enough to join the parent metal. The fuel gas mostly used is Acetylene, because it can produce high flame temperature( 3500°C ) when compared to other gases like Propylene, Propane, Hydrogen and Natural gas”
Answer
Gas welding is a flame balance: neutral for steel, oxidising for copper, carburising never — the ratio decides what the weld becomes.
- Equal volumes of acetylene and oxygen give a neutral flame, and that is the one normally used for steels and most metals.
- More oxygen than acetylene gives an oxidising flame, used for high-conductivity materials like copper but not for steel.
- On steel the oxidising flame decarburises the weld pool and depletes its silicon, so the joint is weak and brittle.
- Excess acetylene gives a carburising flame, the excess decomposing into carbon particles that dissolve into the weld and cause service problems.
Surveyor follow-up: brass flange welded with an oxidising flame and now cracking — which flame, and what did it do to the pool?
Full theory: Shipbuilding Materials, Welding and Weld Defects -
20 Why a SCBA bottle is checked before use, and what provision is there for warning regarding the bottle content. (8
Answer
The set is checked because a soft cylinder kills the wearer before anyone knows, and the warning is a pressure indicator that moves.
- A full cylinder read against the 250 bar test figure is the first check — a soft set is a set that empties in minutes.
- The pressure gauge is the warning: it shows the remaining content and when it falls to 50–60 bar the whistle sounds.
- Before removing any cap, bleed the thread so internal pressure is released — a pressurised cap comes off like a projectile.
- Then prove the demand valve and the face seal, because a full gauge with a dead valve is the failure nobody expects.
Surveyor follow-up: gauge at 200 bar with the whistle silent at 50 — is the gauge, the alarm or the cylinder at fault?
Full theory: LSA Chapter 3: Line Throwing, EEBD & SCABA -
21 Why bursting disc
Answer
The bursting disc is the last line on a bottle that is heated or in fire: it lets the gas out rather than letting the bottle burst.
- A disc is fitted on the bottle head assembly to release pressure before the cylinder can rupture.
- A fire in the CO₂ room raises the bottle temperature, and the CO₂ pressure climbs with it.
- The disc bursts and vents to atmosphere, and that discharge is also what extinguishes a fire in the room.
- A disc is preferred to a spring valve here because it cannot fail closed — which is the whole point of a last line.
Surveyor follow-up: two bottles in the room with discs already replaced and no leak — service, refill or scrap?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
22 all cylinder liner clearances?how to measure?
Answer
Liner clearance is measured with a bore gauge or a telescopic gauge, at top, middle and bottom of the stroke.
- Inside micrometer across the bore at top, middle and bottom, fore-and-aft and athwartships, records ovality and taper.
- For the running clearance, a telescopic gauge in the bore at the same positions, compared with the maker’s figures.
- Piston-to-liner clearance is taken with the piston at the reference crank angle so the bore is truly aligned.
- The record is the trend: the increase since the last gauging, hours run, is what condemns the liner.
Surveyor follow-up: oval bore recorded but the piston-to-liner figure taken at BDC — which measurement does that give?
Full theory: Cylinder Liner Wear, Calibration & Cold Corrosion -
23 corrosion in air bottle
Answer
Air bottles corrode from the inside: condensed water sits on the wall and pits it, and the bottle thins where the water stands.
- Oil and water carry-over from the compressor condense in the bottle and attack the internal surface.
- Corrosion shows as pitting inside, a rough or discoloured surface, and a loss of wall thickness at the bottom.
- Prevent it by keeping the bottle dry — correct drainage, a working moisture trap and no long periods of low pressure.
- A corroded or pitted bottle is a condemned bottle, not one to be cleaned and put back — the test decides, not the eye.
Surveyor follow-up: bottle pitted inside but holding pressure and in date — clean it, coat it, or scrap it?
Full theory: Air Compressor Maintenance — Lapping, Clearances & Overhaul -
24 main air bottle taking lot of time to fill up... reasons
Answer
A slow-filling main air bottle is a leak, a blocked line or a compressor that has lost capacity — find which before blaming the bottle.
- A leaking service valve, moisture trap or a weeping gland lets the air back into the compressor.
- A blocked strainer or a choked after-cooler restricts the delivery to the bottle.
- A compressor losing capacity through worn valves, rings or clearance shows as a slow fill at normal pressures.
- Time the fill from empty at a set pressure and log it — a steadily lengthening fill is the fault announcing itself.
Surveyor follow-up: bottle filling slowly with the valves renewed and the cooler clean — is the bottle, the line or the compressor?
Full theory: Air Compressor Maintenance — Lapping, Clearances & Overhaul -
25 Water leakage from cylinder liner Water leakage from the jacket Oil running hour is over
Answer
Water in the cylinder comes from the liner or the jacket, and the running hours tell you whether the machine is simply old.
- Water from the liner means a crack or a failed seal at the liner bottom; water from the jacket means a leaking head or tube.
- The symptoms differ: jacket water raises the feed and the blowdown, and liner water is found at the drain and dilutes the oil.
- Oil running hours over their limit explains a worn machine generally, but water is a fault, not wear.
- So the action is to find the source before topping up: crack the jacket, pressure test it, and dye-check the liner.
Surveyor follow-up: jacket water rising with the head gasket renewed and the tubes proved sound — where is the water coming from?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead
Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.