Portable Fire Extinguishers — Most Asked Questions
15 questions asked about portable fire extinguishers across the General and Fn 3 papers, heaviest first.
Learn the system first
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1 Portable fire extinguisher
Also asked: “Portable chemical foam extinguisher”
Answer
Portables are first attack by class: water for solids, foam for liquids, dry powder for mixed fires, CO2 for electrics.
- Water gas-cartridge type: plunger pierces the CO2 cartridge, pressure jets water — for wood, paper and textiles.
- Foam types blanket liquid fires; dry powder knocks down mixed and running fires fastest.
- CO2 leaves no residue for electrical and small liquid fires — mind asphyxiation in closed spaces.
- Operation everywhere is pin out, plunger or lever, aim at the base, sweep — and recharge or replace after any use.
Surveyor follow-up: galley deep-fat fire with water and CO2 side by side — which one, and why not the other?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
2 Specify the class of fire against each type of extinguisher for its usage
Answer
Match the bottle to the fuel: soda-acid and water for solids, foam for liquids, CO2 for electrics, dry powder for nearly everything.
- Soda-acid and water types fight Class A wood, paper and textile fires in accommodation spaces.
- Foam — chemical or mechanical — blankets Class B liquid fires by smothering.
- CO2 suits Class B and C electrical fires in machinery spaces but never accommodation or tight spaces where gas kills.
- Dry powder with sodium bicarbonate covers almost all fires and stands by electrics in the engine room.
Surveyor follow-up: switchboard fire with foam and CO2 beside it — which one, and why not the other?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
3 name the 4 prominent type of portable fire extinguisher used on board
Answer
Four bottles cover the ship: water, foam, CO2 and dry powder — soda-acid makes five where still carried.
- Water and soda-acid for Class A accommodation fires.
- Chemical and mechanical foam for Class B liquid fires.
- CO2 for Class B and C machinery and electrical fires.
- Dry powder for mixed risks in the engine room and near electrics.
Surveyor follow-up: point at the nearest extinguisher and name its class — then the one you would never use on it.
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
4 with a simple sketch show components of DCP extinguisher
Answer
Sketch a pressure vessel with a gas cartridge on top, hose and double nozzle below: pin out, plunger down, powder out.
- Body holding dry chemical powder with a sealed CO2 cartridge and striker in the head assembly.
- Safety pin, plunger, swivel guard and vent holes that relieve pressure when opening a blocked head.
- Reinforced hose to a brass double-purpose nozzle giving jet or spray as twisted.
- Operate by pin out and plunger down — the cartridge fires, pressure fluidises the powder and the nozzle sweeps the base.
Surveyor follow-up: draw the gas path from cartridge to nozzle — where does the powder join it?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
5 how the possibility of 2 State the causes of scavenge fire in a two-stroke engine and explain such an occurrence can be reduced. If a Scavenge fire does occur what action should be taken? Discuss the use of CO and dry po
Also asked: “how the possibility of 2 State the causes of scavenge fire in a two-stroke engine and explain such an occurrence can be reduced. If a Scavenge fire does occur what action should be taken? Discuss the use of CO and dry powder for extinguishing such a fire and describe a”
Answer
Scavenge fires burn trunk deposits: stop the fuel feeding them, starve the fire, fight small ones in place and big ones stopped.
- Causes are blow-past carbon, scraped-down cylinder oil, wrong exhaust timing and high back-pressure lighting the bed.
- Prevention is clean combustion, timed valves, drained trunks and controlled cylinder oil — not extra oil.
- Small fire: slow down, cut fuel to the unit, boost cylinder oil, stand clear of doors until it dies in 15–30 minutes.
- Big fire: stop, boundary-cool, shut fuel and air, use fixed smothering — CO2 where fitted, dry powder on open flames, never water into hot oil.
Surveyor follow-up: temperatures falling after fuel cut — when do you open the doors, and what do you carry?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
6 Anti caking and which dcp powder used
Answer
Dry powder is a fine bicarbonate with anti-caking agents — aluminium, magnesium or calcium stearates — and water-repellent silicones.
- Potassium or sodium bicarbonate powder is the base, and it decomposes into carbon dioxide and a residue that smothers.
- Anti-caking agents are the stearates of aluminium, magnesium or calcium, keeping the powder free-flowing.
- Silicones give water repellency, and inert substances such as mica, talc or silica improve the flow.
- Caking is why powder is inspected for granulation and caking and renewed on the schedule — a hardened charge will not flow.
Surveyor follow-up: powder at the base of a canister in granules — will it flow, and what does that cost the discharge?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
7 Cargo fire dcp how to extinguish
Answer
Dry powder knocks a cargo fire down by smothering and chain reaction: aim at the base of the flame from upwind.
- Approach from upwind, above the fire if it has spread, and discharge at the base of the burning flame.
- The powder blanket cuts off oxygen and interrupts the chemical chain reaction, so a small fire dies quickly.
- It has little cooling effect, so a burning cargo can rekindle — watch it and be ready to re-discharge.
- After knockdown, cooling and boundary work continues with water; the extinguisher alone does not finish a cargo fire.
Surveyor follow-up: powder exhausted on a two-tier cargo fire with the hold still hot — what next, and which boundary?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
8 Checks done on cap of extinguisher
Answer
The cap is the seal and the release: check it seals, the vent holes are clear, the plunger is up, and the pin is in.
- Examine the cap seal first and confirm it is in good order — a failed seal is a slowly emptying extinguisher.
- Check the small holes in the sides of the cap are clear, because they release internal pressure before the cap comes off.
- Confirm the ball valve is free, so liquid cannot rise in the internal pipe and dribble from the nozzle in hot weather.
- Check the nozzle outlet and vent holes for clogging, and that the plunger is fully extended and clean.
Surveyor follow-up: soda-acid extinguisher with the cap vent holes painted over — is it sealed, or unable to be opened?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
9 Chemical that prevents caking in dcp
Answer
Caking is stopped with a small percentage of magnesium carbonate or a similar inert additive mixed into the dry powder.
- Dry powder is packed in the extinguisher for months, and it must not consolidate or bridge over the pickup.
- An inert additive — magnesium carbonate is the usual one — is mixed with the powder to keep it free-flowing.
- The additive must not react with the powder or the container, and its proportion is small enough not to spoil the extinguishing action.
- Compaction at the filling plant plus the additive is what keeps a stored-pressure extinguisher able to discharge.
Surveyor follow-up: powder three years in the bottle found hard as a block — additive, compaction, or both?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
10 Class k fire which extinguisher will be used
Answer
Class K is cooking oil and fat: wet chemical, because the agent saponifies the oil into a foam it can smother.
- Class K covers cooking oils and fats, which burn at temperatures no dry powder or CO₂ will truly extinguish.
- Wet chemical saponifies the burning oil into a soapy foam that blankets it and cuts off the oxygen.
- Water on burning cooking oil causes a violent boil-over, so it is never the agent for a galley oil fire.
- Over the range a fixed wet-chemical system is fitted, with the portable wet chemical as the back-up at the galley door.
Surveyor follow-up: galley oil fire with a wet chemical and a powder in the same locker — which do you reach for, and why?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
11 Extinguisher used in galley fire
Answer
Wet chemical for fat and oil, water or foam for solids, and the fixed system over the range — never water on burning oil.
- Burning fat or cooking oil takes wet chemical, which saponifies the oil into a smothering foam.
- A fire in dry solids or food takes water, with foam if the fat has not yet reached its burning temperature.
- Electrical fires in the galley take CO₂ or dry powder; the extinguisher chosen is the one on the class board by the door.
- Shut the burners and isolate the fuel and power first — the extinguisher is the second move, not the first.
Surveyor follow-up: galley fire on a fat fryer with the power on and the wet chemical seal unbroken — which first?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
12 Foam extinguisher.why chemical foam not used
Answer
Chemical foam, the old two-pot soda-acid type, is gone because the protein concentrates and halons did the job better and safer.
- Chemical foam is generated by an acid and an alkali reacting in the body, with the discharge itself making the foam.
- The acid and alkali in one shell corrode the container and can leak at the bottle, and the reaction is uncontrolled.
- The extinguisher has to be made ready before it can be used, so it is useless if the fire has already started.
- Mechanically generated foam from protein, fluoro-protein or synthetic concentrates is now used — better foam, no stored chemicals.
Surveyor follow-up: two-pot extinguisher found on the muster list with an unlabelled bottle — is it serviceable or a hazard?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
13 How many relief hole on fire extinguishers
Answer
The bottle cap carries two small side holes: they vent the internal pressure so the cap can be unscrewed safely.
- There are small holes in the sides of the cap, and their purpose is to release any internal pressure before the cap is fully removed.
- With them sealed, taking the cap off a charged extinguisher sprays its contents across the deck.
- They are the reason a portable extinguisher is checked cap-first rather than by squeezing the trigger to see if it fires.
- On a CO₂ or stored-pressure unit the equivalent function is done by the safety relief in the head assembly.
Surveyor follow-up: cap holes blocked on a soda-acid unit aboard — what happens when the officer first tries to use it?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
14 Types of extinguisher
Answer
Five types cover the ship: soda acid, water, foam, carbon dioxide and dry powder — each matched to its class of fire.
- Soda acid for solid and textile fires, the oldest type still found in accommodation on older ships.
- Water for solids, foam chemical or mechanical for flammable liquids, CO₂ for electrics and confined spaces.
- Dry powder in CO₂ cartridge or stored pressure form, for electrics, low flash liquids and gases.
- Wet chemical is the sixth addition, and the one that actually kills a galley oil fire.
Surveyor follow-up: extinguisher board shows CO₂ for the galley and foam for the paint locker — what is wrong, and what belongs where?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships -
15 What maintenance we do on dcp extinguisher?
Answer
Dry powder is kept moving and honest: cap, nozzle, plunger, gauge, powder condition, discharge test, recharge and hydrostatic test.
- Check the nozzle outlet and vent holes, and clear the cap threads, with the plunger fully extended and the safety pin in place.
- Check the pressure gauge on a stored-pressure set, and the gas cartridge where fitted, replacing it if the charge is low.
- Look inside for granulation and caking — hardened powder will not flow, and that is the failure it is checked for.
- Discharge at least yearly, recharge every year as necessary, and hydrostatic test on the interval set by the regulation.
Surveyor follow-up: powder dense and caked at the base with a good gauge reading — can it still be relied on?
Full theory: Classes of Fire & Portable Fire Extinguishers on Ships
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