Fire Detection & Alarm Systems — Most Asked Questions
27 questions asked about fire detection & alarm systems across the General and Fn 3 papers, heaviest first.
Learn the system first
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1 Fire detection system
Also asked: “Fire detecting and alarming system”, “Fire fighting alarm system”, “Fire detecting and alarming system. a’”
Answer
Detection buys the minutes CO2 cannot give back: heat, smoke, flame and gas heads covering cargo, accommodation and machinery spaces.
- Heat heads: fixed-temperature and rate-of-rise types for galleys, boiler rooms and laundries where smoke heads would false-alarm.
- Smoke heads: obscuration and light-scatter photoelectric types for accommodation, stairways, corridors and escape routes.
- Flame heads reacting to radiation near fuel-handling areas, plus ionisation heads on combustion products; sprinklers double as detectors where fitted.
- Fitted over cargo, accommodation and service spaces, tankers throughout, UMS machinery spaces and ro-ro vehicle decks — test by address, not by hope.
Surveyor follow-up: smoke head keeps alarming with no fire — relocate it or change its type, and what decides?
Full theory: Ship Fire Detectors: Heat, Smoke & Flame Types -
2 Ig alarms n trips
Also asked: “IGG alarms and trips”
Answer
IG alarms warn, trips stop: high oxygen, hot gas, low pressure and lost seals trip the plant before bad gas reaches the tanks.
- Trips: scrubber high level, deck-seal low level, emergency stop, power failure, oxygen above 8%, hot gas, low line pressure after the blower, low seawater to scrubber and deck seal.
- Alarms shadow every trip plus rising oxygen trend, falling pressure and high temperature early warning.
- On trip the blowers stop and deck isolations shut — tanks stay sealed on good gas already delivered.
- Restart only with oxygen back in range, seals remade and scrubber levels normal — log cause, not just reset.
Surveyor follow-up: oxygen reads 9% with pressure normal — trip or alarm, and do you keep feeding the tanks?
Full theory: Ship Fire Detectors: Heat, Smoke & Flame Types -
3 Omd alarms action
Answer
An OMD alarm means a hot spot is making oil mist: slow down, stop with permission, find which unit, open up only when cool.
- Tell the chief and the bridge, get permission, ease load down gradually and stop — never crash-stop a misted engine.
- Read the sampling selector: it points at the crankcase chamber with the hot spot.
- Prove the detector first: zero-check should clear the alarm, test button should drive the meter and re-alarm.
- Cool down fully, inspect bearings, piston, guides and oil flow in that unit, repair, reset the OMD and restart on watch.
Surveyor follow-up: alarm clears on zero-check but returns on one unit only — detector or engine, and what is your next move?
Full theory: Ship Fire Detectors: Heat, Smoke & Flame Types -
4 Explain oil mist detector?
Answer
The OMD sniffs every crankcase in turn: mist scatters the sampling light, photocells unbalance, the alarm marks the hot unit.
- Rotary sampling valve draws each crankcase tube past a reference tube in sequence, lamp and mirrors lighting both.
- Differential photocells sit balanced until mist density bends the measuring beam toward full scale.
- At the limit a magnetic clutch holds the needle, sounds the alarm and parks the indicator on the guilty unit.
- On alarm slow down with permission, stop, ventilate carefully and open up only when cool — the mist is the warning, not the fire.
Surveyor follow-up: alarm on one unit that clears on zero-check — detector or engine, and what is your next move?
Full theory: Marine Turbochargers: Aerodynamics, Bearings, Washing & Surge Mitigation -
5 Sketch and describe the fire detectors -- infrared flame detectors, pneumatic detector and bimetallic detector and their respective applications
Also asked: “Sketch and describe the ea detectors: Infra-Red Flame Detector; Pneumatic Detector and, Bimetallic at wal heir respective applications,”
Answer
Sketch three heads for three fires: infrared eyes for flame flicker, pneumatic tubes for heat rate, bimetallic strips for fixed temperature.
- Infrared flame: lens, filter, photocell and amplifier tuned near 25 Hz flame flicker with time delay against false alarms — high-risk fast-response spaces with machinery and purifiers.
- Pneumatic rate-of-rise: heated air tube driving a diaphragm on fast temperature climb — engine and boiler spaces.
- Bimetallic fixed-temperature: bonded strips bending at set heat to make the contact — galleys, laundries and cabins.
- Never trust radiation heads alone — back them with smoke or ionisation cover in machinery and boiler spaces.
Surveyor follow-up: draw the three heads and name where each goes — then say which two prove a purifier fire first.
Full theory: Ship Fire Detectors: Heat, Smoke & Flame Types -
6 Type of fire detector
Answer
Detectors split heat, smoke, flame and gas: fixed and rate-of-rise heat, scatter and ionisation smoke, infrared and ultraviolet flame.
- Heat: fixed-temperature bimetallic and pneumatic rate-of-rise for galleys, boilers and laundries.
- Smoke: light-scatter and ionisation types for accommodation, corridors and escape routes.
- Flame: infrared and ultraviolet radiation heads tuned to flame flicker for high-risk machinery spaces.
- Fit follows the space: smoke where people sleep, heat where smoke would false-alarm, flame where fire flashes fast.
Surveyor follow-up: smoke head keeps alarming with no fire — relocate it or change its type, and what decides?
Full theory: Ship Fire Detectors: Heat, Smoke & Flame Types -
7 Heat detector reg
Also asked: “Smoke detector reg”
Answer
Heat heads work 54–78 degrees at slow rise with faster response when fire climbs steeply — graded, spaced and testable.
- Fixed-temperature heads trip between 54 and 78 degrees on rises under a degree per minute.
- Rate-of-rise heads answer steep climbs earlier within administration-approved limits against false alarms.
- Drying rooms run to 130 degrees and saunas to 140; grades I to III tune response to ceiling height.
- Every head testable back to normal watch without renewing parts; spacing follows the installation code.
Surveyor follow-up: galley head at 90 degrees rated — fixed, rate-of-rise or wrong head, and what proves it?
Full theory: Ship Fire Detectors: Heat, Smoke & Flame Types -
8 How flame detector works
Also asked: “Flame detector in detail”
Answer
Flame heads watch flicker, not light: filtered infrared or ultraviolet near 1–25 Hz with delay against false alarms.
- Lens and filter pass flame bands only; fixed lamps and hot steel cannot fake the flicker rate.
- Photocell into a selective amplifier tuned to flame frequency with time delay proving persistence.
- Sealed heads suit dusty spaces where smoke heads choke, but never stand alone — back with smoke or ionisation cover.
- Prove with test lamps and hot-air blowers per maker schedule, zones named at the panel.
Surveyor follow-up: head blind in daylight with smoke showing — relocate, clean lens or change type?
Full theory: Ship Fire Detectors: Heat, Smoke & Flame Types -
9 Steering trips and alarms
Answer
Steering trips are few by design, alarms are many: power, oil and control watched with the rudder never tripped on load.
- Overload never trips the rudder motor — alarm only with excess-current cover at twice full load minimum.
- Power-loss, phase-failure, low-oil and control-failure alarms ring on bridge and local panels.
- Engine-room alarm band behind it covers cooling, lube and exhaust trips that would strand steering indirectly.
- Prove alarms on departure checks with local and follow-up control jogged each way.
Surveyor follow-up: overload alarm hard over in heavy weather — stop, slow or steer on?
Full theory: Steering Gear Checks and Tests — Daily Rounds, the 12-Hour Test and Drills -
10 Working of smoke type
Answer
Smoke detectors read light, not heat: obscuration dims the beam, scatter throws it sideways — either imbalance rings the alarm.
- Obscuration heads watch a beam fade as smoke crosses it, tripping at a set dimming level.
- Scatter heads use the Tyndall effect: smoke deflects light onto a shaded cell that sat dark in clean air.
- Balanced twin cells hold steady in clean air currents; smoke tilts the balance and fires the circuit.
- Dust and vapour fool both types — prove with smoke testing, not breath, cigarettes or hot work nearby.
Surveyor follow-up: alarm in clean air with the chamber dusty — sensitivity, siting or housekeeping, and what test proves it?
Full theory: Ship Fire Detectors: Heat, Smoke & Flame Types -
11 Describe the procedure to be adopted to find missing personnel in a smoke filled accommodation area
Answer
Search smoke by team, line and muster: roll call first, then lifelined pairs sweep deck by deck to the muster point.
- Muster and roll call names the missing with last-seen place and time before anyone re-enters smoke.
- Pairs in breathing sets enter on lifelines with thermal cover, keeping contact and escape routes proven.
- Sweep cabins, bathrooms and lockers deck by deck reporting to the fire control station, never freelancing.
- Account the found at first aid with headcounts repeated — re-entry without the bridge’s order is the second casualty.
Surveyor follow-up: one missing in smoke with the muster list showing him signed ashore — search, call or stand down first?
Full theory: Fire Control Plan, Muster List & Flooding Response -
12 AE crankcase level checking ...smoke coming out from there why
Answer
Smoke from an auxiliary crankcase breather means oil mist — the crankcase is breathing oil, and the level and the mist are the first checks.
- Check the sump level first: overfilled, or a returning scavenge oil, is the commonest cause of heavy breather smoke.
- Smoke rather than vapour means mist, so treat the crankcase as a potential mist-detector trip and open nothing hot.
- Check the oil level, the scavenge oil return and the crankcase ventilation, and look at the oil for fuel dilution.
- A crankcase that smokes steadily will trip the oil-mist detector — reduce the cause before the alarm does it for you.
Surveyor follow-up: breather smoking with the level correct and the scavenge return shut off — oil, spray or gasket next?
Full theory: Safety — Crankcase Explosion, Scavenge Fire and Starting Air Line Explosion -
13 Bi-metallic fire Detector
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14 Colour of fire detector
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15 F.O low pressure alarm
Also asked: “Low LO pressure alarm. fe”
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16 Flame detector activation temperature in hyoermist
Answer
A flame detector watches flickering, not heat: it responds to the low-frequency light of a flame and ignores lamps and hot machinery.
- Flame detectors are of infrared or ultraviolet type, responding to radiated heat and light from a flame during combustion.
- They discriminate against fixed light and flickering illumination by responding only to 1–15 Hz flicker typical of flame.
- So there is no activation temperature: the trigger is flame radiation, with heat from hot machinery deliberately ignored.
- Sited clear of steam leak-off points, because a steam jet or spray will otherwise trip the detector.
Surveyor follow-up: hypermist zone tripping on a turbine gland leak — is the detector, the siting or the steam source?
Full theory: Ship Fire Detectors: Heat, Smoke & Flame Types -
17 Higher Exhaust temperature with black smoke
Answer
High exhaust temperature with black smoke is too much fuel for the air: either the engine is overloaded or the air supply is short.
- The first action is to reduce the fuel burnt — cut the load — which brings the exhaust temperature down at once.
- Engine overload: more fuel is burnt than the air supplied, and the surplus cannot burn in the time available, so afterburning follows.
- Air problems: a choked turbocharger air filter, fouled turbine blades, or a choked inlet grid in the exhaust manifold.
- Fuel problems: incorrect injection, late timing or a blocked injector all give the same picture — find which before acting.
Surveyor follow-up: black smoke at full load only with the air filter clean — is it overload, timing or the fuel valve?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault -
18 How to check alarm on scba
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19 Leak alarm in co2 why?
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20 Scaba checks and how to test the alarm function on scaba
Answer
The SCBA alarm is proved by breathing it down: the whistle must sound at 50–60 bar before the cylinder is empty.
- Open the cylinder and read the pressure against the 250 bar test figure, with the reducing valve near 5.5 bar.
- With the cylinder shut, breathe down through the demand valve until the pressure reaches 50–60 bar — the alarm should sound.
- The warning is proved at that point; the breathing itself has already proved the demand valve working.
- Then close the cylinder and exhale with the mask sealed — the face seal is proved by the pressure holding, not by feel.
Surveyor follow-up: SCBA breathing down to 40 bar with no whistle — the alarm, the whistle or the cylinder is the finding?
Full theory: LSA Chapter 3: Line Throwing, EEBD & SCABA -
21 The OCM must activate and sound an alarm whenever freshwater is used for cleaning or zeroing purposes
Answer
The oil content meter must be proven with fresh water: zero it, then feed fresh water and the alarm must sound and the discharge stop.
- Turn the sampling knob to the zero or check position — the alarm should stop — proving the zero side of the instrument.
- Press the check button: the meter should swing on the scale and the alarm should sound, proving the live side.
- Then test the actual trip by charging fresh water through the separator — the 15 ppm alarm must sound and stop the discharge.
- That is the whole point: the meter is proved with fresh water precisely because it cannot be proved with oil safely.
Surveyor follow-up: OCM proved on the check button but the fresh-water trip not tested — which half of the protection is unproved?
Full theory: Oil Content Monitoring and the 15 ppm Trip — Optics, Fluorescence and Testing -
22 Trips and alarms of copt
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23 Type of co2 alarm how u know that co2 alarm it is?
Answer
A CO₂ alarm is triggered by the release cabinet: opening it sounds the siren in the protected space and cuts the ventilation.
- There are two release cabinets — one local in the CO₂ room and one remote at the fire control station, connected in parallel.
- Opening the cabinet operates a micro switch that starts the CO₂ warning alarms and shuts off the ventilation.
- Two pilot cylinders in the cabinet supply the gas that opens the master valve and the bottle head assemblies; one is enough.
- So the identification is the location: the CO₂ release alarm comes from the cabinet, not from a detector.
Surveyor follow-up: release cabinet opened and no alarm but the gas came out — which link failed, the micro switch or the siren?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
24 Types of detectors
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25 What does red, yellow colour indicates in detectors at what temperature
Answer
On a sprinkler bulb the colour is the rating: red near 68°C, yellow near 80°C, green near 93°C, chosen for the heat of that space.
- The quartzoid bulb holds an expansible liquid with a gas space; heat shrinks the space and the bulb shatters at its rating.
- Red 68°C, yellow 80°C, green 93°C are the working grades, with higher ratings available for hotter sittings.
- A wrong rating means either false alarms or a late spray, so the colour is a setting and not a decoration.
- The same idea covers heat detectors: a fixed-temperature head is rated in °C, and the grade sets its response time.
Surveyor follow-up: red heads tripping weekly in a 60°C accommodation space — the rating or the siting first?
Full theory: Ship Fire Detectors: Heat, Smoke & Flame Types -
26 What type of ig present in your ship?various trips and alarms in ig
Answer
Name the ship’s inert gas system type and its trips — scrubber water, deck seal, oxygen content, temperatures and pressures.
- Trips include scrubber water high level and deck seal low water level, either of which floods or starves the tower.
- Emergency stop, power failure, and high oxygen content at about 8% in the atmosphere all stop the system.
- High inert gas temperature, and low pressure in the line after the blower, show the plant is not making gas.
- Low sea water supply pressure also trips — around 0.7 bar to the scrubber tower and 1.5 bar to the deck seal.
Surveyor follow-up: IG tripped on deck seal low level with the sea pressure proved — is the seal, the strainer or the valve?
Full theory: Deck Foam & Inert Gas (IG) Systems on Tankers -
27 how to know crankcase oil level in AE. smoke coming out of dip tube. how would you know which unit blow past is happening
Also asked: “• how to know crankcase oil level in AE. smoke coming out of dip tube. how would you know which unit blow past is happening”
Answer
Find the level with the dipstick, and find the leaking unit by watching the blow-by at the exhaust of each cylinder in turn.
- Check the sump level with the dipstick against the maker’s mark, and inspect the oil for fuel dilution or sludge.
- With the engine running at light load, listen and look at the exhaust pipe of each unit for a puff on the firing stroke.
- The unit that puffs is the one blowing past — the exhaust note goes uneven on that cylinder only.
- Confirm with a compression or blow-by test on the suspect unit, and check its rings, liner and injector before accepting the load.
Surveyor follow-up: smoke at the breather with every unit puffing equally — is it rings, the oil level or the load?
Full theory: Maintenance and Troubleshooting — Overhauls, Tappet Clearance and Reading a Fault
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