Fixed Fire Fighting - Water Mist / Sprinkler — Most Asked Questions
26 questions asked about fixed fire fighting - water mist / sprinkler across the Fn 3 and General papers, heaviest first.
Learn the system first
-
1 Difference between sprinkler and hypermist?
Also asked: “Sprinkler system and hypermist system difference”
Answer
Sprinklers protect accommodation with heat-opened heads; hypermist protects machinery with fine high-pressure mist — different drop size, pressure and purpose.
- Sprinkler: automatic glass-bulb heads open individually at heat, each covering about 16 square metres at 5 litres per minute or more, grouped in sections of 200 heads with visual and audible alarms.
- Hypermist: fine mist from high-pressure nozzles smothers oil fires in machinery spaces with far less water and damage.
- Sprinkler pressure held at the highest head with pump cut-in on pressure drop; stop valves locked open with tamper alarms.
- Test by section alarm valve and head function — never paint a sprinkler head or box it in.
Surveyor follow-up: which system for the purifier flat, and why not sprinklers?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
2 alarm and extinguishing water sprinkler, fire detecting,
Answer
Sprinkler sections watch themselves: water flow rings the gong, the test valve fakes one head, and dry pipes guard freezing spaces.
- Each section carries a non-return alarm valve that rings water-flow alarms on any head opening.
- The test valve discharges like one sprinkler to prove the section alarm without starting a fire.
- The valve also takes up expansion from temperature change so the alarm never false-rings.
- Freezing-prone spaces get dry-pipe sections or antifreeze-charged fresh water — wet pipes would burst before they ever sprayed.
Surveyor follow-up: gong silent with a head fully open — alarm valve, gong line or water supply, and what test proves it?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
3 hypermist system detail
Answer
Hypermist is high-pressure fog for machinery spaces: two detectors agree, plunger pump fires at 70 bar, zone nozzles mist at 50 bar.
- Release needs two detectors in the same zone — one alarm only warns, never floods.
- Fire panel zones the alarm to the hypermist panel, which starts the plunger pump and opens the zone solenoid.
- Pump delivers about 200 litres per minute at 70 bar; each nozzle mists 12–20 litres per minute at 50 bar.
- Visual and audible alarms sound in the space on release; the fog cools, smothers and shields escape routes.
Surveyor follow-up: one detector alarming with smoke showing — wait for the second or go manual, and who decides?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
4 describe the sprinkler head & its operation
Answer
The sprinkler head is a caged quartzoid bulb holding a soft-seal valve shut until heat bursts it.
- Steel cage with deflector carries a liquid-filled quartzoid bulb pressing a soft-metal seal onto the valve.
- Manufactured gas space shrinks as heat expands the liquid until pressure bursts the bulb at rating.
- Common ratings near 68 and 80 degrees with colour coding per temperature band.
- Sections cap at 150 heads with alarms; burst heads spray the deflector pattern until isolated.
Surveyor follow-up: head weeps without bursting at normal temperature — seal, bulb or corrosion, and what do you renew?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
5 Generally fouling is severe in nozzle ring, if fitted
Also asked: “• Generally fouling is severe in nozzle ring, if fitted”
Answer
Nozzle rings foul first where gas is dirtiest: heavy-fuel deposits choke passages until water washing or overhaul clears them.
- Residual-fuel ash and carbon plate the nozzle ring and turbine inlet first.
- Fouling drops boost, lifts exhaust temperature and pushes the turbo toward surge.
- Water washing while running shifts loose deposits; chemical cleaning finishes sulphur-bound layers.
- Prove by pressure ratio and exhaust spread before and after the wash.
Surveyor follow-up: boost low with the filter clean — nozzle ring, cooler or blades, and what proves it?
Full theory: Air Compressor Maintenance — Lapping, Clearances & Overhaul -
6 Hypermist full explain
Also asked: “Hypermist system complete explanation”, “Hypermist sytem explain”
Answer
Hypermist is high-pressure fog for machinery spaces: two detectors agree, plunger pump fires at 70 bar, zone nozzles mist at 50 bar.
- Release needs two detectors in the same zone — one alarm only warns, never floods.
- Fire panel zones the alarm to the hypermist panel, which starts the plunger pump and opens the zone solenoid.
- Pump delivers about 200 litres per minute at 70 bar; each nozzle mists 12–20 litres per minute at 50 bar.
- Visual and audible alarms sound in the space on release; fog cools, smothers and shields escape routes.
Surveyor follow-up: one detector alarming with smoke showing — wait for the second or go manual, and who decides?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
7 Pressure switch setting of hydrophone how to do. What are values
Also asked: “Hydrophore pressure switch setting and method of setting”
Answer
Hydrophore switches stage water pressure: cut-in starts the pump, cut-out stops it — set to maker band with gauges proved.
- Cut-in near the low working limit with cut-out at the high limit per maker and ship routine.
- Set with calibrated gauges on a steady system, proving start and stop pressures twice each.
- Wide bands hunt pumps; narrow bands short-cycle them — adjust differential, not just setpoints.
- Prove alarms on low pressure and high level with the tank gauge agreeing before leaving auto.
Surveyor follow-up: pump short-cycles with settings correct — air charge, leak or switch, and what proves it?
Full theory: Hydrophore & Water Supply — Pressure on Demand -
8 Sprinkler and hyper mist
Answer
Sprinklers wet accommodation with heat-opened heads; hypermist fogs machinery with high-pressure nozzles — different drops, pressures, duties.
- Sprinkler bulbs burst individually at rating, each covering near 16 square metres at 5 litres per minute or more.
- Hypermist needs two-detector agreement, then mists whole zones at 50 bar from a 70-bar pump.
- Sprinkler pressure holds at the highest head near 4.8 bar; stop valves locked open with tamper alarms.
- Fit follows the space: accommodation gets sprinklers, machinery flats get mist.
Surveyor follow-up: purifier flat with sprinklers fitted — compliant or not, and what replaces them?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
9 Hypermist system regulations
Answer
Hypermist earns its place by rule: machinery spaces past 500 m³ and big passenger and cargo ships carry type-approved mist.
- Fixed systems mandatory in machinery spaces of 500 m³ and above with passenger ships and cargo ships past 500 gross tons covered.
- Pumps and installation sit outside the protected space with operating instructions posted at the station.
- Activation by paired heat and smoke detection with power from main and emergency supplies.
- Prove 20-minute supply with nozzles tested for distribution over main-engine, incinerator and purifier zones.
Surveyor follow-up: pump inside the protected space with instructions missing and one zone unproved — compliant or failed?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
10 Hypermist system working
Answer
Hypermist kills fire with fog: two detectors agree, the 70-bar plunger pump starts and zoned solenoids mist at 50 bar.
- Twin-detector coincidence fires the alarm panel, which zones the fire and orders the hypermist panel.
- Plunger pump delivers near 200 litres per minute at 70 bar with nozzles passing 12–20 litres per minute at 50 bar.
- Zoned solenoid valves wet only the burning zone — main engine, incinerator or purifier flat — while alarms sound inside.
- Fog cools, smothers and shields together; reset needs detectors clear, pump stopped and lines drained per drill.
Surveyor follow-up: single detector alarming with the pump running uncommanded — coincidence, panel or valve first to blame?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
11 Co2 ffs & hypermist
Answer
CO₂ and hypermist are complements: CO₂ smothers an enclosed space, hypermist cools and smothers where the system can reach the fire.
- CO₂ works only in an enclosed space where the gas can displace air — in an open space it will not work at all.
- Hypermist does not need a sealed space, needs no shutdown, and can be operated alongside the other systems.
- In a machinery space, purifier room or cargo hold both apply; the choice is what the fire is and what the space allows.
- CO₂ is operated by the chief or second engineer, who are responsible for the whole operation of that system.
Surveyor follow-up: CO₂ released in a half-open purifier room — will it smother, and what should have been sealed first?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
12 Decider water mist regulation about manual and auto ops
Answer
Water mist is manual to release and automatic to discharge: the operator decides, the system does the work once it is released.
- The system detects and alarms; the release is a manual decision, which is what distinguishes a mist system from an automatic sprinkler.
- Once released, the pump starts and the zone solenoids open automatically and the mist runs its full discharge time.
- The advantage is that no gas is released without a human decision, so a detector fault cannot flood a space.
- The rule to quote: detection automatic, release manual, discharge automatic — with the whole sequence proved on the test sheet.
Surveyor follow-up: zone discharging with the release handle still closed — what has failed between the two?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
13 Deck sprinkler system
Answer
A deck sprinkler is a deluge on the weather deck: detection starts the pump, and water discharges from open spray heads over the area.
- Open spray heads or nozzles distribute water over the protected deck area when the system is charged.
- The pump supplying water is put into action automatically by a pressure drop in the system, not by a valve at a head.
- It is proved by test valves, a pressure alarm and a pressure switch for the pump, with shore and fire main connections available.
- On tankers it complements the foam system — water cools the deck and the foam blankets the burning oil.
Surveyor follow-up: deck sprinklers proved with the foam system in bypass — which system is actually covering the spill?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
14 Detetectors for hypermist system
Answer
Hypermist needs two detectors to agree: heat, flame or smoke heads in the protected zone, and the alarm panel that zones the fire.
- Heat and smoke detectors in the machinery space feed the fire alarm panel, and two must agree before release.
- The panel identifies the zone of fire and sends the signal to the hypermist control panel, not directly to the pump.
- Flame detectors are added where the fire is fast and radiant heat low, and the arrangement is proved with the approved test agent.
- Test each head and each zone valve separately — a system proved only at the panel has proved the panel.
Surveyor follow-up: one zone silent on test with the panel and pump proved — is the head, the zone valve or the zone pipe?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
15 Diff in sprinkler and hypermist- why sprinkler not used in er
Answer
A sprinkler is a deluge that floods a whole space; hypermist makes a cooling fog where it is needed — which is why engine rooms take the second.
- A conventional sprinkler has individual thermally operated heads, so water goes only where a head has opened.
- High-pressure water mist uses a much smaller flow at higher pressure to cool and smother without drenching the space.
- In an engine room the concern is oil, steam and hot metal: a deluge of water turns a fire into a steam event and a slumping-oil event.
- Hypermist can be zoned, so a fire in the purifier section does not drown the main engine or trip the whole space’s systems.
Surveyor follow-up: engine room deluge tested with the zone valves open on a hot engine — is that a test or the next accident?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
16 Different bulbs used in sprinkler
Answer
Sprinkler bulbs are colour coded by rating: red near 68°C, yellow near 80°C, green near 93°C — matched to the heat the head sits in.
- The quartzoid bulb holds a highly expansible liquid with a small gas space that shrinks as the liquid expands.
- Pressure builds inside until the bulb shatters at its rating and the valve assembly falls onto the deflector.
- Colour gives the rating at a glance — red 68°C, yellow 80°C, green 93°C, with higher ratings available for hotter sittings.
- Heads are grouped in sections of not more than 150 with an alarm per section, and the bulb rating is chosen for that space, not the ship.
Surveyor follow-up: green bulbs in a 60°C accommodation space tripping weekly — the rating, the siting or the ventilation?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
17 Explain sprinkler system in paint room
Answer
A paint room sprinklers on water detection: heat or smoke starts the pump automatically and water wets the whole room.
- Detection in the paint room alarms and drops the pressure, which starts the sprinkler pump automatically.
- Open heads or spray nozzles discharge water throughout the room to wet down the paint, the shelves and the structure.
- The room is a high fire risk with flammable solvents, so the supply is dedicated and the drains and traps are sealed.
- The system is proved by test valves and alarms, and the water supply kept full — a paint room system is proved dry on test.
Surveyor follow-up: paint room sprinkler proved with the pump not starting on pressure drop — is the switch, the pump or the supply?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
18 How to activate fire detector on hypermist
Answer
The detector does not start the pump: it alarms the panel, the panel zones the fire, and the zone signal starts the high-pressure pump.
- Heat, smoke or flame detectors respond to the fire and signal the fire alarm panel — they do not operate the pump.
- The panel identifies the zone of the fire and sends that zone signal to the hypermist control panel.
- The control panel then starts the plunger pump and opens the solenoid valve for that zone only.
- Test each detector with the approved agent and prove each zone valve separately, so both halves of the chain are known.
Surveyor follow-up: detectors alarming, panel zoned, but no water from one zone — valve, pipe or nozzle first?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
19 Machinery room fire co2 hypermist and foam both
Answer
A machinery room takes CO₂ or hypermist depending on the fire: CO₂ smothers a sealed room, hypermist cools and can run alongside the rest.
- CO₂ is for an enclosed machinery space where the gas can build up — it will not work in an open space.
- Hypermist needs no shutdown of any system and can be operated at the same time as the fire main and boundary cooling.
- Foam is for oil spilled and burning at the deck or on the ship’s side, not for the machinery space itself.
- Decide from the fuel: an oil fire in a sealed room takes CO₂; anything spreading and hot takes hypermist plus cooling.
Surveyor follow-up: purifier fire with the room not sealed and CO₂ already released — which system, and what was missed?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
20 Maintenance on hypermist system
Answer
Hypermist is proved by running it: pump, valves, nozzles and alarms tested with clean water on a schedule that is written down.
- Check the pump, its relief and the bypass, and the plunger seals — a weeping pump loses pressure before it fights a fire.
- Clean the strainers and filters, and check the water quality, because a fouled nozzle is a zone that does not work.
- Test the detectors, the panel zoning, the solenoid valves and the flow and pressure switches, each in turn.
- Discharge every zone with clean water, record the flow and pressure, and re-check the nozzles for blockage afterwards.
Surveyor follow-up: one zone proved low-flow with clean water and all valves open — nozzle, strainer or pump first?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
21 Nozzle ring in tc function ?
Answer
The nozzle ring is the throttle in the gas path: it aims exhaust at the blades and meters how much of it reaches the turbine.
- Gases leaving the cylinder at exhaust opening have enough pressure and heat to drive the turbocharger.
- They are directed onto the turbine blades by nozzles built into a nozzle ring in the axial type, or into the peripheral volute on smaller radial machines.
- The ring converts pressure into a controlled high-velocity jet, so its condition sets turbine speed and efficiency.
- Carbon build-up in the ring chokes the gas path, cuts boost, and is the fouling you see on the turbine side.
Surveyor follow-up: boost down with the turbine clean and the blower washed — is the ring, the wastegate or the filters?
Full theory: Marine Turbochargers: Aerodynamics, Bearings, Washing & Surge Mitigation -
22 Regulation regarding hypermist system on deck
Answer
A hypermist deck system is fitted where the risk warrants it and proved to the code: pump, pressure, nozzles and a periodic test.
- Coverage follows the fire risk of the deck area, with the control station located away from the cargo area.
- Supply and pressure are sized to the coverage, and the system is proved on a schedule with results recorded.
- It does not replace the deck foam system where one is required — it supplements it for cooling and local fires.
- On tankers the arrangement is agreed with class and recorded, and a discharge from it is a pollution event like any other.
Surveyor follow-up: hypermist fitted but the deck foam system removed — is the protection equivalent, and who approved it?
Full theory: Deck Foam & Inert Gas (IG) Systems on Tankers -
23 Sprinkler colour coding temp
Answer
Bulb colour gives the rating at a glance: red near 68°C, yellow near 80°C, green near 93°C — picked for the heat of that space.
- The quartzoid bulb holds an expansible liquid and a small gas space; heat shrinks the gas space and raises the pressure.
- At its rated temperature and pressure the bulb shatters, the valve falls, and water strikes the deflector.
- Red, yellow and green are the working range, with higher ratings available for hotter sittings such as machinery spaces.
- Wrong rating causes either false alarms or a late spray — so the colour is a setting, not a decoration.
Surveyor follow-up: green heads on a 60°C accommodation deck tripping weekly — the rating, the siting or the ventilation?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
24 Testing of hypermist and sprinkler?
Answer
Test each zone in sequence: isolate, alarm, drain, restore, then prove the flow switch — every step is an alarm in its own right.
- Close the section isolating valve, which raises an alarm proving the zone-isolation indication.
- Open the test valve: no water means the non-return valve after the isolating valve is not leaking.
- Open the drain valve to drop the section pressure, which the pressure switch senses and alarms.
- Close the drain, reopen the isolating valve, then open the flow test switch to prove the flow alarm.
Surveyor follow-up: zone test shows no pressure-drop alarm — is the switch, the drain or the test itself at fault?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
25 Working of hypermist system. How will you test it
Answer
Two detectors must agree, the panel zones the fire, and the control panel starts the plunger pump and opens that zone’s solenoid.
- Two detectors agreeing prevents both false trips and false release, and the alarm sounds in the protected space.
- The fire alarm panel identifies the zone and signals the hypermist control panel, which starts the high-pressure pump.
- The plunger pump delivers around 200 litres per minute at some 70 bar, with nozzles passing 12–20 litres per minute at 50 bar.
- Test it by discharging each zone with clean water, reading the flow and pressure, and confirming the flow and pressure alarms.
Surveyor follow-up: pump starts and the alarm sounds but no water at one nozzle — valve, pipe or blocked nozzle?
Full theory: Ship Sprinkler & Hypermist (Water Mist) Systems -
26 working of hypermist
Also asked: “How hypermist works”
Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.