Technical·4 min read
What Are Flame Detectors, and Where Are They Used?
A flame detector steps in where smoke and heat detectors respond far too late or not at all: in large, high-ceiling or open areas it recognises a flaming fire within seconds from the optical radiation the flame emits. In a high-bay warehouse the fire grows before smoke reaches the detector; in an open petrochemical yard the smoke disperses anyway. This article explains, from an engineering viewpoint, exactly what a flame detector solves, how it works (UV, IR, UV/IR, IR3), which areas use it, and where it is not suitable.
A-Pro Engineering
A flame detector steps in where smoke and heat detectors respond far too late or not at all: in large, high-ceiling or open areas it recognises a flaming fire within seconds from the optical radiation the flame emits. In a high-bay warehouse the fire grows before smoke reaches the detector; in an open petrochemical yard the smoke disperses anyway. This article explains, from an engineering viewpoint, what a flame detector solves, how it works, where it is used, and where it is not suitable.
What does it solve? (the problem)
Smoke and heat detectors are passive and convection-dependent: they wait for smoke or hot air to rise and physically reach the ceiling detector. This mechanism breaks down in several cases:
- Height/distance — above 8-10 m ceilings (hangar, high-bay warehouse, atrium) smoke cools and dilutes as it rises; by the time it reaches the ceiling the fire has already grown, and heat may never arrive at all,
- Open air / strong airflow — in open areas such as a petrochemical yard, tank farm, or filling island, smoke disperses instantly in the wind; there is no ceiling/detector concept to begin with,
- Hydrocarbon (flammable-liquid/gas) fire — petrol, solvent, and gas fires produce very little visible smoke yet grow within seconds; there are almost no particles for a smoke detector to see,
- A flame detector, by contrast, relies on a different physics: it does not wait for smoke to travel; it sees the optical radiation the flame emits at the speed of light and from a distance — so in every scenario above it detects within seconds and triggers fast response/suppression.
How does it work? (UV, IR, UV/IR, IR3)
- UV — catches the flame’s ultraviolet radiation very fast; prone to arc/sun false alarms,
- IR — infrared + flicker frequency; robust against hot surfaces/sun,
- UV/IR and IR3 — confirm two methods / reject sun reflections; high immunity in open yards.
Where are they used?
- Petrochemical/refinery, fuel/tank farm, LPG/LNG, filling islands,
- Aircraft hangar, gas turbine/generator hall, paint/solvent areas,
- High-bay warehouses and power plants — large volume + flammable-liquid/gas risk.
Where are they NOT suitable? (their limits)
- Flameless/smouldering fire and cable/electrical — smoke or aspirating (VESDA) detection is needed,
- Blocked line of sight (behind racks/machines/partitions) — cannot see the flame,
- Small enclosed room — usually unnecessary and expensive; a smoke detector is suitable,
- Dense dust/steam/fouled window — false alarm or blinding; does not detect a gas leak.
What to look for when selecting
Correct flame-detector selection depends, beyond the type (UV/IR/IR3), on several critical technical criteria:
- Ex-Proof (ATEX/IECEx) certification — in explosive environments (Zone 1/2) such as petrochemical, fuel, and LPG/LNG, the detector itself must not become an ignition source; an Ex-d/Ex-e certified housing with the correct gas group and temperature class is essential,
- FM / UL approval — the device must be tested and certified against real fires (e.g. FM 3260, a reference n-heptane pan fire); an unapproved device works on paper but is unreliable in the field,
- Coverage area (field of view + range) — the detector’s viewing cone (e.g. 90°-120°) and from what distance it sees a given reference fire (e.g. a 0.1 m² n-heptane fire at 30-60 m); layout is done to this coverage so no blind spots remain,
- Response time — the time between seeing the flame and raising the alarm; in fast-growing hydrocarbon fires seconds are critical (typically <5 s, with adjustable delay),
- False-alarm immunity — the ability to reject sources such as the sun, arc welding, hot surfaces, and headlights; this is why IR3 and UV/IR types are preferred in open yards,
- SIL level, IP rating, and output type — safety integrity (e.g. SIL 2), IP66/67 for outdoor use, and an output suited to plant automation (relay / 4-20 mA / HART / Modbus).
Suitability summary
| Situation / environment | Is a flame detector suitable? |
|---|---|
| Open/high volume + hydrocarbon (petrochemical, hangar) | Yes — its primary application |
| Small enclosed room, office | No — a smoke detector is suitable |
| Cable/electrical, smouldering fire | No — aspirating/smoke + linear heat suitable |
| Volume with blocked line of sight | Limited — layout decides |
| Gas leak (before ignition) | No — gas detection is needed |
We covered the field counterparts in our petrochemical and fuel/tank farm articles, and detector selection in our detector article.
Summary
A flame detector is an optical solution that sees a flaming fire in a large/open/high volume from a distance without waiting for smoke: with UV, IR, UV/IR, and IR3 types it is ideal in areas like petrochemical, fuel, hangar, and turbine; it is not suitable for flameless fires, blocked-line-of-sight volumes, small rooms, and gas leaks. It is based on NFPA 72 / EN 54-10 + ATEX + BYKHY. At A-Pro Engineering we design flame/gas detection integrated with building detection and suppression systems; contact us for your project.
This content is for information purposes. Binding design must be done on a project basis based on the protected risk, volume geometry, environmental conditions, and the actual conditions of the facility, together with NFPA 72, EN 54-10, ATEX legislation, and the current edition of BYKHY.
© 2028 A-Pro Mühendislik. This is original technical content produced by A-Pro Engineering; all rights reserved. Copying, reproducing or republishing it in whole or in part without attribution and permission is prohibited.
Frequently asked questions
What exactly does a flame detector solve?+
A flame detector solves the scenario in which smoke and heat detectors cannot work: detecting a flaming fire in a large, high-ceiling or open volume within seconds, directly from the flame itself, without waiting for smoke or hot air to reach a ceiling detector. In a high-bay warehouse or hangar, smoke disperses as it rises and reaches the detector far too late; in an open petrochemical or fuel yard, smoke disperses instantly in the wind. Also, flammable-liquid and gas fires can produce very little visible smoke and grow very fast. The flame detector fills exactly this gap: it recognises the characteristic radiation a flame emits from a distance, along a clear line of sight, and triggers fast response/suppression.
How does a flame detector work (UV, IR, UV/IR, IR3)?+
A flame detector is an optical device; it detects radiation at specific wavelengths emitted by a flame. The UV type catches the flame's ultraviolet radiation very fast but is prone to false alarms from UV sources such as welding, arcs, and the sun. The IR type detects the flame's infrared radiation (especially the CO2 vibration band) and its characteristic flicker frequency; it is more robust against hot surfaces and sunlight. The most common industrial choices are UV/IR, which requires confirmation from both, and multi-band IR3, which compares three separate IR bands to reject sun/hot-body reflections. IR3 is preferred for hydrocarbon fires because it offers high false-alarm immunity and long range in open, sunlit yards.
In which areas are they used?+
Flame detectors are used in large/open/high volumes with fast-growing, flaming, and often hydrocarbon-based fires: petrochemical and refinery processes, fuel/tank farms and filling islands, LPG/LNG facilities, aircraft hangars, gas turbine and generator halls, paint/solvent areas, high-bay warehouses, and power plants. The common feature is a large volume where smoke/heat detection is inadequate and a flammable-liquid/gas risk. We covered the field counterparts of these risks in our petrochemical, fuel, and hangar articles. Correct application requires detector positioning that keeps the protected area within line of sight and selecting the right type (UV/IR or IR3).
Where is a flame detector NOT suitable?+
A flame detector needs a visible flame and a clear line of sight; therefore it cannot catch flameless, smouldering fires early or cable/electrical fires that first develop with smoke — there, smoke or aspirating (VESDA) detection is needed. It is ineffective in volumes where line of sight is blocked (behind racks, machines, partitions) or where the flame is not directly visible. In small, enclosed rooms it is usually unnecessary and expensive; a simple smoke detector is more suitable and economical. Dense dust, mist, steam, or a fouled optical window can cause both false alarms and blinding. Also, a flame detector does not detect a gas leak (before ignition); gas detection is needed for that. So the tool must be selected by environment and fire type.
What is the difference between a flame detector and a smoke detector?+
A smoke detector waits for smoke to reach it; it is very effective in enclosed, normal-ceiling spaces and for smouldering fires, but responds late in large/open volumes and fast flaming fires. A flame detector does not wait for smoke; it sees the flame's radiation directly from a distance, responding within seconds in open, high volumes and hydrocarbon fires, but it requires line of sight and a visible flame and misses flameless fires. The two are not rivals but complementary tools designed for different fire scenarios; in many facilities smoke/aspirating detection is used in interior spaces and flame detectors in open process areas together.
Which standards govern flame detector selection?+
Detection system design is based on NFPA 72 (and the EN 54 series; EN 54-10 for flame detectors); in industrial and hazardous areas, equipment is selected per explosive-atmosphere (ATEX/Ex) classification. In petrochemical, fuel, and gas facilities, flame/gas detection is often addressed together with relevant process-safety and fire-and-gas (F&G) system requirements; in a performance-based approach, detector range, field of view, and response time are verified against the protected risk. In Türkiye, design is based on these standards together with BYKHY. Correct type selection (UV/IR, IR3) and layout are the key to reducing false alarms and not missing a real fire.
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