Flame detectors sense the light that a fire gives off. A flame detector does not wait for smoke or heat to travel to it. Instead, it looks at the flame itself, and it can react within seconds.
This speed matters where fuel, solvents or gases create fast fires. In this guide, we explain how they work, compare the main types and list the points to check before you choose one.
How do flame detectors work?
Every flame gives off radiation in several parts of the spectrum. A flame detector contains one or more sensors that watch for this radiation. Electronics then analyse the signal.
Most detectors look for a flicker pattern. Real flames flicker at a typical rate, while a hot pipe or a lamp does not. This check helps the detector tell fire from harmless heat or light. When the signal matches a fire, the detector sends an alarm to the control panel.
UV, IR and multi-spectrum flame detectors compared
Detectors differ in the radiation they watch. The right type depends on the fuel and on the site conditions.
| Type | What it senses | Strengths | Watch out for |
|---|---|---|---|
| UV | Ultraviolet light from the flame | Very fast response, good for fuels such as hydrogen | Welding arcs, lightning and some lamps |
| Single IR | Infrared light at one wavelength | Simple and economical | Hot surfaces and sunlight reflections |
| Dual or triple IR | Infrared light at several wavelengths | Better immunity to false alarms and good range | Needs a clear line of sight |
| UV/IR | Ultraviolet and infrared together | Two sensors must agree, so fewer false alarms | Slightly slower than UV alone |
Modern multi-spectrum designs combine several sensors with smart analysis. As a result, they are the common choice for demanding industrial sites.
Where are these detectors used?
Flame detectors protect places where a fire can start suddenly and grow fast:
- Oil, gas and fuel storage and loading areas.
- Chemical plants, paint booths and solvent stores.
- Aircraft hangars and power generation halls.
- Large warehouses and recycling plants with flammable material.
Many of these places are classified as hazardous areas. In that case, choose explosion-proof (Exd) or intrinsically safe (IS) detectors with the correct certificates. See also our page on manufacturing and industrial protection.
What to check before choosing a flame detector
- The fuel. Hydrocarbon, hydrogen and metal fires give off different radiation.
- Range and field of view. The detector must see the whole risk area from its mounting spot.
- Sources of false alarms. Welding, sunlight and hot machinery need a design that ignores them.
- Sensitivity class. The European standard EN 54-10 defines three classes by detection distance.
- Maintenance. A dirty window reduces sensitivity, so plan regular cleaning and testing.
A site survey with a specialist helps you avoid blind spots. Moreover, test every detector with an approved test lamp after installation.
Flame detectors versus smoke and heat detectors
Smoke and heat detectors wait for combustion products to reach them. In a large, open or outdoor area that can take too long, or it may never happen. This approach solves the problem because it needs only a line of sight to the fire.
However, a flame detector does not see smouldering fires without visible flames. For that reason, many sites combine them with linear heat detection or aspirating smoke detection.
Key takeaways
- Flame detectors react to the radiation of a flame, usually within seconds.
- Multi-spectrum detectors give the best protection against false alarms.
- Always match the detector to the fuel, the range and the hazardous area rating.
- Clean windows and regular tests keep them reliable.
Frequently asked questions
How fast are flame detectors?
Many flame detectors react within a few seconds of a flame appearing in view. The exact time depends on the fire size, the distance and the detector type.
Can sunlight or welding cause false alarms?
They can with simple detectors. Multi-spectrum detectors with flicker analysis ignore most of these sources, and good design avoids pointing detectors at them.
Does a flame detector see through smoke?
Infrared detectors cope with light smoke better than UV detectors. Dense smoke or dirt on the window still reduces range, so regular cleaning is important.
Discover our flame detection systems for industrial and hazardous areas. For background reading, see this overview of flame sensing technology.