The LWF Blog

Fire Safety for Facilities Management Personnel – Fire Detection & Fire Alarms – Part 190

February 27, 2023 12:09 pm

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 189, LWF looked at aspirating smoke detection systems and considered their appropriate usage. In part 190, we will discuss flame detectors, what types are available, and how they work in practice.

Flames from a fire emit radiation that may be detected by flame detectors. There are two types of detector able to detect this radiation – infrared and ultraviolet. Infrared detectors use a solid-state infrared sensor and are highly sensitive to hydrocarbon flames; ultraviolet detectors are similar in principle to Geiger-Müller tubes and detect virtually all flames. It is possible to get flame detectors which are both infrared and ultraviolet.

An infrared detector is able to filter out other sources of infrared radiation and not trigger false alarms due to their ability to recognise radiation with the flickering quality of a fire. They are also extremely fast to respond, triggering an alarm at the point of ignition when the flame first appears.

Flame detectors are line of sight devices, which means they must be able to ‘see’ the area they are to cover without obstruction. Flame detectors are also expensive, meaning that they are mainly used for specialist applications, such as flammable liquids plant.

Ultraviolet detectors are often used outdoors, although it is possible to obtain solar-blind infrared detectors where these may be preferable.

For most indoor applications, neither infrared or ultraviolet detectors would be the most obvious choice of detector, however, infrared detectors may be the preferred option indoors where the ceiling height is sufficiently high to mean the products of combustion may not rise to trigger the operation of heat or smoke detectors until the fire is very large. This means that in atrium spaces or a cathedral, for instance, an infrared detector would be able to detect flame at an earlier stage.

An infrared detector system is not the only possible solution for an atrium space, particularly one with multiple storeys opening onto it. In these, it may be more practical to install an aspirating system, as mentioned in part 189 of these blogs.

In part 191 of this series, LWF will talk about combustion gas detectors, a relatively new development in the world of fire detection. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.


Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 35 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.


While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.

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