The LWF Blog

Fire Safety Engineering for Design – Fire Detection & Alarm Systems – Part 153

October 9, 2023 10:32 am

LWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 152, LWF talked about about the available types of fire alarm, including combined or multi-sensor heat and smoke detectors, point-type heat detectors and linear heat detectors. In part 153, we continue with beam detectors.

Beam Detectors

In many standard fire detection system installations, point-type heat detectors or smoke detectors are used, as they will be quick and efficient at triggering in the event of a fire. However, in an area with very high ceilings, such as certain atriums or where a building has very high ceilings throughout, smoke and heat detectors are often inappropriate for use. By the time sufficient heat or smoke had risen to a level to trigger a ceiling height smoke or heat detector, the fire would be very well-established.

Optical beam detectors are suitable for areas/buildings with a very high ceiling height, or for the protection of very large and open spaces.

The beam detector and its transmitter are usually sited opposite each other in a space. The transmitter emits an infrared beam which travels across the protected space to the receiver. In the event of a fire, the infrared light will be reduced as smoke rises.

An alternative arrangement is for the transmitter and receiver to be located together in one unit with a mirror on the opposite side, positioned to reflect the transmitter signal back to the combined unit.

Beam detectors are usually positioned just below ceiling height in buildings where the installation/maintenance or effectiveness of point detectors may prove impractical.

Examples of places where beam detectors may be used include warehousing, aircraft hangars, historic buildings, art galleries, shopping centres, loft spaces and atriums.

When planning the installation of a beam detector fire alarm system (or part thereof), care must be taken to ensure that if the building has the potential to flex, this is taken into account in the positioning of the detectors.

In extremely high spaces, it is possible for the smoke layer to form below ceiling height and where this is the case, detectors must be placed at the appropriate level.

In part 154 of LWF’s series on fire engineering, we will discuss aspirating systems. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.

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.