The LWF Blog

Fire Safety Engineering for Design – Fire Detection & Alarm Systems – Part 150

September 18, 2023 10:41 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 149, LWF looked at manual call points, often referred to as break-glass units. In part 150, we consider the different types of fire detection device and their purpose.

A fire alarm system relies on the detectors installed to identify the presence of by-products from a fire. Most commonly, the detectors work to detect smoke or heat, but there are also detectors that work to identify other combustion products, such as carbon monoxide, or radiation.

Smoke detection

Smoke can be detected by various different types of detector – point ionisation smoke detectors, point optical smoke detectors, optical beam detectors and aspirating systems. The presence of smoke may also be identified by video detection.

Heat detection

The types of detector used to identify sources of heat from a fire include point fixed heat detectors, point rate of heat rise detectors and linear heat detectors.

Flame detection

Detectors designed to detect the presence of flames are ultraviolet and infrared.

The categorisations above are not distinct from each other, however, because some detector units are designed to analyse for multiple signs of fire. Combined heat and smoke detectors are relatively commonplace in fire alarm installations.

The detector type chosen must be suitable for the environment in which it must function. Some detectors may be confused by other elements not related to fire. For example, smoking in a hotel bedroom, steam in bathrooms, cooking smoke in kitchens can all trigger the ‘wrong’ type of fire detector if installed. The wrong type of detector chosen for an environment could lead to repeated false alarms, which would be disruptive and dangerous should the building occupants get too used to hearing the fire alarm sound and become complacent. Potentially, the wrong type of detector for an environment could lead to a fire not being detected where the sensitivity had been adjusted to avoid false alarms.

Traditionally, most smoke and heat detectors are the point type, where each detector covers a specific point in the protected space. Detectors may also be linear or ‘line-type’ and the detector will analyse potential fire signals occurring at some point along its length, this includes linear heat detection and optical beam detection.

In part 151 of LWF’s series on fire engineering, we will look at each type of detector in more detail. 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.

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