The LWF Blog

Fire Safety Engineering for Design – Fire Detection & Alarm Systems – Part 141

July 18, 2023 10:50 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 140, LWF looked at the categorisation of life safety fire alarm systems from L1 to L5, as per BS 5839-1. In part 141, we will look at the category L fire detection and alarm systems in more detail.

BS 5839-1 provides guidance on the various categories of life safety fire alarm systems, or see the breakdown in part 140 of this series.

A category L5 system can vary significantly depending upon the requirements of the building in question. For example, it might be such a small and targeted system that it contains only one or two detectors in total. However, it might also include detection to an L2, L3 or L4 standard.

An airport terminal or other travel terminal (buses, trains) might have a fire alarm system designated as L5. The reason for this is that the majority of areas may be covered by fire detectors, but large open areas, such as concourses without furnishings, platform areas etc. could be omitted. It may also be that there are changes in the offering of manual call points and their locations. Such a system would be considered comprehensive, but because of the deliberate area omissions in the fire alarm strategy, it would not be considered L1-L4.

Manual call points are generally a requirement for category L systems, but some circumstances do not require them, including where they are not considered necessary as part of the fire safety aims of a category L5 system.

Because a category L system is provided with the ultimate aim of sounding an early warning to assist building occupants in safely evacuating the building in case of a fire, fire detectors may need only to be placed where it is necessary to preserve the evacuation route from occupied areas or in areas of particular risk of fire. This can result in an L5 system, or a P2 system where property protection is the main focus.

The type of fire alarm system installed in a building for life safety purposes must be designed specifically for that building and occupancy and maintained appropriately.

In part 142 of LWF’s series on fire engineering, we will look at supervising station fire alarms and manual fire alarms. 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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