The LWF Blog

Fire Safety for Facilities Management Personnel – Fire Detection & Fire Alarms – Part 183

January 9, 2023 12:28 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 182, considered the design codes affecting fire alarm installations. In part 183, we continue to discuss the different types of fire alarm classification.

Following on from the last blog’s round-up of the alphanumeric denominations for fire alarm systems, we look at how they are used in practical terms.

Category M systems are widely seen in smaller establishments where it is more likely that an individual will spot a fire and raise the alarm. They are also only suitable on their own merit for premises where nobody sleeps. However, they are incorporated into life safety systems – L1, L2, L3 and L4 and so in practice are ubiquitous.

It is often the case that a category M system may be included in category P1, P2 and L5 systems, but there are particular instances where a category M system is sufficient to satisfy the requirements of life safety legislation in a building, but where a P2 system may be additionally installed independently to protect a particular type of equipment in a room or area.

The difference between property protection systems and life safety systems may appear to be negligible. It is true that a property protection system installed throughout a building will also act as a fire alarm system for life safety purposes and vice versa. However, there are differences in the way they are used.

For instance a P1 system installed in a building to protect property which is not always occupied might require a means of automatic transmission of fire alarm signals to an alarm receiving centre, so that the fire service can be contacted. It may also require a larger battery as a backup in case an interruption to the main electricity supply is experienced and not spotted while the building is unoccupied.

An occupied building containing an L1 system may not need automatic transmission of a signal because the primary objective of a life safety fire alarm system is to alert building occupants to the fire so that they can evacuate the premises.

As there are eight different categories of fire detection and fire alarm system, it would be insufficient for a building owner, enforcing authority or insurer to specify simply that a system should conform to BS 5839-1. Any reference to suitability of system should include the system category and number. Any specific areas requiring a fire alarm system or particular hazards requiring such will need in-depth information provision so the correct choice of alarm system can be chosen, or designed as per an L5 system.


In part 184 of this series, LWF will begin to look at the components of an installation. 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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