Fire Design Categories

Before a fire protection system can be designed, it is necessary to define the main objectives of the system.


This is normally determined by a Fire Risk Assessment and should be provided as part of the fire system specification.

BS 5839 Fire Alarm Classifications
BS 5839 splits fire alarm systems into 3 system design categories:

Category P Systems
Category L Systems
Category M Systems

Category P Fire Alarm Systems – Property Protection
These types of systems are purely for the protection of property and fall into two classifications, P1 and P2.

The objective of a category P is to provide the earliest warning of a fire to minimise the time taken from ignition of a fire to detection and the subsequent attendance by the fire services, minimising loss to the property.

  • Manual call point units are not essential
  • There are no escape routes – only corridors
  • Heat detectors may be acceptable (in certain circumstances)

P1 protects the whole building, P2 is installed in defined parts of the building only.

Category L Fire Alarm Systems – Life Protection
Life protection systems can be divided into various categories, L1, L2, L3, L4, L5.

L1 provides for Automatic Fire Detection (AFD) to be installed into all areas of a building.

L2 provides Automatic Fire Detection (AFD) as defined in L3 as well as high risk or hazardous areas. Examples of this could be Kitchens, boiler rooms, sleeping risk, storerooms if not fire resistant or if smoke could affect escape routes.

L3 Automatic Fire Detection (AFD) with smoke detection should be installed on escape routes with detection in rooms opening onto escape routes.

L4 provides Automatic Fire Detection (AFD) within escape routes only.

L5 is installed in building with a specific risk that has been identified. An example of this would be if there was an area of high risk that requires detection the category would be L5/M.

Category M Fire Alarm Systems
A BS 5839 Category M Fire Alarm System is a manual operation only system which has call points on all exits as well as corridors where persons are not expected to walk any more than 45m to operate one.

All categories of life protection will have a type M system installed.

The Honeywell Gent Design and Installation Guide provides a simple guide for the provision of a fire detection and alarm system in accordance with the recommendations detailed within the British Standard Code of Practice BS 5839-1:2017.

It is designed to act as an aide-memoire and there is no substitute for reading the full standard, copies of which can be obtained from


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