The LWF Blog

Fire Safety for Facilities Management Personnel – Fire Detection & Fire Alarms – Part 182

January 3, 2023 12:24 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 181, LWF began to look at fire detection and fire alarms and why they are needed in many types of premises. In part 182, we consider the design codes affecting fire alarm installations.

BS 5839-1 Fire detection and fire alarm systems for buildings – Code of practice for design, installation, commissioning and maintenance of systems in non-domestic premises is a British Standard covering the installation of fire alarm systems and applies to all jurisdictions in the UK. When a fire alarm is required by a building’s insurer or the enforcing authority, it will need to be in compliance with this code.

The only exception to this is when fire alarm systems and fire detection systems are installed into domestic premises including houses in multiple occupation, bedsits, sheltered housing schemes etc., when the relevant design code is BS 5839-6.

When planning a fire alarm installation for a hospital, further guidance on the design can be taken from HTM 05-03 Part B, which works alongside BS 5839-1.

There are eight categories of fire alarm/fire detection installation defined by BS 5839-1, as follows:

  1. Category M systems – Manual fire alarm systems with no automatic detectors
  2. Category P1 systems – Automatic fire detection throughout all areas, for property protection
  3. Category P2 systems – Automatic fire detection in part of property, for property protection
  4. Category L1 systems – Automatic fire detection throughout all areas, for life protection
  5. Category L2 systems – Automatic fire detection in part of property, for life protection. Includes all areas defined by L3 system plus high-hazard areas and high-risk areas.
  6. Category L3 systems – Installed only to protect the escape routes, detectors installed in rooms or areas opening onto escape routes, as well as within the escape route.
  7. Category L4 systems – Smoke detection within parts of escape routes forming circulation areas and spaces. The purpose of an L4 system is to warn occupants of fire within the escape routes. Insufficient to protect premises where people sleep, where an L3 is needed as a minimum, but more likely an L1 or L2 system will be required.
  8. Category L5 systems – Designed only to satisfy a specific fire safety objective in protecting life. The areas where detectors are placed are specified for the purpose of meeting a defined objective.

In part 183 of this series, LWF will continue to discuss the different types of fire alarm classification. 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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