8.1 Commentary

8.1.1 General

Before starting system design, defining the system category is crucial as it determines the placement of manual call points and automatic fire detectors, as well as other design parameters. The system category indicates whether the system is manual or automatic and the purpose of an automatic system. The extent of automatic fire detection is usually determined by a fire risk assessment, not by applying a fixed category to all buildings of a certain type or occupancy.

8.1.2 Protection of life

The system category determines the placement of fire detectors and call points, driven by a fire risk assessment.

Categories:

Category M: Manual call points only. Suitable where occupants are awake and can detect fire before it impedes escape routes.
Category L5: Specific areas protected based on a fire risk assessment or part of a fire engineering solution.
Category L4: Smoke detectors in escape routes (corridors, stairways) for reliable smoke warning, e.g., for lone workers in high-hazard areas.
Category L3: Detectors in escape routes and adjoining rooms to warn before smoke blocks escape routes, suitable for buildings with sleeping occupants.
Category L2: Additional detectors beyond L3 areas, necessary if other rooms pose significant risks or need enhanced early warnings (e.g., for disabled occupants).
Category L1: Comprehensive protection with detectors in all areas. Suitable for buildings with high-risk occupants (e.g., hospitals, residential care) or inadequate structural fire precautions.

A Category M system suffices only if no one sleeps in the building and fire is likely detected by occupants before smoke impairs escape.

8.1.3 Protection of property

For property protection, automatic fire detectors must detect fires early, provide timely warnings, and indicate the fire's location. The effectiveness depends on detection speed, response time, firefighter arrival time, and fire spread rate. Adequate protection might require additional measures like compartmentation or automatic suppression systems if the fire spread rate outpaces firefighter arrival.

System Categories:

Category P1: Highest protection, with detectors in all building areas. Suitable for high-value buildings, contents, or critical facilities.
Category P2: Adequate protection for specific high-risk or high-value areas based on a fire risk assessment. The specified protected areas must be clearly defined.

8.2 Recommendations

The following recommendations are applicable.

a) Documentation Requirements: System documentation must clearly identify the system category, protected areas, and detector types. This includes purchase specifications, tender documents, design proposals, submissions for approval, and designer certificates.

b) Category L5 Specifications: Specifications for Category L5 systems must identify rooms or areas protected by automatic fire detectors.

NOTE 1 There might also be benefit in giving a simple description of the objective of the protection proposed, particularly in submissions to enforcing authorities.

NOTE 2 The standard of protection (extent of coverage) of a Category L5 system might be lower or higher than that afforded by Category L2, L3 or L4 systems.

c) Category L3 and L4 Detector Placement: Smoke detectors, multi-sensor detectors, or a mix of smoke and combustion gas detectors should be installed in:

Escape stairways
Corridors
Common escape routes

NOTE 3 Main access and egress stairways normally form part of escape routes, and ought to be treated as escape stairways.

d) Category L3 Additional Requirements: Heat, smoke, combustion gas, or multi-sensor detectors should be in all rooms opening onto escape routes, except for corridors less than 4 m long, if fire-resisting construction separates these from other escape routes.

NOTE 4 For recommendations on the siting of these detectors, see 22.3e).

NOTE 5 An open-plan area of accommodation, in which occupants quickly become aware of fire, need not be protected in a Category L3 or L4 system, even though occupants within the area clearly need to pass through the area in the first stage of escape, unless it forms part of the escape route from other areas. However, in a Category L3 system a heat, smoke, combustion gas detector or multi-sensor detector ought to be installed on the accommodation side of any door that opens into an escape stairway, a corridor of more than 4 m in length or, alternatively, where stairways are approached through low fire risk lobbies, any door that opens onto the lobby.

e) Category L2 Requirements: Follow Category L3 recommendations and additionally install detectors in high-risk rooms.

NOTE 6 Any reference to a Category L2 system (e.g. in a specification, proposal or submission to an enforcing authority) needs to clearly identify the rooms or areas in which these additional detectors are to be installed and identify the type of detector (e.g. heat, smoke or combustion gas) required.

NOTE 7 The first step in designing a Category L2 system is to design a Category L3 system. Thereafter a decision is taken as to which unprotected rooms or spaces warrant further detection, or the detector type or siting needs to be modified.

f) Category L1 or P1 Coverage: Install detectors in all rooms and areas, except low-risk areas such as:

Toilets, shower rooms, and bathrooms
Stairway lobbies and toilet lobbies
Small cupboards (less than 1 m²)
Shallow voids (less than 800 mm depth)

NOTE 8 In some public buildings, such as hospitals and shopping centers, toilets might not be of low fire risk, owing to the potential for malicious ignition.

NOTE 9 A riser in which there is a fire-resisting floor and ceiling may be treated as a cupboard.

NOTE 10 If detection can be excluded from any room or area in a Category L1 system, it can also be excluded from such rooms or areas in a Category L2, L3 or L4 system.

g) Category L1 Escape Route Detectors: Use smoke detectors, multi-sensor detectors, or a mix of smoke and combustion gas detectors in escape routes.

NOTE 11 Some smoke and multi-sensor detectors can be programmed such that they would not then meet the fire sensitivity tests of BS EN 54-7; in that operating mode, the detectors would not satisfy the recommendations of 8.2c) and g).

h) Category P2 Specifications: Clearly identify protected rooms or areas in the specifications. Ensure physical barriers limit smoke and hot gas spread in early fire stages.

NOTE 12 It is not necessarily the case that these physical barriers have a recognized period of fire resistance.

NOTE 13 The physical barriers described in h) might be unnecessary where detectors are installed to detect fires in specific equipment.

8 Relationship between system category and protected areas