Last edited 09 Oct 2017

Fire compartment

The spread of fire can be restricted by sub-dividing buildings into a number of discrete compartments. These fire compartments are separated from one another by compartment walls and compartment floors made of a fire-resisting construction which hinders the spread of fire.

Approved document J, Combustion appliances and fuel storage systems, defines a fire compartment as:

‘… a building or part of a building comprising one or more rooms, spaces or storeys constructed to prevent the spread of fire to or from another part of the same building or an adjoining building. (A roof-space above the top storey of a fire compartment is included in that fire compartment.) A separated part of a building is a form of compartmentation in which part of a building is separated from another part of the same building by a compartment wall. Such walls run the full height of the part and are in one vertical plane.’

Approved document B defines a compartment wall or floor as a ' wall/floor used in the separation of one fire compartment from another.

Fire compartmentation:

  • Prevents the rapid spread of fire which could trap the occupants of a building.
  • Reduces the chance of fires growing and creating a danger to occupants, fire and rescue services, and people in the vicinity of the building.
  • Limits the damage caused to a building and its contents.

The degree of sub-division that should be provided by fire compartmentation will be dependent on:

  • The use of the building.
  • The fire load in the building.
  • The height of the building.
  • The availability of a sprinkler system.

The maximum permissible dimensions of fire compartments (for buildings other than dwellings) are set out in Table 12 of Approved document B2, Fire Safety, Buildings other than dwellinghouses.

Compartment walls and compartment floors form a complete barrier between fire compartments and are required to provide a minimum degree of fire resistance as set out in Appendix A of Approved document B2 and Appendix A of Approved document B1 (for dwellinghouses). This fire resistance is generally expressed in terms of the number of minutes of resistance that must be provided by different parts of a building. Methods for testing fire resistance are set out in BS 476 Fire tests.

Doors within compartment walls, and other openings should have a similar fire resistance to the compartment walls or floors they penetrate.

Joints between fire-separating elements such as compartment walls or floors, should be fire-stopped to maintain the continuity of resistance; and openings for timber beams, joists, purlins and rafters, and pipes, ducts, conduits or cables that pass through any part of a fire-separating element should be kept as few in number as possible, kept as small as practicable; and should be fire-stopped.

Approved document B, defines a fire stop as: ‘A seal provided to close an imperfection of fit or design tolerance between elements or components, to restrict the passage of fire and smoke.' See Fire stopping for more information.

Fire dampers are installed in the ducts of heating, ventilation and air conditioning systems which penetrate fire-resistant constructions and will automatically close on the detection of heat. See Fire damper for more information.

Spaces that connect fire compartments, such as stairways and service shafts, need to be protected to restrict fire spread between the compartments. These are described as ‘protected shafts’.

There are a number of additional requirements depending on the type of building, for example:

  • Parts of a building that are occupied for different purposes should generally be separated from one another by compartment walls and compartment floors.
  • Walls common to two or more buildings should be constructed as compartment walls.
  • Compartment walls in the top storey beneath a roof should be continued through the roof space.
  • Walls separating semi-detached houses or terraced houses must be compartment walls.
  • Garages should be separated from attached houses by compartment walls and compartment floors.
  • There are additional requirements for; flats, institutional buildings, other residential buildings and non-residential buildings.

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