18.1The build-up of smoke and heat as a result of a fire can seriously inhibit the ability of the fire and rescue service to carry out rescue and firefighting operations in a basement. The problem can be reduced by providing facilities to make conditions tenable for firefighters.
18.2Smoke outlets (also referred to as smoke vents) provide a route for heat and smoke to escape to the open air from the basement level(s). They can also be used by the fire and rescue service to let cooler air into the basement(s). (See Diagram 53.)
Provision of smoke outlets
18.3Where practicable each basement space should have one or more smoke outlets, but it is not always possible to do this where, for example, the plan is deep and the amount of external wall is restricted by adjoining buildings. It is therefore acceptable to vent spaces on the perimeter and allow other spaces to be vented indirectly by opening connecting doors. However if a basement is compartmented, each compartment should have direct access to venting, without having to open doors etc into another compartment.
18.4Smoke outlets, connected directly to the open air, should be provided from every basement storey, except for any basement storey that has:
- aa floor area of not more than 200m2 and
- ba floor not more than 3m below the adjacent ground level.
18.5Strong rooms need not be provided with smoke outlets.
18.6Where basements have external doors or windows, the compartments containing the rooms with these doors or windows do not need smoke outlets. It is common for basements to be open to the air on one or more elevations. This may be the result of different ground levels on different sides of the building. It is also common in 18th and 19th century terraced housing where an area below street level is excavated at the front and/or rear of the terrace so that the lowest storey has ordinary windows and sometimes an external door.
Natural smoke outlets
18.7Smoke outlets should be sited at high level, either in the ceiling or in the wall of the space they serve. They should be evenly distributed around the perimeter to discharge in the open air outside the building.
18.8The combined clear cross-sectional area of all smoke outlets should not be less than 1/40th of the floor area of the storey they serve.
18.9Separate outlets should be provided from places of special fire hazard.
18.10If the outlet terminates at a point that is not readily accessible, it should be kept unobstructed and should only be covered with a non-combustible grille or louvre.
18.11If the outlet terminates in a readily accessible position, it may be covered by a panel, stallboard or pavement light which can be broken out or opened. The position of such covered outlets should be suitably indicated.
18.12Outlets should not be placed where they would prevent the use of escape routes from the building.
Mechanical smoke extract
18.13A system of mechanical extraction may be provided as an alternative to natural venting to remove smoke and heat from basements, provided that the basement storey(s) are fitted with a sprinkler system in accordance with paragraph 0.16 (It is not considered necessary in this particular case to install sprinklers on the storeys other than the basement(s) unless they are needed for other reasons.)
Notes:Car parks are not normally expected to be fitted with sprinklers (see paragraph 11.2).
18.14The air extraction system should give at least 10 air changes per hour and should be capable of handling gas temperatures of 300degC for not less than one hour. It should come into operation automatically on activation of the sprinkler system; alternatively activation may be by an automatic fire detection system which conforms to BS 5839-1:2002 (at least L3 standard). For further information on equipment for removing hot smoke refer to BS EN 12101-3:2002.
Construction of outlet ducts or shafts
18.15Outlet ducts or shafts, including any bulkheads over them (see Diagram 53), should be enclosed in non-combustible construction having not less fire resistance than the element through which they pass.
18.16Where there are natural smoke outlet shafts from different compartments of the same basement storey, or from different basement storeys, they should be separated from each other by non-combustible construction having not less fire resistance than the storey(s) they serve.
Basement car parks
18.17The provisions for ventilation of basement car parks in Section 11 may be taken as satisfying the requirements in respect of the need for smoke venting from any basement that is used as a car park.
- Diagram 1 Gallery floors with no alternative exit
- Diagram 2 Flat where all habitable rooms have direct access to an entrance hall
- Diagram 3 Flat with restricted travel distance from furthest point to entrance
- Diagram 4 Flat with an alternative exit but where all habitable rooms have no direct access to an entrance hall
- 5 Multi-storey flat with alternative exits from each habitable room except at entrance level
- Diagram 6 Multi-storey flat with protected entrance hall and landing
- Diagram 7 Flats served by one common stair
- 8 Flats served by more than one common stair
- Diagram 9 Common escape route in small single stair building
- 10 Travel distance in dead-end condition
- 11 Alternative escape routes
- 12 Inner room and access room
- Diagram 13 Exits in a central core
- Diagram 14 Open Connections
- Diagram 15 Merging flows at final exit
- Diagram 16 Subdivision of corridors
- Diagram 17 Dead-end corridors
- Diagram 18 Maximum travel distances in a small two or three storey premises with a single protected stair to each storey
- Diagram 19 Progressive horizontal evacuation in care homes
- Diagram 20 Refuge formed by compartmentation
- Diagram 21 Refuge formed in a protected stairway
- Diagram 22 Max travel distance in a small three storey premises with a single stair to each storey
- Diagram 23 Max travel distance in a small two storey premises with a single open stair
- Diagram 24 External protection to protected stairways
- 25 Fire resistance of areas adjacent to external stairs
- Diagram 26 Lighting diffuser in relation to ceiling
- Diagram 27 Layout restrictions on Class 3 plastic rooflights TP-b rooflights and TP b lighting diffusers
- Diagram 27a Layout restrictions on small Class 3 plastic rooflights TP b rooflights and lighting diffusers
- Diagram 28 Compartment floors illustration of guidance in paragraph 8.16
- Diagram 29 Compartment walls and compartment floors with reference to relevant paragraphs in Section 8
- Diagram 30 Junction of compartment wall with roof
- Diagram 31 Protected shafts
- Diagram 32 Uninsulated glazed screen separating protected shaft from lobby or corridor
- Diagram 33 Provisions for cavity barriers
- Diagram 34 Cavity wall excluded from provisions for cavity barriers
- Diagram 35 Fire-resisting ceiling below concealed space
- Diagram 36 Provisions for cavity barriers in double-skinned insulated roof sheeting
- Diagram 37 Pipes penetrating structure
- Diagram 38 Enclosure for drainage or water supply pipes
- Diagram 39 Flues penetrating compartment walls or floors
- Diagram 40 Provisions for external surfaces or walls
- Diagram 41 Relevant boundary
- Diagram 42 Notional boundary
- Diagram 43 Status of combustible surface material as unprotected area
- Diagram 44 Unprotected areas which may be disregarded in assessing the separation distance from the boundary
- Diagram 45 The effect of a canopy on separation distance
- Diagram 46 Permitted unprotected areas in small residential buildings
- Diagram 47 Limitations on spacing and size of plastic rooflights having a Class 3 or Class D-s3 d2 or TP b lower surface
- Diagram 48 Example of building footprint and perimeter
- Diagram 49 Relationship between buildings and hardstanding access roads for high reach fire appliances
- Diagram 50 Turning facilities
- Diagram 51 Provision of firefighting shafts
- Diagram 52 Components of a firefighting shaft
- Diagram 53 Fire-resisting construction for smoke outlet shafts
- Diagram C1 Measurement of door width
- Diagram C2 Cubic capacity
- Diagram C3 Area
- Diagram C4 Height of building
- Diagram C5 Number of storeys
- Diagram C6 Height of top storey in building
- Diagram C7 Free area of smoke ventilators
- Diagram D1 Classification of Purpose Groups
- Diagram E1 Recessed car parking areas
- Table 1 Limitations on distance of travel in common areas of blocks of flats - see par 2.23
- Table 2 Limitations on travel distance
- Table 3 Minimum number of escape routes and exits from a room tier or storey
- Table 4 Widths of escape routes and exits
- Table 5 Maximum distances of travel in small premises with a protected stair
- Table 6 Minimum widths of escape stairs
- Table 7 Capacity of a stair for basements and for simultaneous evacuation of the building
- Table 8 Minimum width of stairs designed for phased evacuation
- Table 9 Provisions for escape lighting
- Table 10 Classification of linings
- Table 11 Limitations applied to thermoplastic rooflights and lighting diffusers in suspended ceilings and Class 3 plastic rooflights
- Table 12 Maximum dimensions of building or compartment - non-residential buildings
- Table 13 Maximum dimensions of cavities in non-domestic buildings - purpose Groups 2-7
- Table 14 Maximum nominal internal diameter of pipes passing through a compartment wall-floor - see par 10.5 onwards
- Table 15 Permitted unprotected areas in small buildings or compartments
- Table 16 Limitations on roof coverings
- Table 17 Class 3 or Class D-s3 d2 plastic rooflights limitations on use and boundary distance
- Table 18 TP a and TP b plastic rooflights limitations on use and boundary distance
- Table 19 Fire and rescue service vehicle access to buildings excluding blocks of flats not fitted with fire mains
- Table 20 Typical fire and rescue service vehicle access route specification
- Table A1 Specific provisions of test for fire resistance of elements of structure etc
- Table A1 continued
- Table A2 Minimum periods of fire resistance
- Table A3 Limitations on fire-protecting suspended ceilings (see Table A1 Note 4)
- Table A4 Limitations on the use of uninsulated glazed elements on escape routes]
- Table A5 Notional designations of roof coverings
- Table A6 Use and definitions of non-combustible materials
- Table A7 Use and definitions of materials of limited combustibility
- Table A8 Typical performance rating of some generic materials and products
- Table B1 Provisions for fire doors
- Table C1 Floor space factors
- Table D1 Classification of Purpose Groups
- Table Maximum dimensions of building or compartment (non-residential buildings)