Items where Subject is "Section 16: Venting of heat and smoke from basements – flats"
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- Section 16: Venting of heat and smoke from basements – flats (15)
Book Section
Heat and smoke from basement fires vented via stairs can inhibit access for firefighting personnel. This may be reduced by providing smoke outlets, or smoke vents, which allow heat and smoke to escape from the basement levels to the open air. They can also be used by the fire and rescue service to let cooler air into the basements (Diagram 16.1).
Outlets should not be placed where they prevent the use of escape routes from the building.
If basement storeys are fitted with a sprinkler system in accordance with Appendix E, a mechanical smoke extraction system may be provided as an alternative to natural venting. Sprinklers do not need to be installed on the other storeys unless needed for other reasons.
Car parks are not normally expected to be fitted with sprinklers (see Section 11 of Approved Document B Volume 2).
The air extraction system should comply with all of the following.
a. It should give at least 10 air changes per hour.
b. It should be capable of handling gas temperatures of 300°C for not less than one hour.
c. It should do either of the following.
i. Be activated automatically if the sprinkler system activates.
ii. Be activated by an automatic fire detection system that conforms to BS 5839-1 (minimum L3 standard).
Further information on equipment for removing hot smoke is given in BS EN 12101-3.
Outlet ducts or shafts, including any bulkheads over them (see Diagram 16.1), should be enclosed in construction of class A1 rating and fire resistance at least equal to that of the element through which they pass.
Natural smoke outlet shafts should be separated from each other using construction of class A1 rating and fire resistance at least equal to that of the storeys they serve, where the shafts are either of the following.
a. From different compartments of the same basement storey.
b. From different basement storeys.
Each basement space should have one or more smoke outlets.
Where this is not practicable (for example, the plan area is deep and the amount of external wall is restricted by adjoining buildings), the perimeter basement spaces may be vented, with other spaces vented indirectly by opening connecting doors. This does not apply for places of special fire hazard (see paragraph 16.7).
If a basement is compartmented, each compartment should have one or more smoke outlets, rather than indirect venting.
A basement storey or compartment containing rooms with doors or windows does not need smoke outlets.
Smoke outlets connecting directly to the open air should be provided from every basement storey, except for any basement storey that has both of the following.
a. A maximum floor area of 200m2.
b. A floor a maximum of 3m below the adjacent ground level.
Strong rooms do not need to be provided with smoke outlets.
Smoke outlets should be both of the following.
a. Sited at high level in either the ceiling or wall of the space they serve.
b. Evenly distributed around the perimeter, to discharge to the open air.
The combined clear cross-sectional area of all smoke outlets should be a minimum of 1/40 of the area of the floor of the storey they serve.
Separate outlets should be provided from places of special fire hazard.
If the smoke outlet terminates at a point that is not readily accessible, it should be kept unobstructed and covered only with a class A1 grille or louvre.
If the smoke outlet terminates in a readily accessible position, it may be covered by a panel, stallboard or pavement light that can be broken out or opened. The position of covered smoke outlets should be suitably indicated.
Image
Basement outlet with break-out or openable cover
Stallboard outlet with grille or removable cover
See para 16.1