Basement Smoke Extract Ductwork Systems

Basements require an extract system suitable for clearing smoke and fumes. Either natural or mechanical methods may be used to ventilate the basement.

Natural Ventilation

Smoke outlets should be sited at high level of the space they serve and be distributed evenly around the perimeter of the building. (Approved Document B, Fire Safety, Section B5 Clause 18.7)

  • The combined clear cross-sectional area of all smoke outlets should not be less than 1/40th of the floorarea of the storey they serve. (Approved Document B, Fire Safety, Section B5 Clause 18.8)
  • Separate outlets should be provided from places of special fire hazard. (Approved Document B, Fire Safety, Section B5 Clause 18.9)
  • If 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 (Approved Document B, Fire Safety, Section B5 Clause 18.10)
  • If the outlet terminates in a readily accessibe 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. (Approved Document B, Fire Safety, Section B5 Clause 18.11)
  • Outlets should not be placed where they would prevent the use of escape routes from the building.

Mechanical Smoke Extract

  • A system of mechanical extract may be provided as an alternative to natural venting to remove smoke and heat from basements, providing 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 sprinkles on the storeys other than the basement(s) unless they are needed for other reasons.) (Approved Document B, Fire Safety, Section B5 Clause 18.13)
  • The air extraction system should give at least 10 air changes per hour and should be capable of handling gas temperatures of 300°C 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). (Approved Document B, Fire Safety, Section B5 Clause 18.14)
  • Fire dampers should not be used in any basement extract system.
  • Ductwork must retain at least 90% of its cross sectional area throught the entire system (BS:EN 1366-8:2004 Clause 11.2.2)

Basement smoke extract system

The basement extract ductwork system ( shown ) must be suitable for clearing fumes and smoke from the basement level. The system should normally be rated for a minimum of one hour integrity and maintain at least 90% cross sectional area.

Where the ductwork leaves the compartment from which it serves ( shown ) it must maintain integrity and insulation fire ratings for the same period of time as the compartment through which it passes.

Fans classified to EN 12101-3 must be used in run and standby configuration.

Any in line equipment such as attenuators, VCD's etc. must be tested.

All fire rated ductwork and penetration seals must be tested to BS:EN 1366 Part 8 and classified in accordance with BS:EN 13501-4 by a recognised NAMAS/UKAS accredited laboratory.

Note: Final approval must always be obtained by the local building control and fire consultant before commencement of construction.