Basement smoke extract system

A basement smoke extract system consists of smoke outlets/vents to provide a route for heat and smoke to escape to the open air.

  • Either natural or mechanical means may be used to ventilate smoke/heat from basements.
  • Where a system of mechanical ventilation is used a sprinkler system must be fitted - Approved Document B, Fire Safety B5, section 18.13.
  • The air extraction system should give at least 10 air changes per hour - Approved Document B, Fire Safety B5, section 18.14.
  • The fire duct must be constructed to resist water impingement from any sprinkler system.

Basement smoke extract system

In the diagram

The fire rated ductwork system (shown Cream) must be suitable for clearing smoke within the compartments and normally rated for one hour stability and integrity to resist hot smoke and fire from inside (Type B). Insulation fire rating is not required in the first compartment.

Where the basement duct rises through the shop (shown Cyan) it must maintain stability, integrity and insulation fire rating for the same period of time as the compartment through which it passes - this may also be required for the remainder of the route the ductwork travels, through the building to outside.

In some circumstances the insulation requirements may be waived or varied by the regulatory authority if there are no combustible materials within 500mm of the duct, such as in the plantroom (shown Green) (BS 9999:2008, clause W.4).

In all areas the duct must retain at least 75% of the cross sectional area, for the same period of time as the compartment through which it passes.

All fire rated ductwork and penetration seals must be tested to BS 476-24/ISO 6944 or BS EN 1366-1 and classified in accordance with BS EN 13501-3 by a recognised NAMAS/UKAS accredited laboratory.

Note: Final approval must always be obtained by the local building control officer/fire department prior to commencement of construction