Basement and enclosed car park systems

Basement and enclosed car parks require an extract ductwork system suitable for clearing smoke and fumes. Either natural or mechanical methods may be used to ventilate basement and enclosed car parks.

  • Natural ventilation requires the permanent opening of the floor area, at 2.5%, to provide a through draft (Approved Document B, Fire Safety, B3 Section 11.5).
  • Mechanical ventilation must provide six air-changes per hour in normal conditions and ten in the event of a fire. Extract points must be arranged so that 50% are at high level and the remainder at low level (Approved Document B, Fire Safety, B3 Section 11.6).
  • All components of the system must have a minimum melting point of 800°C (Approved Document B, Fire Safety, B3 Section 11.6).
  • Fire dampers should not be used in any basement or enclosed car park extract system (BS 9999:2008 Clause 33.4.4.2).
  • Ductwork must retain at least 75% of its cross sectional area - in the fire compartment and in adjacent compartments.

Basement and enclosed car park systems

In the diagram

The car park extract ductwork system, (shown Cream) must be suitable for clearing fumes and smoke from the car park. The system should be normally rated for a minimum of one hour with stability and integrity resisting hot smoke and fire from inside (Type B). All components of the ductwork system must have a minimum melting point of 800°C and, therefore, aluminium grilles and fixings, etc, are not permitted.

Where the extract leaves the car park and crosses into another area, (shown Cyan) it must maintain stability, integrity and insulation fire ratings for the same period of time as the compartment through which it passes. In some circumstances, 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 void before the plant room, (shown Yellow) (BS 9999:2008 Clause W.4).

In the area (shown Green) the plant room may have been constructed as a total fire rated compartment. However, in order that 75% of cross-sectional free-area be maintained, fire rated ductwork would require stability and integrity. If combustible materials were within 500mm of the duct, insulation would also be required.

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