Pressurisation ductwork systems

Pressurisation ductwork is the ductwork used as part of a pressurisation system. Typically used in protected stairways, lobbies, corridors and fire fighting shafts, a pressurisation system is a special form of mechanical ventilation which maintains a positive pressure in critical areas to prevent smoke entering from adjacent areas.

  • Pressurisation ducts must be able to maintain an air supply to critical areas for the duration of the fire.
  • Air supply must be maintained, fire dampers cannot be used.
  • All ductwork penetrating fire compartments must be fire rated in order to maintain compartmentation.
  • Pressurisation plant should be in a dedicated plant room or separated from other equipment by a one hour fire resistant enclosure – BS 5588 part 4, clause 6.3.4.

Pressurisation ductwork systems

In the diagram

Ductwork (shown Red2) is passing through a dedicated plant room supplying air and requires a minimum rating of one hour for stability and integrity to resist fire from outside (Type A).

Where it passes through the ofice (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 ductwork route through the building to the pressurised lobbies. Ductwork within the lobby or corridor (shown Purple) needs to be fire rated.

Ductwork (shown ) is in a protected shaft contructed to method 2 of BS 9999:2008 with other services, and in some circumstances insulation requirements, waived by the regulatory authority if there are no combustible materials or other services within 500mm of the duct – BS 9999:2008, clause W.4.

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