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.

In the diagram

Ductwork (shown ) 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 ) 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 ) 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