Smoke make up duct systems
Smoke make up fire duct is used to supply air to the fire compartment to assist with the air balance when smoke is being extracted from the building.
- Smoke extract requires appropriate means to allow make up air. These systems are designed to either limit the extent of smoke spreading and/or to reduce the build up of heat in the compartment.(BS9999:2008 ref. A.6.4)
- Fire dampers should not be used in smoke makeup systems
- If the duct is contained within a dedicated shaft or there is at least 500mm separation between the ductwork and combustible materials (e.g. in car parks) stability and integrity ratings may only be required within the area to be protected.
In the diagram
Office supply/smoke makeup duct (shown) must be suitable for supplying air to assist in the clearing smoke within the compartments. This is normally rated to provide one or two hours of stability and integrity - resisting hot smoke and fire from outside (Type A). Fire insulation is not required in the last compartment.
Where the office extract duct crosses the escape corridor, (shown ), it must maintain stability, integrity and insulation fire rating for the same period of time as the compartment through which it passes - this will be required for the remainder of the duct route through the building to the end of the system.
In some circumstances, insulation requirements may be waived or varied to low temperature insulation by the regulatory authority such as in the plant room, (shown ) (BS 9999:2008 Clause W.4).
Fire rated ducting may not be required within the service shaft, (shown ). However, if there is combustible material within 500mm of the duct stability and integrity will be required, full or low temperature insulation would also be required. Building Regulations and BS 476-24/ISO 6944 or EN 1366-1 stipulate that all fire rated ductwork should be tested and installed to comply with the full ‘cellulosic’ time/temp fire test curve (ISO 834 Fire Curve). A fire engineered solution designed by a qualified fire engineering consultant for lower smoke temperature may be allowed by the designer and regulatory authority, thus reducing the insulation requirement only.
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 designer and local building control officer prior to commencement of construction.