Smoke Extract and Dual Ventilation

Caswell Firesafe non coated fire rated ductwork has been assessed as suitable for Smoke Extract systems. Smoke extract systems should be tested for Type A (fire outside) and Type B (fire inside) to BS 476 –part 24 for a specified time for Stability, Integrity and Insulation (if required)

Dual smoke extract combined with; supply or /and extract systems can operate in two different modes to provide a solution for ventilation and smoke extraction. In the daily operational mode the ductwork system can be either supply or extract and when under fire conditions operate as a smoke extract system. This can be a particularly economic solution to smoke extract.

Smoke extract ductwork is required to retain 75 % of its cross sectional area within the fire compartment and neighbouring compartment, this is tested under BS 476 –part 24

Where a smoke extract duct crosses an escape corridor, it must maintain its stability, integrity and insulation fire rating for the same period of time as the compartment through which it passes.

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 a riser or a plant room, (BS 9999:2008 Clause W.4). Air Extraction must be maintained and Fire Dampers must not be used.

System Description Material Stability & Integrity Insulation
Smoke Extract Galvanised Mild Steel Up to 4 Hours Up to 2 Hours*

*Insulation values are obtained through the application of specific insulation

European Standards (Smoke Extract)

A set of harmonised European Standards have been published for Smoke Control Ducts, however, it is only possible to classify insulated systems under the current regime. In addition the size range that is covered for CE marking smoke control ducts is up to 1250mm wide x 1000mm high (or 1000mm diameter) as there is no EXAP (Extended Field of Application) standard published as yet. BS476-part 24 remains a suitable alternative standard for uninsulated systems, and for systems which fall outside the above scope subject to the approval of the local authority.

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Non Coated galvanized ductwork has significant commercial and environmental savings on systems using intumescent or flame retardant coatings that require energy and chemicals to degrease, etch, prime , paint and dry but also alleviates the inherent problems of damaging these coatings during assembly and installation and compromising the fire resistance of a coated system.

LPS-SD198(appendix B12)
BS476 part 24 1987
Cert - LPCB Ref 1345a

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