Fire Rated Fume cupboard extract systems tested to BS476 Part 24

When choosing ductwork for a fume cupboard extract system, the type of fumes likely to be produced must be taken into account.

Plastic ductwork presents a problem when the fumes to be extracted are acidic and/or solvent; in this circumstance fire dampers are impractical and an alternative solution must be used. As a solution, plastic ductwork can be enclosed within a fire rated casing. The outer casing would resist fire from inside (Type B) and from outside (Type A), maintaining stability and integrity.

  • Fire dampers should not be used where plastic ductwork is installed to resist acidic fumes and solvents.
  • Alternative solutions must be found for crossing means of escape and going from one compartment to another.
  • Ductwork conveying polluted air must take into account the particular hazard involved and the likely contribution to fire spread– BS 9999:2008, clause 33.4.3.1.

Fume cupboard extract systems

In the diagram

Duct (shown Purple) is a plastic duct installed inside an outer fire rated casing (duct within a duct).

Where the fume extract duct crosses the escape corridor (shown Red2) the duct would resume stability, integrity and insulation for the same period of time as the compartment through which it passes - this may also be required for the remainder of route of the ductwork, through the building to the outside.

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