Non-domestic kitchen extract ductwork

Non-domestic kitchen extract ductwork is sometimes referred to as grease ducting, and should be tested for Type A fire outside and Type B fire inside. Both tests are required to prevent flammable grease from either catching fire when it passes through an adjacent area or, if the grease itself is already alight, causing a fire to start within the adjacent area by radiant heat.

  • Non-domestic kitchens must have separate and independent extract systems (BS 9999:2008 Clause 33.4.7).
  • Fire dampers should not be used in kitchen extract ductwork (BS 9999:2008 Clause and
  • Access doors must be installed at three metre intervals where possible (BS 9999:2008 Clause 33.4.7) and internal surfaces must be smooth to enable easy cleaning of the grease.
  • Care must be taken to ensure combustible deposits in the duct cannot ignite in adjacent compartments.

Non-domestic kitchen extract ductwork

In the diagram

Kitchen extract ductwork presents a particular hazard in that combustible deposits, such as grease, are likely to accumulate on its internal surfaces. Therefore, the ductwork needs to resist fire from the inside (Type B) and must be rated for stability, integrity and insulation for the same period of time as the compartment through which it passes, (shown Cyan).

A fire in an adjacent compartment, through which the kitchen extract ductwork is passing, could initiate a fire within the ductwork, which in the absence of fire dampers might prejudice the safety of the kitchen’s occupants. For this reason, it should also be tested to fire outside (Type A), with the additional requirement that the internal surface of the ductwork within the compartment must meet the insulation criteria.

In some circumstances, insulation requirements may be waived or varied by the regulatory authority, for example, if the duct passes through an area where fire cannot be present, (shown Red), such as a protected shaft. However, stability and integrity must still be maintained for the relevant period of time.

Ductwork within the kitchen (the first compartment) does not have to be fire rated (shown in White).

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