Non-Domestic Kitchen Extract Systems
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 9999:2017 Clause 32.5.4).
- Fire dampers should not be used in kitchen extract ductwork (BS 9999:2017 Clause 184.108.40.206 and 32.5.4).
- As kitchen extract should not be provided with fire dampers, only fire-resisting ductwork should be used when immediate discharge to the outside of the building is not possible. Where fire-resisting ductwork is used, it should be a complete system from canopy to atmosphere. (BS 9999:2017 Clause 32.5.4).
- Non-domestic kitchens should have separate and independent extraction systems and the extracted air should not be recirculated. (BS9999:2017 Clause 32.5.1)
- Access doors must be installed at maximum 2 metre intervals where possible ( DW/172 Second Edition 2018 Clause 18.14 ) 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.
Ductwork within the kitchen that exhausts directly to the outside of the building does not have to be fire rated. DW144 ductwork can be used. ( Shown ).
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 integrity and insulation for the same period of time as the compartment through which it passes from hood to discharge, ( shown ).
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.
Fans classified to EN 12101-3 must be used. Refer to TR/172 for fan type.
It is good practice to discharge the ductwork system 2m vertically from the highest point of the building to prevent fire igniting the building structure or other services.
All fire rated ductwork and penetration seals must be tested to BS:EN 1366-1 including kitchen extract or ductwork with combustible linings test 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