Page 13 - Caswell Firesafe Manual 2018

Insulation

In addition to the stability and integrity rating of the Kitchen Extract duct it is often specified that the
ductwork be insulated for a rated period of either 30,60,90 or 120 minutes.

In a commercial kitchen there is a likelihood of large flames being created during the cooking process.
As these flames travel up into the kitchen extract duct they can easily ignite grease deposits lining the
internal faces and create a rapidly spreading and very intense fire within the ductwork. The radiant heat
created could then ignite combustible materials in close proximity to the steel duct, leading potentially to
the spread of fire into another compartment.

With regards to Kitchen Extract systems there is a further criteria on Test A (Fire Outside) in which failure
would deem to have occurred if the temperature on the inside of the duct exceeds the above limits inside
the fire compartment; this temperature is measured by what are commonly known as the ‘T3
Thermocouples.’

If a fire was to break out in a room through which a Kitchen Extract duct runs, the grease inside the duct
could be ignited relatively quickly if the duct was not externally protected. For the same reason, cleaning
regimes on Kitchen Extract ducts need to be both more regular and thorough than with standard ventilation
ductwork.

The subject of fire rated insulation is covered in more detail in Section 7, however the general guidance is
to include insulation if combustible materials are located within 500mm of fire resisting ductwork.

Cleaning

In order to minimize the build-up of combustible materials (grease) on the inside of kitchen extract systems,
it is recommended - in both the Building Regulations and DW 172 - that systems are regularly cleaned.

To facilitate thorough cleaning, fire resisting access doors should be positioned every 2m along the
ductwork. In addition, fire resisting access doors should be positioned - on either one or two sides - where
the ductwork takes a change of direction and adjacent to any inline plant such as fans, balance dampers,
attenuators and heat recovery coils.

BESA (Building Engineering Services
Association) document TR/19
Internal cleanliness of ventilation
systems provides comprehensive,
best practice guidance.

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CASWELL FIRESAFE System - Access Door Detail

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