Guide to good practice internal cleanliness of ventilation systems
Specific Considerations for Kitchen Extract Systems
7.1 The kitchen extract system presents particular hazards due to the potential for the accumulation of grease. Accumulated grease within an extract system forms a hidden combustion load. Under certain circumstances ﬂame or very high temperature within the duct can ignite the grease causing ﬁre to spread rapidly through the duct. Flame and heat within the duct can ignite surrounding materials at various points along the ductwork path and transfer fire in ways that are difficult to predict and control by designers,
installers and ultimately fire fighters.
7.2 Kitchen extract ventilation systems are defined here as the extract systems intended to collect and remove contaminants, heat and moisture from cooking appliances (See also DW/172). A kitchen extract system would typically comprise of the following components:-
Canopy – Also referred to as hood, canopy hood, extraction hood, cooking hood, cooker hood, cooking canopy or extraction canopy. This would most likely include a vertical canopy skirt running around the perimeter of the canopy. Aé€nUa€”‘ channel on the bottom edge of the skirt; a canopy roof sitting horizontally on the top of and joining the skirts; a grease filter housing assembly (with grease filters and traps) hanging within the boundary of the skirts.
CanopyIExtract plenum – This is typically the area immediately behind the grease ﬁlter housing and below where the ducting commences.
Ducting -Beyond the canopy/extract plenum, extraction ductwork would be connected. This may involve short transition ducts connected directly to the suction side of an extract fan or could include many linear metres of horizontal and/or vertical ductwork. Vertical ductwork, also referred to as riser may pass through many levels of a building. Contained within the ducting there may be attenuators, ﬂow control dampers, ﬁre dampers, air turning vanes and sensors.
Extract Fan – To create extraction from the canopy an extract fan would be connected to the ductwork, some extract fans (roof mounted) discharge directly to atmosphere via a cowl.
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