Ductwork air systems can be a source of spreading disease, infections and fires. With this greater understanding the requirement for access into the ductwork systems for maintenance, inspection and cleaning has increased.
The importance of regularly cleaning ductwork ventilation systems is well established. This can be cleaning of ductwork as part of a building maintenance programme or of new ductwork systems prior to handover.
The cleanliness of ductwork, both existing and new; location of access doors; and the cleaning and maintenance of ventilation systems are all closely linked. 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.
TR/19 is a good practice guide for the internal cleanliness of ventilation systems. The guide was first published in 2005 as an amalgamation of the TR/17 guide.
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. 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.
Canopy/Extract 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 which if not cleaned to TR-19 can impose a fire risk. Possibly contained within the ducting there may be attenuators, flow control dampers, fire dampers, air turning vanes and sensors. Please also note that grease deposits within systems also pose hygiene, odour, vermin and mechanical efficiency hazards. Poorly designed and installed or damaged ductwork can leak grease, thus extending the fire risk, hygiene, odour and vermin hazards. Also, where ductwork distorts under fire conditions, burning grease can leak out and spread the fire to duct surroundings.
Extract Fan – To create extraction from the canopy an extract fan would be connected to the ductwork, some extract fans can be roof mounted discharge and directly to atmosphere via a cowl.
Other systems such as ventilated ceilings and directly ducted extraction are also used. It is important that the person responsible for implementing cleaning regimes clearly understands the breakdown of the system so that any cleaning regime is compliant with the terms of buildings insurance relevant to the kitchen extract maintenance.
|Usage||Daily Usage||Frequency of Cleaning|
|Heavy Use||12-16 hours per day||Every 3 months|
|Medium Use||6 - 12 hours per day||Every 6 months|
|Light Use||2 - 6 hours per day||Every 12 months|