AUST – Essential Property Services advises that it is important to remind building owners and managers of the dangers associated with an essential safety measure known as kitchen exhaust canopies. Managers should anticipate extensive damage when a fire occurs in a commercial kitchen at the cooking appliance and then spreads into the exhaust canopy. Kitchen exhaust canopies are usually installed in restaurants (under a building permit), cafes and takeaway food premises above commercial cooking appliances. Fire spread into an exhaust canopy is usually attributable to a single dominant factor – poor maintenance resulting in a build-up of cooking oil and fat.
When a fire spreads through the filter bank, even extinguishing agents from correctly engineered systems may not be effective in controlling fire spread within the ductwork. Fire, once within the ductwork, will usually continue to spread throughout the full length of the ductwork and will eventually destroy the duct and exhaust fan.
Fire-fighters have great difficulty in extinguishing these fires due to poor access. Heat radiated from a duct that is on fire internally can cause adjacent combustible materials to ignite.
Fire brigades respond to these developing situations by cutting access points in nearby ceilings. Unless the fire is quickly brought under control, significant damage can result or, in extreme cases, the fire can grow to such an extent that the building (or part) can be destroyed.
Safeguarding against these sorts of outcomes requires regular maintenance and cleaning must be carried out on the exhaust canopies and also the entire ductwork system.
Tenants, under lease agreements, may also be accountable under the relevant Australian Standard.
AS/NZS 1668.1 ‘The use of ventilation and air-conditioning in buildings Part 1: Fire and smoke control in multi-compartment buildings’ also specifies that certain precautions be implemented when installing kitchen exhaust canopies and their ductwork and, if not met, the potential for fire is increased.
Kitchen exhaust canopies ductwork presents two fire hazards: a fire within the duct itself and a fire within the fire compartment in which it is installed. Fire dampers are not allowed to be installed on kitchen exhaust ductwork and fire spread between ducts can compromise a building’s passive fire protection.
Fire dampers are not permitted within the duct system because their effectiveness is questionable as grease on the downstream side would likely ignite before damper closure. The potential for false operation is also increased and closure, other than in a fire situation, could have serious consequences.
Some commercial kitchen exhaust canopies have their own in-built suppression system to reduce the risk of fire spreading into the duct, while in others, fire baffles may be incorporated as an integral part of a proprietary kitchen hood assembly to further reduce the risk of fire spread.
Ducts should be installed vertically or near-vertically wherever practicable. Ducts installed horizontally must be kept to a minimum and be installed rising in the direction of airflow.
Access openings, large enough to enable cleaning of ducts, shall be provided at each change in direction and in horizontal runs at intervals not exceeding 3 m. A drain fitted with a grease-tight tap or plug shall be provided at the lowest point of each run of ducting.
Following the above-mentioned requirements of the Building Code of Australia (BCA) will limit the risk of fire spread within the ductwork, between adjacent ducts and between fire compartments.
Building Legislation Table
Fire Safety Compliance: Essential Safety Measures