Fire risks in commercial kitchens

Every year, commercial kitchen fires cause millions of dollars of damage. The fires most often start in deep-fat fryers, cooking ranges, grills and other equipment. But it is the kitchens’ exhaust canopies and ductwork, combined with the airflow through ducting, that can ‘inflame’ a minor flare-up into a major catastrophe.

Almost all types of food give off grease vapours during cooking. The kitchen exhaust system removes these vapours from the kitchen, but inevitably some of the oil and grease builds up inside the exhaust system and ducting. This grease residue is combustible at approximately 370°C. Cooking appliance flare-ups often generate temperatures above 1000°C, which can easily ignite the grease residue throughout the ventilation system, spreading uncontrolled fire throughout the whole building.

Such a series of events occurred at Heathrow Airport in 1998. The fire had spread through more than 200 metres of ducting before the 100 firemen could stop it. In the meantime, three terminals had been shut down and more than 300 flights cancelled or diverted. The physical damage bill for the fire was far exceeded by the hundreds of millions of dollars of consequent losses. In 2014, five fires in commercial kitchens resulted in $30 million worth of damage.

Fire-related hazards in commercial kitchens include:

• flames, sparks and hot gases from food preparation, which can ignite residues in exhaust ducts  
• food preparation equipment left without supervision during operation  
• failure to switch off equipment, especially at the end of activity  
• overheated oils that can lead to spontaneous combustion  
• food preparation equipment based on solid fuels  
• gas blowtorches used for browning some foods  
• poorly operating thermostats or a lack of thermostat or fault-detecting equipment  
• faulty or overheating electrical equipment  
• metal exhaust flues that conduct heat and ignite nearby material or debris  
• ovens without igniters/pilot lights (lit with burning pieces of paper).

Common safety faults in commercial kitchen exhaust ventilation systems include:

• a grease removal device too close to the heat source
• poor maintenance/poor access
• split maintenance responsibilities
• ducts too close to inappropriate materials
• multiple ducts from multiple compartments
• wood-fired ovens and charcoal heaters
• incorrect installation.

How to minimise fire risks in your exhaust system

There are simple ways to avoid commercial kitchen ventilation systems fires, and it is imperative that they are implemented:

• Systems need to be designed and installed in accordance with the established rules
• Ongoing cleaning, maintenance and inspection should be targeted to the actual usage of the facility and its delivery should be verified.

Step 1: Obey the rules

The National Construction Code (NCC V1 2016) requires that commercial kitchens are provided with kitchen exhaust hoods in compliance with AS/NZS 1668.1-2015 and AS 1668.2-2012. In order for a hood to comply with AS/NZS 1668.1, the whole exhaust system must comply. These standards have been updated and it is important that designers and installers are working to the correct editions. The NCC and AS 1668.2-2012 determine where kitchen exhaust hood systems are required, the minimum ventilation rates, the construction details in terms of functionality and hygiene and, importantly, the minimum distances between the grease removal device and the heat source. The NCC and AS/NZS 1668.1-2015 specify the design and installation precautions that need to be included to mitigate the results of any fire that occurs in the exhaust system.

Step 2: Keep it clean

Keeping ventilation and exhaust systems clean and minimising grease residues will reduce the potential for fires to take over. In fact, Australian Standard 1851.6 – 2012 requires each commercial kitchen exhaust system to be thoroughly cleaned at least once a year. As well as for health and safety, compliance can be crucial from an insurance point of view.

Cleaning method options include:

• manual scraping and washing by hand
• wet washing using steam or hot water and detergent
• robotic systems using compressed air, rotating brushes, dry ice, vacuum or pressurised water.

There are companies that specialise in commercial kitchen exhaust system cleaning and maintenance. When using these companies, it is reasonable to request:

• before-and-after photographs
• a detailed system diagram of the kitchen exhaust system for future reference
• a full report on its condition
• a certificate of compliance.

Step 3: Call in experts

The Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH) has released ‘Fire safety — Kitchen hood exhaust systems’, a free online technical bulletin that offers an in-depth look at the special fire risks associated with commercial kitchen ventilation systems. 

The bulletin aims to highlight the main fire safety issues, promote a common language and improve understanding of the risks and resulting responsibilities of all participants in the supply chain, from design and installation through to operation and continuing maintenance.

The technical bulletin was prepared by AIRAH in collaboration with a range of AIRAH members, industry regulatory organisations, state governments, fire authorities and individuals.

Developed with a wide-ranging focus, the bulletin can be used by everyone from technical service providers and facilities managers to operators of commercial kitchens, building surveyors, body corporates, local councils, property assessors and insurance companies.

To download the technical bulletin, go to www.airah.org.au/resources.

To sum up

If you think your kitchen exhaust ventilation system does not meet current standards or represents a fire risk, you should contact an HVAC professional or kitchen exhaust ventilation company to do a fire risk assessment. The single most important thing you can do to keep your systems safe is to regularly inspect and keep the system clean. Make sure you are correctly insured and discuss with your cleaning contractor any safety hazards or compliance issues in your system.