Can Metal Grease Extract Ductwork Spontaneously Combust?
As summer temperatures rise, vigilance regarding kitchen safety, particularly in restaurants, becomes crucial. Recent incidents of restaurant fires reported by the London Fire Brigade raise an important question: Can metal grease extract ductwork spontaneously combust? We explore this possibility and the factors involved.
Spontaneous combustion is often linked to the high temperatures of cooking oils during processes such as deep-frying, with auto-ignition temperatures generally ranging from 300°C to 360°C. This means that if cooking oil is heated to these critical temperatures, it can ignite without an external ignition source.
In the context of Fats, Oils, and Grease (FOG) deposits that accumulate in ductwork, the scenario changes slightly. For these deposits to ignite solely from hot gases, extraordinarily high temperatures would be necessary. While theoretically possible, such situations are not typical. Fire suppression experts have demonstrated that disabling thermostats and high-temperature cutouts can allow oil to superheat, reaching auto-ignition temperatures that would lead to ignition. However, in most cases, ignitions stem from flames or sparks entering the ductwork rather than from accumulated grease deposits.
To mitigate the risk of ignition, it’s crucial to maintain appropriate temperature levels within the ductwork. One effective method involves interlocking extract fans with the fuel supply of cooking equipment. This safety measure ensures that the fuel remains inactive unless the extract fans are operational, preventing temperatures from reaching dangerous levels.
AXA Insurance emphasises the importance of safety features for deep-fat fryers, including a functional adjustable thermostat and a non-resettable high-temperature thermostat or cut-out device. These components are vital in preventing oil from reaching its auto-ignition temperature, thus enhancing kitchen safety.
Another critical factor to consider is the degradation and oxidation of cooking oils over time. As oils are reused, their safe working temperatures decrease, raising the risk of reaching auto-ignition at lower temperatures. Regular oil replacement is not only essential for maintaining food quality but also for ensuring safety in the kitchen.
Gary Nicholls, MD of Swiftclean explains about a situation that Swiftclean experienced a few years ago.
“We had a client who was unable to engineer access to a section of ductwork about three meters from their extraction canopy. This resulted in a heavy buildup of grease in a section of ductwork about two meters in length. The system was being cleaned monthly due to the speed of grease accumulation in this busy burger restaurant. Over 18 months into our contract, they experienced a fan failure during cooking, and the gas safety interlock between the fan and gas failed to function.
What is supposed to happen is that the gas interlock valve will be in a closed position unless air pressure caused by the running extraction fan is sensed. However, on this particular occasion the interlock failed, and this led to elevated temperatures of the extraction system. The grease in the section of ductwork that was not cleaned due to the access restrictions started to smoke and would probably have ignited if it had been allowed to continue and reach a critical temperature. Fortunately, on this occasion, the smoke bellowing out of the extraction system led to an evacuation of the building and cessation of cooking, which lowered the temperature. The restaurant was then closed until remedial works were completed.”
In conclusion, while spontaneous combustion of ductwork is possible under certain conditions, the implementation of safety measures makes such occurrences extremely unlikely. Adopting best practices in kitchen safety, regular maintenance of cooking equipment, and ensuring proper grease management can significantly reduce the risks associated with grease buildup and overheating. By prioritising safety, restaurants can operate with confidence and protect both staff and patrons alike.
If you’d like Swiftclean to help with your compliance, please contact us on 0800 243 471 or email info@swiftclean.co.uk
