Chimney Fires in Professional Kitchens and Main Reasons
Main reasons of kitchen fires are; accumulation of solid fuel (wood,coal) grills and hobs in hood channels and chimneys. Accumulation of fat and oil in hood exhaust channels, Lack of cleaning of exhaust system, Unsuitable channel and fan selection, No electrical grounding.
As result of the burning hydrocarbon fuels such as wood and coal on the grids, ash and soot accumulate in the channels over in time. There are also fuel dusts in the unburned state due to incomplete combustion. This may cause narrowing of the sections of the exhaust ducts, thus adversely affecting the smoke extraction.
The soot and fuel powders are also flammable. In case of proper conditions, they can ignite in channels and cause kitchen fire.
The accumulation of oil fume is the most serious danger in cooking areas in a professional kitchen. During cooking, fats and oils pass from solid or semi-solid to liquid phae. The atomized oil is then charged with steam. This oil vapor also contains water molecules in the form of steam.
This mixture in the form of an aerosol is transported from the cooking surface to the hood and from there through the ventilation system (Fan) and the negative pressure generated by the heat streams emitted from the cooking equipment. We can see this as a rising cloud of oil and smoke.
Higher cooking temperatures produce more oil mist. When the oil vapor cools, it becomes solid again. These oil residues accumulated in the channels are flammable. The igniton temperature of the oil residues is slightly lowe than the initial ignition temperature. This causes fire hazard in hoods and ducts.
In particular; fish and meat cooked in solid fuel grills produce high volumes of oil mist. When steam comes into contact with the metal surface, it forms a dry but a sticky layer. On this layer is relatively heavier ash, unburned carbon and so on. as well as combustion products accumulate over time. In systems that are not regularly cleaned, the accumulation of oil, ash and soot may cause an excessive accumulation, especially in horizontal channels.
How does it start?
In order to ignite the fats in the flue and smoke ducts, it is necessary that the accumulated oil is gassed or vaporized. These vapors form a flammable mixture as soon as they reach a sufficient amount. The heat source must reach a sufficient temperature in order for the mixture to reach its spontaneous ignition temperature.
Generally, excessive heat and flames on the cooking surface bring about a glare. The most common cause of the glare event is the flames that occur as a result of exposure to excessive heat or direct contact with the flame.
The fire spread in the kitchen exhaust system is basically two-way:
- First of all, flammable oil deposits in the exhaust duct ignite and continue in fire channels and chimney,
- In the second stage, this fire formed in the channels continues to the fan and the metal forming the channel becomes hot. It can be used to ignite the heat energy from metal surfaces. Building elements burn by fire.
Preventing Kitchen Fires
Many measures must be taken to prevent chimney fires in restaurants and professional kitchens.
- Oil, oil loaded steam, unburned carbon, ash, etc. All cooking processes that produce flammable substances must have an automatic fire extinguishing system.
- The mechanical exhaust system of a hotel, restaurant, cafeteria etc. should be independent from the systems serving other parts of building and channels must be at least 500 mm open from flammable materials, the exhaust should be directly thrown out and at least 5 meters away from any air inlet opening from outside the kitchen.
- Passing exhaust duct must be structurally coated with a material such as a fire resistance period. If the channel passes through a brick shaft it must be seperated from other parts of the shaft and other ducts or service elements.
- No fire damper should be placed in the ktichen exhaust ducts!
Despite being very important, these measures are intended to put on the fire or the fire from spreading once it occurs. However Borasco Duct Type Ozone Generator System is designed to keep the inside of the kitchen channels and chimneys clean at all times and thus minimize the risk of fire and chimney fire.
Borasco not only minimizes the risk of fire, but also eliminates at least 85% of your cooking odors and you will be able to save money on channel cleaning costs. Because your channels will always remain clean.