Wet Chemical Fire Extinguisher Guide
A relatively newer variety of fire extinguishers, the wet chemical fire extinguisher was developed with the specific purpose of tackling deep fat cooking fires. Coming with a yellow panel label and relevant instructions, the first wet chemical extinguisher on the UK market was the Chubb Fry Fighter.
The introduction of wet chemical extinguishers to the existing fire extinguisher types offered a superior fire protection method of extinguishing Class F fires. It was reflected in the BS 7937: 2000, a new British Fire Standard dedicated to the use of portable fire extinguishers on cooking oil fires.
How Do Wet Chemical Fire Extinguishers Work?
As the oil/fat of a deep fat cooking fire forms a barrier between the fire extinguisher, fire and actual source of heat, ordinary-use fire extinguishers are ineffective as they have no way of cooling the oil – which can burn at temperatures up 340 degrees centigrade – as well as the potential danger of splashing oil making contact with the agent of the extinguisher.
Potassium acetate is the active ingredient in wet chemical fire extinguishers and it is typically used in addition to potassium bicarbonate or potassium citrate. A key function of the Class F wet chemical fire extinguisher is that when in use, it creates a mist that can cool any flames whilst preventing any oil splashing.
The active ingredients will then rest on the surface of the oil, with the potassium salts creating a saponification effect, causing a slippery, viscous foamy liquid that then envelopes the hot fat, preventing any chance of re-ignition. This foam substance will also assist in cooling the hot fat, breaking the fire triangle.
What is Saponification?
Saponification is a process far closer to home than you would believe; in fact, saponification is the exact same process used to manufacture many commercial soaps. Put in simple terms, saponification refers to the reaction between fats/oils with a metallic alkali or base.
The metallic base reacts with the oil and then converts it into alcohol and hydrolysed acid, which, effectively, converts fat or cooking oil surfaces into non-combustible soap.
A great side effect of the saponification process is that the foamy soap that is created just so happens to be endothermic: absorbing heat from the remaining hot oil/fat and cooling it in the process.
How to Use a Wet Chemical Extinguisher Correctly
A wet chemical fire extinguisher will typically have a long lance, much like other specialist extinguishers. This long lance allows a user to stand far away from the fire – ensuring their safety – whilst spraying the contents directly, gently and evenly across the surface of the fire.
This is done by using the PASS (Pull, Aim, Squeeze and Sweep) system for discharging fire extinguishers. Usually, workplaces, such as commercial kitchens and food manufacturing plants, should provide ample training to staff for the correct and effective use of a wet chemical fire extinguisher.
Interestingly, unlike the majority of other classes of fire extinguishers, the correct use of a Class F/wet chemical fire extinguisher requires the entire contents to be emptied into the deep fat fryer to accelerate the cooling process.
When Should You Not Use a Wet Chemical Extinguisher?
It is crucial for businesses and employees to remember that Class F fire extinguishers are formulated to work with only vegetable oils and animal fats, so they cannot and should not be used on Class B type fires that involve flammable liquids such as alcohol, diesel or petrol.
Wet Chemical Fire Extinguishers and Electricity
Wet chemical fire extinguishers should not be used on electronics or electrical equipment, though it is understandably difficult to avoid such items and electricity cables in a commercial kitchen, during the heat of the moment.
Fortunately, wet chemical fire extinguishers manufactured by reputable companies will have a lance that is not conductive of electricity and is BSi 35kv conductivity test compliant.
Other Fire Extinguishers Found in Commercial Kitchens
Historically, commercial kitchens were typically outfitted with ABC/dry powder or foam fire extinguishers, with employees mistakenly believing that such extinguishers should be used to extinguish deep fat fryer fires.
Nowadays, wet chemical fire extinguishers are commonly installed in such places to deal with Class F fires, along with water fire extinguishers which are suitable for extinguishing fires involving combustible materials (Class A). If no other fire extinguisher is available, a wet chemical fire extinguisher can be used on a Class A fire.
During a professional fire risk assessment, the engineer will typically recommend that Class F fire extinguishers are kept close to other fire safety instruments such as CO2 extinguishers (for electrical devices) and fire blankets which can be used to smother small pan fires (though not for fires in commercial fryer fires).
Need to install a new fire extinguisher in your commercial kitchen or food manufacturing plant? Buy a wet chemical extinguisher today.
