If your business premises has a professional kitchen or fries foods onsite, you’ll need a wet chemical fire extinguisher.

Wet chemical fire extinguishers are primarily used in professional restaurants to extinguish Class F cooking oil fires and are secondarily used to control Class A fires. In some rare cases, wet chemical extinguishers can even be used on Class B fires.
Sometimes referred to simply as Class F extinguishers, this fire safety tool uses potassium salts to control fires. They are the only fire extinguisher for cooking oil fires – nothing else can be used safely.
How Do Wet Chemical Fire Extinguishers Work?
Inside a wet chemical fire extinguisher, you’ll find a potassium solution. This solution primarily contains potassium acetate, which is often mixed with potassium bicarbonate and potassium citrate.
This solution, which is sometimes referred to as ‘potassium salts’, is released once the lever on the extinguisher is pulled.
Wet Chemical extinguishers put out the fire using two methods:
- The mist effect that gets released from the nozzle brings the temperature of the flames down and partially removes the ‘heat’ side of the fire triangle. This initial fire covering also reduces the risk of receiving splash-backs from the burning oil or fat.
- A chemical reaction occurs between the potassium salts and the burning oil or fat in a process that is known as saponification. The result of this process is a soapy layer of foam forming on top of the burning liquid, which cuts off oxygen to the fire and contains it.
What Is A Wet Chemical Fire Extinguisher Used For?
You’ll most commonly find wet chemical fire extinguishers in restaurants, hotels, chip shops, and burger vans.
Basically, you’ll find a wet chemical fire extinguisher anywhere that a fire linked to burning fat or oil might happen. If the contents of a deep fat fryer combust, a wet chemical fire extinguisher could be used to control the fire before it spreads.
Like most fire extinguishers, wet chemical fire extinguishers are not useful in containing an out-of-control fire.
You’ll rarely find a wet chemical fire extinguisher on its own. It can often be found sat alongside a CO2 extinguisher or a foam extinguisher, for example.
What Type Of Fire Is A Wet Chemical Extinguisher Used For?
These fire extinguishers are designed for the kitchen. However, they can be used for a few other purposes.
Class F Fires
Above all else, wet chemical fire extinguishers are built for controlling and extinguishing Class F fires. Class F is the most specific fire rank and relates to fires caused by cooking oil and fat.
Typically, wet chemical fire extinguishers are used to extinguish flames that are supported by burning cooking oil, vegetable oil, butter, and olive oil.
Although Class F fires could be seen as a sub-category to Class B fires (flammable liquids), they are classed separately due to the extremely high temperatures involved.
Class A Fires
Some wet chemical fire extinguishers can also be used to tackle Class A fires (fires caused by flammable textiles, woods, papers, light plastics, etc.).
Before using a wet chemical fire extinguisher on a Class A fire, refer first to the label on the side to see if it has been approved to tackle this fire level.
Class B Fires
Just like some wet chemical fire extinguishers have been cleared to tackle Class A fires, others have also been Class B fire-approved.
Class B fires start with flammable liquids, similar to Class F. Again, before using a wet chemical fire extinguisher on a Class B fire, check that the extinguisher has been approved.
What Not To Use Wet Chemical Extinguishers For
Some wet chemical fire extinguishers are only designed for Class F fires, meaning they are unsuitable for use on Class A and B fires.
You should also never use a wet chemical extinguisher on the following:
Electrical fires
You should not use a wet chemical extinguisher on a fire involving electrical equipment (sometimes described as a Class E fire).
Instead, you should use a CO2 fire extinguisher for electrical fires.
Class C fires
Class C fires include fires started by flammable gases such as propane, butane, or methane.
Like electrical fires, wet chemical extinguishers should not be used on Class C fires as the potassium solution can worsen the fire. Instead, you should only use a dry powder extinguisher on a Class C fire.
What Colour Is A Wet Chemical Fire Extinguisher?
Wet chemical fire extinguishers have a yellow label on a red cylinder.
You can distinguish a wet chemical fire extinguisher from other types by its yellow label, which reads ‘WET CHEMICAL’ in big letters.
See Also: Colours of fire extinguishers – a guide on how to identify extinguishers via the label colour coding system.
How To Use A Wet Chemical Extinguisher
When using a wet chemical fire extinguisher, you need to take extra precautions. Accidentally splashing burning fat or oil could cause you serious burns.
The design of a wet chemical extinguisher is slightly different from other models due to the long hose attached. This has been added to make it easier for the user to keep a safe distance from the flames.
Step 1 – Take out the safety pin
Remove the safety pin to break the seal and get the wet chemical extinguisher ready for use.
Step 2 – Cut the heat source
As long as you can approach it safely, you should try to turn off the fryer or other heat source if possible.
Step 3 – Aim the nozzle
Keep the nozzle 1 metre away from the fire itself. The potassium solution will be able to project itself across this distance.
Step 4 – Pull the lever
Pull the lever and cover the whole fire area in a circular motion with the potassium solution. Reduce the risk of the fire reigniting by using the entire contents.
Step 5 – Ventilate the area
After the fire has been extinguished, try to make the room as ventilated as possible. Toxic fumes are created by the saponification process, which lingers around the area for a time after. Kitchens should already be ventilated, but open extra windows and doors if possible. It may also be wise to evacuate the room for the time being.
Final Thoughts
Wet chemical extinguishers should be a part of every kitchen’s fire safety tools. The only solution for cooking oil fires is a wet chemical extinguisher, which can safely cool and extinguish a chip pan fire.
A vital part of any fire safety precautions, some wet chemical extinguishers can also be used on Class A and B fires.
Further Reading
- Fire extinguishers in the workplace – An easy to read guide on the regulations on extinguishers in work environments.