Wet Chemical Fire Extinguisher: How It Works, Colour & Limitation


Wet chemical fire extinguisher employs a pressurized solution of alkali salts in water to extinguish fire. It is also known as Class F’ fire extinguishers or class ABF’ fire extinguishers in some versions.

Generally, wet chemical extinguishers are suitable for use on Class A & F Fires. The class A and F fires are fires involving cooking oils and fats (Class F fires), such as lard, olive oil, butter, vegetable oil, and on flammable solids (Class A), such as papers, woods, plastics, etc.


Why Is Wet Chemical Fire Extinguisher Best For Class F Fires

Due to high auto-ignition temperatures of cooking oil fires, they are difficult to extinguish. However, to extinguish these fires, it needs to be cooled sufficiently which conventional extinguishers are not as effective due to risk of flash back and re-ignition.

Moreover, the wet chemical extinguisher works best in this situation because it rapidly knocks the flames out, cools the burning oil and chemically reacts to form a soap-like solution, sealing the surface of the fire and preventing re-ignition.


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Wet Chemical Fire Extinguisher Colour

This type of fire extinguisher has a YELLOW coloured label stating ‘Wet Chemical’.

According to the British standard, the main body of this extinguisher should be Red, and they should have a Large Yellow Banner across the top on the front of the extinguisher with Red writing stating “Wet Chemical”.


Wet Chemical extinguishers that are manufactured to BS EN 3 should have a red body (RAL 3000) and a yellow band covering 5-10% of the fire extinguishers surface area.

This extinguisher are available in sizes like; 2 litre, 3 litre, 6 litre, etc.


How Does Wet Chemical Fire Extinguisher Work

It works by forming a soapy film on the surface of the fire. This is made possible by the wet chemical fire extinguishing agent (Potassium) present in the wet chemical fire extinguisher. This smothers the fire, with the added benefit that the mist also creates a cooling effect.

In summary, this extinguisher acts in two ways:

  • It produces mist which cools the fire and lowers the temperature to stop the fire spreading, also prevents splashing of the hot oils/fat.
  • The potassium salts react with the hot oil and causes the process of saponification, coating the surface of the cooking oil or fat in soapy foam that is non combustible and acts as a barrier between the fat and oil.


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How To Use A Wet Chemical Fire Extinguishers:

The wet chemical must be applied using the extended applicator or lance in slow circular movements, giving a gentle, yet thorough application in fine spray form, covering and emulsifying the burning cooking oil or fat to prevent re-ignition.

To operate the extinguisher, aim the applicator tip from a distance of about 1 meter from of the fire, squeeze the levers on the operating head together and attack the fire from the base in slow circular movements covering the complete area.

Breakdown of the steps to follow in extinguishing class F fire:

  1. Turn off the source of heat if safe to do so.
  2. Hold the lance at arm’s length, well above the fire with its nozzle at least 1 Metre away from the fire.
  3. Holding the lance still, discharge so that the spraying wet chemical falls gently onto the surface of the fire.
  4. Even if the fire appears to go out quickly, discharge the entire contents of the extinguisher.


Locations You Can Use The Wet Chemical Fire Extinguisher

Some locations we could place the wet chemical extinguisher are:

  • Kitchen
  • Fish and chip shops
  • Burger bars, etc.


Limitation Of This Extinguisher

This type of fire extinguisher can produce toxic fumes, hence, areas should be ventilated if a wet chemical extinguisher has been used.


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