Wet Chemical Fire Extinguishers are especially designed for use on fires involving burning oil and deep fat fryers (Class F fires).
These extinguishers come with a special, long application lance which allows you to safely lay a cooling layer of foam on top of the burning oil. They can also be used on Class A fires, although their fire fighting power for general risks is not very strong.
NEVER use pressurised water, powder, CO2 or foam extinguishers on fires involving burning fat, as the pressurised jet can cause the burning oil to be carried out of the pan onto surrounding surfaces causing more damage and a larger fire to tackle. You can, however use “Dry Water Mist” extinguishers on oil and fat fires, as the fine mist does not enter the surface of the hot liquid but stifles the supply of oxygen while cooling the liquid. It also creates a safe layer between the user and the fire.