Wet Chemical Fire Extinguishers

Which fire extinguishers are suitable for kitchen fires?

Kitchen fires caused by cooking oil and fats are Class F fires, and must only be tackled by extinguishers which have been certified for this use. Wet chemical extinguishers are designed to fight Class F fires by forming a blanket on top of burning materials to suffocate and then cool the blaze. These extinguishers should be installed in areas such as kitchens and garages where this type of fire is a common risk. Some other extinguishers, such as some Water Mists, may have small F ratings for use in home kitchens.

WARNING: Using the incorrect extinguisher on a Class F fire may splash burning oil, causing the fire to spread.

How do wet chemical extinguishers work?

The extinguishing agent used in wet chemical extinguishers expands upon contact with the burning oil to form a blanket on top of it, which prevents re-ignition by cooling and smothering the area as well as blocking access to oxygen. They are usually supplied with a long lance which helps the user keep a safe distance from the fire and deploy the foam at low pressure, rather than 'spraying' the deep fat fryer which risks causing splashes and spreading the fire on burning droplets of oil.

It is important that the full content of the wet chemical extinguisher be discharged even after the flames have been extinguished, to ensure the oil or fat remains blocked from oxygen until it has cooled enough to prevent reignition.

Can water mist extinguishers be used on cooking oil fires?

Some small Water Mist extinguishers are certified for use on cooking oil fires. These extinguishers have a small Class F rating to demonstrate that they are effective at fighting a small, domestic kitchen fires. For example, a 5F rating suggests that an extinguisher could be used to fight a fire involving up to 5 litres of cooking oil, making them ideal for most home kitchens. For catering premises or deep fat fryers, a wet chemical extinguisher should be installed: wet chemical agent can be effective on fires involving much larger quantities of cooking oil.

How do water mist extinguishers work?

The Water Mist extinguishers' supersonic nozzle creates a microscopic mist curtain which reduces the oxygen content (required for combustion) around the fire, extinguishes the flames and creates a highly effective cooling blanket on the hot fuel, preventing re-ignition.

While water should not be used to extinguish an oil fire due to the risk of splashing and vaporization, Water Mist is effective against small cooking fires up to 5F (typical household deep fat fryer) due to the design of its nozzle.