Fire Extinguishers

A fire extinguisher is an active fire protection device used to extinguish or control small fires, often in emergency situations. It is not intended for use on an out-of-control fire, such as one which has reached the ceiling, endangers the user (i.e., no escape route, smoke, explosion hazard, etc.), or otherwise requires the expertise of a fire department. Typically, a fire extinguisher consists of a hand-held cylindrical pressure vessel containing an agent which can be discharged to extinguish a fire. Fire extinguishers manufactured with non-cylindrical pressure vessels also exist, but are less common.


Fires involving organic solid materials such as wood, cloth, paper, plastics, coal etc. Water has a great cooling effect on the fuel’s surface and thereby reduces the pyrolysis rate of the fuel

Fires involving solids and burning liquids, such as paint and petrol but not suitable for chip or fat pan fires. Safe on fires caused by electricity if tested to 35kV (dielectric test) and a 1m safety distance is adhered to.

For fires involving solids, point the jet at the base of the flames and keep it moving across the area of the fire. Ensure that all areas of the fire are out. For fires involving liquids, do not aim the jet straight into the liquid. Where the liquid on fire is in a container, point the jet at the inside edge of the container or on a nearby surface above the burning liquid. Allow the foam to build up and flow across the liquid.

They are mainly water based, with a foaming agent so that the foam can float on top of the burning liquid and break the interaction between the flames and the fuel surface.

These specialist powder extinguishers are designed to tackle fires involving combustible metals such as lithium, magnesium, sodium or aluminum when in the form of swarf or powder. There are three special powders based on graphite, copper and sodium chloride.

This extinguisher works by forming a crust which insulates the metal to prevent access to other combustible material nearby and smothering the fire to prevent oxygen from the atmosphere reacting with the metal

Live electrical equipment, although it allows re-ignition of hot plastics. Now mainly used on large computer servers, although care has to be taken not to asphyxiate people when using the extinguisher in small server rooms..

Carbon dioxide extinguishers work by suffocating the fire. Carbon dioxide displaces oxygen in the air. However, once discharged, the CO2 will dissipate quickly and allow access for oxygen again, which can re-ignite the fire.

Wet chemical fire extinguishers are ideal for Class F fires, involving cooking oils and fats, such as lard, olive oil, sunflower oil, maize oil and butter.

Most class F extinguishers contain a solution of potassium acetate, sometimes with some potassium citrate or potassium bicarbonate. The extinguishers spray the agent out as a fine mist. The mist acts to cool the flame front, while the potassium salts saponify the surface of the burning cooking oil, producing a layer of foam over the surface. This solution thus provides a similar blanketing effect to a foam extinguisher, but with a greater cooling effect. The saponification only works on animal fats and vegetable oils, so most class F extinguishers cannot be used for class B fires. The misting also helps to prevent splashing the blazing oil.

Tests have established that a 6 liter wet chemical fire extinguisher with a 75F rating can deal with a fat fire of maximum 0.11 m2 surface area.