Classes of fire
There are six different types or classes of fire, each of which has extinguishers to tackle the specific types of fire. Newer fire extinguishers use a picture/labelling system to designate which types of fires they are to be used on. Additionally, the majority of fire extinguishers have a numerical rating which is based on tests conducted by professional fire-fighters that are designed to determine the extinguishing potential for each size and type of extinguisher.
- A: SolidThe numerical value on an extinguisher designed to tackle Class A fires represents the size of fire in cubic metres that the extinguisher can put out.
- B: LiquidThe numerical value represents the amount of litres of flammable liquid that can be extinguished.
- C: GaseousNo numerical value. Flammable gas is very difficult to measure in cubic metres–it depends on the ratio of gas to air there is in the local atmosphere.
- D: MetalThe numerical value represents the size of fire in cubic metres that the extinguisher can put out.
- E: ElectricityNo numerical value. Once the source of the electricity is shut down, the electrical fire will revert to a different class.
- F: Cooking oilsThe numerical value represents the amount of litres of flammable liquid (cooking oils etc) that can be extinguished.
Choosing an extinguisher
Water extinguishers are one of the cheapest and most widely used extinguishers available. They are good for tackling fires involving burning paper, wood and soft furnishings, as the water soaks into the materials (Class A fires).This type of extinguisher does not leave a residue , but does have a comparatively low rating. Due to this factor water extinguishers are larger and heavier to overcome their lacking in fire fighting power. It is important to remember that water is a electrolyte and conducts electricity. Care must therefore be taken with regards to accidental use on mains power. These problems can, however be overcome by installing water extinguishers with additive. This type of extinguisher has a higher fire rating, which therefore reduces the weight of the extinguisher and removes the risk of self-electrocution.
Foam extinguishers are more versatile than the water extinguisher. They can be used on fires involving wood, paper, textiles, plastics and flammable liquids: such as paraffin, petrol, and oil; and are suitable for areas where soft furnishings and carpets are present (Class A and B fires).Foam extinguishers are safe to use with regards to electrical risk. This type of extinguisher usually contains additives which are carcinogenic, making the cleaning process of the premises after the event of a fire more problematic.
CO2 (Carbon Dioxide) Extinguishers
CO2 extinguishers contain only pressurised CO2 gas and leave no residue. This type of extinguisher is suitable for use on fires involving burning liquids (Class B fires), but is also an excellent solution for quenching fires involving computer equipment and other electrical appliances , as it does not cause damage to the electrical items and does not cause the system to short circuit. It is important to remember that when using CO2 extinguishers there is a possibility that once the gas has floated away the fire may re-ignite if the source of the fire is not removed (eg switching off the power supply). Please be aware that CO2 extinguishers that are not fitted with double-lined swivel horns may cause your fingers to freeze to the horn during the deployment of the CO2 gas.
Multi-purpose powder extinguishers are suited to fighting class A, B and C fires–and hence are also called ABC extinguishers. That means they can be used on fires involving wood, paper, textiles, plastics, flammable liquids (such as paraffin, petrol, oil), flammable gasses (such as propane, butane, methane) and also those fires involving electricity.
Powder extinguishers have a good fire fighting capacity, but this agent does not soak into materials and does not have a cooling effect on the fire. This could result in the fire re-igniting, if it is not properly extinguished. Care must be taken when using powder extinguishers and they should not be used in small confined spaces where there is a risk of inhalation of the powder.
Wet Chemical Extinguishers
Wet Chemical fire extinguishers are suitable for use with fires involving burning oil and deep fat fryers (Class F fires). These extinguishers come with a special application lance which lays a cooling layer of foam on top of the burning oil. Alternatively a fire blanket can be placed over the pan containing the burning oil. The pan should then be left to cool down. NEVER carry the pan outside or lift the fire blanket after a short period of time to inspect the burning oil as introducing oxygen through this action could re-ignite the fire. NEVER use pressurised water, powder or foam extinguisher on fires involving burning oils as the pressurised jet will cause the burning oil to be carried out of the pan onto surrounding surfaces causing more damage and a larger fire to tackle.