Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. Fire are group into classes based on the source of its fuel. This the area of concentration for this article; Classes of Fire.

Classes of fire

There are basically five (5) classes of fire; though some quaters add the 6th (Class E – Electrical fires)

• Class A Fires – These types of fires involving solid materials such as wood, paper or textiles.
• Class B Fires – These types of fires fires involving flammable liquids such as petrol, diesel or oils.
• Class C Fires – These types of fires involving gases.
• Class D Fires – These types of fires involving metals.
• Class E Fires – These types of fires involving live electrical apparatus. (Technically ‘Class E’ doesn’t exists however this is used for convenience here)
• Class F Fires (Class K Fires) – The areas use F or K for the class of fire. These types of fires involving cooking oils such as in deep-fat fryers.

Class A Fire

Class A fires are fires involving solids, i.e, it uses solid fuels. Example could be paper and cardboard, common in offices and manufacturing. It could be furniture, or fixtures and fittings. It could even be the structure of the building.

Class A fire is one of the most common types of fire because solids are the most common type of fuel and one that is hard to eliminate.

Good housekeeping will help to keep materials like packaging and waste reduced, minimising risks.

The only type of fire extinguisher that should be used on a class A fire is the water extinguisher.

Class B Fire

Class B fires are fires involving liquids. Many of the fluids, liquids and chemicals used in workplaces can be flammable or explosive. Like cleaning fluids, solvents, fuels, inks, adhesives and paints.

According to statistics, in 2010/11 flammable liquids accounted for only 2% of fires, but a massive 21% of fatalities. These fires are less common than class A fires but more deadly than other types of fire.

Class B fires can be extinguished using foam or powder Fire extinguishers.

Class C Fire

Class C fires are fires involving gases. This could be natural gas, LPG or other types of gases forming a flammable or explosive atmosphere.

While extinguishers can be used on class C gas fires, the only safe method to attack this type of fire is to shut off the gas supply. The best type of extinguisher to put out the fire after the supply of gas is cut off, is a dry powder extinguisher.

Class D Fire

Metals are not often thought of as a combustible material, some types of metal can be, like sodium. Metals are also good conductors, helping a fire spread. All metals will soften and melt at high temperature, which can be a big problem when metal joists and columns are present in a fire as structural elements.

Water can actually act as an accelerant on metal fires. class D fire can be tackled using dry powder extinguishers. The powder inside the extinguisher may vary depending on the type of metal risk it is designed for. Small metal fires can sometimes be smothered with dry earth or sand.

Class E Fire (Electrical Fires)

This is not strictly a class of fire, because electricity is more or a source of ignition than a fuel. This is why most quarters exclude electrical fires as a class of fire.

However, fires in live electrical equipment are an additional hazard. You do not want to be using water, or any other conductor as that could be fatal.

NOTE: According to the “The Fire Safety Advice Centre ” Electrical fires are not given their own full class, as they can fall into any of the classifications. After all it is not the electricity burning but surrounding material that has been set alight by the electric current.

You can use carbon dioxide, and dry powder extinguishers in low voltage situations. Always turn off the power supply if you can.

Class F Fire

Deep fat frying and spillages of flammable oils near to heat sources in kitchens can result in a class F fire.

Never leave food or frying equipment unattended during use. The only type of fire extinguisher approved for use on cooking oils and fats is the wet chemical extinguisher. For small class F fires, you could also use a fire blanket.

Further Reading

Automatic fire extinguisher: How it works & Types

Fire extinguisher price based on types and sizes

Fire extinguisher regulations: OSHA & General Regulation

ABC Fire extinguisher: All you need to know

Wet chemical fire extinguisher: How it works, colour & Limitation