Fire Safety - the 6 fire classes and 5 types of extinguishers

A fire in the workplace can be destructive and even fatal if not treated quickly and with the correct protocols and precautions in place. These include the installation of a smoke detector or fire alarm, Essential to this is carrying out an effective fire risk assessment, boosting protection for your organisation, staff, and customers alike.

The ignition of a fire requires 3 elements: oxygen, fuel, and heat. These make up the Fire Triangle which, with the addition of a chemical reaction (the Fire Tetrahedron), should be considered when creating your risk assessment. Removing these components will break the Fire Triangle (also known as the Combustion Triangle) and, therefore, extinguish the fire. In order to do this, you will require knowledge of what types of fire occur and what fire extinguisher should be used on each, so...

What are the fire classifications?

Before using a fire extinguisher you must first establish what type of fire you are dealing with, as that will determine what kind of extinguisher you should use. Fires can be categorised into 6 different classes: Class A, Class B, Class C, Class D, Electrical, and Class F.

Class A fires

Combustible solid materials are responsible for Class A fires. In the workplace, these materials could include cardboard, textiles, wood, or paper, as well as furniture and even the building's structure. This makes environments such as schools and offices vulnerable to this type of fire due to the materials commonly stored in these facilities.

The presence of ash is a good indicator of a Class A fire, whilst examples of ignition sources for Class A fires include matches, heaters, and cigarettes.

Class B fires

Class B fires are caused by flammable liquids. These flammable or combustible liquids, which can include cooking fats, petrol, paint, melting plastic, or wax, are known as hydrocarbon fuels. Hydrocarbon fuels, as the name suggests, represent the fuel element of the Fire Triangle. Class B fires pose a threat to businesses that are involved in the preparation of food, schools, hospitals, retail stores, factories, and warehouses, amongst others.

Understanding the nature of these liquids and the appropriate measures that should be taken, such as safely storing chemicals and wearing the appropriate protective clothing, is essential to the Control of Substances Hazardous to Health (COSHH), as well as increasing your businesses protection from a fire in the workplace. For more information, check out our guide to COSHH.

Class C fires

Class C fires occur when gas burns. Butane, propane, and methane are the three flammable gasses that most commonly fuel this type of fire. Similar to flammable liquids, gasses that can burn and cause dangerous reactions, like a Class C fire, should be stored properly. Class C fires can be very dangerous as they are not usually ignited in a controlled method, can spread ferociously, and are often violently explosive.

Facilities that store these flammable gasses can be susceptible to Class C fires, whilst heating systems also use these gasses, leaving places such as schools, hospitals, and even your own home with a chance of being exposed to this fire classification should they ignite.

Class D fires

A Class D fire is a result of burning metal, most commonly magnesium or titanium. Other combustible metals include sodium, calcium, and lithium. This fire class can also be very dangerous as ignition of these flammable metals is often rapid and the fire can propagate very quickly, too.

Staff in manufacturing facilities that work with combustible metals should be aware of the dangers they can cause if ignited.

Electrical fires

Electrical fires are slightly different from the other 5 fire classes as they can be counted within any of the other classifications. In an electrical fire, it is not the electricity itself that is burning, rather the electrical current causes other materials around it to set alight.

To avoid an electrical fire, proper installation of electrical equipment and installations should be ensured, with thorough checks regularly carried out thereafter, assuring that these are safely maintained. Before using an extinguisher on an electrical fire, the electrical equipment should be switched off.

Class F fires

When using cooking oil or fat, there is a danger that these cause a fire. This type of fire is classified as Class F. These can be caused by cooking equipment such as deep fat fryers and chip pans.

Given these fires are linked with cooking, those who work in kitchens or other facilities that prepare food should be mindful of the dangers these oils and fats pose. Class F fires can be avoided by being vigilant when cooking or preparing food, ensuring surfaces are wiped and cleaned, and that the oil in the deep fat fryers is changed frequently.

What are the different types of fire extinguishers and what are they used for?

Now that you're aware of the different fire classes, it should be clearer to you why different fire emergencies require.

Fire extinguishers are not one-size-fits-all. There are multiple types of extinguishers, 8 in total and 5 main types, with two versions of Water and Dry Powder extinguishers. These all have their own uses, for example, a water-based extinguisher should only be used on Class A fires.

Here's a list of the 5 main types of extinguisher, how to identify them, and on which types of fire they should be used:

1. Water (Red)

Identified by red and white writing and label, water extinguishers are most often found in places such as schools, offices, shops and hospitals. A water-based extinguisher should only be used on one type of fire: Class A.

This type of extinguisher is not suitable for other fire classes. For example, many hydrocarbon fuels have a relevant density of less than 1.0, meaning that if a water-based extinguisher was used on a Class B fire, a liquid such as oil or petrol would rise to the surface of the water and continue to burn.

Water Mist (White)

Similar to water-based extinguishers, extinguishers that use water mist should be used on Class A fires. However, found with a white label, this type of fire extinguisher can be used for 4 other fire classes: Class B, Class C, Electrical and Class F.

2. Foam (Cream)

With a cream label, you'll likely find a foam-based fire extinguisher also in offices, shops and hospitals, as well as apartments. These use foam to smother fires, removing oxygen, an element in the Fire Triangle, in order to put them out.

Foam extinguishers can be used to put out Class A and Class B fires. However, foam extinguishers cannot be used for an electrical fire as they also contain water.

3. Dry Powder (Blue)

A dry powder extinguisher can be used on almost all types of fire: Class A, Class B, Class C, Class D and Electrical fires. As the only fire extinguisher that can be used effectively on Class D fires (burning metal), these are commonly found in facilities such as garages and boiler rooms, as well as welding factories, and can be identified by their blue label.

4. CO2 (Black)

Less messy than a powder-based extinguisher, CO2 extinguishers work best on Electrical fires and, therefore, are often found in workplaces where electrical equipment and fittings are commonplace, for instance in offices and server rooms. A CO2 extinguisher, which you'll find with a black label, can also be used on minor Class B fires (flammable liquids), however, it is not as effective on this type of fire.

5. Wet Chemical (Yellow)

Yellow-labelled extinguishers are known as wet chemical fire extinguishers and function by reducing oils that are burning to a non-combustible state through chemical changes, in turn eliminating the fire. Designed to be used for Class F fires (cooking oil and fat), wet chemical extinguishers can be found in kitchens, although can also be used on fires involving organic materials (Class A).

Protect your organisation with Fire Safety training

Used correctly, fire extinguishers can save your workplace, staff, organisation and even home. Fire Safety training helps you safeguard against the devastating impacts of a fire and establish an effective action plan and protocols to prevent future fires.

To find out further benefits of having a fire extinguisher and how to carry out inspections on your own extinguisher, check out our blog.

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