What do fire classes A, B, C, D, Electrical and F really mean?

Fire classes identify the material or fuel involved in a fire and help determine the correct extinguishing method. In the UK, Classes A, B, C, D and F cover defined fuel types, while electrical equipment is treated separately because the presence of electricity can affect which extinguishing agents are suitable for use.

From this article, you will learn:

• What Classes A, B, C, D and F mean
• Why electrical fires require separate consideration
• Which fuels belong to each recognised fire class
• How the main extinguisher types differ
• Why choosing an unsuitable extinguishing agent can be dangerous
• How cooking oil and metal fires differ from more common incidents
• What to check before selecting fire protection for a building or workplace
• What about lithium-ion battery fires? 
• Is there one fire extinguisher suitable for all classes of fire?

What Are the Main Classes of Fire in the UK?

The classes of fire group fires according to the material that is burning. Under the classification commonly used in the UK and Europe, Class A covers solid combustible materials, Class B covers flammable liquids, Class C covers flammable gases, Class D covers combustible metals, and Class F covers cooking oils and fats.

The classification matters because different fuels react differently when an extinguishing agent is applied. Conventional fire extinguishers, such as water, foam and powder extinguishers, are not suitable for every fire class. This limitation does not apply to Firexo’s innovative fire extinguishers. Firexo uses a specially formulated water-based extinguishing agent with additives, designed and tested to tackle all fire classes, including Class F fires involving cooking oils and fats.

Classification	What is burning	Common examples
Class A	Solid combustible materials	Wood, paper, textiles and many plastics
Class B	Flammable liquids	Petrol, diesel, paint and solvents
Class C	Flammable gases	Propane, butane and methane
Class D	Combustible metals	Magnesium, sodium and some metal powders
Electrical	Energised electrical equipment	Electrical panels, appliances and machinery
Class F	Cooking oils and fats	Deep-fat fryers and commercial cooking oil

Understanding UK fire-class terminology helps businesses identify the hazards present on their premises before selecting fire protection equipment.

Class A, B and C Fires Explained

Class A fires involve ordinary solid combustible materials. Paper, cardboard, timber, fabrics and similar materials fall into this group. These fires are common in offices, warehouses, schools, workshops and residential buildings.

Class B covers flammable or combustible liquids rather than burning solids. Petrol, certain fuels, solvents and paints are typical examples. A burning liquid can spread across a surface, so the extinguishing method must account for the fuel’s behaviour.

Class C covers flammable gases such as propane, butane and methane. Gas fires can involve both flames and an ongoing fuel supply. Where it can be done safely by trained personnel, isolating the gas source is an important part of controlling the incident. Fire procedures must also account for the possibility that unburned gas may continue to escape.

What do Class D, Electrical and Class F Mean?

Class D fires involve combustible metals. Examples can include magnesium, sodium, potassium, lithium metal and certain metal powders. These incidents require particular care because some metals can react strongly with conventional water or extinguishing agents that have not been tested and approved for the specific hazard.

Electrical incidents are different. Energised electrical equipment is often described informally as an electrical fire, but electricity is not a separate formal fire class under the European EN 2 classification. The underlying burning material may belong to another class. The electrical supply creates an additional hazard because the extinguishing medium must be suitable for use around live electrical equipment.

Class F covers fires involving cooking oils and fats, particularly at high temperatures. Commercial fryers are a common example. These fires behave differently from ordinary Class B liquid fires and require an extinguishing method suitable for hot cooking oils. Conventional water extinguishers are not suitable for Class F fires. However, Firexo’s specially formulated water-based extinguishing agent contains additives that enable it to tackle Class F fires as well as other fire classes.

Why Cooking Oil, Metal and Electrical Hazards Need Special Attention

Some fire hazards cannot be judged by flame appearance alone. A burning fryer, an electrical cabinet and metal powder may all produce visible flames, but the correct response differs because the fuel and surrounding hazards vary.

Key distinctions include:

• Class D metals may react dangerously with inappropriate extinguishing media
• Energised electrical equipment presents a risk of electric shock until the supply has been isolated
• Class F oils can remain hot enough to reignite after visible flames have been suppressed
• Water applied directly to burning cooking oil can cause violent splashing and rapid fire spread
• Electrical equipment should be assessed according to both the electrical hazard and the material that is actually burning

These differences explain why conventional fire extinguisher classes and markings must be checked carefully, as no single conventional extinguishing agent is suitable for every type of fire. Firexo addresses this limitation by providing one extinguishing solution tested for use across all fire classes.

How do Extinguisher Types Relate to Individual Fire Classes?

Traditional classes of fire extinguishers are based on the fire types for which each extinguisher has been tested and approved. Conventional water extinguishers are primarily associated with Class A fires. Foam is commonly used for Classes A and B. Dry powder can cover several fire types depending on its formulation, while carbon dioxide is widely used for certain Class B fires and electrical equipment. Wet chemical extinguishers are principally associated with Class F cooking oil and fat fires. These conventional categories should not be interpreted as meaning that every water-based extinguishing agent has the same limitations as a standard water extinguisher.

The classification and rating shown on an extinguisher are therefore more important than its appearance alone. Users should read the product label and follow the applicable fire risk assessment, local regulations and manufacturer instructions.

Our extinguishers take a different approach. Firexo developed the world’s first fire extinguishers capable of extinguishing all fire classes. Our specially formulated extinguishing agent is water-based with additives and can extinguish Class A, B, C, D, electrical and Class F fires. This means its water-based formulation does not limit it to Class A fires or exclude cooking oil and fat fires.

How Should Businesses Choose Fire Protection for Different Risks?

The correct fire protection arrangement starts with the hazards present in the building. A commercial kitchen, engineering workshop, warehouse and office can contain very different fuels, machinery and ignition sources. Businesses should therefore identify combustible materials, electrical equipment, cooking operations and any specialist hazards as part of a fire risk assessment.

The recognised fire classes provide a framework for matching fire hazards with suitable extinguishing equipment, but classification is only one part of the decision. Extinguisher certification, ratings, placement, quantity, staff training and local regulatory requirements also matter.

In the UK, commercial extinguishers used as part of a building’s required fire protection must meet the relevant market and certification requirements. Suitability for a particular fire class and regulatory approval for the intended market are separate considerations. Businesses should therefore check both the product’s extinguishing capability and the certification required for its intended use.