The 5 Classes of Fire Explained (A to E)

Safety Note: Follow the guidance of your local fire authority about the safety equipment best for you. If there is an active fire, evacuate yourself from the vicinity of the fire and call your fire emergency hotline immediately. The information in this article is provided for general purposes only and may not best represent your particular needs.

We classify fires into different types or ‘classes of fire’ so we know how best to control them.

The most common time you’ll come across the different types of fire is when you look at fire extinguishers.

Not all fire extinguishers are the same. Different fire extinguishers are designed to fight different types of fires.

You wouldn’t want to put out an oil fire with a water-based extinguisher, for example, because oil floats on water. Similarly, a water extinguisher wouldn’t be great for an electrical fire because water is a conduit for electricity.

Related Article: The 5 Best Fire Extinguishers for the Home, Kitchen and Garage

The 5 Classes of Fire (USA)

Note that the following 5 fire classifications follow the USA standard system for classifying fires. European and Australian classifications slightly differ (see here for international comparison chart).

The 5 classes of fire are:

  • Class A: Ordinary Combustible
  • Class B: Flammable Liquids and Gases
  • Class C: Electrical Equipment
  • Class D: Combustible Metals
  • Class K: Cooking Oils and Fats

Class A: Ordinary Combustibles

Ordinary combustibles are the sorts of materials that will often be found around the house. They are very common fuels for house fires.

Examples of ordinary combustibles include:

  • Wood: such as logs for fireplaces, furniture, and wood building structures.
  • Paper: such as paper you might find in the trash, as well as books on your book shelf.
  • Plastic: such as tupperware containers.
  • Cloth: such as clothing and curtains.
  • Rubber: such as the rubber found in shoes.

To extinguish ordinary combustible fires, it is possible to use most fire suppression techniques, including:

  • Water: Such as water from a garden hose or tap.
  • Dry Chemicals: Dry chemicals are found in ABC fire extinguishers. The most common dry chemical you will find is 
  • Other Methods: Fire blankets can deprive a dry chemical fire of oxygen.

Because ordinary combustibles are so common in house fires, it is recommended that you get a fire extinguisher that includes a ‘Class A’ rating (Most common fire extinguishers are class ABC).

Class B: Flammable Liquids and Gases

In the United States, all flammable liquids and gases are classified as Class B. In Europe and Australia, flammable liquids are Class B and flammable gasses are Class C. Flammable liquids and gases are commonly found in garages and workshops. You might also find other Class B flammables around your house, such as in your paint kit, alcohol cabinet, and your household heating if you use natural gas. 

Flammable liquids include:

  • Gasoline: The gas (petrol) you put in your car fits in this category. Diesel is also included in this category.
  • Most oils: The oil you put in your car, as well as oils you put on your chainsaw car bike chains are included.
  • Most paints: Oil based paints are considered flammable liquids.
  • Alcohol: The spirits on your cocktail shelf are also considered flammable liquids.

Flammable gases include:

  • Hydrogen: Commonly used in party balloons (to help them float above air) and as a fuel for some bus transport systems.
  • Butane: There’s a good chance you’ll find this in your cigarette lighter. It may also be used in your refrigerator as part of the cooling process.
  • Methane: If you use natural gas to heat your home, it’s full of methane. It’s also often used in cooking and hot water systems.
  • Ethylene: Often used in the agriculture industry.

The best techniques for extinguishing a Class B fire are:

  • Halon: Used to be commonly used in fire extinguishers until the 1990s when it was found to be bad for the Ozone layer.
  • Dry Chemical Fire Extinguisher: Your regular ABC household fire extinguisher is a dry chemical extinguisher capable of fighting Class B fires.
  • Foam: Can be effective for extinguishing liquid gas fires.

Water is not usually recommended for Class B fires as water can scatter the liquid fuel. Further, some liquids float on water, meaning the water is not the best substance for separating the fuel from an oxygen source.

Common household fire extinguishers that are designated ABC can be used to suppress flammable liquids and gases (check your extinguisher – most fire districts mandate an ABC extinguisher for your home).

Class C: Electrical Equipment

In the United States, electrical equipment is considered Class C flammable material. Electrical appliances are considered Class K materials in Europe and Class E materials in Australia (see comparison chart below).

Electrical fires are incredibly common household fires. In the United States, fire fighters are called out to 44,880 electrical-related household fires per year.

Electrical equipment that commonly causes fire includes:

  • Clothes Dryers: Clothes dryers can cause fires when they are not properly maintained. Lint build-up acts like kindling for sparks and poorly installed or maintained lint traps can cause a problem.
  • Wiring and Cords: Poorly installed wiring can cause sparks. Overloaded power banks can lead to short circuits and power surges.
  • Space Heaters: It is common for people to leave space heaters near loose cloth like bedding, curtains and clothing left to dry.

The best techniques for extinguishing electrical fires include:

  • Dry Chemical Extinguisher: The ideal way to fight a small electrical fire is to use a dry chemical fire extinguisher such as an ABC rated household extinguisher.

It’s important to note that fire and water are not very good at extinguishing electrical fires because it is an electrical conduit. However, it is also notable that electricity itself does not burn – it is  the spark and heat required to burn surrounding fuels. Once the electrical source is removed the fire may resemble another class of fire depending on the fuel that is burning.

Class D: Combustible Metals

Class D fires are fires that involve combustible metals as the fuel for the fire. The US, Europe and Australia all consider combustible metals to be ‘Class D’.

Combustible metals usually have a very high flash point, so high amounts of heat need to be exposed to the metal before it begins to burn. However, sodium is a metal that can burn upon contact with air or water. Metal shavings are a particular hazard because the high accessibility of oxygen to the metal surfaces can make combustion more likely.

Combustible metals include:

  • Sodium: A highly reactive metal that can cause combustion when exposed to air or water.
  • Lithium: Such as in laptop and smart phone batteries.

The best techniques for extinguishing combustible metal fires include:

  • Dry powder: Not to be confused with dry chemical extinguishers, dry powder extinguishers are dedicated for extinguishing Class D fires.

Combustible metals are less common in households and more common in industrial fires. It is therefore common that fire control districts will not mandate Class D extinguishers be present in a household (check for your local circumstances).

A regular household ABC fire extinguisher is not usually recommended for fighting Class D fires and may in some instances exacerbate the fire’s intensity. A very hot combustible metal fire may break water down into hydrogen gas and oxygen, both of which can be used as reactants for spurring the fire on.

Class D dry powder extinguishers are designed to absorb heat and separate the metal from oxygen sources.

Class K: Cooking Fires involving Oils and Fats

Class K fires are fires that involve cooking oils and fats. In Europe and Australia, these are considered ‘Class F’ fires.

Common materials in class K fires include:

  • Vegetable Oil: Oils such as vegetable oil, canola oil, butter, etc. that are used in cooking are included in this category.
  • Cooking Grease: Grease can accumulate behind and under cooking appliances. Safety inspections of industrial kitchen will usually check to ensure there is no build-up of grease present as it poses a serious fire risk.

Typical substances used to suppress fires include:

  • Water Mist: Water is not recommended for Class K fires, but misty water can be effective suppressants. 
  • Foam: Most Class K fire extinguishers operate using a special substance that turns oils into foams.
  • Fire Suppression Blanket: Fire blankets are often used in kitchens if the fire is small enough to be covered entirely by the blanket. The blanket will suffocate the fire by denying its access to oxygen.

Many industrial kitchens, restaurants, etc. are mandated to have a Class K fire extinguisher proximal to the kitchen. Check your local requirements.

International Classes (Europe & Australia)

MaterialsExamplesUSAEuropeAustralia
Ordinary Combustibles. Wood, trash, paper, plastic.Class AClass AClass A
Flammable and Combustible Liquids.Gasoline, most oils, oily paints, ethanol.Class BClass BClass B
Flammable and Combustible Gases.Hydrogen, butane, methane, ethylene.Class BClass CClass C
Electrical Fires.Extension cords, space heaters, toasters, hair dryers.Class CClass KClass E
Flammable Metals.Lithium, potassium, magnesium, titanium, zirconium.Class DClass DClass D
Cooking Oils and Fats.Vegetable oil, unsaturated fats, lard, butter.Class KClass FClass F

Conclusion

There are 5 common classes of fire. Fires are split into these different classifications in order to identify the best ways to suppress them. There are different forms of fire extinguishers used to suppress different types of fires. Make sure you use a fire extinguisher that is the type mandated by your local fire district for your specific establishment and keep it in an approved fire extinguisher cabinet.