What Are The 5 Classes of Fire Extinguishers?

The one reason people should have fire extinguishers in their home or work facility is safety. But the key is to know which fire extinguisher you need. There are five main types of fire extinguishers available to you. So, before purchasing one, you need to know what you are looking for.

The 5 different types of fire extinguishers relate directly to the type of fire they are used to for.

Before learning what the classes of fire extinguishers are, it’s important to know the different types of fires they are designed to suppress.

What Starts a Fire? The Fire Triangle

The Fire Triangle is composed of four necessary components to start a fire. Fire extinguishers put out fires by removing one or more of these parts.

A fire can only start with all three of these parts present:

  • Oxygen
  • Fuel
  • Heat

A fourth part, a chemical reaction, is also necessary between them to ignite a fire. The fire triangle (or fire tetrahedron) has the chemical reaction as the center component.

Fire extinguishers put the fires out by removing one or more of these necessary parts.

Fire Extinguisher

The 5 Different Types Of Fires

There are different types of fires that extinguishers are designed to fight. These include:

  • Class A – a fire started with normal combustibles such as wood, paper, and cloth.
  • Class B – a fire started with flammable and combustible liquids and gases such as gasoline and paints.
  • Class C – a fire started by energized electrical equipment such as power transmission cables or wiring.
  • Class D – a fire started by flammable metals such as sodium, potassium, and lithium.
  • Class K – a fire started by cooking oils, animal fats, or grease (kitchen fires).

The 5 Classes of Fire Extinguishers

There are five different fire extinguisher classes that match up with the different types of fires:

  • Class A
  • Class B
  • Class C
  • Class D
  • Class K
  • Mult-Class: Class ABC, Class BC, etc.

Each rating describes the type of fire the extinguisher can effectively fight.

Class A Fire Extinguishers

Class A fire extinguishers are used for ordinary combustibles, such as wood, paper, cloth, and even plastic. These are well suited for putting out ordinary household fires, making this type great for use in home kitchens and garages. These extinguishers usually use water or dry chemical powders to blanket a fire and/ or absorb the heat.

Type Used: Water & Foam

Works For: Class A fires only

The heat of the fire is removed by the water component, while the oxygen is removed by the foam.

Class A extinguishers are rated based on their water equivalency. Each A is matched to 1 1/4 gallons of water. Examples of these ratings include 1-A, 2-A, 4-A, 6-A, 10-A.

Class B Fire Extinguishers

Class B fire extinguishers put down fires that start from flammable liquids and gases. These include oils, fuels, kitchen grease, solvents, and oil-based paints. This makes this type of extinguisher good for use in homes, offices, and workshops.

Class B extinguishers are rated based on the number of square feet of fire they can suppress.

For example, A 5-B extinguisher can cover 5 square feet of fire. Other numerical ratings include 1-B, 2-B, 10-B, 20-B, and 40-B.

Class C Fire Extinguishers

Class C fire extinguishers are designed to put out electrical fires originating from live wires, circuit breakers, machinery, and appliances. The extinguisher sprays materials that inhibit the conduction of electricity. These types are well suited for garages, workshops, and industrial facilities.

Unlike other classes, this class does not have a numerical rating.

Class D Fire Extinguishers

Class D fire extinguishers are used on fires originating from combustible metals, including magnesium, titanium, aluminum, and sodium. This type is often found in laboratory or industrial settings.

Type Used: Dry Chemical Powder

This type works similarly to other chemical powder extinguishers, in that it removes the heat and/or separates the fuel from oxygen. However, this type is only designed to fight combustible metal fires.

Works For: Class D fires

Class K Fire Extinguishers

Class K fire extinguishers are well designed to put out fires starting from greases, cooking fats, and kitchen oils. This makes them well suited for use in restaurants and home kitchens.

They put out fires by a process called saponification. This happens when alkaline mixtures, such as potassium citrate, potassium acetate, or potassium carbonate, come into contact with burning fat or cooking oil.

This process creates a soapy foam on the surface that holds onto the steam and vapors and puts out the fire.

Type Used: Wet Chemical

This extinguisher removes heat and creates a barrier between oxygen and fuel so a fire cannot be re-ignited. The chemicals are sprayed as a mist, creating a barrier between the oxygen and the fuel and removing the heat.

Works For: Class K fires

Multi-Purpose Fire Extinguishers

Multi-purpose fire extinguishers are designed to suppress different types of fires. For example, A-B-C fire extinguishers can be used for all three of these types of fires. They can also cover other combinations of fire types, such as A-B or B-C, depending on the extinguisher.

Carbon Dioxide

Carbon dioxide is used in multi-purpose fire extinguishers. This gas takes the place of the fire’s oxygen, breaking the chemical reaction. Since it comes out quickly in a blast, it removes the heat of the fire as well.

Works For: Class B and C fires

Dry Chemical

Dry Chemical fire extinguishers are the most popular and versatile type because they can be used for several different classes of fires. The chemical powder contained in them disrupts the chemical reaction of the fire when released. There are two types: multi-purpose (Class A, B, and C) and ordinary dry chemical extinguishers (Class B and C).

Works For: Class A, B and C fires

Water Mist

This extinguisher is designed to remove the heat of the fire only by supplying a dense water mist. This is a general-purpose type fire extinguisher that is well suited for dealing with small fires and protecting nearby people from heat burns.

Works For: Class A and C fires

Clean Agent

Also called halogenated fire extinguishers, these include Halon 1301 or Halon 1211 or newer halocarbon agents which do not deplete the ozone layer. These extinguish a fire by interrupting its chemical reaction and are sprayed in a liquid form.

Works For: Class B and C fires

Cartridge Operated Dry Chemical Extinguishers

Cartridge-operated extinguishers are designed to be rechargeable and separate the propellant (nitrogen, CO2, or dry air) and the extinguishing agent into different cylinders. These types are well-suited for heavy equipment industries and construction sites. They are also built robust and able to withstand harsh environments. Front-line firefighters can be found using this type of extinguisher along with other equipment.

Similar to other dry chemical powder types, this extinguisher interrupts the chemical reaction of the fire by separating the oxygen and the fuel. They also are capable of putting out a variety of types of fires.

Works For: Class A, B and C fires

Fire Extinguisher Markings

Fire extinguishers have markings on them that show their rating level which matches their specific capacity. These meet the ANSI/UL 771: Rating and Fire Testing of Fire Extinguishers.

A is rated by the water equivalency. Each #A is matched to 1 1/4 gallons of water. B is rated by the square feet of coverage. For example, 20B is equivalent to 20 square feet of coverage. There is no numerical rating for Class C, Class D or Class K fires. 

For example, an extinguisher that is rated 3A:10B:C indicates the following:

Intended for Class A, B, and C fires and contains 3.75 gallons of water extinguishing capacity, covers 10 square feet of area, and works on electrically charged equipment.

Fire extinguishers play a critical role in keeping your work or home safe from devastating fires. Knowing which one to buy is crucial to suppressing a fire if one breaks out. Now that you know which fire extinguisher classes are out there, you can pick which one best suits your safety needs.

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Nick Klamecki, Author
About Nick Klamecki, Author

Nick Klamecki is a certified Fire and Workplace Safety expert with 15 years experience in product research and testing. He has a degree from U.C. Davis, is an active outdoorsman and spent years ensuring the safety of special needs children. Nick researches and tests workplace, industrial and safety products and provides advice on their safe use. Learn more about Nick here or connect with him on LinkedIn | Medium