What Are Fire Classes?

Integrated Fire SystemsFire & Life Safety Updates

The 5 Fire Classes and How to Extinguish Them

Fires come in all shapes and sizes. There are a lot of variables that determine how a fire starts, grows, and is put out. These variables organize fires into five fire classes; Class A (Ordinary Combustibles), Class B (Flammable Liquids and Gasses), Class C (Electrical), Class D (Flammable Metals), Class K (Cooking Oils and Greases).

Certain fire classes use different fire extinguishers to extinguish fires. Read below to learn about each of the different classes and how each of them should be properly extinguished.

Class A

Class A contains ordinary combustibles. These fires often have a common flammable material as their source of fuel. The Fire Equipment Manufacturers’ Association (FEMAL) states that “wood, paper, cloth, rubber, and many plastics” fuel Class A Fires.

Water and Foam, Multipurpose Dry Chemical, Clean Agent, Water Mist, and Cartridge Operated Dry Chemical fire extinguishers all extinguish Class A fires. Water and Foam and Multipurpose Dry Chemical are the most common. Even though Clean Agent can be used, “smaller sized handheld extinguishers are not large enough to obtain a 1A rating and may carry only a Class B and C rating”. So, if you have a Clean Agent extinguisher check to make sure it is rated for Class A fires before assuming it can be used to extinguish them.

Class B

The class contains flammable liquids and gasses. FEMAL states that Class B fires are often fueled by materials “such as gasoline, petroleum gasses, tars, oils, oil-based paints, solvents, [and] alcohols”. They can also involve gasses like propane and butane.

Carbon Dioxide, Dry Chemical, Clean Agent, and Cartridge Operated Dry Chemical fire extinguishers all extinguish Class B fires.

Class C

This class contains electrical fires. FEMAL explains that they involve “energized electrical equipment such as computers, servers, monitors, transformers, and appliances. The main component of a Class C fire is the electricity that powers these devices.

Carbon Dioxide, Dry Chemical, Clean Agent, Water Mist, and Cartridge Operated Dry Chemical fire extinguishers all extinguish Class C fires.

Class D

This class contains flammable metals. This can include magnesium, titanium, zirconium, sodium, lithium, and potassium. This can be a difficult fire to extinguish because people do not often know when these metals are burning.

Many different extinguishing methods can make this type of fire worse, which makes them hazardous to fight. This makes Dry Powder fire extinguishers the recommend fire extinguisher for Class D fires.

Class K

This class contains cooking oils and greases. These types of fires often occur in commercial kitchens, but can also break out in homes.

It is important to never spray water onto a Class K fire. Because of this, Wet Chemical fire extinguishers are the recommend extinguishers. FEMAL explains that this is because they “were developed for modern, high efficiency deep fat fryers in commercial cooking operations”.

Types of Fire Extinguishers
Water and Foam

According to FEMAL, “water and foam fire extinguishers extinguish the fire by taking away the heat element of the fire triangle”. The foam portion of these extinguishers, “also separate the oxygen element from the other elements”.

Carbon Dioxide

FEMAL explains that these work by “taking away the oxygen element of the fire triangle and also be removing the heat with a very cold discharge”.

Dry Chemical

All Dry Chemical fire extinguishers interrupt a chemical reaction that occurs in the fire triangle. The most common type of fire extinguisher “is the multipurpose dry chemical that is effective on Class A, B, and C fires”. Ordinary Dry Chemical fire extinguishers are not as commonly used, but only work on Class B & C fires. If you have a Dry Chemical extinguisher it is important to note which version you have so you don’t use an Ordinary on a Class A fire.

Wet Chemical

This is a new kind of fire extinguisher. FEMAL explains that it works by, “removing the heat of the fire triangle and prevents re-ignition by creating a barrier between the oxygen and fuel elements”.

Clean Agent

These extinguishers have halon agents that are better for the ozone than previously used halocarbon agents. FEMAL says that, “they extinguish the fire by interrupting the chemical reaction and/or removing heat from the fire triangle”.

Dry Powder

FEMAL explains that this “is similar to a dry chemical except that they extinguish the fire by separating the fuel from the oxygen element or by removing the heat element of the fire triangle”.

Water Mist

These extinguishers are a new development that are an alternative to a Clean Agent extinguisher and can be used when there is a concern for contamination. FEMAL explains that they work “by taking away the heat element of the fire triangle”.

Cartridge Operated Dry Chemical

FEMAL explains, “Cartridge Operated Dry Chemical fire extinguishers extinguish the fire primarily by interrupting the chemical reaction of the fire triangle”.

-The IFS Team