What is a Class B Fire – the best suited Fire Extinguisher?

6 December 2022 in Building

What is a Class B Fire – the best suited Fire Extinguisher?

Life and property can depend on the use of the correct fire extinguisher on a fire. This is especially true when fires include flammable liquids. These are called Class B fires.

In this blog you will learn what constitutes a Class B fire, what types of extinguishers are Class B fire extinguishers, and better understand what they can be used for.

What Are Class B Fires?

Class B fires are ones where flammable liquids and/or gases are involved. They are the fuel source in the fire triangle (fuel, heat, oxygen + chemical reaction).

Flammable liquids include petrol, diesel, oils, tars, greases, solvents, alcohols, and oil-based paints. Flammable gases include things like hydrogen, and butane.

The fuel sources of class B fires (gases and liquids) can be volatile and cannot be extinguished by water, which will only make the fuel source spread. That is why it is important only to use extinguishing agents and methods designed specifically for Class B fires.

What Types of Extinguishers are Rated as Class B Fire Extinguishers?

Due to the nature of the Class B fires’ fuel, the best way to extinguish this type of fire is to separate the fuel from its oxygen supply.

There are a variety of fire extinguisher types designed to accomplish this very task specifically on Class B fires:

CO2: A carbon dioxide fire extinguisher works on a Class B fire by expelling CO2 to suffocate the fire, removing the oxygen necessary to keep it burning. It also helps with removing the heat, as the discharge is very cold.

However, note that due to how quickly the CO2 gas disperses, this extinguisher is only effective at a relatively close range.

Foam: These extinguishers work on both Class A and B fires. The foam agent works on Class B fires by separating the fuel and the oxygen by creating a seal on the surface of the flammable liquid. However, these extinguishers will only be effective when the flammable liquid is not free-flowing.

Dry Chemical: Dry chemical extinguishers, whether regular or multipurpose models are classified for B fires as their agent extinguishes a fire by interrupting the chemical reaction of the fire triangle. These extinguishers have a better range, as they use a compressed, non-flammable gas that can propel the dry extinguishing agent further.

Clean Agent: A clean agent extinguisher uses an extinguishing agent that works by interrupting the chemical reaction of a fire and/or removing the heat, and is effective on Class B and C fires, and sometimes class A fires (depending on the size of the extinguisher).

They are called “clean” agents, as they rely on halogen and halocarbon agents that are safer for people and the environment and do not require the same level of clean up after use.

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