What is a fire extinguisher?

Fire extinguisher classes are based on the types of fires they can fight. The classes actually refer to different kinds of fires, rather than to the fire extinguisher itself.

The most common fire extinguisher type is ABC—meant to fight fires of classes A, B, and C.

“[The ABC fire extinguisher] is a combination-type fire extinguisher, and that’s typically what you find in a home,” says retired professional firefighter and CSIA President Chuck Roydhouse.

BC fire extinguishers (without the A) are also available for home use.

Aside from the fire extinguisher classes, they also come in varied sizes, denoted by the weight.

“10-pound fire extinguishers are great for home workshops or garages,” says Roydhouse. “5-pound fire extinguishers are great for kitchens and laundry rooms, and 2-pound fire extinguishers are great for keeping in your car.”

Here are the different classifications of fire:

Class A

Fires fuelled by ordinary combustibles such as paper, wood, cloth, or plastic. Water and chemical suppressants (wet or powder) can extinguish Class A fires.

Class B

Fuelled by flammable liquids or gases, such as gasoline, petroleum oil, or propane. You should never use water to put out a Class B fire, as the water will spread the fuel source and thus, the fire. Dry chemical suppressants or CO2 are effective ways to fight Class B fires.

Class C

Fires involving electronic equipment. Any other class of fire that involves electronic equipment can also be a Class C fire. These fires are best fought with dry chemical or CO2 suppressants, as water can conduct electricity from the fire through the body of the person holding the fire extinguisher, causing serious injury.

Class D

Fires involving combustible metals like lithium, potassium, or magnesium.

According to Roydhouse, Class D fires aren’t particularly common in home settings.

“You’ll usually only find these in different sheet metal shops,” says Roydhouse. “If you put regular water on the [metal] fire, it burns so hot that it pulls the oxygen out of the water and burns the water to basically pure oxygen. It will explode like a flashbulb going off in your face.”

Needless to say, Class D fires aren’t as straightforward as Classes A-through-C.

“For these situations,” says Roydhouse, “there’s a special fire extinguisher called MET-L-X, which uses what looks like graphite or pencil shavings to form a shell over the fire. If you were to have a metal fire outside, you could also cover it with dirt.”

Class D fires usually require specialist intervention, but fortunately you’re unlikely to experience one at home.

Class K

Fires involving cooking oils and fats. Generally, that means kitchen fires. These are similar to Class B fires, but their unique qualities get them a separate rating. You should never use water to extinguish a Class K fire, as water can spread out the fuel source and make it much more dangerous. Class K extinguishers (or other equipment like fire blankets) are the best way to put out a Class K fire.

A note about Class K fires:

Although your kitchen is one of the places in your house most prone to fires, you may not actually need a Class K extinguisher; they’re designed for commercial kitchens. An ABC fire extinguisher (combined with good kitchen fire safety practices) should be enough for your home kitchen.

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