1 Fire Extinguisher Classes

#66 – Ultimate Guide to
Fire Extinguisher Classes:
Servicing and Use
June 8, 2017
All portable fire extinguishers can
stop small fires before they get out of
hand, but each extinguisher is
specifically suited to only some types
of fires

Portable fire extinguishers defend homes, offices, and commercial
buildings everywhere against fires. But not all fires and their fuel sources
are alike. An extinguisher that doesn’t match the type of fire or doesn’t
have enough power may do nothing at all—or make things even worse.
In this article, we take a look at fire classifications and fire extinguisher
classes, explaining which extinguishers are best suited to a particular
type of fire. Then, we provide an overview of fire extinguisher inspection
and help you better understand the basics of purchasing an extinguisher
to fit your building’s needs.
Need to shop for an extinguisher now? Feel free to click here to view our
selection of fire extinguishers.
How many fire classifications are
there and what are they?
Fire classifications simplify the task of matching a fire extinguisher to the
expected type of fire. Water, for example, performs well against fires
involving wood or plastics—but it would spread fires burning grease or
gasoline.
In the United States, fires belong to one of five fire classifications:
 Class A Fire: Ordinary combustibles such as wood, paper,
cloth, trash, and plastics.
 Class B Fire: Flammable liquids (excluding grease and
cooking oils) like gasoline, petroleum, oil, and paint. Also
includes gasses, like propane and butane.
 Class C Fire: Energized electrical equipment like appliances,
transformers, and motors. The electricity source must be
turned off to aid extinguishing efforts.

 Class D Fire: Combustible metals like titanium, magnesium,
aluminum, potassium, sodium, and others.
 Class K Fire: Animal and vegetable fats, cooking oils and
greases, and other liquids generally used in food preparation.
In some cases, a fire may belong to two, three, or even more of these
classes—in the end, a fire’s class is determined by a mix of the fire’s fuel
source and other special hazards that emerge as the material burns.
How does a fire extinguisher work
and how should it be used?
Any fire has three essential elements:
 Extreme heat
 Oxygen (or another type of gas)
 Fuel—the burning material
A fire stops burning when any one of these elements is removed. The
relationship between these factors is often visualized as a “fire triangle”
(pictured below). But while it’s the easiest to visualize, the fire triangle
has been largely replaced by the fire tetrahedron. The tetrahedron adds
one more element: chain reactions, which create a gaseous fuel that
sustains fires.

The “fire triangle” illustrates the elements needed for a fire to ignite.
Removing any one of these three elements stops the fire from burning.
Image source: Wikipedia.
Some extinguishing agents smother the fire, depriving it of oxygen.
Others cool the burning material, removing heat. All fire extinguishers
are similar in the sense that they deprive the fire of one or more of these
elements. But not all extinguishers are effective against the same fires.
Some can’t penetrate deeply enough to stop fires in ordinary
combustibles, for example, while others can’t stop fires in flammable
liquids—and can even spread the fire.

What are the types of fire
extinguishers and their uses?
Most fire extinguishers operate in a fashion similar to an aerosol can. The
tank contains compressed gas, pressurized liquid, or a combination of
the two with an added extinguishing agent. Squeezing the fire
extinguisher’s lever creates an opening that allows the compressed
material to escape through a nozzle or short hose.
But beyond those mechanical similarities, fire extinguishers vary widely.
There are at least eight types of fire extinguishers:
Carbon Dioxide (CO2)
Carbon dioxide extinguishers are Class B and Class C fire extinguishers.
They remove the oxygen from the fire triangle and infuse a cold
discharge to cool the fire. Unlike water or some other extinguishing
agents, CO2 does not conduct electricity, making it especially well-suited
for electrical (Class C) fires.