There are basically four different types or classes of fire
extinguishers, each of which extinguishes specific types of
fire. Newer fire extinguishers use a picture/labeling system
to designate which types of fires they are to be used on.
Older fire extinguishers are labeled with colored geometrical
shapes with letter designations. Both of these types of labels
are shown below with the description of the different classes
of extinguishers. Additionally,
Class A and Class B fire extinguishers have a numerical rating
which is based on tests conducted by Underwriter’s Laboratories
that are designed to determine the extinguishing potential
for each size and type of extinguisher. Click on any of the
topics listed below for additional information that may be
helpful to know.
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Class A Extinguishers will put out fires in ordinary combustibles,
such as wood and paper. The numerical rating for this class
of fire extinguisher refers to the amount of water the fire
extinguisher holds and the amount of fire it will extinguish.
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Class B Extinguishers should be used on fires involving flammable
liquids, such as grease, gasoline, oil, etc. The numerical
rating for this class of fire extinguisher states the approximate
number of square feet of a flammable liquid fire that a non-expert
person can expect to extinguish.
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Class C Extinguishers are suitable for use on electrically
energized fires. This class of fire extinguishers does not
have a numerical rating. The presence of the letter “C”
indicates that the extinguishing agent is non-conductive.
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Class D Extinguishers are designed for use on flammable metals
and are often specific for the type of metal in question. There
is no picture designator for Class D extinguishers. These extinguishers
generally have no rating nor are they given a multi-purpose
rating for use on other types of fires.
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Many
extinguishers available today can be used on different types
of fires and will be labeled with more than one designator,
e.g. A-B, B-C, or A-B-C. Make sure that if you have a multi-purpose
extinguisher it is properly labeled. |
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This is the new style of labeling that shows this extinguisher
may be used on Ordinary Combustibles, Flammable Liquids, or
Electrical Equipment fires. This is the new labeling style with
a diagonal red line drawn through the picture to indicate what
type of fire this extinguisher is NOT suitable for. In this
example, the fire extinguisher could be used on Ordinary Combustibles
and Flammable Liquids fires, but not for Electrical Equipment
fires. |
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Dry
Chemical extinguishers are usually rated for multiple purpose
use. They contain an extinguishing agent and use a compressed,
non-flammable gas as a propellant.
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Halon
extinguishers contain a gas that interrupts the chemical reaction
that takes place when fuels burn. These types of extinguishers
are often used to protect valuable electrical equipment since
them leave no residue to clean up. Halon extinguishers have
a limited range, usually 4 to 6 feet. The initial application
of Halon should be made at the base of the fire, even after
the flames have been extinguished.
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Water
These extinguishers contain water and compressed gas and should
only be used on Class A (ordinary combustibles) fires.
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Carbon
Dioxide (CO2) extinguishers are most effective on Class B
and C (liquids and electrical) fires. Since the gas disperses
quickly, these extinguishers are only effective from 3 to
8 feet. The carbon dioxide is stored as a compressed liquid
in the extinguisher; as it expands, it cools the surrounding
air. The cooling will often cause ice to form around the “horn”
where the gas is expelled from the extinguisher. Since the
fire could re-ignite, continue to apply the agent even after
the fire appears to be out.
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