Class A Extinguishers will put out fires in
ordinary combustibles such as wood and paper. The numerical rating
refers to the amount of water the fire extinguisher holds and the
amount of fire it is designed to extinguish.
Class B Extinguishers are used on fires involving
flammable liquids like grease, gasoline, oil, etc. The numerical
rating states the approximate number of square feet of a flammable
liquid fire that can be extinguished.
Class C Extinguishers are for use on electrical
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.
Class D Extinguishers are designed for flammable
metals and are often built for a specific type of metal. These
extinguishers generally have no rating nor are they given a
multi-purpose rating for use on other types of fires.
Many extinguishers available today can be used on
different types of fires and will be labeled with more than one
designator.
Types of Fire Extinguishers
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.
Halon extinguishers contain a gas that interrupts
the chemical reaction that takes place when a fire is burning. These
types of extinguishers are often used to protect electrical equipment
because they leave no residue. The initial application of Halon should
be made at the base of the fire.
Water extinguishers contain water and compressed
gas and should only be used on Class A fires.
Carbon Dioxide (CO2) extinguishers are effective on
Class B and C fires. These extinguishers are only effective from 3 to
8 feet. The carbon dioxide is stored as a compressed liquid in the
extinguisher. When released, it expands and cools the surrounding air.
The cooling will often cause ice to form around the nozzle where the
gas is discharged.