Fire Extinguishers

There are basically four different types or classes of fire extinguishers, each of which extinguishes specific types of fire.

• 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 fuels burn.  These types of extinguishers are often used to protect valuable electrical equipment since they leave no residue to clean up.  Halon extinguishers have a limited range, usually 4 - 6 feet.
• Water These extinguishers contain water and compressed gas and should only be used on Class A (ordinary combustibles) fires.
• 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 - 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-0ignite, continue to apply the agent even after the fire appears to be out.

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 Underwriters Laboratories that are designed to determine the extinguishing potential for each size and type of extinguisher.

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.     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.     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.       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.

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.