There are four basic 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 displaying a letter designation.
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 of each size and type of extinguisher.
Fire Extinguisher Ratings:
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 of 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 extinguisher 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 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.
Multi-Class Ratings:
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.
Types of Fire Extinguishers:
Dry Chemical extinguishers are usually rated for multi-purpose uses. They contain an extinguishing agent and use a compressed, non-flammable gas as a propellant.
Halon extinguishers contain 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 to 6 feet. The initial application of Halon should be made at the base of the fire, even after the flames have been extinguished.
Water 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 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 reignite, continue to apply the agent even after the fire appears to be out.
How to Use a Fire Extinguisher:
Even though extinguishers come in a number of shapes and sizes, they all operate in a similar manner. Here is an easy acronym for fire extinguisher use:
P A S S = Pull, Aim, Squeeze, and Sweep:
Pull the pin at the top of the extinguisher that keeps handle from being accidentally pressed. (Note: a common mistake when pulling the pin is to be squeezing the handle, which puts pressure on the pin and won’t allow it to come out.)
Aim the nozzle toward the base of the fire.
Stand approximately 8 feet away from the fire and squeeze the handle to discharge the extinguisher. If you release the handle, the discharge will stop.
Sweep the nozzle back and forth at the base of the fire. After the fire appears to be out, watch it carefully, it may reignite!
Congratulations -- You did it !!!
Contact OMAG Loss Control Services if you have questions or suggestions for other topics related to Municipal Workplace Safety Issues. 1 (800) 234-9461 or email: kprichard@omag.org.
