Do you know what’s in your extinguisher?


FIRE CAN OCCUR ANYWHERE AT ANYTIME. Electricians must be prepared to respond. The Occupational Safety and Health Administration (OSHA) requires an appropriate fire extinguisher be available on the job site.

In order to understand the classifications and proper use of fire extinguishers, you need to first understand something about fire and how it works. A fire is a chemical change that releases heat, light and is accompanied by flame. For a fire to start, the following three things must be present at the same time:

? Fuel—a material that is combustible or capable of catching fire and burning

? Oxygen—this gas must be present surrounding the fuel to allow the fire to burn

? Heat—a heat source to raise the fuel to its ignition temperature

If one of these components is missing, a fire either can’t ignite or will be extinguished. Fire extinguishers put out a fire by removing any one of these components. A key to the successful operation of the fire extinguisher is matching the type of fuel with the class of extinguisher. If they don’t match, it is very probable the fire will be made much worse. For example, if water is used to extinguish an oil fire, the oil may float on the water and spread the fire to other areas.

Fires are divided into the following classes according to the kind of fuel it needs:

Class AThese fires are the most common. They involve a material such as wood, clothing, rubber and plastics acting as fuel.

Class B—This type of fire uses a flammable liquid or gas as its fuel.

Class C—These fires are electric fires where the heat source of the triangle is caused by energized electrical circuits.

Class DThese fires use a metal as a fuel source. Combustible metals include magnesium, titanium, zirconium, potassium and calcium. Magnesium and titanium fires are more common.

The different types of fire extinguishers are distinguished by the chemicals used to put out the fire or extinguishing media and the way that these chemicals are expelled from the container. These two factors determine what type of extinguisher should be used on a particular fire.

Dry Chemical: These extinguishers are filled with a fine powder and pressurized by nitrogen. The fire is extinguished by coating the fuel with a thin layer of powder. This layer separates the fuel from the oxygen in the air as well as interrupting the chemical reaction of fire. This type of extinguisher is usually rated for multiple-purpose use.

Water: It is used to remove the heat on the surface of the fuel in the “Triangle of Fire.” It is the most common chemical for fighting Class A fires. These extinguishers contain water and compressed gas as well as traces of other chemicals to prevent the extinguisher from rusting.

Carbon Dioxide: These extinguishers are filled with nonflammable carbon dioxide gas under severe pressure. They extinguish the fire by moving the oxygen-rich air as well as cooling the fire somewhat. These are commonly used in laboratories and areas where flammable liquids or sensitive electrical instruments are stored or used.

Just as fires are classified as A, B, C and D, fire extinguishers, with their various extinguishing media as described above, are classified using the same lettering system. An extinguisher with the letter corresponding to the fire classification should be used to fight it. The letter or symbols will be on the extinguisher to help determine if it is to be used to fight a particular fire.

Many fire extinguishers have multiclass ratings. This means that they can be used on different types of fires. The extinguishers will be labeled accordingly. For example, “B–C” indicates it can be used on Class B or C fires.

Make sure the right fire extinguisher or extinguishers are maintained on the job site. They must be inspected monthly and have a maintenance check performed on them annually to ensure their operability. To help clarify which extinguisher type would be best suited to your needs and to learn more about fire extinguishers, consult the OSHA Web site ( For training materials, checklists and other forms to help with compliance, the NECA Safety Expert System is an excellent resource. Call 301.657.3110 or visit the NECA Store at     EC  
