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Green Valley Fire District (GVFD):
Learn All About Fire Extinguishers
Knowing about the Fire Triangle helps to understand how a fire extinguisher works. The Fire Triangle represents the three ingredients necessary to have fire: Fuel, Oxygen, and Heat (also known as an ignition source). By removing heat, oxygen or fuel, a fire extinguisher can extinguish a fire. The chart shows the different type of fire extinguishers. Type ABC will extinguish most household fires. Type C for electrical fires. For metal fires, a Class D is recommended but check to be sure the metal you work with can be extinguished by a Class D fire extinguisher.
Let us examine how each agent in the fire triangle is addressed by each class of extinguishers.
Class A: Contains pressurized water. Water addresses the heat and oxygen components of the fire triangle. Water cools the fire (heat) and simultaneously smothers the (oxygen) supply to the fire.
Class B: Contains carbon dioxide. Carbon dioxide removes oxygen, suffocating fire. Class B can be used on flammable liquids such as alcohol, ether, oil and grease and gasoline. Note only use Class B for flammable gas fires if the source of the gas can be turned off.
Class C: Contain dry chemicals that suffocate a fire (remove oxygen) are the only safe extinguishers for electrical fires. Water and foam conduct electricity and should never be used for electrical fires as these agents can electrocute the fire fighter.
Class ABC: These contain dry powders that will suffocate fire (remove oxygen) and are safe for Type A, B and C fires. Thus, they are generally indicated for most households.
Class D: Specifically for metals. They are powders that absorb heat and cut off oxygen. They are specifically recommended for metal fires, with some exceptions. If working with metals check to see what extinguisher is recommended for the specific metal.
Class K: These contain alkaline mixtures that turn into soapy foams when in contact with fats and oils. The foam will extinguish the fire by preventing release of vapors and steam. These extinguishers are often used in commercial kitchens with higher risks of flammable liquid fires, such as a deep fryer.
A special note: Never use water on a grease/oil fire or any flammable liquids. Water is not only ineffective for flammable liquids but may also cause the fire to spread. Never use water on an electrical fire as this poses a risk of electrocution. Electrical currents can spread into the ground and travel into a water stream such a hose. This can cause electrocution to the person putting out a fire with the hose. Never use water for a metal fire as there could be an adverse outcome, or the type of metal fire may have a chemical reaction to water.
Think “PASS” when using an extinguisher:
P: Pull the pin. This unlocks the lever.
A: Aim by pointing the nozzle/extinguisher at the base of the fire.
S: Squeeze the lever (or press button for some extinguishers) to release the extinguishing agent.
S: Sweep from side to side. Continue to aim at the base of the fire while sweeping back and forth. Move carefully toward the fire sweeping and aiming at the base.