For most homes and business applications, the Fire Division recommends a fire extinguisher that is rated for the three most common types of fires (listed below). The A, B, C multi-purpose extinguishers are available at most hardware stores. Business owners will want to consult a fire extinguisher company since the rules for maintaining fire extinguishers in a business are different than in a private home.
Extinguish ordinary combustibles by cooling the material below its ignition temperature and soaking the fibers to prevent re-ignition. Use pressurized water, foam or multi-purpose (ABC-rated) dry chemical extinguishers. Do not use carbon dioxide or ordinary (BC-rated) dry chemical extinguishers on Class A fires.
Extinguish flammable liquids, greases or gases by removing the oxygen, preventing the vapors from reaching the ignition source or inhibiting the chemical chain reaction. Foam, carbon dioxide, ordinary (BC-rated) dry chemical, multi-purpose dry chemical, and halon extinguishers may be used to fight Class B fires.
Extinguish energized electrical equipment by using an extinguishing agent that is not capable of conducting electrical currents. Carbon dioxide, ordinary (BC-rated) dry chemical, multi-purpose dry chemical and halon* fire extinguishers may be used to fight Class C fires. Do not use water extinguishers on energized electrical equipment.
Extinguish combustible metals such as magnesium, titanium, potassium and sodium with dry powder extinguishing agents specially designed for the material involved. In most cases, they absorb the heat from the material, cooling it below its ignition temperature.
Note: Multipurpose (ABC-rated) chemical extinguishers leave a residue that can harm sensitive equipment, such as computers and other electronic equipment. Because of this, carbon dioxide or halon extinguishers are preferred in these instances because they leave very little residue.
ABC dry powder residue is mildly corrosive to many metals. For example, residue left over from the use of an ABC dry powder extinguisher in the same room with a piano can seriously corrode piano wires. Carbon dioxide or halon extinguishers are provided for most labs and computer areas on campuses.
How to Identify the Proper Fire Extinguisher
All ratings are shown on the extinguisher faceplate. Some extinguishers are marked with multiple ratings such as AB, BC and ABC. These extinguishers are capable of putting out more than 1 class of fire.
Class A and B extinguishers carry a numerical rating that indicates how large a fire an experienced person can safely put out with that extinguisher.
Class C extinguishers have only a letter rating to indicate that the extinguishing agent will not conduct electrical current. Class C extinguishers must also carry a Class A or B rating.
Class D extinguishers carry only a letter rating indicating their effectiveness on certain amounts of specific metals.
When using a fire extinguisher, remember the acronym, "P.A.S.S." - Point, Aim, Squeeze, and Sweep.
Remember, leave the area immediately and call 911 if:
Your path of escape be threatened
The extinguisher runs out of agent
The extinguisher proves to be ineffective
You are no longer be able to safely fight the fire