ABC extinguisher

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fire extinguishers

Extinguishers that are effective on one kind of burning material don't necessarily work well on another. To indicate the kinds of fire for which an extinguisher is suitable, it will usually be labeled with an Underwriters Laboratory (UL) rating using the code letters A, B, C, or D.

Class A
Burning wood, paper, cloth, and other everyday materials. Enough water can extinguish such fires.
Class B
Burning liquids, such as kitchen grease, gasoline, oil, and other flammable liquids. Putting water on such fires may simply spread them.
Class C
Fires involving electrical equipment. Spraying such a fire with water might not be a good idea.
Class D
Burning combustible metals, such as magnesium and sodium. This is not a problem in the home; D-class extinguishers are special items.

The code letters A and B are prefixed with numbers indicating the relative size of the fire the extinguisher can out out. For example, a 2-A extinguisher could put out a paper fire twice the size of the biggest fire a 1-A extinguisher could handle.

The UL ratings capture almost everything one needs to know about the extinguisher. The one exception is the extent of the damage done by the extinguisher itself. Most modern extinguishers spray powder, in many cases baking soda, in others ammonium phosphate. In most situations if the powder is promptly cleaned up afterwards no harm is done. But if the powder gets into a computer or other electronic gear, the equipment will probably be ruined. Halon extinguishers, formerly used for fighting fires in such circumstances, are no longer allowed except for very special circumstances (airplane cockpits), because Halon is a fluorocarbon that destroys the ozone layer. A carbon dioxide extinguisher might be a useful compromise.

A good size for each floor of a home is a 3-A:40-B:C, unless residents are too frail to use one this heavy (eight to ten pounds). The kitchen needs a small extinguisher of its own, one specifically designed for grease fires (that is, no A rating is needed). Inexpensive 5-B:C models are sold.

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