Reading the Label

Every household extinguisher is labeled A, B, or C, which tells you the types of fires the extinguisher is effective against. A is ordinary combustibles like wood, paper, and cloth; B is flammable liquids, such as gasoline or cooking oil; and C is live electricity.

In the fine print on the label, these letters are preceded by numbers — for example, 3-A:40-B:C — which are the extinguisher's classification rating. The numbers, assigned by Underwriters Laboratories, tell the extinguisher's relative effectiveness against each type of fire, regardless of its weight or the chemical it uses. The higher the number, the greater the effectiveness (and likely the higher the price). So an extinguisher with a 4-A rating is more effective on ordinary combustibles than a 2-A one. The C designation carries no number; it just means the extinguisher's chemicals won't conduct electricity.

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