Fire Extinguisher Guide

Part 2: Fire Extinguisher Classes/Ratings

The following symbols and/or letters should be visible on the fire extinguisher label. They indicate which type of fire the extinguisher should be used on. All new fire extinguishers will use the larger symbols below as opposed to the previous style (a letter in a colored shape) shown next to each class name.

Class A – Ordinary Combustibles
(Wood, Paper, Cloth, etc.)

Fires whose fuel is paper, wood, cloth or other ordinary combustibles (not liquid, electric, or metallic) would be classified as an ‘A’ fire. Most fires we encounter are class ‘A’ fires. Since they are the most common, the majority of fire extinguishers can extinguish a class ‘A’ fire. Class ‘A’ fires can either be smothered or drowned to extinguish them. Look for an extinguisher with the symbol to the left if you need to extinguish a class ‘A’ fire.

Class B – Burning Liquids/Gases
(Gasoline, Cooking Fats, Oils, etc.)

Fires fueled by liquid (not ordinary, electric, or metallic) combustibles like gasoline, kerosene, propane, cooking fats, and oils would be classified as a ‘B’ fire. To extinguish a class ‘B’ fire, either physical or chemical smothering must occur. DO NOT throw water on a class ‘B’ fire as it will not extinguish the fire and often will cause the burning liquid to splash. Look for an extinguisher with the symbol to the left if you need to extinguish a class ‘B’ fire.

Class C – Live Electrical Equipment
(Motors, Appliances, Switches, etc.)

Fires ignited by live electrical equipment (not ordinary, liquid, or metallic) such as computers, appliances, and switches are classified as a ‘C’ fire. Class ‘C’ fires must be smothered. NEVER use water or other liquids that might serve as a conductor for electricity. Look for an extinguisher with the symbol to the left if you need to extinguish a class ‘C’ fire.

Class D – Combustible Metals
(Magnesium, Lithium, etc.)

Fires fueled by combustible metals like magnesium and lithium (not ordinary, liquid or electrical) are different enough to receive their own classification, class ‘D’. Look for an extinguisher with the symbol to the left if you need to extinguish a class ‘D’ fire.

Class K – Cooking Materials
(Cooking oils/fats/grease)

This is a newer classification of fire. Class ‘K’ extinguishers are specifically designed to supplement fire suppression systems in kitchens. These extinguishers are designed for cooking oil, fat, and grease fires. Look for the letter ‘K’ symbol or the symbol to the left if you need to extinguish a class ‘K’ fire.

Multi-Class – Combinations of the classes above.

What if your fire is gasoline (class B) soaked rags (Class A) or what if you have a live electric wire (class C) igniting magnesium (class D). Many scenarios exist for multi-class fires to exist. Which fire extinguisher should you use? Is it necessary to maintain five different extinguishers? You can, but it is not necessary. The majority of extinguishers can take care of multiple classes of fires. Most common extinguishers can handle A, B, and C class fires but remember to always check the label first before use. Class ‘D’ and Class ‘K’ are for less common applications and are not likely to be combined with other fire extinguisher classes.

Up Next: Fire Extinguisher Types