You might come across a fire extinguisher labeled 2A:10B:C. The numbers indicate the size rating of each extinguishing agent. Here’s how it works…

The Class A size rating represents the water equivalency. Each number represents 1 ¼ gallons of water. For instance, 2A means the extinguisher is just as effective as 2 ½ gallons of water. 4A is equivalent to 5 gallons of water.

The Class B size rating indicates the square footage the extinguisher can cover. 10B means that as long as you sweep the nozzle side to side, there is enough extinguishing agent inside the canister to provide 10 square feet of coverage.

There is no size rating for Class C. After all, a Class C electrical fire is nothing more than a Class A or Class B fire with energized components requiring a non-conductive extinguishing medium. To effectively fight Class C fires, choose your extinguishers based on the Class A and Class B size ratings.

There is also no size rating for Class D fires. The effectiveness is detailed on the nameplate based on the specific combustible metal for which the extinguisher is recommended.