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What Do the Numbers Mean On a Fire Extinguisher?

Posted on: April 20, 2017

When it’s time to purchase fire extinguishers for your business, you may be confused by the different letters and numbers on the label. To ensure you buy the right type and size for the application you have in mind, learn more about fire extinguisher classes and size ratings.

Fire Extinguisher Classes

The letter on a fire extinguisher indicates its classification:

  • Class A puts out ordinary combustible fires (wood, paper, plastic, etc.)
  • Class B puts out flammable liquid fires (oil, gas, petroleum, etc.)
  • Class C puts out electrical fires
  • Class D puts out combustible metal fires (magnesium, titanium, potassium, sodium, etc.)
  • Class K puts out cooking fires ignited by flammable oil and grease

Since Class A, B, and C fires are all found in conventional homes and businesses, ABC fire extinguishers are designed to put out all three types of fires.

Fire Extinguisher Size Ratings

You might come across a fire extinguisher labeled 4A:20B: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. 20B means that as long as you sweep the nozzle side to side, there is enough extinguishing agent inside the canister to provide 20 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.

Get Help Purchasing the Right Fire Extinguishers

Let Guardian Fire Protection assist you in selecting code-compliant fire extinguishers for your business. We can advise particular types and sizes based on your building’s square footage and fire risks. For the help you need, please contact us today. We have over 40 years of experience helping Maryland, DC, and Virginia business owners achieve optimal fire safety and code compliance.

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