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What Do the Numbers Mean On a Fire Extinguisher?

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.

Category: Fire Extinguishers

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Fire Pros & Fire Systems of Michigan Rated 4.9 out of 5 stars based on 3991 customer reviews

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Riser #5 high air psi.




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T.J is an excellent mechanic that knows our system and the history of problems that we experience.


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Map of Tustin, MI

Unprofessional and sloppy




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Technician left while alarm panel was still in alarm mode. When asked about it replied that it wasn’t his job. Forgot to turn on valve on dry sprinkler compressor causing system to lose pressure and activate, flooding the attic. Did not drain water in compressor.


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Map of Detroit, MI

Great service!




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Friendly, knowledgeable and prompt. Would definitely recommend to others.


good service




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George Smith was very professional and it was my first inspection he showed me what to do in case of a fire what fire extinguisher to use and what to pull if the fire extinguisher doesnt work very helpful


manager




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Robert Greenwood, has been my go to for 4yrs. His ability to supply the demand for the different projects of multiple sqft. He has been fantastic, especially when meeting the demands for inspections and service. He's just a phone call away. Thanks for the great service.


Very courteous and efficient!




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We had a blood drive going today and he made sure to wait to test the alarm until they donors were settled. He was very informative and showed me how to reset the fire pulls with a "B Key".


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We are always treated so well and our inspections are done very efficiently.


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Fast and professional service, very nice gentlemen that came to our location he was very patient during a time we was busy and couldn't assist him to the property right away.


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Ryan  F.

Ryan F.

Near Brockton Dr SE, Kentwood, MI 49512
John  R.

John R.

Near W North St, Pewamo, MI 48873
David H.

David H.

Near W North St, Pewamo, MI 48873
William S.

William S.

7- East wall: Perform a 5-year internal assessment of system piping that is due for systems #1, #3, #5, #7, #9, & #11 . If an obstruction is present, this can render the sprinkler system not properly operate in the case of a fire. The customer will provide the lift. NFPA 25 (14.2.1.1) An assessment of the internal condition of piping shall be conducted at a minimum of every 5 years or in accordance with 14.2.1.2 to inspect for the presence of foreign organic and inorganic material. 1- East wall: Perform a 5-year internal inspection of the system check valves for all 12 systems. NFPA 25 (13.4.1.2) Alarm valves and their associated strainers, filters, and restrictions orifices shall be inspected internally every 5 years unless tests indicate a greater frequency is necessary. 1- East wall: INFORMATIONAL PURPOSE ONLY: The 5-year Hydrostatic test of the FDC is due. Although, due to the inaccessibility of the check, the requirement of permits, and specialty equipment, the testing can no

Near Greenville W Dr, Greenville, MI 48838
Terrence  J.

Terrence J.

Sprinkler Survey Survey to assess FM has with heads in cooler Deficiency: Dry pin sprinkler head in cooler and the head in the freezer must be replaced with longer heads

Near Greenfield Rd, Southfield, MI 48076
Eduardo  A.

Eduardo A.

Near 44th St SW, Wyoming, MI 49519
Terrence  J.

Terrence J.

Sprinkler Inspection Annual Sprinkler Inspection (1) Wet Sprinkler System

Near Lawton St, Detroit, MI 48208
Jared J.

Jared J.

Portable Extinguishers and Industrial/Dry Chemical Suppression Inspection

Near E Grand River Ave, Howell, MI 48843
Mark S.

Mark S.

Near Church St, Ann Arbor, MI 48104
John  R.

John R.

Near Ottawa Ave, Holland, MI 49423
Art L.

Art L.

Portable Extinguishers Repair

Near Fillmore St, West Olive, MI 49460
Robert G.

Robert G.

Near Baker Rd, Dexter, MI 48130
Terrence  J.

Terrence J.

Sprinkler Inspection Annual Sprinkler Inspection (1) Wet Sprinkler System

Near Toledo St, Detroit, MI 48216
Ron  R.

Ron R.

Near Forest Creek Ct SE, Kentwood, MI 49512
Mark S.

Mark S.

Near Greenfield Rd, Berkley, MI 48072
Gary B.

Gary B.

Semi-annual Fire Extinguisher Inspection (31 FE's) Per request from Eugene Vis - Need to bring out and install (3) New Red Ridged Plastic 10# Cabinets for Outdoor Extinguishers. (2) currently have super old Cabinets and (1) is covered with a very faded Vinyl Cover Portable Extinguishers Inspection

Near Kiddville St, Belding, MI 48809
Terrence  J.

Terrence J.

Sprinkler Inspection Annual Sprinkler Inspection (1) Wet Sprinkler System

Near Clark Ave, Detroit, MI 48209
George S.

George S.

Near Dequindre St, Detroit, MI 48212
Robert G.

Robert G.

Near Dexter Ann Arbor Rd, Dexter, MI 48130
John  R.

John R.

Near Maryland Ave NE, Grand Rapids, MI 49505
Mark S.

Mark S.

Near Schoenherr Rd, Shelby Township, MI 48315
Robert G.

Robert G.

Near N Parker Rd, Dexter, MI 48130
Alex H.

Alex H.

Near S Ortonville Rd, Clarkston, MI 48348
Alex H.

Alex H.

Near S Ortonville Rd, Clarkston, MI 48348
Terrence  J.

Terrence J.

Sprinkler Inspection Annual Sprinkler Inspection (1) Wet Sprinkler System

Near W Fort St, Detroit, MI 48216