Fire Extinguisher Ratings
Fire extinguishers are classified by fire type. The A, B, C rating system defines the kinds of burning materials each fire extinguisher is designed to fight. The number in front of the A, B, or C indicates the rating size of fire the unit can extinguish.
Located on the fire extinguisher label is the UL rating (Fire Extinguisher Ratings). The UL rating is broken down into Class A and Class B:C ratings. These numerical ratings allow you to compare the relative extinguishing effectiveness of various fire extinguishers.
For example: An extinguisher that is rated 4A:20B:C indicates the following:
– The A rating is a water equivalency rating. Each A is equivalent to 1 1/4 gallons of water. 4A = 5 gallons of water.
– The B:C rating is equivalent to the amount of square footage that the extinguisher can cover, handled by a professional.
20B:C = 20 square feet of coverage.
– C indicates it is suitable for use on electrically energized equipment.
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When analyzing these ratings, note there is not a numerical rating for Class C or Class D fires. Class C fires are essentially either a Class A or a Class B fire involving energized electrical equipment where the fire extinguishing media must be non-conductive.
The fire extinguisher for a Class C fire should be based on the amount of the Class A or Class B component. For extinguisher use on a Class D fire, the relative effectiveness is detailed on the extinguisher nameplate for the specific combustible metal fire for which it is recommended.
Here are some fire extinguisher ratings:
- 1-A, 2-A, 3-A, 4-A, 6-A, 10-A
- 1-B, 2-B, 5-B, 10-B, 20-B, 30-B, 40-B
NOTE: For Class A fires the size test is conducted using a fire comprising an open latticework of wooden sticks approx 40mm square x 500mm long piled 14 high.
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