What does the UL rating for a fire extinguisher indicate?

Answer 1

In short, the UL rating indicates the fire type and approximate size fire the extinguisher is rated for.

The letters indicate fire type and number, if present (usually for type A and B) indicate fire size. Any number associated with the letter B is based on approximate square footage. The number with A is a bit more technical, but suffice it to say, that a 2A extinguisher has twice the extinguishing potential as a 1A.

Letters are as follows:

A - Suitable to extinguish Class A Fires, involving wood, paper, trash, etc...

B - Suitable to extinguish Class B Fires, involving flammable liquids and even gases,

C - Suitable for extinguish Class C Fires, or fires involving energized electrical equipment.

D - Suitable for Class D fires, or fires involving flammable metals.

K - Suitable for Kitchen releated grease fires (and has a compatibility with fixed fire suppression systems for kitchen hoods.)

For more information about the different types and classifications of fire extinguishers, try the following link...

Answer 2

Class A and B fire extinguishers have a numerical rating based on tests conducted by UL (Underwriter’s Laboratories). 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 gal. of water.
The B:C rating is equivalent to the area (square footage) that, related to the degree of training and experience of the operator, the extinguisher can cover. 20 B:C=20 square feet of coverage.
C indicates it is suitable for use on electrically energized equipment.
When analyzing these ratings, note that there is not a numerical rating for Class C or Class D fires. Class C fires are essentially either a Class A or Class B fire involving energized electrical equipment where the fire extinguishing material must be nonconductive. 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.