What do B-1 B-2 or B-3 on a fire extinguisher mean?

Answer 1

B-number ratings are used by the US Coast Guard regulations to identify the necessary capacity of a fire extinguisher, depending upon the type of extinguishing agent used. Only extinguishers meet all USCG requirements can say "USCG approved".

Class B fires involve flammable or combustible liquids such as gasoline, kerosene, grease and oil.

The numerical rating BEFORE the letter B, for UL ratings of class B extinguishers, indicates the approximate number of square feet of fire it can extinguish (i.e., with no significant depth).

The numerical rating (I, II, III, IV, V) AFTER the letter B indicates Coast Guard classification. For example, a UL 5-B:C, rated for 5 sq ft of flammable liquid fire, would be a USCG B-I extinguisher (with 2 pounds of dry chemical).

To obtain a USCG B-II rating you would need the equivalent of 10 pounds of dry chemical, such as having two UL 3-A, 40-B:C extinguishers, or a 15-pound CO2 extinguisher, or 2 1/2 gallons of AFFF "foam" (UL 3-A:20B).

A 20-pound dry-chemical (120-B:C) would meet USCG B-III requirements, 30 pounds for B-IV and 50 pounds for B-V. Similarly, carbon-dioxide or foam-type extinguishers of various capacities fall within USCG ratings (e.g. 4 pounds CO2 for B-I, 15 pounds for B-II, etc).