B-I and B-II refer to the relative fire extinguishing capacity of approved USCG fire extinguishers, depending upon the type of extinguishing agent used.
Class B fires involve flammable or combustible liquids such as gasoline, kerosene, grease and oil.
The numerical rating BEFORE the letter B, for 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) AFTER the letter B indicates Coast Guard classification. For example, a UL 5-B:C, rated for 5 sq ft of 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.
USCG ratings go as high as V, which is a big extinguisher on wheels.
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