A extingushers will put out fires in ordinary combustibles, such as wood and paper. The ratings refer to the amount of water they hold, and therefore the amount of fire that they will put out.
Ratings refer to the approximate amount of fire that a non-expert operator can extinguish.
This rating simply means that the extinguishing agent is non-conductive. These extingushers generally have no rating, and are not given a multi-purpose rating for use on other types of fires. There is no picture designator for Combustible Metals. Every exingusher of this type must be clearly labeled, and if it is not, insist that the proper label be applied. This is the old style of labeling, designating suitability on Class A, B, and C fires.