What is the fire extinguisher rating for units that are classified as 4-A:20-B:C?

The correct answer relates to the fire extinguisher rating system, which categorizes extinguishers based on their effectiveness against different types of fires. The classification "4-A:20-B:C" indicates the performance characteristics of that particular extinguisher.

The "4-A" rating signifies that the unit is suitable for extinguishing Class A fires, which involve ordinary combustibles such as wood, paper, and textiles. The number "20" in the "20-B" portion indicates the extinguisher is effective for Class B fires, which involve flammable liquids like gasoline or oils, at least equivalent to 20 square feet of burning material. The "C" signifies that the extinguisher can be used on electrical fires, but it does not correspond to an additional numerical rating since the effectiveness against electrical fires is generally universal for other ratings provided.

This context elaborates that "4-A" is indeed the fire extinguisher's primary classification for its ability to handle Class A fires. Thus, "4-A" accurately reflects the specific capability against a broader category of fires compared to the other ratings presented in the options.