How would you interpret a fire extinguisher labeled 3-A:40-B:C?

• A. It is rated for 3-A level of Class A fires, up to 40-B for Class B fires, and safe for electrical fires (C)
• B. It is rated only for Class A
• C. It is rated only for Class B
• D. It is rated for Class D and K only

Answer: (C)

Fire extinguisher ratings tell you what kinds of fires and how large a fire it can handle. The 3-A part shows effectiveness against ordinary combustibles like wood and paper. The 40-B part shows effectiveness against flammable liquids, with the number indicating the relative capacity against those fuels. The C indicates it is suitable for electrical fires, meaning it’s safe to use on energized equipment (as long as you de-energize if possible). Put together, this labeling means the extinguisher is intended for both Class A and Class B fires and is suitable for electrical fires as well. It is not limited to just one class, and it does not imply ratings for Class D or Class K.