What type of fires can ordinary dry chemicals put out?

Ordinary dry chemical extinguishers are designed to effectively combat Class B and Class C fires.

Class B fires involve flammable liquids, such as gasoline or oil, and require extinguishing agents that can suffocate the flames or inhibit the chemical reaction that sustains the fire. Dry chemicals work by forming a barrier between the fuel and the oxygen, thereby preventing combustion.

Class C fires involve energized electrical equipment. The use of water or other conductive extinguishing materials can pose serious risks in these situations. Ordinary dry chemicals are non-conductive, making them safe to use on electrical fires. They interrupt the combustion process effectively without posing risks of shock to the user.

While some dry chemical extinguishers can be rated for Class A fires, which involve ordinary combustibles like wood and paper, the specific type referred to in the question primarily handles Classes B and C. This is why that is the correct choice, as ordinary dry chemicals are not universally effective for all fire classes, particularly Class A in some cases.