Which type of fire is a B:C extinguisher not effective against?

A B:C fire extinguisher is specifically designed to combat fires involving flammable liquids and electrical fires. The "B" class indicates its effectiveness against flammable liquids, such as gasoline, oil, and paints, while the "C" class denotes its suitability for electrical fires, meaning it can be used safely on live electrical equipment without risking electrocution.

However, this type of extinguisher is not effective against fires in combustible metals, which fall under Class D. Combustible metals such as magnesium, titanium, and sodium react violently to water and other common extinguishing agents. Therefore, for fires involving combustible metals, specialized extinguishing agents are required that are specifically designed to handle that type of material, which is why a B:C extinguisher would not be effective in that scenario.