Which type of dry chemical extinguisher is effective against both Class B and C fires?

The multi-purpose dry chemical extinguisher is effective against both Class B (flammable liquids such as gasoline, oil, and grease) and Class C (electrical fires) fires due to its formulation. This type of extinguisher typically uses an agent such as monoammonium phosphate, which is effective at interrupting the chemical reaction of a fire.

In a Class B fire, the multi-purpose dry chemical can smother the flames and prevent re-ignition by covering the surface of the flammable liquid. For Class C fires, the extinguisher works by displacing the oxygen and effectively cooling the fuel source, while being safe to use because it is non-conductive, thereby preventing any risk of electric shock.

Options like regular dry chemical extinguishers may not always specify effectiveness against electrical fires, limiting their use, while foam extinguishers are mainly designed for Class B fires and are not suitable for electrical fires. Water extinguishers, on the other hand, are ineffective for either Class B or C fires, as water can spread flammable liquids and can conduct electricity, posing a serious safety risk.