Which type of fire extinguisher is generally used for combustible metals?

The correct choice is a Class D fire extinguisher, which is specifically designed for fires involving combustible metals such as magnesium, titanium, sodium, and potassium. These metals can ignite and burn at extremely high temperatures, and standard extinguishing agents may exacerbate the fire or react violently with the burning metal.

Class D extinguishers contain agents like dry powder that effectively smother the metal fire without reacting with the burning material, effectively preventing the fire from spreading and allowing for safe suppression. Ordinary extinguishers designed for other classes of fire would not be effective and could potentially make the situation worse, emphasizing the necessity of using the correct extinguisher for its intended purpose.