Which extinguisher is specifically used for certain metal fires?

The potassium chloride extinguisher is specifically designed to combat fires involving certain metals, such as potassium, sodium, and magnesium. These types of fires, known as Class D fires, require specialized agents that can effectively smother and extinguish burning metals, which can react adversely with water or common extinguishing agents. Potassium chloride forms a crust over the burning material, effectively isolating it from oxygen and preventing further combustion.

In contrast, the other extinguishers listed are not suitable for metal fires. Mono ammonium phosphate and potassium phosphate extinguishers are typically used for Class A and B fires, while sodium chloride is also primarily effective on Class D fires but is not the preferred agent for certain metal types as potassium chloride is. Hence, the choice of potassium chloride stands out as the best option for responding to specific metal fires.