Fires involving metals like sodium and magnesium are classified as:

Fires involving metals such as sodium and magnesium are classified as Class D fires. These types of fires involve combustible metals that react with water and can burn at extremely high temperatures. Class D fire extinguishing agents are specifically designed to put out these fires without causing a reaction that could exacerbate the situation.

Understanding the classification of fires is crucial for firefighting, as it determines the appropriate firefighting method and extinguishing agents to be used. For instance, water is effective on Class A fires (involving ordinary combustibles) but can be dangerous and inappropriate for Class D fires due to the potential for explosive reactions. This knowledge ensures the safety and effectiveness of firefighting efforts.