Final answer:
Fires involving combustible metals like sodium, potassium, titanium, and magnesium are classified as Class D. These require special dry powder extinguishing agents and cannot be put out with water or foam.
Step-by-step explanation:
Fires resulting from combustible metals such as sodium, potassium, titanium, and magnesium are classified as Class D fires. These types of fires involve metals that can burn at high temperatures and require special extinguishing agents that do not react with the metal. Regular water or foam extinguishers cannot be used as they might exacerbate the fire. Often, a dry powder agent specifically designed for metal fires is used to smother and absorb the heat from the fire.
Magnesium, for example, is an active metal and one of the metals that fall under this category. It is known to burn with a brilliant light in forms such as powder, ribbons, and filaments. Magnesium, along with these other metals, does not react with water and oxygen as rapidly as some other metals, allowing uses in construction and various applications despite their reactive nature when exposed to flame.