Class D fire extinguishers are commonly found in a chemical laboratory and industrial settings. They are for fires that involve combustible metals, such as magnesium, titanium, potassium, and sodium. These types of extinguishers also have no numerical rating, nor are they given a multi-purpose rating - they are designed for class D fires only. This is due to the materials burning at high temperatures and will react violently with water, air, carbon dioxide, and other chemicals.