“Class D” refers to fires involving combustible metals such as magnesium, titanium, and potassium. These types of fires are relatively uncommon and are typically found in industrial or laboratory settings where these metals are used or stored.
Class D fire extinguishers use dry powder agents specifically designed for the type of metal that is burning. These agents smother the fire by creating a barrier between the metal and the oxygen, which cuts off the fire’s oxygen supply. They are labeled with a “D” on them, to indicate that they are safe to use on metal fires.