<P> In Europe, "electrical fires" are no longer recognized as a separate class of fire as electricity itself cannot burn . The items around the electrical sources may burn . By turning the electrical source off, the fire can be fought by one of the other class of fire extinguishers . </P> <P> Class D fires involve combustible metals - especially alkali metals like lithium and potassium, alkaline earth metals such as magnesium, and group 4 elements such as titanium and zirconium . </P> <P> Metal fires represent a unique hazard because people are often not aware of the characteristics of these fires and are not properly prepared to fight them . Therefore, even a small metal fire can spread and become a larger fire in the surrounding ordinary combustible materials . Certain metals burn in contact with air or water (for example, sodium), which exaggerate this risk . Generally speaking, masses of combustible metals do not represent great fire risks because heat is conducted away from hot spots so efficiently that the heat of combustion cannot be maintained . In consequence, significant heat energy is required to ignite a contiguous mass of combustible metal . Generally, metal fires are a hazard when the metal is in the form of sawdust, machine shavings or other metal "fines", which combust more rapidly than larger blocks . Metal fires can be ignited by the same ignition sources that would start other common fires . </P> <P> Care must be taken when extinguishing metal fires . Water and other common firefighting agents can excite metal fires and make them worse . The National Fire Protection Association recommends that metal fires be fought with dry powder extinguishing agents that work by smothering and heat absorption . The most common agents are sodium chloride granules and graphite powder . In recent years, powdered copper has also come into use . These dry powder extinguishers should not be confused with those that contain dry chemical agents . The two are not the same, and only dry powder should be used to extinguish a metal fire . Using a dry chemical extinguisher in error, in place of dry powder, can be ineffective or actually increase the intensity of a metal fire . </P>

What type of fire can plain water be used on