Fire Classes 5
Fire Classes 5 : Metal: Certain metals are flammable or combustible. Fires involving such are designated "Class D" in both systems. Examples of such metals include sodium, titanium, magnesium, potassium, uranium, lithium, plutonium, andcalcium. Magnesium and titanium fires are common. When one of these combustible metals ignites, it can easily and rapidly spread to surrounding ordinary combustible materials. With the exception of the metals that burn in contact with air or water (for example, sodium), masses of combustible metals do not represent unusual fire risks because they have the ability to conduct heat away from hot spots so efficiently that the heat of combustion cannot be maintained - this means that it will require a lot of heat to ignite a mass of combustible metal. Generally, metal fire risks exist when sawdust, machine shavings and other metal 'fines' are present. Generally, these fires can be ignited by the same types of ignition sources that would start other common fires. Water and other common firefighting materials can excite metal fires and make them worse. The NFPA recommends that metal fires be fought with "dry powder" extinguishing agents. Dry powder agents work by smothering and heat absorption. The most common of these agents are sodium chloride granules and graphite powder. In recent years powdered copperhas also come into use. Some extinguishers are labeled as containing dry chemical extinguishing agents. This may be confused with dry powder. The two are not the same. Using one of these extinguishers in error, in place of dry powder, can be ineffective or actually increase the intensity of a metal fire. 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
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