Final answer:
Fires involving combustible metals and highly reactive flammables are classified as Class D fires, which require special extinguishing agents to safely manage. These materials include alkali metals, some alkaline earth metals, and certain metal powders or shavings, which are highly reactive and may ignite spontaneously.
Step-by-step explanation:
Fire involving combustible metals and highly reactive flammables is classified as a Class D fire. These fires are unique because they involve substances such as metallic alkali metals (e.g., lithium, potassium, sodium) and some alkaline earth metals (e.g., magnesium, calcium) which require special extinguishing agents that do not react with the burning metal. Class D fires also include combustible metal powders, shavings, and flakes.
Metals, in particular, have a high temperature of combustion and can react explosively with water. Combustible metals also possess a high level of metallic character, meaning they tend to lose electrons and ignite more readily. As the most reactive metals are found in the lower left portion of the periodic table, metals like cesium and francium are extremely reactive and can combust spontaneously in air.
Oxidizing chemicals, like potassium dichromate, can further exacerbate these fires by providing additional oxygen, supporting the combustion of other materials. Additionally, waste materials such as used solvents with low flash points or ignitable compressed gases can also be a source of Class D fires.
Precautions must be taken to handle these materials safely, including following strict instructions on the handling of flammable chemicals to prevent incidents. It's also important to be aware that fireworks, which often incorporate metal salts from alkali and transition metals like iron, copper, and strontium, can be another source of Class D fires.