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A material that is pyrophoric will spontaneously combust at normal temperatures. Substances are pyrophoric when their autoignition point is extremely low, allowing them to start burning in regular air. Some of these materials will also ignite in water, occasionally triggering remarkably explosive reactions. Special precautions need to be observed when handling such materials to reduce the risk of spontaneous ignition and potential injury or damage.
Solids, gases, and liquids such as potassium, phosphine, sodium, phosphorous, uranium, and iron sulfide can all be pyrophoric. In some cases, the ignition can be triggered by division of the substance, as for example when someone cuts uranium into thin slices or rubs iron sulfide to create fine particles. In other instances, the material simply combusts while it is in an inert state. Pyrophoricity can also cause materials to appear to glow or smolder.
Depending on the material, various safety precautions need to be observed when working with pyrophoric substances, ranging from avoiding temperatures that can lead to ignition to working in an environment filled with inert gases like argon. Since humans cannot survive in such environments, supportive breathing apparatus is needed in these situations. Special fire extinguishers are required to put out fires created by pyrophoric materials.
In laboratories and industries where people handle materials which can spontaneously ignite, specific protocols are typically developed for each substance. These guidelines depend on the conditions under which the substance will ignite, and the risk of spontaneous combustion. Typically, personnel need to wear protective garments to make risk of physical injury less likely, and safety measures such as fume hoods and specialized tools are also available. It is also important to observe precautions when disposing of such materials.
Individuals who work in environments where such materials are handled should make sure that they are aware of all of the safety precautions. Even a laboratory technician or a janitor is at risk of serious injury or death if he or she is not aware of what to do, and training should be provided as part of the job. If such training is not provided, it should be requested, and the lack of proper preparation should be reported to the organization or official responsible for overseeing safety.
These materials do have practical applications. For example, pyrophoric metals are used in lighters to create a spark; users make the spark by striking the metal to create particles, encouraging it to spontaneously ignite. The spark in turn fuels a flame which is sustained by a flammable liquid inside the lighter. Flint and steel also relies on pyrophoric properties, in this case making a spark which is used to ignite something such as a fire.