Literally, ash that flies. Fly ash consists of fine particles of ash created as a byproduct of the combustion of solid fuels such as coal and garbage. This fine material is prevented from escaping into the atmosphere using devices called electrostatic precipitators. Once collected by the precipitator, the ash can be reused in materials ranging from roofing and concrete paving to oil well casings.

Fly ash created by generating plants is similar to airborne ash produced by volcanoes and forest fires, and consists mostly of carbon. However, when generating plants produce fly ash, they tend to produce it continuously over long periods of time, and the production of this ash typically occurs in or near densely-populated areas, which is not the case with volcanic or forest fire ash.

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