What Is Coal Ash and How Dangerous Is It?

What Is Coal Ash and How Dangerous Is It? Coal ash refers to the hazardous byproducts of coal combustion at coal-based power plants — namely, fly ash, bottom ash, and boiler slag — which contain toxic materials such as arsenic and lead. It is a highly controversial type of industrial waste, given that the U.S. Environmental Protection Agency (EPA) didn’t begin regulating its disposal until 2015. In its natural state, coal is mildly hazardous. It can emit fine particulate pollution when sitting uncovered in stockpiles or being transported by trains, especially during windy weather conditions. But when coal is combusted or burned — such as in a power plant, when coal is burned in a boiler; heat from the furnace converts boiler water to steam; and the steam spins turbines to turn generators — it releases a hazardous brew of toxic pollutants into the air, including: - sulfur dioxide (SO2), which contributes to acid rain and respiratory illnesses, - nitrogen oxides (NOx), which contribute to smog a