According to reports, a reaction in a meltshop furnace at AK Steel Works in Butler County, Pa., yesterday caused an explosion that sent an employee to a hospital with non-life-threatening injuries. A second employee was treated on-site for minor injuries. The impact also blew part of the roof off the building.

The cause of the incident is being investigated by AK Steel. The type of furnace that exploded was an electric-arc furnace that has a capacity of 175 tons and reaches temperatures of more than 3000°F.

AK Steel’s Butler Works performs electrical and stainless steel melting and casting, hot and cold rolling, and finishing operations.