A person was killed and multiple others were injured after an explosion at a coke plant near Pittsburgh, Pennsylvania, police said. Two people remain missing after the explosion at about 11am local time at the Clairton Coke Works plant, which is owned by US Steel, a subsidiary of Nippon Steel. Coke is produced by heating coal at high temperatures and the process creates a lethal mix of methane, carbon dioxide and carbon monoxide. It is used in blast furnaces as part of the process of making