One year after an explosion at U.S. Steel’s Clairton Coke Works killed two employees, federal investigators say the disaster “should never have happened.” The process releases coke oven gas, a highly flammable, toxic and colorless mixture containing hydrogen, methane, nitrogen and carbon monoxide. Workers told investigators that coke oven gas residue could accumulate around valve seats and sometimes prevent a valve from closing completely. The valve catastrophically failed, and approximately 19 pounds of toxic and highly flammable coke oven gas escaped into the surrounding area. Its fifth recommendation calls for a comprehensive process safety management system covering all coke oven gas processes at Clairton.