An explosion in a coke battery Wednesday morning rocked U.S. Steel's Clairton Works, sending 17 people to hospitals, a thick black cloud of smoke skyward and inspectors scrambling for clues to the cause. The explosion injured 14 U.S. Steel employees and six contractors. A dozen workers remained hospitalized last night with severe injuries. One suffered burns on nearly a third of his body, and several were hooked to breathing machines because flames and smoke had damaged their airways. Three workers received on-site treatment, the company said. "It was a big boom, and then everything just went black," said John Chappell,...