After an outside Pittsburgh, workers scrambled into the wreckage alongside firefighters. A cloud of black smoke rose above a charred pickup truck as rescuers sprayed the scene with streams of water.

By the time the scene was secure, , including one who spent hours trapped in rubble left Monday by the blast that was powerful enough to shake nearby homes.

Video from Pittsburgh television station WTAE showed workers in orange jumpsuits and hard hats running toward the wreckage at the U.S. Steel coking plant in Clairton. A reporter described seeing someone being pulled from the debris and loaded onto a gurney. The station’s footage later showed a mountain of charred rubble spilling from a hole left by demolished walls.

Investigators worked Tuesday to determine the cause of the blast, whi

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