Investigators seek clues to cause of blast that injured 20 at US Steel plant near Pittsburgh

Investigators were looking for clues Thursday into what caused an oven at a U.S. Steel plant near Pittsburgh to explode, injuring 20 workers and starting a fire that burned for hours.

The powerful blast in the coke oven at Clairton Coke Works happened around 9:30 a.m. Wednesday, Allegheny County spokesman Kevin Evanto said. Most of the injured workers were burned; one suffered chest pains.

"It's a miracle that anybody even walked away from that," Allegheny County Emergency Services Chief Bob Full said. He said the explosion was so mighty it bent steel beams and destroyed block walls.

The Occupational Safety and Health Administration had a team of investigators on site, spokeswoman Leni Fortson said.

"It was a big boom and then everything just went black," janitor John Chappell, 59, of Clairton, told the Pittsburgh Tribune-Review as he left UPMC Mercy. He was not injured.

"It was pitch black but you could tell there was debris flying all over the place," Chappell said. "I'm just blessed because I know it could have been worse."

An air quality inspector at the plant at the time of the blast said he saw a large cloud of smoke that dissipated quickly, said Jim Thompson, manager of the Allegheny County Air Quality Program. Thompson said that and other factors indicate the explosion may have been caused by the gas used to heat one of the coke ovens.

A maintenance worker died in a September 2009 explosion at the plant, which sits in a valley along the Monongahela River about 20 miles south of Pittsburgh.

The company said 14 employees and six contractors were injured. About 1,500 people work at the plant, said Michael Wright, head of the health, safety and environment department for the United Steelworkers union.

A raw material used in steelmaking, coke is coal that is baked for a long time at a high temperature to remove impurities. The coal is baked in special ovens, several of which make up a coal battery; there are 12 batteries at the Clairton plant.

U.S. Steel says the plant is the biggest coke manufacturing facility in the U.S., producing about 4.7 million tons per year.

The battery where the explosion happened was shut down, but a U.S. Steel spokeswoman said the rest of the plant was operating normally.

At Pittsburgh's West Penn Hospital, two workers in their 50s were in critical condition with chemical burns in their airways as well as burns to their heads, necks and faces, said Dr. Larry Jones, the hospital's director of emergency medicine.

"The burns themselves are serious burns, but with the inhalation injury on top of it, these are very, very serious, a very serious situation," Jones said.

A third worker, in his 40s, was in serious condition with burns on his head, neck, face and hands, and an ankle fracture, Jones said.

Five patients were in burn units at another hospital, four in critical condition and one in serious condition.

Elaine Lawrence, 53, whose son works at the plant, was lying on the couch at her Clairton home when her daughter told her there had been an explosion. The daughter drove her to the plant, but they weren't allowed in; they headed to a hospital, and that's when her son called.

"He said he had just passed where the explosion happened to go to the other block and suddenly he heard an explosion," Lawrence said. Martin Lawrence, 19, was not injured and remained at work, she said.

"I was real concerned, because that's my only son," she said.