CLAIRTON, Pa. (AP) -- The section of a U.S. Steel plant near Pittsburgh where an oven exploded was idle Thursday as investigators looked for clues into the powerful blast that injured 20 workers and started a fire that burned for hours the day before.
The blast bent steel beams and destroyed block walls at Clairton Coke Works around 9:30 a.m. Wednesday. 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.
The Occupational Safety and Health Administration had a team of investigators on site, spokeswoman Leni Fortson said.
OHSA also had investigated a September 2009 blast in a different part of the plant that killed maintenance worker Nicholas Revetta, but they issued no citations against U.S. Steel.
"To have one of these explosions every 25 years would be a problem, but two of them in less than a year is really scary," said John Gismondi, a lawyer representing Revetta's family. "It makes you wonder what is going on at Clairton."
County air quality officials say the large cloud of smoke generated from the blast and other evidence indicate the explosion may have been caused by the gas used to heat one of the coke ovens.
"A lot of these accidents are very complicated," said Michael Wright, head of the health, safety and environment department for the United Steelworkers union. "You almost always find those things could have been anticipated."
Coke, a raw material used in steelmaking, is coal that is baked for a long time at a high temperature to remove impurities. Several special ovens make up a coal battery; there are 12 batteries at the Clairton plant.
In all, 14 employees and six contractors were injured. Several remained hospitalized Thursday, including two people in critical condition at West Penn Hospital and three in critical condition at UPMC Mercy.
Most suffered burns on their faces, necks and arms. The most critically injured also were suffering from chemical burns to their airways.
Workers inside the plant said they felt lucky to be alive.
"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."