An explosion so powerful that it blew out concrete-block walls rocked U.S. Steel's Clairton coke plant this morning, leaving 20 people with burns and injuries ranging in severity from minor to life-threatening.
The patients were taken to UPMC Mercy, UPMC Presbyterian, UPMC McKeesport, Jefferson Regional and West Penn, which received three workers, two of them in critical condition.
A decontamination facility was set up at UPMC McKeesport, where the injured workers were treated initially before being sent to other hospitals, according to Gloria Kreps, UPMC spokeswoman.
"It is a miracle that no one was killed outright by the blast," said Allegheny County's emergency management chief, Bob Full.
Chief Full could not say yet what caused the blast, other than saying it was sparked by coke oven gas, which is produced in the coke-making process and is used to bake the impurities out of coal.
Helping in the investigation are the federal Occupational Safety and Health Administration and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.
Chief Full said the ATF usually investigates crimes, but in this case the agency was called in because of its expertise in determining what causes explosions.
"They have resources you can't believe," he said.
The explosion was reported at 9:37 a.m., and the resulting fire burned until about 2:45 p.m., Chief Full said.
Allegheny County spokesman Kevin Evanto said all workers at the plant had been accounted for.
"What I have right now is there was a fire and explosion in number 2 B battery and apparently there was flammable gas that ignited and exploded and the result was that  employees were transported to area hospitals. Some were severe," said Robert Szymanski, the director of OSHA's Pittsburgh office.
Jim Thompson, manager of the Allegheny County Air Quality Program, said initial reports from a Health Department inspector at the scene indicate the explosion may have been caused by a gas explosion at the B battery, the largest coke-making battery at the Clairton complex with 75 ovens. All operations at the battery have been shut down, he said.
"A coke oven battery uses coke oven gas to heat itself, and if there's a leak there's always a potential for an explosion, but right now that's pure speculation. I have no confirmation on that," Mr. Thompson said.
When the explosion occurred, the Health Department inspector was in a trailer about a quarter mile from the blast, he said.
"He said the windows of the trailer were rumbling pretty good when the explosion happened," Mr. Thompson said.
A "senior operator" at K&H Construction Inc., a U.S. Steel subcontractor with offices inside the coke plant, said employees were summoned to an emergency meeting shortly before 10 a.m.
"At the meeting we were told there was an explosion at B battery and the fire trucks were down there and they were going to suspend operations until they determine the cause," said the man, who would not give his name.
The man said the battery is centrally located in the plant, while most subcontractors are at the south end. He said he did not hear any explosion this morning.
There are 12 batteries at the coke works.
Dr. Larry Jones, director of the burn unit at West Penn Hospital, said he expected the three patients there to survive. But he said the two in critical condition, both men in their mid-50s, have chemical burns in their airways that complicate their situations.
One of those men has burns over 30 percent of his body; the other has burns to 10 percent. The third worker, a man in his mid-40s, is in serious condition with burns over 10 to 12 percent of his body and an ankle fracture.
All have burns to the neck, head and face, Dr. Jones said.
He did not identify the men. Family members were at the hospital but they didn't not want to talk to reporters, a spokeswoman said.
Six victims were taken by ambulance to UPMC Mercy Hospital. Doctors said all the men were covered in black soot when they arrived around 10:30 a.m. and had to be cleaned before they were treated.
One of the victims was treated for a soot-related injury and released.
The other five remain at the hospital. One is in critical condition because of an inhalation injury caused by heat, Dr. Alain Corcos said. The other four are in serious condition.
Dr. Corcos said all the victims, men with ages ranging from their 20s to 50s, suffer from second and third degree burns caused by flames.
He said their burns ranged from 15 to 40 percent of their bodies.
In September, a man was killed and another injured at an explosion at the plant.
Several State Street residents who live near the plant said they heard no explosion this morning.
Joanne Panza, 64, who was standing at the northern end of the plant this morning near her house as an ambulance siren wailed in the background, said she noticed that around 10:30 a.m. the coke works' hallmark smell became strikingly more pungent.
"I can tell you this, I smell it. It's better now, but it was a bad chemical smell before. The air seems to have cleared," Ms. Panza said.
Chief Full said no evacuations were ordered in Clairton or in Lincoln, the borough across the Monongahela River from the plant. The coke oven is at the rear of the plant, near the river, Chief Full said.
"The county has responded to many steel mill accidents over the years," he said. "This is a very dangerous business."
The Health Department said it would continue to monitor the air around the plant. Although the blast produced a black cloud, no long-lasting effects have been measured.