A natural gas well exploded Friday morning, killing two workers, leaving a third man remarkably uninjured and sparking a smoky fire that smoldered into the late afternoon.

A team of oil- and gas-well firefighting experts were flying from Texas to help put out the fire, which was still burning Friday afternoon.

A three-man crew, employed by a maintenance contractor, were working on oil tanks at the well in Indiana Township when the blast happened at 9:50 a.m., rocketing one of the tanks more than 70 yards into the woods, said Allegheny County Emergency Director Robert Full. Two of the workers were killed.

The exact cause has not been detailed in full, but state officials believe "people were welding at the site and there was an explosion and the well caught fire," said Helen Humphries, a spokeswoman for the state Department of Environmental Protection.

The resulting fire spewed thick, black smoke and scorched the workers' truck, melting the tires. Some 200 firefighters and rescue personnel responded, dousing the fires with thick, heavy foam, though part of the blaze was still burning about seven hours after the explosion.

Firefighters were hindered by the site's remote location, about 15 miles northeast of Pittsburgh, and the fact that access could be gained only by a single, steep gravel road. As a result, firefighters had to "hand-jack" between 3,000 and 4,000 feet of hose, Full said.

Temperatures over 90 degrees also caused problems, and three firefighters had to be taken to hospitals for heat-related ailments.

Still, Full said the fact that the fire was still burning was a good sign.

"As long as the well is burning we know that the gas is being consumed," Full said.

A team from Wild Well of Texas was flying to Pittsburgh on a charter plane to help put the fire out. Depending on their efforts, the blaze could be put out Friday night or Saturday, Full said.

Full said the two workers who died had not been identified nor was the company they worked for. They had been hired by the well's owner, Monroeville-based Huntley & Huntley Inc., to do maintenance work, Full said.

The well, dubbed Murray Heirs No. 6, is shallow — about 3,500 feet deep — and was drilled in May 2008, Humphries said. It was considered to be a producing well, she said.

The department won't be able to determine the environmental impact until after the fire is extinguished, Humphries said.

Travis Novak, a 16-year-old who lives about a half-mile away, said he was sleeping when he was woken up by the explosion. "Then I got up and looked and heard another loud explosion," he said.

The teenager and his friend Cory Drischler, 14, walked toward the site and saw "smoke just pouring out of the woods and then a loud bang. You could hear this loud noise like the gas was rushing down the hill."

Huntley & Huntley operates 389 gas wells in the state, according to DEP figures, and is also active in Oklahoma.

Humphries said the privately held firm does not have a record of violations.

The accident is the latest misfortune to strike the region's burgeoning natural gas industry.

Last month, a well in north-central Pennsylvania without proper pressure-control systems exploded as a crew was preparing to hook it up to a pipeline. No one was injured.

A few days later, seven people were injured in a rig explosion in West Virginia's Northern Panhandle when the drilling crew struck a pocket of methane gas while sinking a natural gas well through an abandoned coal mine.

In May, a worker at a Susquehanna County drilling site was killed when he was hit on the head by a pipe, a death that the coroner ruled an accident.

DEP Secretary John Hanger said in an e-mail message that the well where the accident occurred Friday is not part of the lucrative Marcellus Shale, a rock formation that drillers began tapping about two years ago.

As of 2007, Pennsylvania had more than 65,000 producing oil and gas wells, the vast majority of them drilled no deeper than 3,000 feet into the shallow sands underneath western Pennsylvania. The DEP estimates that as many as 350,000 wells have been drilled in the state going back to 1859.


Associated Press writer Marc Levy in Harrisburg, Pa., contributed to this report.