Updated

An oil storage tank at a natural gas well exploded Friday morning, killing two workers, leaving a third man remarkably uninjured and sparking a smoky well fire that smoldered for hours.

A team of oil- and gas-well firefighting experts flew in from Texas to help local crews figure out how to put out the fire, which was extinguished around 8:30 p.m., officials said.

A three-man crew, employed by a maintenance contractor, was 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 fire with thick, heavy foam.

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.

A team from Wild Well of Texas flew to Pittsburgh on a charter plane to help put the fire out.

Full said the identities of the victims were not being released immediately, nor the name of their employer. The Allegheny County Medical Examiner was investigating their deaths and autopsies will likely be performed Saturday, a deputy said.

The men worked for a contractor 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 and was still producing gas, Humphries said. The well required no crew to produce natural gas, but crews sometimes went there to maintain or repair it, she said.

Full explained that shallow wells often bring up a small amount of oil along with the natural gas they produce. The tank that exploded, about 12 feet high and 8 feet in diameter, was used to store that oil, not natural gas, Full said. Firefighters were dousing another oil tank like it to lessen the chance that it would burn or explode, he said.

Humphries had said environmental officials won't be able to determine any impact on the area until after the fire is extinguished.

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

The teenager said he 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. President Keith N. Mangini said in statement released Friday night that the company "will undertake a full investigation and cooperate fully with authorities."

"Our deepest sympathies and heartfelt prayers are with the families of the victims of this accident," Mangini said.

Humphries said the privately held company 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 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 contributed to this report.