A natural gas well where welders were believed to be working exploded Friday, killing two people and sparking a fire that spewed black smoke for hours.
The blast happened around 9:50 a.m. in a remote, wooded area of Indiana Township, northeast of Pittsburgh, police said. Firefighters doused the resulting fire with foam, and part of the blaze was still burning about three hours after the explosion.
The cause wasn't yet known, 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.
"Why they were welding or what caused the explosion, I don't know yet," she said.
The well, dubbed Murray Heirs No. 6, is a shallow well, 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.
The well is owned by Huntley & Huntley, a company that says it operates more than 350 gas wells in and around Pittsburgh and is also active in Oklahoma. The company confirmed its workers had arrived at the well but a spokeswoman said she had no further information.
Humphries said Huntley & Huntley 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 northeastern Pennsylvania, state environmental officials said construction flaws in gas wells were responsible for allowing gas to seep into the area's groundwater.
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 have begun tapping only recently.
Associated Press writer Marc Levy in Harrisburg, Pa., contributed to this report.