CHARLESTON, W.Va. -- At least five workers remained hospitalized in a Pittsburgh burn center Monday following an explosion over the weekend at an Antero Resources natural gas well in Doddridge County.
Federal and state authorities, along with two firms hired by Antero, have begun investigations into what caused the blast, which occurred at about 4 a.m. Sunday at the Hinterer 1H well near New Milton.
The incident occurred near the end of the process of drilling and completing the well -- prior to commercial natural gas production -- when water and chemicals used in the process were coming back to the surface, a company official said.
"We assume it was a gas explosion, but we don't know if it came from the well or the flowback," said Al Schopp, spokesman for Denver-based Antero.
Local emergency officials had indicated Sunday that seven -- and perhaps eight -- workers were injured in the blast, with some going to area hospitals in private vehicles.
But Schopp said Monday that there were only five victims, and that all were taken to the West Penn Burn Center in Pittsburgh. Their names and conditions have not been released.
Leni Uddyback-Fortson, a spokeswoman for the U.S. Occupational Safety and Health Administration, said that three of the injured workers were employed by Nabors Completion and Production Services Co., an Antero contractor. The other two workers were employed by two other contracting firms, C & R Downhole Drilling LLC and Willowbend Investments Inc., Uddyback-Fortson said.
DEP spokeswoman Kathy Cosco said that the blast ruptured two tanks containing flow back water that Antero had been reusing, but the secondary containment system captured the fluid as designed and none left the site. There was no contamination to any nearby streams, she said, and the nearest home is about a half-mile away so it was unaffected.
DEP investigators suspect that methane vapors inside one of the tanks exploded, Cosco said, "but we're not 100 percent sure of what the ignition source was, either."
Investigators are looking at whether it might have been a pump that the crew was working on, but Cosco said the mechanics of the blast itself will be OSHA's focus.