Oct. 12—The explosion that rocked western Schuylkill County Monday morning erupted as employees of Maine Drilling & Blasting Co. disposed of discarded explosives boxes, an investigation by the state Department of Environmental Protection and other agencies found.

"The explosion occurred while burning waste bags and what was believed to be empty explosives boxes," DEP said in a statement released Tuesday morning. "The material was being burned in the back of what was an old quarry dump truck body."

The department's statement says the actual cause of the explosion has not been confirmed.

State police at Frackville, however, reported the explosion occurred as employees of Maine Drilling & Blasting were disposing of boxes that previously contained boosters used in the blasting process. A booster is a type of detonator.

The explosion occurred about 11:40 a.m. at the Maine Drilling & Blasting Co. Good Spring site, which is on property owned by Stavola Summit Quarry in Porter Twp.

Thomas Branch, Stavola vice president of regulatory compliance and safety, said Maine Drilling & Blasting was not doing explosives work in the quarry at the time of the incident.

"They were operating a burn pit," he said, "and somehow, someway, an explosive entered into the burning and caused the explosion."

Safety regulations require a detailed accounting of explosives leaving the site and returning to the site, Branch said.

The powerful blast damaged equipment, storage facilities, surrounding buildings and employee vehicles on site, DEP reported. Debris from the explosion has been found about 500 feet from the impact area.

Two employees of Maine Drilling & Blasting received non-life threatening injuries, according to state police. One of the employees was hospitalized, but details on the type or extent of injuries are not available.

Residents who live near the blast site reported seeing ambulances going to a medical helicopter landing site on a ballfield near Joliett, a village a mile or so from the blast site.

Trooper John F. Burns, a state police fire marshal, was called in to investigate the incident. A separate investigation by the DEP mining department is ongoing.

The DEP-Pottsville District Mining office, the Joliett Fire Company and state police responded to the incident.

The Occupational Safety and Health Administration, the Mine Safety & Health Administration and the Bureau of Alcohol Tobacco, Firearms and Explosives were notified, but did not immediately assign investigators.

The explosion was heard throughout a wide area from Valley View to Pine Grove in western Schuylkill County. There were reports of it being heard in Grantville, Dauphin County.

Jason Fisher was in the bathroom Monday morning when a blast shook the walls of his Joliett home.

"The whole wall went in and out," he said, "and I thought the windows were going to blow out."

The blast was loud enough, Fisher said, that it reminded him of explosions he heard during a 2005 tour of duty with the Army in Iraq.

Scott Bailey, who works at Werner Lumber Ace Hardware in Pine Grove, said it sounded like something had fallen on the building's roof.

"It was pretty major," Bailey said. "You not only heard it, you felt it."

Andy Martin, a mechanic at Wheels Coal Co., said the company garage shook in the wake of the explosion.

"I got a call from my wife in Valley View, and she said the whole house shook," he said. "My daughter was asleep in bed, and the sound woke her."

Contact the writer: rdevlin@republicanherald.com; 570-628-6007