Although the investigation to determine the cause of an explosion in Woolwine last week is not completed, officials believe liquid oxygen prompted the blast at Thomas Industrial Fabrication.

The liquid oxygen was held in a foam cooler with rags inside of the cooler, according to Patrick County Emergency Coordinator Steve Allen, who added the oxygen is used to freeze parts before they are used.

The cooler was last used around 9:30 a.m. on Wednesday, July 25, Allen said in an emailed statement.

The blast occurred around 12:30 p.m., he said.

Shortly before the explosion, employees used equipment that included a grinder and a welder, Allen said.

Three people were injured in the blast, according to a company representative who declined to be named. Other employees were either out to lunch or not in the shop area at the time, the representative said.

Those injured were transported to medical facilities for treatment of minor injuries, the representative said. All were treated and released, according to the representative and Allen.

The incident remains under investigation by the Virginia Occupational Safety and Health (VOSH) Program, which is a division of the Virginia Department of Labor and Industry.

Lee Willis, Southwest Regional Safety Director for the Virginia Department of Labor and Industry, said the investigation into the cause of the blast could take up to six months to complete.

“But generally, it doesn’t take that long; usually it takes 10 to 12 weeks,” he said.

Damage to the building is estimated at $250,000, according to Allen.