(Patrick County, Va.) – The Occupational Safety and Health Administration is leading the investigation into a plant explosion that sent three Patrick County plant workers to the hospital.

It happened around 1:00 Wednesday afternoon at Thomas Industrial Fabrication facility in Woolwine.

Three people were injured in a blast that witnesses said sounded like a cannon firing. Two of the workers were treated and released from a Martinsville hospital, while a third was airlifted from the scene. The extent of that individual’s injuries is not known.

Workers were on lunch break when a loud explosion rocked the manufacturing facility, knocking holes through the building. The blast could be heard a half-mile away.

The cause of the explosion is not known. OSHA and the Virginia Department of Labor are investigating the incident.