Several workers suffered severe burns following a Friday morning explosion in central Mississippi.

The explosion happened at a salt water disposal site in Madison County, WLBT-TV reported.

At least six people sustained burns on at least 50% of their bodies, with one being burned from head to toe, said Minor Norman, the Madison County Fire Coordinator. Two people were airlifted to the University of Mississippi Medical Center for treatment.

Norman said the cause of the explosion was still under investigation Friday.

“We’re not sure what caused it,” Norman said. “There were four storage tank facilities to hold products from oil wells. They (the workers) were in the process of changing out two tanks with new fiberglass tanks. They were getting ready to go into service when the older tank exploded.”

The Mississippi Department of Environmental Quality was called to the site to investigate.

The injured people are employees of W.S. Red Hancock, a Mississippi-based “welding and fabrication” company. Company officials told WLBT-TV they were assessing the situation Friday but had no additional information.