One employee remains in critical condition following an explosion at a Coweta County aluminum plant, the company said late Thursday.

Five people were injured Wednesday morning at Bonnell Aluminum in Newnan in an explosion that damaged the roof of the plant and some equipment, a company spokesman said. One person was treated at the scene and three others were taken to hospitals for treatment and later released. A fifth person, whose name was not released, was flown to Atlanta Medical Center in critical condition.

“We continue to keep our injured co-workers in our thoughts and prayers, hoping for speedy recoveries,” Brook Hamilton, Bonnell president, said in an emailed statement.

The plant was evacuated and closed Wednesday while the U.S. Occupational Safety and Health Administration worked with the company and local investigators to determine the cause of the explosion.

On Thursday, the company released preliminary findings, though the investigation is not complete.

“Based on what we have been able to determine at this time, employees were performing their duties during a cast, the process when molten metal is turned into extrusion logs, when water came into contact with a relatively small amount of molten metal,” the company said. “A steam explosion ensued, that for the most part, sent its force upward, removing a section of the roof, and damaging surrounding casting equipment.”

Other areas of the plant re-opened Thursday morning, a spokesman said. Counselors were at the plant to assist employees.