Preliminary investigations indicate molten aluminum hitting water caused explosions that injured more than 30 employees at a southeast Missouri aluminum plant, a federal agency said.

The U.S. Department of Labor’s Occupational Safety and Health Administration is investigating the explosions that happened Aug. 4 at the Noranda Aluminum plant in New Madrid County, about 170 miles south of St. Louis.

OSHA officials said preliminary findings suggest molten aluminum came into contact with water, causing the explosions.

OSHA said 33 workers were hurt, but Noranda spokesman John Parker said none of the injuries were critical. One worker was treated for smoke inhalation and 32 for eye and throat irritation, OSHA said. Some also had ringing in the ears.

Parker said the explosions occurred in the caste house, where the company produces extrusion billet, a length of metal with a cylindrical shape. OSHA said much of that building appeared to be destroyed, though other buildings were undamaged.

“OSHA is on scene and will conduct a thorough investigation at Noranda Aluminum facility to see if any violations of safety procedures contributed to this tragic incident,” David Keim, OSHA’s assistant area director in St. Louis, said in a statement.

It will be the second investigation at the plant in a little over a month. OSHA opened an investigation on June 30 after the company reported that a worker suffered second- and third-degree burns. That investigation has not been completed, spokeswoman Rhonda Burke said.

Noranda employs about 900 workers in New Madrid County, where the plant serves as the primary aluminum smelter for Franklin, Tennessee-based Noranda.