An Edwardsville, Illinois, Amazon warehouse is under investigation by the U.S. Occupational Safety and Health Administration (OSHA) after it collapsed on Friday night. Six workers were killed when the building collapsed as a result of a deadly tornado, one among a wave of twisters that hit six different states.

At least 45 employees were able to make it out safely. OSHA has up to six months to investigate the building and what led to its collapse. It can issue citations and propose monetary penalties if any violations of health regulations or workplace safety measures are found, Scott Allen, a U.S. Department of Labor regional director for public affairs, told Reuters.