The US Occupational Health and Safety Administration is investigating workplace conditions at the Amazon warehouse in Illinois that collapsed Friday, killing as many as 6 people, writes Business Insider.

Agency spokesperson Scott Allen said in a statement that OSHA has had compliance officers on the scene since Saturday to assist in the aftermath of the tornado that caused the roof of DLI4 to cave in.

“OSHA has six months to complete its investigation, issue citations and propose monetary penalties if violations of workplace safety and or health regulations are found”, - Allen said.

On Saturday, the Retail, Wholesale and Department Store Union president Stuart Appelbaum said it was “inexcusable” Amazon employees were working at the warehouse when severe weather hit.

“The site received tornado warnings between 8:06 and 8:16, and site leaders directed people on site to immediately take shelter”, - an Amazon spokesperson told Insider. “At 8:27, the tornado struck the building. Our team worked quickly to ensure employees and partners could get to the designated shelter in place area, and we want to thank them for everything they were able to do”.