EDWARDSVILLE, Il. (AP) — The federal Occupational Health and Safety Administration said Monday it has opened an investigation into the collapse of an Amazon warehouse in Edwardsville, Illinois, after it was struck by a tornado on Friday, leaving six people dead and another hospitalized.

OSHA inspectors, who have been at the site since Saturday, will look into whether workplace safety rules were followed and will have six months to complete the investigation, said spokesperson Scott Allen.

Amazon, meanwhile, said workers at the warehouse had little time to prepare when the National Weather Service declared a tornado warning on Friday night. The tornado arrived soon after, collapsing both sides of the warehouse and caving in its roof.

“There was a tremendous effort that happened that night to keep everybody safe,” said John Felton, Amazon’s senior vice president of global delivery services, speaking alongside Illinois Gov. J.B. Pritzker in Edwardsville on Monday and pledging a review of all the events that took place Friday.

Amazon spokesperson Kelly Nantel said the warehouse received tornado warnings between 8:06 p.m. and 8:16 p.m. Friday, and site leaders directed workers to immediately take shelter. At 8:27 p.m., the tornado struck the building.