The Department of Labor's workplace safety arm is investigating the collapse of an Amazon warehouse that caused the deaths of six workers during a tornado that ripped through six states and caused historic levels of devastation.

The Occupational Safety and Health Administration has launched a probe into the catastrophe that is legally required to be completed in six months, Reuters reports. The Amazon facility that sustained a direct hit from a tornado on Friday was a last-mile distribution center known as a delivery station in the town of Edwardsville, Illinois, from which 45 people were confirmed to have escaped alive.

The Edwardsville facility, one of three Amazon operates in the town, opened last July with 40-foot-high walls made of 11-inch-thick concrete — walls that buckled inward under the force of winds that reached at least 158 miles per hour at their peak, qualifying it as an EF-3 tornado according to the National Weather Service, The New York Times reports. It was one of several tornadoes that made landfall Friday, with others causing damage as far south as Mississippi and as far west as Missouri and Arkansas.

The collapse of another industrial building, a factory producing scented candles in Mayfield, Kentucky, caused an even greater loss of life during the extreme weather event, with eight fatalities among workers, Reuters reports. More than 70 people were killed on Friday in Kentucky alone, as 1,000-plus homes were destroyed in the path of the tornado that also felled the two industrial facilities, making it the most destructive national disaster in the state's history, Gov. Andy Beshear said at a press conference, the Times reports.

With their wide footprints and high, single-story walls, warehouses like the Amazon center are among the most vulnerable buildings to the wind damage wrought by tornadoes. Compounding matters are reports from workers in both the Amazon and Mayfield facilities that management discouraged them from leaving the buildings to find shelter when tornado alerts sounded on their phones minutes before impact, Reuters reports.

Amazon warehouse workers from across the country have said on social media in the days since the tornado that they have rarely, if ever, received workplace training on disaster preparedness or run drills for fires, tornadoes and other such events, The Intercept reports. A spokesperson for Amazon told Reuters that the company is cooperating with the OSHA investigation, adding that it is standard protocol for any workplace fatality.