[jcranmer]

A large warehouse is pretty much built as a thin steel shell that would be expected to fail in more or less this manner in a tornado. However, there is usually an interior building within the warehouse that is built much more strongly (probably cinder-block masonry) that should withstand a tornado strike much more securely. That interior building would contain the warehouse offices, the bathrooms, etc., and it doesn't appear to be in the collapsed portion of the warehouse.

[2xpress]

At least for Amazon warehouses that are not in tornado areas, warehouse workers are instructed by the managers to go to the center of the warehouse building during extreme weather events.

I do not know for sure if that same procedure would have applied to DLI4. But my feeling is that unless the state of Illinois, Madison County, or the city of Edwardsville have a specific regulation requiring such buildings to have tornado shelters, then there was no such shelter at DLI4, and workers were instructed to assemble in the center of the building.

Internal office sections of large Amazon fulfillment centers are off-limits to non-managers, and unauthorized entry is prevented thru the use of door badge scanners, which will not unlock the door unless the badge owner has sufficient permissions.

I can't imagine what an awful, dehumanizing, and absolutely terrifying experience it was.