> The safest place to be is a reinforced concrete building, but if that’s not an option a basement really is your best bet. An analysis of the Oklahoma tornado outbreak of May 1999, which featured an EF5 (i.e., scale-topping monster) twister, found that out of 40 deaths, 133 severe injuries, and 265 minor injuries, the total harm inflicted on people holed up in basements amounted to just one minor injury.
https://washingtoncitypaper.com/article/217899/straight-dope...
not sure where they sourced from but shouldn't be too hard to find given the exact numbers quoted.
The ideal scenario is that the warehouse would have a reinforced concrete tornado shelter (or multiple given the size) and a mandatory work stoppage whenever a tornado emergency is declared.