More info. here:
It sounds as if what happened was that there was an initial warning at 6 pm for an earlier storm (than the big one): Everyone sheltered*, but that storm passed or lifted or dissipated, the sirens stopped, and everyone went back to work around 6:30 pm. Then the sirens went off again at 9 pm, everyone sheltered* again, and the big tornado hit shortly thereafter.**
My guess is that it was at or after 6:30 pm that employees started asking to leave, when there was no imminent threat, but, local TV had been talking for well over a day about a likely outbreak of severe weather and likely tornados. Some employees may well have heard by phone from friends that really nasty weather was coming in from further to the southwest.
*In any event, the factory did not have satisfactory shelter — I can’t see policy not letting people leave. Possibly this was just a supervisor on a power trip - all too common.
**Multiple accounts SEEM to indicate a rather short warning from the sirens. That baffles me — I was watching local tv and the local tv mets had this thing pegged as to size, storm history, persistence, and likely track: At least 20 minutes B4 it hit Mayfield I was asking my wife to phone or text friends there that a large tornado on the ground was headed for them... I don’t recall when NWS posted a warning that included any part of Graves County, but my understanding is a warning that clips any part of a KY county sets off the sirens throughout. Graves is a big county (by east of the Mississippi standards): If areas in SW Graves county got adequate warning from NWS, even with a fast moving storm like this one, those sirens in Mayfield (in the center of the county) should have gone off with plenty of time to for people to get out to better shelter.
Wowee. Thanks for that. O.o