One possibility is the gas released when the janitor accidentally dumps too much bleach into the water, or combines bleach with an ammonia based cleaner. Can't count the number of times people forget bleach is chlorine (mustard gas) or the bleach-ammonia deadly combination.
Another possibility is the use of chemical agents in stripping the tile. Again the janitor forgot to ventilate the area.
Another possibility is that a floor service coated the wood in one of the department stores with a fresh coat of poly which required the use of a bonding agent instead of sanding the floor. I used a bonding substance called Wil-Bond on a floor once that released vapors that could knock a moose over in a heartbeat.
Just some amateur ideas on the cause that's not terror related...Funny how 9-11 changed how we see a half-wit janitor's bright idea of combining bleach and ammonia as a terror plot.
The same thing happens if you poor bleach on urine -- because of the ammonia. I used to have to do this to do this to clean my kids' bathroom, then I'd shut the bathroom door and run for it. Ended up killing my Bamboo plant.