the hope is that the tarp will create a barrier between the cold concrete floor and the humidity in the air, so that the humidity doesn't end up as condensation on the cold concrete floor. 

and, these floors are unusually cold, to the point that i've wondered if they're cooled, but the concerns i've brought up have been met with denials - just like the smoking and everything else.

but, even if it doesn't work as intended due to potential seepage under the floor, at least it's the floor that gets damaged and not my furniture or gear.