A chemical reagent flask containing 3 kg of isopropanol is accidentally spilled on the floor of a laboratory. The liquid quickly spreads on the floor (3 m X 4 m surface area) and starts to vaporize. Now a couple of exhaust fans are switched on to ventilate the room after the spill. It takes 5 minutes to completely vaporize all the liquid. Assuming that the isopropanol vapor diffuses out from the liquid surface through a stagnant film of air, calculate the thickness of the air film.