Your careless, clumsy lab mate has accidentally allowed carbon monoxide to leak out of a reactor, causing your lab's co monitor alarm to sound. after you quickly put on the appropriate personal protective equipment, you find the leak and seal it. then, you close your lab door, shut the windows, and call osha to report the hazard when osha technicians arrive, they begin ventilating the 3000-ft laboratory by pumping 25 ft/min of fresh air into the room and removing the contaminated air at the same rate. they put a shop fan in the laboratory, such that the air is well-mixed. they also install a digital co composition monitor, which currently reads 2 mol%. osha tells you that the laboratory is safe when there is less than 35 ppm of co in the lab. how long must you wait to get back to work?