Correct Option: A

Breathing sixteen times every minute an average volume of air amounting to 30 cubic inches, we find that the expired air amounts to no less than 17 cubic feet per hour. This contaminated air contains only 16 per cent of oxygen, and 4.5 per cent of carbonic acid gas, and is sufficient to vitiate no less than 3,000 cubic feet of fresh air. Pure fresh air contains from 0.03 to 0.04 per cent of carbonic acid gas, or at the most, .4 volumes per thousand volumes of air. Careful investigation shows that when further carbonic acid gas has been added raising the amount to more than .6 volumes per 1000 of fresh air that an unpleasant odour rapidly becomes perceptible and the air gets to be “close,” musty, or foul. According to these figures a person in a room ten feet square by ten feet high containing a 1000 cubic feet of air requires to have this air completely replaced twice during the hour so as to furnish 3,000 cubic feet of fresh air hourly in order to prevent the carbonic acid gas exceeding .06 per cent.