Good Ventilation a Necessity to Health
By J. J. Bell, M. D.
THE importance of an abundance of pure air for respiration is seen when we understand that the delicate mucous membrane of the lungs, through which we take in oxygen and give off carbon dioxide and other organic poisons, would cover an area of about two thousand square feet, or from one hundred to one hundred and thirty times the area of the skin covering the body. Inspired air contains 79.15 per cent of nitrogen, 20.8 per cent of oxygen, and .04 per cent of carbon dioxide, moisture,12traces of ammonia and nitric acid, dust, and bacteria. Expired air contains 79.30 per cent of nitrogen, 16 per cent of oxygen, 4.38 per cent of carbon dioxide, an increase in moisture, also effete organic matter termed crowd-poison, some traces of hydrogen, marsh gas, etc. We estimate the purity of the air by the percentage of carbon dioxide which it contains. Carbon dioxide, however, is not the only harmful ingredient present in expired air; but we know that when the percentage of carbon dioxide is high, other organic bodies, or crowd-poison, must be present in a correspondingly large proportion. It is not the lack of oxygen, nor is it the amount of carbon dioxide in the air of a moderately crowded room which makes it injurious to breathe; for the blood flowing in the lung tissue can obtain the necessary amount of oxygen from air containing as low as ten to fifteen per cent of oxygen, and breathing air containing one or two per cent carbon dioxide made by chemical methods is not harmful. But expired air containing one per cent of carbon dioxide is decidedly injurious because of the organic poisons present. The nose can detect very readily the impurity of the air of a crowded room, provided the individual enters directly from the fresh air outside. Those occupying the room may detect no unpleasantness because the olfactory nerves gradually become accustomed to the foul air as its impurities increase little by little. Air containing two parts of carbon dioxide in five thousand we regard as pure. When carbon dioxide is present in the proportion of three parts in five thousand volumes, the air is impure and unfit to breathe. With every breath we exhale more than one cubic inch of carbon dioxide, which would thus render impure five thousand cubic inches of air, because five thousand cubic inches of pure or inspired air already contains two cubic inches of carbon dioxide. Five thousand cubic inches equal about three cubic feet. Thus we spoil three cubic feet of air at each expiration. Since we breathe about eighteen times a minute, we render impure three thousand cubic feet of air an hour. In a room having a capacity of one thousand cubic feet, with one inhabitant, in order to have the air pure the entire atmosphere would need to be changed at least three times an hour. In order to ventilate a room without causing a draft, each inhabitant should have from seven hundred to one thousand cubic feet of space. Allowance should be made for furniture; and the area above fifteen feet high should not be reckoned. Various methods have been in use for providing a means of ventilation. Two things, however, are a necessity, whatever system we adopt,—one or more fresh-air inlets, and a foul-air outlet. The latter must be equal in size to the combined area of all the inlets. The greater in number the inlets, and the fewer the outlets, the less will be the draft.