Shakespeare speaks of sleep as “Nature’s second course.” Fresh air may well be called “Nature’s tonic.” Everything else necessary for good health may be provided, but if there is not a sufficient amount of fresh air the tissues of the body can not perform their functions. It is quite as necessary to have plenty of fresh, pure air as it is to have a proper amount of wholesome food and pure water. Ordinarily not enough attention is given the subject of ventilation, especially of the average home.
The average adult breathes at the rate of seventeen or eighteen respirations per minute. At each respiration about thirty cubic inches of air passes in and out of the lungs. The air in the lungs loses 4% of oxygen and absorbs about 3.5% to 4% carbon dioxide. The nitrogen remains the same. The temperature of expired air is raised to about 98.4% F. and contains approximately 5% aqueous vapor.
This volume of air inspired and expired during gentle respiration, which is, as has been said, about thirty cubic inches, is known as tidal air. By forced inspiration another 100 cubic inches of air in addition to the tidal air may be taken into the lungs. This is known as complemental air. By forced expiration it is possible to expel from the lungs 100 cubic inches of air over and above the 30 cubic inches of tidal air; this is known as the supplemental air. There is another 100 cubic inches which can not be expelled by the most violent expiration; this is the residual air. The supplemental air can, by forced expiration, be expelled from the lungs, but the residual air can not. Altogether there is in the lungs during forced inspiration about 330 cubic inches of air. An average adult gives off about 0.71 cubic feet of carbon dioxide per hour.
Taking into consideration the amount of air breathed into the lungs per hour and the amount of impurities carried into the breathing zone by the expired air, it can readily be seen that the problem of supplying a sufficient volume of pure air in the house is no small problem.
The amount of fresh air needed for the average adult is estimated to be 3,000 cubic feet per hour. The ventilating system that does not provide this amount of air per hour without objectionable draughts does not meet the requirements of modern hygiene.
In a system of ventilation it is not only a question of providing a certain volume of air from the outside, but the great problem is to provide a sufficient volume of pure air of proper temperature and of proper humidity. Air that is laden with smoke, dust and suspended matter, or that which contains gas or foul odors, is objectionable and does not meet the requirements. Therefore, the source of the air becomes important. The ventilating system must also keep the air in proper circulation at a proper velocity.
The ventilating system of an ordinary building might seem a very simple proposition, but when considered carefully it is a very great problem and one that requires the careful attention of engineers trained in that particular line.
It is not the object of ventilation to provide an indoor condition identical with that outdoors, but it is to maintain a condition indoors conducive to a normal expression of indoor life. It is quite obvious that if indoor conditions were maintained identical with outdoor conditions the desired results could not possibly be obtained, for indoor life demands a much different environment. It is necessary to give any system of ventilation as much attention as is given a heating system in order to obtain the best results. No system will work itself.
Sources of Impurities in Air
There are many processes carried on within the house that add to the impurities of the air. Such sources may be classified as follows: respiration of persons, impurities from heating and illumination, and accidental sources from processes carried on within the house, such as house cleaning and laundering.