CHAPTER XI
VENTILATION
The purity of air in any habitable enclosure is determined by the amount of CO2 (Carbonic acid gas) included in its composition. The process of ventilation is that of adding fresh air to the impure atmosphere of houses, until a desirable quality is attained. In the opinion of hygienists, when air does not exceed 6 to 8 parts of CO2, by volume in 10,000, the ventilation is desirable. Ordinary outdoor air contains about 4 parts of CO2 to 10,000, while very bad air may contain as high as 80 parts to the same quantity. The quantity of air required for the ventilation of a building is determined by the number of people to be provided. The amount of air required per individual per hour necessary to produce a desired condition of ventilation is determined by adopting a standard of purity to suit the prevailing circumstances.
In hospitals where pure air is considered of greatest importance 4000 and 5000 cubic feet per inmate per hour is not uncommon. The practice of supplying 30 cubic feet of air per person per minute (1800 cubic feet per hour) seems to fulfill the average requirements. It is the amount commonly specified for school-rooms.
The quantity of fresh air required per person to insure good ventilation will depend on the type of building to be supplied and varies somewhat with different authorities. The De Chaumont standard is that of 1 cubic foot of air per second or 3600 cubic feet per hour, for each person to be accommodated. De Chaumont assumed a condition of purity which will permit less than 2 parts in 10,000 of CO2 over that carried by country air. In considering the same problem from the basis of permissible CO2, if 6 parts of CO2 in 10,000 represents purity of the required air, then 3000 cubic feet per person per hour is necessary. Likewise, the varying amounts for different degrees of purity are given by Kent in the following table. The upper line gives the permissible number of parts of CO2 per 10,000, while below each factor appears the number of cubic feet of air required per hour for each person supplied.
| 6 | 7 | 8 | 9 | 10 | 15 | 20 | = Parts of CO2 per 10,000 |
| 3,000 | 2,000 | 1,500 | 1,200 | 1,000 | 545 | 375 | = Cubic feet of pure air per hour |
It is generally recognized, that it is possible to live under conditions where no attempt is made to change the air in a building. It is also an established fact that the only preventive and cure for tuberculosis is that of living constantly in an atmosphere of the purest air. The greatest attainable degree of health is enjoyed by those who live in the open air, because oxidation is one of the most efficient forms of prevention and elimination of disease, and an abundance of pure air is the only assured means of sufficient oxidation.
The De Chaumont standard is intended to represent the limit beyond which the sense of smell fails to detect body odors or “closeness” in an occupied room. The amount of CO2 that air contains is not an absolute index of its purity, but it gives a standard under ordinary conditions, makes possible the requirement of a definite quantity of air. If it were possible to express the amount of oxygen contained in the atmosphere, the same relative condition might be attained.
The ordinary man exhales 0.6 cubic foot of CO2 per hour. Some forms of lighting apparatus produces this gas in greater amounts. The ordinary kerosene lamp gives out 1 cubic foot of CO2 per hour. A gas light using 5 cubic feet of gas per hour produces 3.75 cubic feet of CO2 in the same time. Any form of combustion permitting the products to escape into the air of the room tends to lower the quality of the atmosphere by adding to its content of CO2.