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.