2nd. To ensure the maintenance of this standard, 3,000 cubic feet of pure air must be supplied per head per hour.
3rd. In order to supply this amount of pure air, with ordinary means of ventilation, 1,000 cubic feet at least must be allowed per head in buildings always occupied.
[CHAPTER XXI.]
PROBLEMS AS TO VENTILATION.
The following formula enables many problems relating to ventilation to be solved. Let p = the amount of poison (carbonic acid) in every cubic foot of fresh air, viz. ·0004 cubic foot. Let A = the number of cubic feet of fresh air delivered or available, P = the amount of carbonic acid exhaled, and x = the amount of carbonic acid per cubic foot in the room at the end of a given time. Then—
x = p + P ∕ A, whence A = P ∕ (x - p).
If the carbonic acid in the air of a room is ·75 per 1,000 volumes (that in the outer air being ·4 per 1,000 volumes), and there are five persons in the room, how much air is entering the room per hour?
- Here x = ·00075.
- p = ·0004.
- P = ·6 (i.e. number of cubic feet of carbonic acid expired by each person per hour).
- Now x = p + P ∕ A.
- ·00075 = ·0004 + ·6 ∕ A.
Therefore A = about 1,700.
Thus 1,700 cubic feet are required for each individual to keep the air within the given limit, and five times this amount will be required for five persons = 8,500 cubic feet.