Ventilation (or the process of introducing a continuous supply of fresh air and of removing that already vitiated) is a question of importance in rooms and buildings where people are gathered together. A successful scheme of ventilation demands that there shall be no draughts, no stagnation of the air, and no undue moisture in the fresh air introduced. It is especially necessary to prevent overcrowding. Ideally, each individual should have as much as 1000 cubic feet of air space, although in practice financial considerations necessitate a much smaller figure.
In the case of sick people, the amount of cubic space allowed must be increased, and this must be borne in mind when considering the planning of a hospital or similar institution.
Supposing that 1000 cubic feet have been allowed for each person, the air in this space will require to be changed three times in the hour, but in cases of a smaller allowance per head more frequent changing will be necessary. It becomes clear that there will be more risk of draught in securing adequate ventilation for a smaller room than for a large one.
The hot, impure air in a room tends to rise to the ceiling, and unless it is removed, it descends on cooling and is inspired once again by the occupants of the room.
It is essential to ascertain that the whole of the air in any given room is being put in motion and changed. This can be done quite simply by holding up smoking brown paper, and observing the currents of smoke which result.
In ordinary dwelling rooms the chimney forms a sufficient ventilator in itself, without the installation of any special apparatus. With the fire burning, a current of air is maintained up the chimney, and fresh air can enter the room through the doors or windows if these are opened sufficiently. In addition, building materials are porous, and thus a good deal of ventilation takes place, insensibly as it were, through the walls, ceiling, and floor, assisted by the force of the wind blowing on one side of the building.
In apartments where people are confined together for long periods, as in factories and workshops, additional devices are employed to ensure adequate ventilation. Thus the space between the upper and lower sashes of the windows may be utilised, as in Hinckes-Birds' window ventilator.
Similarly, openings may be made in the wall, or perforated bricks may be placed at intervals round the wall at the level of the skirting. The windows may be ventilated by a circular ventilator or by the louvred window pane.
If on entering a room a feeling of stuffiness be experienced it is certain that the ventilation is inadequate, and as this first sensation is rapidly lost its warning should be acted upon instantly. We see this whenever we enter a crowded railway carriage. The first breath often makes us gasp, yet in a few minutes we become unaware of the vitiated atmosphere.