20 ppm Barely can smell 5 ppm Damage to cillia of respiratory tract Ventilation rates are primarily determined by moisture, temperature, and air quality conditions. This equation can estimate house ventilation requirements. The exit air is not controlled. Examples are ceiling tubes and wall brooders. Incoming air may or may not be controlled.
Examples are adjustable air intake slots with black-out exhaust fixtures.
Regardless of method used, a house must be well sealed to achieve total air control. Tunnel ventilation is the most popular ventilation system presently used. It is effective because of the massive amount of air moved in a short period. Foggers in the main airstream are especially effective with the tunnel ventilation system. Total control of air movement includes control of air speed, air direction and air volume.