Outdoor air pollution can have a bearing on the effectiveness of indoor air and the quality of ventilation. There is a pressing need to reflect on the potential type and effect of occurrences (e.g. smog, or chemical accidents) and to develop technical, operational and organisational measures which must be taken with mechanical ventilation units in the case of polluted outdoor air situations. A polluted outdoor air situation is present when a ventilation process leads to the intake of pollutants in the interior and to the enrichment of these pollutants to an unacceptably high concentration.
This work deals with problems of the air humidity in inhabited dwellings. A new approach is presented here which renders the definite diagnosis of humidity problems possible. The room air humidity from two buildings with different air ventilation systems with eight dwellings each is examined, The efficiency of the different ventilation systems is presented applying the new value, the so called "standardized room air humidity".