Indoor air quality began to be referred to as a problem at the end of the 1960s, although the first studies did not appear until some ten years later.
Although it would seem logical to think that good air quality is based on the presence in the air of the necessary components in suitable proportions, in reality it is the user, through respiration, who is the best judge of its quality.
They have been obtained by measuring adverse effects on health resulting from exposure to contaminants in the environment.
These standards are therefore useful as general guidelines for an acceptable quality of indoor air, as is the case with those proposed by the World Health Organization.
Technical criteria such as the threshold limit value of the American Conference of Governmental Industrial Hygienists (ACGIH) in the United States and the limit values legally established for industrial environments in different countries have been set for the working, adult population and for specific lengths of exposure, and cannot therefore be applied directly to the general population.
The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) in the United States has developed a series of standards and recommendations that are widely used in assessing indoor air quality.
Concentrations of contaminants in the indoor air of these structures are usually of the same order as those commonly found in outdoor air, and are much lower than those found in air in industrial premises, where relatively well-known standards are applied in order to assess air quality.
Even so, many building occupants complain of the quality of the air they breathe and there is therefore a need to investigate the situation.
The situation is comparable to what happens with the detailed composition of an item of food and its taste: chemical analysis is inadequate to predict whether the food will taste good or bad.
There are few conclusive studies on the subject, whether relating to public buildings and offices or private dwellings.
Series of standards for outdoor air quality exist and are relied on to protect the general population.
This would certainly be true if we were dealing with building materials, furniture and ventilation systems as they were used 50 years ago, when bricks, wood and steel predominated.
But with modern materials the situation has changed.
In addition, for many contaminants present in the air, the effects of acute exposure are well known, whereas there are considerable gaps in the data regarding both long-term exposures at low concentrations and mixtures of different contaminants.