Reduced infiltration and ventilation rates in buildings, proposed as important energy conservationmeasures, can lead to elevated levels of indoor-generated air contaminants. Chemical andbiological contaminants released into indoor environments are undesirable, but often unavoidablebyproducts of human activity and from the use of building materials and furnishings within closedspaces. Typical indoor contaminants include gaseous and particulate pollutants from indoorcombustion processes (such as cooking, heating, tobacca smoking), toxic chemicals and odorsfrom cooking and cleaning activities, odors and viable microorganisms from humans, odormaskingchemicals used in several activities, and a wide assortment of chemicals released fromindoor construction materials and furnishings.

When these contaminants are generated in indoor environments in excessive concentrations,they may impair the health, safety, or comfort of the occupants. The random introduction ofoutdoor air by infiltration (through cracks in the building envelope), or its regulated introductionby natural ventilation (opening doors and windows) or mechanical ventilation (fan andduct systems of varying complexity), is the usual way in which building occupants are protectedfrom the accumulation of undesirable indoor air contaminants

In recent years, there have been several reasons for a closer analysis of the use of ventilationin buildings. Studies of outdoor air pollution, indicating that under certain circumstances"fresh" outdoor air may be more contaminated than indoor air, has motivated an examination of the quality and use of outside air for building ventilation.

The ultimate objective is to reduce energy consumption as much as possible without impairingthe health and comfort of the occupants. At the present time, there are major gaps in theunderstanding of what positive steps must be taken to assure good air quality in buildings.