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Indoor air quality (IAQ) can cause or contribute to a variety of symptoms, or even illness, in building occupants, negatively impacting their health and productivity. Americans, on average, spend 90% of their time indoors, where air quality is dependent on local ventilation and conditions. Climate change, extremes of heat and cold, and changes in seasonal conditions impact IAQ, both directly due to changes in moisture and dust content in the air, as well as indirectly due to increased reliance on recycled/conditioned air. In such scenarios, concentrations of some endogenous pollutants inside buildings may exceed standards established for outdoor concentrations.

Building-related illness (BRI) encompasses health problems that develop in nonindustrial settings that are customarily considered nonhazardous, such as homes, schools, and offices. In such settings, indoor air contamination has been linked to a wide variety of building materials and consumer products. In contrast, sick-building syndrome (SBS) has been a popular misnomer in past decades, with the label “sick-building” previously defined as the occurrence, in more than 20% of the building occupants, of a variety of nonspecific symptoms with minimal or no objective findings that are not linked to a specific diagnosis. Current literature has seen the SBS term drop out of favor, and is considered more part of the nonspecific BRI type.


Potential indoor air contaminants can be classified as: (1) contaminants released from the building or its contents, including asbestos, formaldehyde, and radon; (2) contaminants generated by such diverse human activities as cooking, heating, cigarette smoking, and cleaning; and (3) infiltrated contaminants, or agents that enter the house or building along with the outside air, but in lower concentration (typically by 25–75%).

Contaminant concentration is influenced not only by the exposure source but also by the exchange rate between indoor and outdoor air. The introduction of outdoor air into a home or building occurs either by implemented ventilation or by infiltration. Infiltration occurs through cracks or other leaks in the structure or through open doors and windows. The amount of infiltration depends on the type of building, the amount of insulation, and other weather-proofing and climatic conditions. Implemented ventilation, for example, forced-air heating or air-conditioning systems, may provide substantial amounts of outdoor air but also may be designed to recirculate preconditioned air with minimal fresh-air intake.

The amount of air exchange often is expressed in air changes per hour (ACH). ACH may vary from 0.2 in tightly sealed homes to 0.7 in an average home to 60 or more in some industrial settings with implemented ventilation. Alternatively, with implemented ventilation, the amount of outdoor air supplied may be expressed in cubic feet per minute (cfm) per occupant or liters per second per occupant.

The concentration of contaminants at any location within a building will be influenced by the location of the source and the ...

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