The three strategies, in order of effectiveness, for reducing pollutants in the
indoor air environment are source control, ventilation, and air cleaning. (1) Source
control eliminates individual sources of pollutants or reduces their emissions, and
is generally the most effective strategy. (2) Ventilation brings outside air indoors.
It can be achieved by opening windows and doors, by turning on local exhaust
fans, or, in some situations, by the use of mechanical ventilation systems, with or
without heat recovery ventilators (air-to-air heat exchangers). However, there are
practical limits to the extent ventilation can be used to reduce airborne pollutants.
Costs for heating or cooling incoming air can be signifi cant, and outdoor air
itself may contain undesirable levels of contaminants (Society of Heating, Refrigerating,
and Air Conditioning Engineers, 1997). (3) Air cleaning may serve as an
adjunct to source control and ventilation. However, the use of air cleaning devices
alone cannot assure adequate air quality, particularly where signifi cant sources are
present and ventilation is insuffi cient.