generation rate (N), by increasing the rate of removal of allergens from air (E), or by diluting airborne allergens (V_o). For some allergens, which are airborne only sporadically and in association with specific human activities (e.g., house dust mite allergens), source control is the best option. For others (e.g., outdoor allergens such as pollen) removal by filtration (E) is the usual method.

The physical causes usually associated with problem buildings include two basic inadequacies: (1) design inadequacies, which include system and equipment problems, and (2) operational inadequacies, which consist of inappropriate control strategies, lack of maintenance and housekeeping, and ineffective load management of building systems (Cone and Hodgson, 1989; EPA, 1991a; Molhave, 1987; Morey, 1984, 1988; Morey and Singh, 1991; NRC, 1987b; Robertson, 1988; Stolwijk, 1984; Woods, 1988, 1989a, 1989b, 1991). Table 7-1 summarizes some of the data on the physical causes of problem buildings.

The remainder of this section on principles and strategies discusses various source and exposure control strategies as they relate to building design, HVAC system design, building operation, and remediation. This is followed by a section that summarizes some practical control strategies in general, and as they apply to residential and commercial buildings. The chapter ends with conclusions and recommendations.