1989; Molhave, 1987; Morey and Singh, 1991; NRC, 1987b; Stolwijk, 1984). Sick building syndrome is suspected when occupants complain of symptoms associated with acute discomfort (e.g., eye, nose or throat irritation, sore throat, headache, fatigue, skin irritation, mild neurotoxic symptoms, nausea, odors) that persist for more than 2 weeks at frequencies significantly greater than 20 percent; a substantial percentage of the complainants report almost immediate relief upon exiting the building. Building-related illness is suspected when exposure to indoor pollutants results in clinical signs of a recognized disease that is clearly associated with building occupancy (e.g., some kinds of infections, building-related asthma, humidifier fever, hypersensitivity pneumonitis).

Accurate estimates of the relative occurrences of SBS and BRI in problem buildings have not yet been established. However, an initial analysis of more than 30 problem building investigations indicated that approximately two-thirds of the cases involved complaints and symptoms associated with SBS, while about one-third involved symptoms and signs associated with BRI and SBS—no cases of BRI without concomitant SBS were observed (Woods, 1988). The percentage of existing buildings that are causally associated with occupant exposure to allergens in either the SBS or BRI categories is unknown.

The most frequently reported characteristics in problem building investigations include inadequate quantity or quality of outdoor air provided by heating, ventilation, and air-conditioning (HVAC) systems for ventilation (incidence rates of 64–75 percent), and inadequate distribution of air supplied to and returned or exhausted from occupied spaces for thermal and air quality control (46–75 percent incidence) (Woods, 1989a, 1991). These characteristics are described as ventilation efficiency or ventilation effectiveness (ASHRAE, 1989b).

Equipment problems that have been most frequently reported in problem building investigations include inadequate specification and installation of air filters for removal of inert particulates and bioaerosols (incidence rates of 57–65 percent), inadequate specification and installation of drain pans and drain lines for removal of water condensed from cooling coils and humidifiers (60–63 percent incidence), inadequate specification and installation of duct work to prevent microbial contamination (38–45 percent incidence), and inadequate specification of humidifiers to prevent microbial or chemical contamination in the humidifier and subsequently in the air (16–20 percent incidence) (Woods, 1989a; 1991).

PRINCIPLES AND STRATEGIES

To achieve the twofold objectives of indoor environmental control (i.e., prevent or minimize deleterious exposures and provide for occupant comfort



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