NIOSH, in studies of over 1,000 IAQ episodes, categorized
the major sources or factors as follows: (estimates are rounded to nearest 10%)
50% related to deficiencies in the ventilation of the
building, (e.g., lack of outside air, poor air distribution, uncomfortable temperatures
and humidities and sources of contaminants in the system.)
30% related to some indoor air contaminant (e.g.,
formaldehyde, solvent vapors, dusts, and microbiological agents.)
10% could be attributed to an outdoor source (motor vehicle
exhaust, pollen, fungi, smoke, construction dusts.)
10% had no observable cause.
Of the indoor sources, about 5% were related to suspected
microbial contamination, and about 5% were attributed to furnishings and fabrics.
NIOSH, in its studies of IAQ problems,
could not identify any sources or causes in about 10% of the cases it investigated. When
mass psychogenic illness was suspected, the following characteristics were often present:
- Gender-specific complaint rates.
- Complaints appear to have influenced others to
"discover" similar complaints.
- Labor/management problems existed.
- Persistence of complaints following removal of supposed
- Socially powerful people became effected.
- Nonspecific symptoms or complaints.
- Boring and repetitive work.
- Excessive work loads.
- Rigid management structures.
- The feeling of "lack of control."
- Poor work environment.