Environmental Engineering Reference
In-Depth Information
100
90
80
70
60
50
40
30
20
10
Acrolein
Toluene
Diisocyanate
Formaldehyde
0.1 1.0 10.0 100
Concentration (ppmv)
Figure 11.20
Log-linear relationship between irritant response and exposure con-
centrations in mouse bioassays. (From Alarie, Y.,
Environ. Health Perspect
., 42, 9, 1981.)
HVAC systems themselves may be a source of contaminants. This is
notably the case with units that provide cooling. Condensate waters and
wetting of nearby porous insulation have been widely reported to be sources
of biological infestation and contaminant generation. Such infestation may
result in exposures that cause allergenic responses in some building occu-
pants and, in some cases, outbreaks of hypersensitivity pneumonitis. Duct
liner materials may also serve as a source of particulate dusts on deteriora-
tion, and may emit a variety of gas-phase substances.
In addition to contaminant/human response relationships, other factors
may confound the effectiveness of ventilation in reducing occupant symp-
toms and improving satisfaction with air quality. Significant evidence exists
to indicate that health complaints in buildings are caused by a variety of
factors, so that the prevalence of symptoms or a group of symptoms may
be a cumulative result of responses to a variety of exposures. In cross-
sectional epidemiological studies, it is common to identify multiple risk
factors which appear to contribute to health complaints. These have included
exposures to VOCs, floor dust components, handling carbonless copy paper,
working with photocopy machines and photocopied paper, working with
video display terminals, psychosocial factors, biological contaminants, etc.
A number of these factors may not be air quality concerns (e.g., handling
photocopied and carbonless copy paper, working with video display termi-
nals, etc.), and thus would not be responsive to changes in ventilation rates.
In other cases, exposure may be localized (e.g., resuspension of surface dust),
and therefore not controllable by general dilution ventilation.
B.
Local exhaust ventilation
When contaminants or potential contaminants are generated by high-emis-
sion sources such as specific equipment types, appliances, processes, or room
