Environmental Engineering Reference
In-Depth Information
to produce harmless CO
2
and H
2
O vapor, and that the levels of O
3
used are
not harmful to the health of human occupants. Studies conducted on these
devices indicate that, when operated as recommended, O
3
concentrations
generated are not adequate to significantly reduce VOC concentrations; they
are, however, above ambient air quality and occupational exposure limits
(particularly for individuals in the near vicinity of operating devices). As a
consequence of potential consumer exposure hazards, a number of states have
sued manufacturers of O
3
generators, alleging they pose a substantial risk to
public health. Ozone generators continue to be widely sold in North America.
The deliberate introduction of O
3
into indoor spaces poses several addi-
tional concerns. As a powerful oxidant, O
3
bleaches fabric dyes and cracks
rubber and plastic products. As indicated in Chapter 4, it initiates indoor
chemical reactions that produce a variety of new irritants.
III. Air cleaners as contaminant sources
Though air cleaners are designed to clean air, they have been reported to be
sources of indoor contaminants such as VOCs and microbial organisms and
products. There have been reports of significant emissions of toluene and
xylene from oil-treated particle filters, and a variety of odorous aldehydes
(hexanal, heptanal, octanal, nonenal) and small organic acids from filters
infested with microorganisms. Filters can also be a source of fibrous particles
shed through HVAC systems and, as indicated previously, electronic air
cleaners can be a significant source of O
3
.
Filters in HVAC systems can capture and retain fungal spores and myce-
lial fragments which subsequently grow on collected dusts. Such growth can
penetrate filter media, contaminating other filters, air, and surfaces down-
stream. These fungi can produce allergens that can be detected in building
air independent of mold spore/particle concentrations.
Biocides are commonly used in filters. Though there is some potential
for them to become airborne, biocide levels in indoor air associated with
filter use have not been evaluated and reported.
Oxidizing media such as KMnO
4
have the potential to produce a variety
of small aldehydes and ketones in addition to CO
2
and H
2
O vapor. They
also have the potential to produce HCl from the oxidation of chlorinated
solvents such as methyl chloroform, commonly found in indoor environ-
ments. Studies on such potential contaminants have not been conducted. As
indicated previously, ozonation is the deliberate introduction of O
3
for what
is described as air cleaning purposes. It poses both direct and indirect indoor
air quality/indoor environment concerns.
Readings
American Lung Association,
Residential Air Cleaning Devices: Types, Effectiveness and
Health Impact
, Washington, D.C., 1997.
