Environmental Engineering Reference
In-Depth Information
icantly lower. Indoor NO
levels in homes with gas cooking stoves have been
reported to be in the range of 18 to 35 ppbv.
Gas cooking appliances are used intermittently so that exposures vary
significantly. In low income areas of many northern U.S. cities, building
occupants often use opened gas ovens as a continuous supplemental source
of heat during cold winter conditions. Such use would be expected to result
in higher exposure concentrations and longer exposure durations.
2
D. Gas fireplaces
Gas-burning fireplaces are widely used in North American homes for aes-
thetic reasons. Historically, emissions from these fireplaces were vented to
the outdoor environment the same way as wood-burning fireplaces. In recent
years, large numbers of ventless fireplaces have been sold and installed in
new homes. Limited research studies have been conducted to determine the
impact of their use on indoor contaminant levels. In one study, combustion
by-products such as CO were reported to be low, while significantly higher
concentrations were reported in higher-altitude Colorado studies. Carbon
dioxide levels often exceeded 5000 ppmv, the OSHA 8-hour exposure limit.
Gas fireplace emissions are likely to be similar to those of gas heaters.
Because of the intermittent use of ventless gas fireplaces, exposure to com-
bustion by-products would, in most cases, be less than that associated with
the use of gas heaters. Some users have reported moisture condensation and
an oily film on windows, which they believe to be associated with ventless
fireplace use. Along with elevated CO
levels, high production rates of water
2
vapor may be expected.
III. Miscellaneous sources
Combustion sources described above are characterized by their use as home
space heating or cooking appliances. There are a variety of other sources of
combustion-generated substances which are common causes of indoor air
contamination or cause contamination under relatively limited or unique
circumstances. The most important of these is tobacco smoking. Other
sources include candles, incense, and use of propane-fueled floor burnishers,
propane-fueled forklifts and similar equipment, propane-fueled rink ice-
making machines, arena events involving gasoline-powered vehicles,
entrainment of motor vehicle emissions, and re-entry of flue gases.
A. Tobacco smoking
Approximately 24% of the adult population of the U.S. (~35 million individ-
uals) smoke tobacco products daily. In nonresidential, nonindustrial build-
ings, smoking has either been banned or severely restricted. As a conse-
quence, such buildings are unlikely to experience significant tobacco smoke-
related contamination. However, significant indoor contamination continues
