Environmental Engineering Reference
In-Depth Information
problem occurs during the heating season when houses are under strong
negative pressure at their base. Indeed, this negative pressure is enhanced
as a result of the operation of combustion appliances such as furnaces and
fireplaces. Re-entry occurs by infiltration (see Chapter 11) caused by pressure
differences associated with indoor/outdoor temperature differences and
wind speed. Wood smoke odor can re-enter houses through bathroom
exhaust systems and chimneys with more than one flue liner.
Because of its unique odor, it is easy to detect re-entry phenomenon
associated with wood smoke. Since combustion by-products associated with
natural gas, propane, and oil are more difficult to detect by odor, little is
known about the re-entry of flue gases from these sources. They may be
inferred to be similar to those from wood smoke by analogy and from tracer
gas studies which have been conducted to characterize re-entry problems
in buildings.
Re-entry commonly occurs in large buildings where flue gas discharges
are located close to outdoor air intakes. This is especially the case when
intakes are located downwind of short boiler chimneys. Elevated levels of
CO (several ppmv) have been reported in buildings associated with flue gas
re-entry phenomenon.
IV. Health concerns and health effects
Combustion-generated contaminant exposures can pose a variety of acute
and chronic health risks. These may include acute, potentially lethal, and
sublethal effects from exposure to CO; irritation-type symptoms of the eyes
and mucous membranes of the upper respiratory system; irritation of the
upper airways that may cause asthmatic symptoms in individuals with
asthma or contribute to the development of asthma; initiation of pulmonary
symptoms and pulmonary function changes; development of lung and res-
piratory system cancers; and development of heart disease. Health risks
depend on the nature of exposures, contaminants and their levels, and the
duration of exposure.
A. Carbon monoxide
Carbon monoxide is emitted from all combustion sources. Exposures vary
considerably with source type, both in terms of peak and average exposure
concentrations, as well as duration. There are two major concerns: short-
term exposure to relatively high concentrations that have the potential to
cause death or acute illness, and chronic exposures to relatively low concen-
trations that may be associated with unvented combustion appliances and
other circumstances.
Carbon monoxide poisoning episodes associated with malfunctioning
combustion appliances and systems are not uncommon in North America.
Many dozens of deaths due to CO poisoning are reported in North America
each year, as are numerous other cases of near-fatal occurrences. In addi-
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