Environmental Engineering Reference
In-Depth Information
ducted to identify differences in contaminant types and levels in order to
determine whether complaints are consistent with exposures.
The number of sampling locations may be increased if electronic direct-
read instruments are available. This is particularly true for CO and CO
.
2
Sampling for CO
should be conducted in return, supply, and outdoor air
to determine the relative percentage of outdoor air being provided to a space,
zone, floor, or building.
Sampling locations will, in many cases, be determined by the nature of
the contaminant and potential exposures. In residential environments,
USEPA recommends that sampling for radon be conducted in the lowest
livable space. In some houses this would be the basement; in two-story
houses on a slab or crawlspace, the first floor. Because of the effects of wind
on building pressures, radon testing should always be conducted near the
center of the dwelling.
Sampling locations in dwellings should be selected to represent poten-
tial sources as well as exposures. These would include rooms with obvious
mold infestation or odor, and rooms occupied by individuals with health
problems.
2
When air sampling is conducted is an important consider-
ation in problem building investigations, investigations in dwellings, and
for screening measurements such as radon.
As indicated previously, concentrations of many airborne contaminants
vary with time, and knowledge of such variation is important in conducting
sampling and interpreting results. Time is described in the context of a single
day when an investigation is being conducted; a specific hour or day when
elevated concentrations may be expected; or a season when high, moderate,
or low values may occur.
In poorly ventilated buildings, CO
c.
Time.
levels reach their peak in early to
mid-afternoon. If longitudinal (real-time sampling conducted over a period
of hours) sampling is conducted, it should include those hours when peak
CO
2
levels can be expected. Sampling CO
only at the beginning of building
2
2
occupancy would be misleading.
In problem environments where exposure to CO is expected, high CO
levels are likely to occur episodically. Multiple measurements may be neces-
sary over the course of a single day, as well as measurements on other days
if elevated levels are not initially observed. Elevated CO levels are more likely
to occur during the heating season, especially when heating systems are active.
Formaldehyde levels vary over the course of the year and usually reach
maximum values when temperature, relative humidity, and ventilation con-
ditions are optimal. Such optimum conditions occur in the spring and fall,
and in air-conditioned dwellings in summer.
With the exception of radon, the winter season in cold climates is a poor
time to measure contaminant levels in residential buildings. Because of
relatively high infiltration air flows, and lower thermostat settings and rel-
ative humidity (in the case of HCHO), many airborne contaminants in
