Environmental Engineering Reference
In-Depth Information
Figure 9.10
Calibration of N-6 Andersen sampler with a wet test meter.
adjusted to account for multiple single site impactions when counts are
relatively high (>50/plate); statistical charts have been developed for this
positive-hole correction methodology. Selected positive-hole correction val-
Sample handling for bacteria begins as soon as samples are collected. It
is desirable to transport bacteria samples to the laboratory immediately, as
delayed temperature control provides a selective advantage to organisms
that grow at ambient temperatures.
d. Total mold spore/particle sampling.
With the exception of
media/culturing concerns and the need for disinfection, sampling consider-
ations described for culturable/viable sampling above apply to total mold
spore/particle sampling as well. These include flow rates, duration, and
sample analysis.
i. Collection. Flow rates recommended for total mold spore sam-
pling are in the range of 10 to 15 L/min. It is common to use a sampling
duration of 10 minutes. In very dusty environments, particle overloading
occurs and accurate counts of mold spores and particles cannot be made
easily. In such environments, a sampling duration
≤
5 min is recommended.
ii. Preparation. Samples can be prepared and counted microscopi-
cally within an hour after sampling. They do not, however, require imme-
diate preparation and can be stored indefinitely for future microscopic eval-
uation and enumeration. Examination of slide samples at 1000
×
magnification is recommended because lower magnifications (circa 400 to
500
) result in significantly lower counts. Both spores and hyphal fragments
are counted on a fraction of the collection surface (5%) using horizontal
traverses. The count is converted to a concentration based on volume of air
sampled, expressed as spores or structures per cubic meter (S/m
3
).
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