Figure 2-2. Bag for collecting grab samples
(2) Partial period samples. In this kind of sampling, the sample is collected
for a portion of some standard period such as workday or shift. Partial period sampling
should not be conducted for less than 70the period of the standard (for example, 5 l/2
hours of an 8-hour work period). To collect partial period samples, it is necessary to
collect atmospheric air and pass it through a device or a series of devices in which the
contaminant can be concentrated for later analysis.
(3) Full period single samples. A full period single sample is one sample
collected continuously throughout the full period of the standard (for example, the work
shift or workday). As was the case with the partial period sample, it is necessary to
draw in atmospheric air and process it through some device (like a charcoal tube),
which collects and/or concentrates the contaminant for later analysis.
(4) Full period consecutive samples. Several samples of equal or unequal
time are taken for the full period of the standard. This sampling method yields the most
dependable results because there are no unsampled periods of time throughout the
workday. Furthermore, because there is more than one sample for the work period, it is
easier to pick out, from the results, periods or "excursions" of chemical exposure that
might exceed the STEL limits for a particular chemical. Unfortunately, because of the
number of samples that must be analyzed, generally by an analytical laboratory, this
method is the most expensive and labor-intensive sampling.