Air
Sampling Methods:
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Air sampling is usually conducted before and during abatement, to monitor
workers' exposure, and to ensure that the site has been adequately cleaned
(post-abatement, or clearance monitoring).
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Two methods are used to analyze air samples: Phase Contrast Microscopy (PCM)
and Transmission Electron Microscopy (TEM):
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PCM:
The advantages of PCM are the inexpensive cost, the wide-spread availability,
the minimal sample preparation, and quick results. PCM is also the OSHA
analytical method. The disadvantages are that it is not asbestos specific and
fibers smaller than a given size are not counted.
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TEM:
Unlike PCM, TEM is specific for asbestos and even the smallest of fibers are
counted. The disadvantages are the expensive costs and slow turnaround times.
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The clearance level for PCM analysis is 0.01 fibers/cubic centimeter of
air (f/cc). Levels above this indicate the need for further cleaning or
analysis with TEM to confirm the presence of asbestos fibers opposed to
non-asbestos fibers present on the sample. Clearance levels for TEM analysis
are less than 70 structures per square millimeter of filter area. The current
Occupational Safety & Health Administration, OSHA, Permissible Exposure
Limit (PEL-TWA) for asbestos is 0.1 f/cc for an 8-hour day.
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The
National Institue for Occupational Safety and Health, INIOSH, has not
established an exposure limit for asbestos, since NIOSH has not identified
thresholds for carcinogens that will protect 100% of the population. NIOSH
recommends that occupational exposure to carcinogens, including asbestos
fibers, be limited to the lowest feasible concentration.
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