Air sampling is used to detect the presence of asbestos
fibers in an area. PCM and TEM are two methods used to analyze air samples
associated with asbestos fibers. In
addition to determining if the air in a particular area contains asbestos
fibers, sampling can also be an indication of how well or how poorly an
asbestos removal project is proceeding.
During an asbestos removal project, it is important to keep fiber counts
as low as possible to reduce potential exposure to workers, building occupants
and to determine if and when the work area is suitable to be reoccupied.
Phase Contrast Microscopy analysis (PCM) is most often used
in the asbestos abatement industry. PCM
analysis is not as accurate as Transmission Electron Microscopy (TEM). The PCM method of analysis can count fibers
but cannot positively identify the fibers as asbestos. Using PCM analysis, fibers of a certain width
to length ratio are assumed to be asbestos fibers and counted accordingly. In comparison, TEM sampling methods use a
higher magnification thereby allowing smaller fibers to be detected and
allowing the technician to positively identify an asbestos fiber or a
non-asbestos fiber (see photo below).
PCM air sampling analysis is the most common method of
determining asbestos fiber counts. It is
far less expensive as compared to TEM analysis and turn-around time is much
faster with PCM methods. In fact, PCM
air samples can be read on site immediately after the sample has been taken by
the technician.
Some advantages and disadvantages of analysis methods are as
follows.
METHOD ADVANTAGES DISADVANTAGES
PCM Less
costly Not
as accurate lower magnification
Faster Turn Around Can’t
positively identify
asbestos Could
result in false positive result
TEM Greater accuracy More
costly
Positive
asbestos identification Slow
turn-around, usually 2-3 days Less chance of false positive result
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