Asbestos Information


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).

Two methods are used to analyze air samples. Phase Contrast Micoscopy (PCM) and Transmission Electron Microscopy (TEM):

  • 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.
  • TEM
    Unlike PCM, TEM is specific for asbestos and even the smallest of fibers are counted. The disadvantages are the expensive costs and slow turn around times.
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, Permissble Exposure Limit (PEL-TWA) for asbestos is 0.1 f/cc for an 8-hour day.

The National Institute for Occupational Safety and Health (NIOSH), has not established an exposure limit for asbestos, since NOISH has not identified thresholds for carcinogens that protect 100% of the population. NIOSH recommends that occupational exposure to carcinogens, including asbestos fibers, be limited to the lowest feasible concentration.


For questions concering Asbestos, call 243-6091 from 8am to 5pm, Monday - Friday.

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EPA Health Information on Asbestos Exposure at High Levels in Dust Samples

University of Montana-Missoula Asbestos Operations and Maintenance Plan
Revised January 23, 2009