Airborne concentrations of asbestos are determined by PCM and TEM.
Phase Contrast Microscopy (PCM) is widely used to measure fiber concentrations of air samples. This is routinely done at asbestos abatement sites and can be applied for environmental monitoring, personnel monitoring, and clearance testing for minor abatement projects. The PCM technique has the advantage of fast turnaround time and low cost. This technique, however, does have significant limitations. This light microscope technique operates at magnifications of only 400X and will not resolve fibers below 0.25 microns (um) in diameter. Furthermore, PCM can not distinguish asbestos fibers from other fibers (ex: gypsum, mineral wool, fiberglass, cellulose etc.).
Consequently, an analysis by PCM indicating high fiber counts does not necessarily indicate the presence of asbestos. Likewise, low fiber counts by PCM can not conclude an asbestos free environment. PCM merely provides an index of the total airborne fibers present in a given size range. Because of the limitations of this technique, many consultants and public agencies now require the use of TEM for certain monitoring and clearance activities. The current revision of the National Institute of Occupational Safety and Health (NIOSH) Method 7400 is employed for this analytical technique. Accreditation is provided for the laboratory through the American Industrial Hygiene Association (AIHA) and for individual laboratory analysts through the AIHA Asbestos Analysts Registry (AAR) Program. Extensive Quality Assurance and Quality Control (QA/QC) regimens are performed as part of our ongoing certification program. Proficiency testing is primarily conducted through the Proficiency Analytical Testing Program (PAT) administered by AIHA. On-site technical evaluations are also primarily conducted through AIHA.
Transmission Electron Microscopy (TEM) represents the most sophisticated technology available for characterizing asbestos minerals. This technique is now the standard for most airborne investigations including post abatement clearance testing as well as diagnostic and environmental monitoring activities.
Using magnifications routinely at 20,000X or greater and employing powerful chemical (EDXA) and mineralogical (SAEDP) tools, the TEM can differentiate, not only asbestos from non-asbestos fibers, but also can classify the several species that comprise asbestos minerals. The sample preparation and analysis process precludes turnarounds that would be available for PCM. Typical TEM RUSH analysis on a set of AHERA samples can be conducted in four to six hours.
Airborne samples are routinely investigated employing methods from NIOSH, EPA, the Asbestos Hazard Emergency Response Act (AHERA) guidelines, and International Standards Organization (ISO 10312). Accreditation is primarily provided by the National Institute of Standards and Technology (NIST) through the National Voluntary Laboratory Accreditation Program (NVLAP).
Extensive Quality Assurance and Quality Control (QA/QC) regimens are performed as part of an ongoing certification program. Proficiency testing is primarily conducted through the Proficiency Analytical Testing Program (PAT) administered by NVLAP. On-site technical evaluations are also primarily conducted through NVLAP.