What is PCM?
Phase contrast microscopy (PCM), which is commonly used for personal air sample analysis and as a screening tool for area air monitoring, cannot distinguish between asbestos fibers and other kinds of fibers which may be present in the air. PCM is performed on air filter samples that have been collected to monitor asbestos conditions prior to, during, and after asbestos remediation. Large jobs require sampling during all 4 terms of abatement during background, prep, endurance, and final. However, Minor jobs only require sampling during background and final.
What is TEM?
Transmission Electron Microscopy (TEM). Transmission electron microscopy is used to identify asbestos fibers in air and bulk samples. The TEM is capable of analyzing samples at high magnification (20,000X and higher) and identifies asbestos fibers by morphology, crystalline structure and elemental analysis.
PCM vs. TEM comparison
While both of these methods are useful in ascertaining the concentration of asbestos fibers in a work area, both methods have their shortcomings. Although PCM is the standard used by the EPA and OSHA, it has its deficiencies. The primary problem with PCM is that it can be skewed high by non-asbestos fibers. PCM testing doesn’t specifically look for asbestos itself; only fibers around the size of asbestos and is only concerned with the total fiber concentration in the air. For example, if there was a release of fiberglass fibers into the air during air testing, a PCM could potentially fail even though there were no asbestos fibers in the air. Another drawback of PCM is that it cannot distinguish fibers less than 5 microns (µm) in length and 0.25 µm in width, which may lead to small fibers being undetected. Alternatively, TEM can view fibers less than 0.5 µm in length and 0.01 µm in width. TEM also can positively identify asbestos directly, distinguishing it from other fibers by scanning for its morphology and elemental composition. Recent research has shown that the concentration of Chrysotile asbestos fibers greater than 5 µm will be 4 times higher when analyzed by TEM compared to PCM.