Phase contrast microscopy (PCM) – The traditional technique for measurement of asbestos fibers in air and upon what many regulations are based (e.g., occupational exposure). Results are often used to estimate health risk from asbestos in air. PCM has limited utility because it cannot differentiate between asbestos and non-asbestos fibers. Thus, PCM use in Libby has been limited to specific purposes, often in conjunction with another analytical technique such as TEM.

Transmission electron microscopy (TEM) – TEM is more complex than PCM or PLM, and it uses a more sophisticated analytical instrument. TEM can distinguish between asbestos and non-asbestos fibers and asbestos types. It can be used at higher magnifications, enabling identification of smaller asbestos fibers than can be seen by other techniques. In Libby, two TEM methods (AHERA and the more complex ISO 10312) are used, depending on the data need.
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