Asbestos samples can be air or small pieces of the building material.
Asbestos air samples are analyzed at TEM or PCM methods and standards.
Asbestos bulk samples are analyzed using PLM methods and standards.
Air TEM (Transmission Electron Microscopy)
TEM is used for asbestos clearance. This method uses high powered microscopes and looks only for asbestos fibers in the air.
The machinery required is not mobile and is sophisticated. SEM microscopes magnify objects at least 20,000 times their actual size. This method is asbestos-specific; so specific that it can indicate the type of asbestos fibers in the air sample.
TEM is most appropriate for final clearance samples. This is due to regulation (AHERA) or liability issues. By law, schools, etc., must use this method. TEM is best for litigation and real estate transactions.
TEM samples are considered the gold standard for asbestos air testing.
Air PCM (Phase Contrast Microscopy)
PCM is used to determine if an area is safe for workers. PCM is less expensive because it uses a lower power microscope and looks for all fibers, not just asbestos.
NIOSH 7400 Method samples use a light microscope to see all fibers. The microscope magnifies objects approximately 400 times their actual size.
All asbestos bulk samples collected are sent to an accredited asbestos environmental laboratory.
The main disadvantage of PCM methodology is that it is not asbestos specific. The analyst counts any fiber that falls into a field of view that is greater than or equal to 5 μm in length, with a 3:1 aspect ratio (three times longer than its width).
You need to be aware of this when requesting that we use PCM analysis. Items such as carpets, wood, fiberglass, and drywall can produce fibers that fall in this size range and will be counted along with asbestos fibers in determining exposure.
To successfully test we need dust free environment with negative air machines running is recommended, per industry standards.
Dust or bulk PLM (Polarized Light Microscopy)
PLM is used to determine if asbestos abatement needs to be done before a remodel or demo.
The polarized light microscopy technique utilizes the unique features of polarized light to observe mineral specific optical properties. In this manner, PLM can differentiate asbestos from non-asbestos fibers and further classify the various species that compose the asbestos mineral family. Moreover, the technique records the identity of the non-asbestos fibrous component of each bulk building material sample.
The PLM procedure provides an economical technique for screening large numbers of samples. As with PCM, there are limitations to light microscopy testing due to the magnification (100-400X) used. The dust collected in the air sample may have other fibers that may be counted as “asbestos”.
PLM results are reported as a percentage of the total sample. This method utilizes a few protocols for the quantification process. These include visual estimation and point counting. Depending on the sample matrix, PLM analytical sensitivity can be a fraction of a percent. Gravimetric reduction protocols (ELAP 198.1, EPA 600) further enhance this technique’s ability to accurately quantify and qualify asbestos.
The current method employed for these analyses is found in EPA 600/R-93/116. Other procedures are also utilized to supplement this method such as NIOSH 9002, and OSHA ID 191. Accreditation is primarily provided by the National Institute of Standards and Technology (NIST) through the National Voluntary Laboratory Accreditation Program (NVLAP).