Transmission Electron Microscopy – TEM- Asbestos Air Samples uses electrons to create images, fine crystal patterns, and analyze the chemical makeup of fibers or structures encountered in the air sample. The machinery required is not very mobile and is very sophisticated. It magnifies objects at least 20 times their actual size. This method also is asbestos-specific. So specific that it can indicate the type of asbestos fibers in the air sample. This method is often used when there are interfering fibers which causes the PCM results to be very high but asbestos fibers are not suspected as the cause of their high-fiber count.
This method is most appropriate for final clearance samples either due to regulation (AHERA) or liability issues. By law, schools, etc., must use this method. This is also most appropriate for litigation and real estate transactions.
The client should be aware that the two methods – TEM v PCM - are not readily comparable. An air sample could pass (clear) PCM but fail TEM clearance or vice versa. The reason for this discrepancy was simply the power of the TEM microscope. At a 20,000 power minimum magnification, the TEM method is able to see very thin fibers that will not even be detected by the PCM 400 power microscope. In addition, the TEM method counts any fibers greater than 0.5 micrometers in length with a 5:1 aspect ratio. It is seen in counting much smaller fibers than PCM.
On the other hand, one could fail PCM but clear by TEM. This is usually the case when there are other interfering fibers besides asbestos. PCM will count these; TEM will not count them because they are not asbestos.
No one said understanding asbestos testing is quick or easy. All personnel at American Air Testing have taken many lengthy courses and passed government required testing. Because of the complexity of asbestos, the testing choice is really best left to licensed professionals.
