Glossary
TEM
Also: Transmission Electron Microscopy
An electron microscopy method that can confirm fiber composition and is required for AHERA clearance air sampling in schools.
TEM stands for Transmission Electron Microscopy. The method passes a beam of electrons through a sample on a thin support film and records the resulting image at high magnification.
Two TEM methods are common for asbestos analysis. The AHERA TEM method (40 CFR Part 763 Appendix A) is required for clearance air sampling in schools subject to AHERA. NIOSH 7402 is a TEM confirmation method used when PCM results need to be checked for asbestos content (versus other fibers).
TEM has two advantages over PCM: it can count smaller fibers than PCM can resolve, and it can confirm asbestos identity through electron diffraction or energy-dispersive X-ray analysis.
TEM is slower and more expensive than PCM. It is required where the regulation specifies it (AHERA school clearance) and is used selectively for confirmation in non-school work. Most exposure monitoring uses PCM and only escalates to TEM when results are equivocal or the project specification calls for it.