AHERA TEM Method

The AHERA TEM method is the transmission electron microscopy procedure EPA requires for clearance air testing after asbestos abatement in schools under the Asbestos Hazard Emergency Response Act. It counts asbestos structures at least 0.5 micrometers long, identifies them by electron diffraction and chemistry, and compares air inside the work area with air outside.

Origin

Congress passed AHERA in 1986, and EPA's 1987 rule for school asbestos (40 CFR Part 763, Subpart E) included the TEM method as an appendix. Because the method was spelled out in detail and became a federal requirement, it was widely adopted for clearance testing outside schools as well.

Significance in Asbestos Context

Before a school area can be reoccupied after a large abatement, AHERA requires clearance air samples analyzed by TEM, with a stated analytical sensitivity, and the work area passes only if its asbestos concentrations are low enough compared with outside or blank samples. The method counts much smaller structures than phase contrast microscopy, which is why it is preferred for clearance. In litigation, AHERA TEM results from schools and other buildings can show whether asbestos was present in the air during or after work, and AHERA inspections and management plans can show what materials a building contained. Experts sometimes reanalyze AHERA data or compare it with other methods, so knowing which method produced a number helps explain what it means.

Example Sentence

The gymnasium passed clearance only after a second round of AHERA TEM samples, because the first inside samples were too high compared with the outdoor samples.

Related Terms

AHERA, Clearance Air Testing, Transmission Electron Microscopy (TEM), Structure Counting, Direct-Transfer Method, Analytical Sensitivity, Abatement

Notes

• Schools must keep asbestos management plans available; they can show what materials a building contained.
• If you worked in a school during abatement, note the dates and areas; clearance records may exist.