Asbestos TEM clearance is required by law in schools and some other public buildings.
Asbestos clearance is normally performed by sampling the air inside an asbestos containment chamber with the air scrubbers turned on. There are two types of asbestos air analysis. TEM looks only for asbestos fibers and uses a high magnification. PCM looks for any particle of a similar size to asbestos fibers and uses a low power microscope. PCM is normally used to confirm worker safety. TEM is normally used in schools, hospitals, private homes, businesses, etc. More about TEM and PCM here.
Asbestos fibers can’t be seen without magnification, so there is no way to tell if all the asbestos fibers have been removed from the air. The air scrubbers are left running so no fibers escape the containment. That’s why we test for asbestos outside containment when we have failed containment.
This is failed containment:
The purpose of this containment was to prevent asbestos fibers from contaminating drapes that are unseen behind the plastic shown. The drapes has to be discarded in a toxic dump because this containment failed. Asbestos fibers have hooks on the ends and usually can’t be removed from fiber products.