Glossary
Clearance Air Sample
Air samples taken at the end of an asbestos abatement project to verify that fiber concentrations in the work area meet the clearance criterion before the area is re-occupied.
A clearance air sample is taken at the end of an asbestos abatement project after the visual inspection passes, with the goal of confirming that airborne fiber concentrations inside the work area are low enough to release the area for re-occupancy.
In schools subject to AHERA, the clearance criterion is set by 40 CFR Part 763 Appendix A and uses TEM (transmission electron microscopy) analysis. In non-school abatement, the common criterion is 0.01 fibers per cubic centimeter by PCM (phase contrast microscopy), though some project specifications require TEM for non-school work as well.
Clearance sampling is performed by an independent third party (industrial hygienist or project monitor) rather than by the abatement contractor itself, to avoid the obvious conflict of interest. The sampling is done under aggressive air conditions (using leaf blowers and fans inside the work area) to challenge the cleaning.
A failed clearance means the abatement contractor re-cleans and the area is re-sampled. A passed clearance closes out the work area.