
The Fallacy of Phase Contrast Microscopy (PCM) Clearance Air Sampling, or 5 Reasons Why We Should Stop Using PCM for Clearance.
The Environmental Protection Agency’s (EPA’s) Asbestos Hazard Emergency Response Act (AHERA) regulation introduced the requirement of clearance sampling after an asbestos abatement project was completed. Remember the AHERA regulation applies to schools from Kindergarten to 12th grade (K-12), both public and private schools. However, for all intents and purposes, the AHERA method serves as the industry standard when final clearance is performed for most asbestos abatement projects, especially when areas are to be re-occupied. The requirements for clearance are found in two sections of the rule: Response Actions; §763.90 (i) Appendix A (to Subpart E) – Interim Transmission Electron Microscopy Analytical Methods – Mandatory and NonMandatory – and Mandatory Section to Determine Completion of Response Actions AHERA allows final clearance air sampling to be done by phase contrast microscopy (PCM) methodology for projects less than or equal to 160 square feet (SF) or 260 linear feet (LF) by the National Institute for Occupational Safety and Health (NIOSH) 7400 methodology (Issue 3: 14 June 2019 is the current issue). For projects greater than 160 SF or 260 LF clearance shall be done by the AHERA transmission electron microscopy (TEM) method (requirements at 763.90 (i) (4) and Appendix A). Since this article’s purpose is to discuss why we should not be using the PCM method we will focus our discussion on this method specifically. An important point to remember is that the method was designed for personal sampling of workers in environments with actual asbestos exposures. AHERA adapted the method for clearance requiring that each sample must be less than or equal to a limit of quantitation (LOQ) for PCM of 0.01 fibers per cubic centimeter (f/cc). Over the years, it has become abundantly clear that the PCM method should not be used for clearance sampling. The top five reasons it should not be used for clearance sampling are: Size of the Fibers Analyzed The rules for




