Which statement about PCM and TEM sampling is true?

• A. PCM counts asbestos fibers in air samples to estimate exposure; TEM identifies fiber type and confirms asbestos presence, used solely for regulatory decisions.
• B. TEM identifies fiber type and confirms asbestos presence; PCM is used for regulatory decisions.
• C. PCM counts asbestos fibers in air samples to estimate exposure; TEM identifies fiber type and confirms asbestos presence, used for regulatory and clearance decisions.
• D. Neither PCM nor TEM are used in asbestos sampling.

Answer: (C)

In asbestos air sampling, two methods play different but complementary roles. PCM (phase-contrast microscopy) counts all fibers in an air sample to estimate exposure, giving a fiber concentration that informs how much people might have been exposed. It cannot tell which fibers are asbestos. TEM (transmission electron microscopy), on the other hand, identifies the fiber type and confirms the presence of asbestos by examining fiber morphology and composition. Because TEM provides the specificity needed to confirm asbestos and distinguish it from other fibers, it is used to support regulatory decisions and clearance assessments after work or remediation. So the statement that PCM counts fibers to estimate exposure and TEM identifies fiber type and confirms asbestos presence, used for regulatory and clearance decisions, reflects how both methods are applied in practice. The other options misstate these roles, such as claiming TEM is used solely for regulatory decisions or that PCM is used for regulatory decisions, which aren’t accurate descriptions of their primary purposes.