What is the typical PCM-based clearance criterion for final re-occupancy air samples?

• A. 0.01 f/cc or lower in final re-occupancy air sample
• B. 0.1 f/cc
• C. 1.0 f/cc
• D. 0.001 f/cc

Answer: (A)

In PCM-based final re-occupancy clearance, the goal is to ensure airborne asbestos is at a very low level after cleanup. You measure the air with polarized light microscopy and report the concentration as fibers per cubic centimeter. The standard target is 0.01 f/cc or lower, meaning the final air samples should show no more than ten thousandths of a fiber per cubic centimeter on average.

Why this value fits best there is a balance between practicality and safety. It reflects a conservative level that is generally achievable after thorough cleaning and gives confidence that residual fibers are near background levels, reducing occupants’ exposure risk. If the final PCM samples average above 0.01 f/cc, additional cleaning and retesting are typically required before re-occupancy.

The other numbers don’t align with the common PCM criterion. A threshold of 0.1 f/cc would allow ten times as many fibers, which is not considered protective enough for final clearance. A threshold of 1.0 f/cc is far too high for re-occupancy. A value like 0.001 f/cc is more stringent than standard PCM practice and is typically associated with more sensitive methods or stricter programs, not the usual PCM clearance criterion.