Air Monitoring, Clearance, and Recordkeeping
Air Monitoring
Air monitoring verifies exposure control and clearance. Personal monitoring measures worker exposure; area monitoring measures containment conditions. Phase contrast microscopy (PCM) counts fibers but cannot distinguish asbestos from other fibers; transmission electron microscopy (TEM) identifies asbestos fibers specifically. Clearance typically uses TEM after final cleaning.
Clearance
Clearance requires visual inspection (no visible debris), final cleaning, and air sampling that meets the clearance criterion. The containment remains under negative pressure until clearance is achieved. Candidates should know that clearance is a process, not a single sample, and that re-cleaning may be required if results fail.
Traps to Watch
Frequent traps: (1) assuming PCM is sufficient for clearance (TEM is typically required); (2) assuming visual inspection alone is clearance (it is not); (3) forgetting that negative pressure must be maintained until clearance; (4) mixing personal and area monitoring; (5) forgetting recordkeeping retention periods. Also watch for questions about aggressive sampling and about who may perform clearance.
Rule of Thumb
Use the "see it clean, then prove it clean" rule: visual inspection first, then air sampling that meets the criterion.
Worked Example
A contractor wants to remove containment after a visual inspection shows no debris. The correct answer is no - air sampling must meet the clearance criterion before containment comes down.