Air Monitoring, Clearance, and Recordkeeping
What to know
Air monitoring serves two purposes: exposure monitoring for worker protection (personal samples in the breathing zone, compared to the PEL and STEL) and clearance monitoring to confirm the work area is safe to reoccupy. Clearance typically uses aggressive sampling: the space is disturbed (air movers, sweeping) to suspend settled fibers, then samples are collected and analyzed. Phase contrast microscopy (PCM) is the standard field method for fiber counts; transmission electron microscopy (TEM) may be required for certain clearances and gives fiber type and size.
Clearance criteria depend on the standard and project specification; a common construction-standard visual plus PCM threshold is 0.01 f/cc, and TEM clearances often require no asbestos structures above a set limit. Visual inspection must pass before sampling, and containment stays up until results are in.
Recordkeeping: exposure monitoring records, medical surveillance records, training records, fit-test records, waste manifests, and clearance reports must be kept for the periods the standards specify (often 30 years for exposure and medical records).
Traps
Questions test whether you know clearance sampling is aggressive, not passive, and that visual inspection precedes sampling. Another trap: confusing PCM (counts fibers, cannot identify type) with TEM (identifies fiber type and size). Watch for claims that containment can come down while results are pending.
Rule of thumb
Visual first, then aggressive sampling, then results: containment comes down only after a passing visual and passing air results.