Air Monitoring and Bulk Sampling
Air monitoring basics
Air monitoring measures airborne fiber concentration. Personal sampling uses a pump worn in the breathing zone with a filter cassette; results are compared to the PEL. Area sampling assesses containment or background. Clearance sampling verifies that a work area is safe to reoccupy after abatement.
Analysis methods: phase contrast microscopy (PCM) counts fibers and is the standard for compliance (NIOSH 7400). Transmission electron microscopy (TEM) identifies fiber type and counts finer fibers; it is often used for clearance in sensitive settings. Scanning electron microscopy (SEM) can also identify fibers.
Bulk sampling
Bulk samples determine whether material contains asbestos. Take samples from multiple locations, use wet methods and a glove bag or mini-enclosure, and seal samples in labeled containers. Polarized light microscopy (PLM) is the standard bulk method; it estimates percentage and identifies fiber type. Point counting improves accuracy.
Traps
- Confusing bulk analysis (PLM) with air analysis (PCM/TEM).
- Forgetting that clearance sampling requires the containment to remain up until results are acceptable.
- Assuming one bulk sample represents a whole building; multiple samples are needed.
- Mixing up personal and area sampling purposes.
Rule of thumb
Bulk = what is it (PLM); air = how much (PCM/TEM). For clearance, follow the project's specified method and acceptance criteria.
Worked example
A supervisor needs to confirm a containment is clean. PCM air samples show acceptable fiber counts, but the project spec requires TEM clearance. The correct action is to collect TEM samples per the spec before dismantling containment.