8.1 Air Monitoring: Personal Sampling, Area Sampling During Abatement & PCM vs. TEM Analysis

8.1 Air Monitoring During Asbestos Abatement

Quick Answer: Personal samples measure worker exposure against OSHA's 0.1 f/cc TWA and 1.0 f/cc excursion limits. They are collected in the breathing zone on 25-mm mixed cellulose ester filters at 0.5-2.5 L/min and analyzed by phase contrast microscopy (PCM). Area samples on New Jersey subcode projects are collected by the AST: at least three per 8-hour shift, with one in the clean room and two adjacent to the work area. Results must not exceed 0.01 f/cc outside containment or 0.02 f/cc in the clean room. Clearance samples come after clean-up (Section 8.3). PCM counts all fibers of countable size. TEM identifies asbestos specifically.

Three Kinds of Air Sampling

Some projects also collect baseline samples before work begins to document existing conditions. They are useful when a later area result is questioned, but the subcode's area-sampling limits are fixed numbers, not "above baseline."

Personal Sampling (OSHA Appendices A and B to 1926.1101)

• Filter and cassette: A mixed cellulose ester (MCE) filter designated for asbestos counting, in the preferred 25-mm cassette with an open-faced 50-mm electrically conductive extension cowl. The non-mandatory Appendix B procedure specifies a 0.4 to 1.2 micrometer pore size. A 37-mm cassette requires written justification.
• Flow rate: Mandatory Appendix A sets 0.5 to 2.5 L/min for the 25-mm cassette. Aim for a filter loading of 100 to 1,300 fibers per square millimeter. If the filter darkens or shows loose dust, start a second sample.
• Position: The open-face cassette is clipped to the collar or lapel, open side down, about 10 cm (4 inches) from the nose and mouth.
• Volumes: Appendix B suggests a minimum of 25 L for TWA samples and 48 L for 30-minute excursion-limit samples, with lower maximum volumes in dusty removal environments to avoid overloading.
• Calibration: Calibrate each pump before and after sampling with a representative cassette in line, using a primary standard such as a bubble burette or electronic flow calibrator.
• Representativeness: Samples must represent the full-shift and 30-minute exposures of each employee in each work area. For short-term samples, target the tasks most likely to exceed the excursion limit, such as gross removal and bag-out.

Results are reported in fibers per cubic centimeter (f/cc). Employees must be notified within 5 working days after the employer receives the results.

Area Sampling During Abatement on Subcode Projects

Unoccupied Buildings (N.J.A.C. 5:23-8.21(b)1)

• At least three samples per 8-hour shift: one at the beginning of the shift, one every four hours thereafter, and one at the end of the contractor's workday.
• Locations:
  • One stationary sample inside the clean room of the decontamination unit.
  • Two samples adjacent to the work area, but remote from the decon entrance. Rooms next to critical barriers and the work area get preference.
• Limits: Results must not show more than 0.01 f/cc outside the containment barrier or more than 0.02 f/cc inside the clean room.
• If a limit is exceeded: The AST immediately directs corrective action and gives a verbal report within 24 hours to the contractor, owner, and project designer. Written notice follows, with a copy to the enforcing agency and DCA within three business days of receiving the results (N.J.A.C. 5:23-8.10(d)6).

Occupied Buildings (N.J.A.C. 5:23-8.19(c)4-5)

• At a minimum, collect one sample at the beginning of each shift, one every four hours, and one at the end of the workday for every 10,000 square feet of occupied space next to the work area. Place them where fiber migration is most likely.
• Add samples at work-area entrances, at interior spaces supplying make-up air, and in stairwells, shafts, elevators, plenums, and in-service ducts passing through the work area.
• Collect at least one sample inside the work area during each shift. That result does not trigger the contingency plan.
• On-site analysis, or results within four hours, by an analyst listed in the AIHA Asbestos Analyst Registry (or equivalent), using NIOSH 7400.
• 10% of samples are re-analyzed at a laboratory within 24 hours for quality control.
• Daily occupancy is allowed only if every sample is 0.010 f/cc or less by PCM. Above that, the contingency plan applies:
  1. Investigate the engineering controls.
  2. Take a second PCM sample, which may be split. If it is 0.010 f/cc or less, the contingency ends.
  3. If it is still above 0.010 f/cc, either clean and retest by PCM, or analyze the split by TEM. If TEM also exceeds 0.010 f/cc, cleaning is required, including wet wiping and misting the air.
  4. If results are not at or below 0.010 f/cc within 24 hours of the first high result, evacuate the building.
• A written chain of custody for samples is part of the ASCM's approved plan.

Pumps, Laboratories, and Turnaround

PCM vs. TEM

Because PCM cannot tell asbestos from other fibers, a high PCM result during drywall demolition next door might not be asbestos. TEM (for example, NIOSH 7402 analysis of the same filter, or the occupied-building split-sample procedure) can resolve that question. Until it is resolved, treat the high PCM result as a warning and investigate the containment.

Exam Traps

• Clean room versus outside containment: The limit is 0.02 f/cc in the clean room and 0.01 f/cc outside containment.
• Sampling frequency: Beginning of shift, every four hours, and end of day, the same schedule as the pressure checks.
• Cassette position: Open face down, about 10 cm from the nose and mouth.
• PCM is not asbestos-specific.
• Who samples on subcode jobs: the AST, employed by the ASCM, which the owner hires. The contractor still does its own OSHA personal monitoring.

Scenario

On an unoccupied-school subcode project, the AST's mid-shift sample in the decon clean room reads 0.024 f/cc, above the 0.02 f/cc clean-room limit. The adjacent-room samples read 0.004 and 0.006 f/cc.

1. The AST immediately directs corrective action. Inspection finds a shower-to-clean-room curtain taped open to run a hose, and a clean room that was not wet-wiped.
2. The contractor restores the three-layer curtained doorway, wet-wipes and HEPA-vacuums the clean room, and verifies the pressure differential.
3. The AST gives the verbal report within 24 hours to the contractor, owner, and project designer, and sends the written report to them, the enforcing agency, and DCA within three business days of receiving the result.
4. Follow-up samples in the clean room must be at or below 0.02 f/cc.