Asbestos air sample analysis

The sampling medium must be mixed cellulose ester filter membranes designated by the manufacturer as suitable for asbestos counting. Laboratories performing asbestos air monitoring must use these filters (or an equivalent method) for compliance purposes as described in Appendix A to 1926.1101.

The preferred collection device is the 25‑mm diameter cassette with an open‑faced 50‑mm electrically conductive extension cowl; a 37‑mm cassette may only be used if there is a written justification accompanying the sample results. See the cassette size and justification requirements in Appendix A to 1926.1101.

No — cassettes must not be reused or reloaded for asbestos sample collection. Appendix A to 1926.1101 explicitly states that cassettes shall not be reused or reloaded; labs and employers must follow this requirement when collecting samples (Appendix A to 1926.1101).

Use an air flow rate between 0.5 and 2.5 liters per minute for the 25‑mm cassette, and between 1.0 and 2.5 liters per minute if the 37‑mm cassette is used. These flow rate ranges are specified in Appendix A to 1926.1101.

Collect a sufficient air volume so the filter yields between about 100 and 1,300 fibers per square millimeter; if the filter darkens or loose dust is visible, start a second sample. Appendix A explains the target fiber density and the action to take if dust or darkening is observed (Appendix A to 1926.1101).

Ship samples in a rigid container with packing material that prevents dislodging the collected fibers, and avoid packing materials with a high electrostatic charge (for example, expanded polystyrene). These shipping precautions are specified in Appendix A to 1926.1101.

Personal sampling pumps must be calibrated both before and after use with a representative filter cassette installed between the pump and the calibration device. Appendix A requires this pre‑ and post‑use calibration to ensure accurate flow measurements (Appendix A to 1926.1101).

Personal samples must be taken in the worker's breathing zone — attached to or near the collar or lapel close to the worker's face. Appendix A specifies breathing‑zone placement for personal sampling (Appendix A to 1926.1101).

Count fibers by positive phase contrast microscopy using an 8–10× eyepiece and a 40–45× objective (approximately 400× total magnification) with a numerical aperture of 0.65–0.75, and fit the microscope with a green or blue filter. Appendix A specifies these microscope optics and filter requirements for asbestos counting (Appendix A to 1926.1101).

The Walton‑Beckett eyepiece graticule must be calibrated for a field diameter of 100 micrometers ± 2 micrometers. Appendix A requires that calibration for accurate fiber counting (Appendix A to 1926.1101).

The microscope's phase‑shift detection limit must be about 3 degrees, measured using the HSE phase shift test slide; the test slide is placed on the stage, focused, and the grooved line sets evaluated per Appendix A instructions. Appendix A describes the HSE slide test and the visibility criteria for sets 3, 4, 5, 6, and 7 to determine acceptable microscope optics (Appendix A to 1926.1101).

Only count fibers equal to or longer than 5 micrometers, measuring curved fibers along the curve, and in the absence of other information count as asbestos any particles with a length‑to‑width (aspect) ratio of 3:1 or greater. These counting rules are given in Appendix A and must be followed for compliance sample analysis (Appendix A to 1926.1101).

Fibers entirely within the graticule boundary count as 1; fibers crossing the boundary once (one end inside) count as one‑half (½); do not count fibers that cross the boundary more than once, and reject any fibers that cannot be scored under these rules. Appendix A provides these graticule counting rules to ensure consistent counts (Appendix A to 1926.1101).

Count a bundle of fibers as one fiber unless you can identify individual fibers by observing both ends of an individual fiber; Appendix A requires counting bundles this way to avoid overestimating fiber counts (Appendix A to 1926.1101).

Count enough graticule fields to yield 100 fibers, with a minimum of 20 fields counted; stop counting at 100 fields regardless of fiber count if 100 fibers are not reached. Appendix A specifies these minimums and stopping rules for counts (Appendix A to 1926.1101).

Blind recounts must be conducted at a rate of 10 percent. Appendix A includes this requirement as part of the counting and quality control procedures for asbestos analysis (Appendix A to 1926.1101).

Each set of samples must include field blanks equal to 10 percent of the set or at least two field blanks, drawn from the same filter lot; blank results are averaged and subtracted from analytical results before reporting, and any samples associated with a field blank above the detection limit must be rejected. Appendix A describes these field blank requirements and rejection rules (Appendix A to 1926.1101).

Mount samples by the acetone/triacetin method or a method with an equivalent index of refraction and similar clarity. Appendix A prescribes the acetone/triacetin mounting technique as the standard mounting medium for asbestos sample slides (Appendix A to 1926.1101).

Laboratories must establish an intralaboratory quality assurance program (blind recounts and comparisons among microscopists) and implement an interlaboratory program that includes participation with at least two other independent labs and round‑robin testing at least every six months. Appendix A outlines both the intralaboratory and interlaboratory QA requirements to monitor and control counting variability (Appendix A to 1926.1101).

Laboratories should participate in national sample testing schemes such as the Proficiency Analytical Testing Program (PAT) or the AIHA Asbestos Registry, and all individuals performing asbestos analysis must have taken the NIOSH course for sampling and evaluating airborne asbestos dust or an equivalent course. Appendix A recommends these proficiency programs and training requirements to ensure competent analysis (Appendix A to 1926.1101).

Yes — employers required to conduct air monitoring under paragraph (f) must utilize analytical laboratories that use the OSHA reference procedure in Appendix A, or an equivalent method, for collecting and analyzing samples. This requirement appears directly in Appendix A to 1926.1101 and applies to monitoring obligations under 1926.1101(f).

If the filter darkens in appearance or loose dust is seen on the filter, the sampler must start a second sample. Appendix A states this as the proper action to avoid undercounting or compromised samples (Appendix A to 1926.1101).

Avoid packing materials with a high electrostatic charge on their surface (for example, expanded polystyrene) because electrostatic charge can cause loss of fibers to the sides of the cassette; Appendix A warns against such materials and requires packing that prevents dislodging collected fibers (Appendix A to 1926.1101).

If different microscopes contribute to counting differences, the effect of the microscopes must be evaluated and the microscope replaced as necessary to reduce variability. Appendix A requires evaluation and replacement of microscopes when optics cause systematic differences between counters or laboratories (Appendix A to 1926.1101).

Laboratories must participate in round‑robin testing at least every six months with the other labs in their interlaboratory group, submit slides typical of their workload, and design and analyze the round‑robin using appropriate statistical methodology to evaluate results. Appendix A requires this interlaboratory program and statistical analysis to monitor lab‑to‑lab variability (Appendix A to 1926.1101).