Asbestos air sample analysis

The samples must be collected on mixed cellulose ester filter membranes designated by the manufacturer as suitable for asbestos counting, per the mandatory OSHA Reference Method - Mandatory, Appendix A to 1910.1001.

• Use only filters the manufacturer designates for asbestos counting.
• Field blanks must come from the same filter lot as the samples (see the field blanks requirement in the same Appendix).

The preferred collection device is the 25‑mm diameter cassette with an open‑faced 50‑mm electrically conductive extension cowl; if you use a 37‑mm cassette you must include a written justification with the employee’s exposure monitoring record explaining the need for the 37‑mm cassette, as required by 1910.1001AppA.

• Do not reuse or reload cassettes for asbestos sampling (also stated in the Appendix).

Select 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 for the 37‑mm cassette, per 1910.1001AppA.

• Choose the specific flow within those ranges to reach the target fiber density on the filter (see the fiber density guidance in the Appendix).

Where possible, collect a sufficient air volume so the filter yields between 100 and 1,300 fibers per square millimeter, per 1910.1001AppA.

• If a filter darkens or loose dust is visible, start a second sample rather than relying on the overloaded filter.

Ship samples in a rigid container with enough packing material to prevent dislodging collected fibers, and avoid packing materials with high electrostatic charge (e.g., expanded polystyrene) because they can cause loss of fibers to the cassette sides, as required by 1910.1001AppA.

• Use non‑electrostatic packing and secure samples to prevent movement during shipment.

Each personal sampling pump must be calibrated before and after use with a representative filter cassette installed between the pump and the calibration device, as stated in 1910.1001AppA.

• Calibrate with the same cassette type you will use for sampling so the measured flow reflects in‑line resistance.

Personal samples must be taken in the employee’s breathing zone, i.e., attached to or near the collar or lapel close to the worker’s face, per 1910.1001AppA.

• Position sampling equipment so it represents inhalation exposure, not a tool or backpack location.

Fibers must be counted by positive phase contrast microscopy using an 8–10× eyepiece and a 40–45× objective (approximate 400× total magnification) with a numerical aperture of 0.65–0.75 and a green or blue filter, as required in 1910.1001AppA.

• The Walton‑Beckett eyepiece graticule calibrated to a 100 µm (±2 µm) field diameter is also required (see the Appendix for graticule requirements).

The microscope must be fitted with a Walton‑Beckett eyepiece graticule calibrated for a field diameter of 100 micrometers (±2 micrometers), as specified in 1910.1001AppA.

• Use the calibrated field to apply the Appendix counting rules (boundary, half‑count, and exclusion rules).

The phase‑shift detection limit of the microscope must be about 3 degrees, measured using the HSE phase shift test slide procedure described in the Appendix to 1910.1001AppA, which involves focusing specified grooved line sets and verifying visibility criteria, per 1910.1001AppA.

• If the microscope fails the test, clean and adjust optics or consult the manufacturer; replace the microscope if it cannot meet the requirement.

Each set of samples must include field blanks equal to 10% of the samples or at least 2 field blanks; blanks must come from the same filter lot as the samples, and the averaged field blank result must be subtracted from sample results before reporting, per 1910.1001AppA.

• Any samples represented by a field blank with a fiber count above the method detection limit must be rejected (see the Appendix for rejection rules).

Filters must be mounted using the acetone/triacetin method or a method with an equivalent index of refraction and similar clarity, as required by 1910.1001AppA.

• Use mounting media and procedures that preserve optical clarity for reliable phase contrast counting.

Count only fibers that are at least 5 micrometers long, and in the absence of other information count all particles with a length‑to‑width (aspect) ratio of 3:1 or greater as asbestos, per 1910.1001AppA.

• Measure curved fibers along their curve when determining length (the Appendix specifies this explicitly).

Fibers entirely within the graticule field get a count of 1; fibers crossing the boundary once (one end inside) count as one half (1/2); do not count any fiber that crosses the graticule boundary more than once — such fibers are rejected and not counted, according to 1910.1001AppA.

• Bundles of fibers are counted as one unless individual fibers can be identified by observing both ends (see the Appendix for bundle rules).

Count enough graticule fields to yield 100 fibers, but count a minimum of 20 fields; stop counting at 100 fields regardless of whether you have reached 100 fibers, per 1910.1001AppA.

• This balances statistical reliability with practical counting time.

Blind recounts must be conducted at a rate of 10 percent, and laboratories must implement an intralaboratory QA program (blind recounts and comparisons) plus interlaboratory programs and round‑robin testing, as specified in 1910.1001AppA.

• Interlaboratory round robins must include at least two other independent laboratories and occur at least once every 6 months.

Each laboratory analyzing asbestos samples for compliance must participate in an interlaboratory quality assurance program with at least two independent labs and perform round‑robin testing at least every 6 months; laboratories are also advised to participate in national sample testing schemes such as the Proficiency Analytical Testing (PAT) Program or the AIHA Asbestos Registry, per 1910.1001AppA.

• Submit slides typical of the lab’s workload for round‑robin testing and analyze results using appropriate statistics.

All individuals performing asbestos analysis must have taken the NIOSH course for sampling and evaluating airborne asbestos dust or an equivalent course, as required by 1910.1001AppA.

• Maintain documentation of training and equivalency records in the laboratory’s QA files.

If using different microscopes contributes to variability between counters or laboratories, evaluate the effect and replace microscopes as necessary to ensure equivalent performance, per 1910.1001AppA.

• Post current QA program results in the laboratory so microscopists are informed of variability and corrective actions.

Yes. Employers required to conduct air monitoring under 1910.1001(d) must utilize analytical laboratories that use the Appendix A procedure or an equivalent method for collecting and analyzing asbestos air samples, as stated in 1910.1001AppA.

• Ensure the laboratory documents equivalency if not using the exact Appendix A method.

No. The Appendix explicitly states do not reuse or reload cassettes for asbestos sample collection, per 1910.1001AppA.

• Always use a new, manufacturer‑approved cassette for each sample to avoid contamination and fiber loss.

Curved fibers must be measured along the curve when determining length, and only fibers equal to or longer than 5 micrometers are counted, as specified in 1910.1001AppA.

• This ensures consistent inclusion/exclusion of curved fibers in counts.

Any samples represented by a field blank having a fiber count in excess of the detection limit must be rejected, and the Appendix requires that field blank results be averaged and subtracted from analytical results before reporting, per 1910.1001AppA.

• Replace or repeat the affected sampling set and investigate the source of contamination.

Although the Appendix sets the analysis method, property remediation work involving asbestos‑containing building materials (ACBM) is often covered by OSHA’s construction asbestos standard, 29 CFR 1926.1101, rather than the general industry standard 1910.1001, as explained in OSHA’s Letter of Interpretation on asbestos remediation protocols (see https://www.osha.gov/laws-regs/standardinterpretations/2024-11-14).

• If your remediation work involves construction‑type activities with ACBM, consult the construction standard [1926.1101] and the cited Letter of Interpretation to determine which standard applies.