OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

October 7, 2015

Mr. Donald A. Alford, Jr.
ALEC Services LLC
185 3rd Street
Troy, New York 12180

Dear Mr. Alford:

Thank you for your letter to the Occupational Safety and Health Administration's (OSHA) Directorate of Standards and Guidance. Your letter was referred to OSHA's Directorate of Enforcement Programs for a reply. You asked if your asbestos sampling protocol would meet the exposure assessment requirements of OSHA's Asbestos Construction standard, 29 CFR 1926.1101. This reply letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any question not detailed in your original correspondence. We apologize for the delay in our response. After a summary, your paraphrased question and our reply are below.


Background and Summary of Sampling Protocol: You provided an asbestos sampling and evaluation protocol to help building owners assess the extent of asbestos contamination inside their buildings after an asbestos-containing material (ACM) is incidentally disturbed. You emphasized that this protocol is only to be used to assess asbestos contamination in areas where there is no visible ACM debris but there exists the potential for the contamination of dusts due to the disturbance of an ACM, such as an area adjacent to or adjoining an area with visible debris.

Your protocol includes the collection and analysis of five (5) non-aggressive area air samples and five (5) vacuumed dust samples collected within areas of up to 5,000 square feet.1 Air samples are analyzed by NIOSH Method 7402, which uses phase contrast microscopy (PCM) by direct-light microscope to count total fibers of specific size, followed by an examination of phase-visible asbestos fibers using transmission electron microscopy (TEM). Consistent with NIOSH Method 7402, the protocol then applies the ratio of asbestos fibers to total PCM-visible fibers to the PCM count.

Dust samples are collected using a vacuum sampling technique and analyzed by TEM, per ASTM D5755 (microvacuum sampling of settled dust2), to estimate the number of fibers that might be suspended in the air from the layer of settled dust. This method is often used to determine the presence of asbestos dust on surfaces, and some asbestos professionals use it to evaluate relative levels of contamination. The method determines the concentration of fibers collected on a filter from a 100 cm2 area. The standard detection limit for the method is about 1,000 fibers/cm2 based upon seeing four (4) asbestos fibers in a specified number of TEM grid openings.

Upon receipt of analytical results from your air and dust samples, your protocol makes specific calculations to average sample results and factor for room volumes. The calculated results are then compared with the asbestos airborne clearance level of 0.01 fiber per cubic centimeter (f/cc) contained in 40 CFR Part 763, Subpart E, of the Asbestos in Schools Rule, issued by the U.S. Environmental Protection Agency (EPA).

Question: Since OSHA's permissible exposure limits (PELs) for occupational exposure to asbestos are much higher than EPA's standard for public exposures to asbestos, would OSHA consider an assessment finding from my protocol, when it meets the EPA's standard, as sufficient "objective data" under the OSHA Asbestos Construction standard's requirement at 29 CFR 1926.1101(f)(2)(iii)(A)?

Reply: No. First, OSHA does not approve or endorse any employer's specific protocol used to obtain objective information regarding expected employee exposures to air contaminants, including asbestos.

Your particular protocol is proposed to apply to a scenario where installed asbestos-containing materials have been incidentally disturbed in a building and causing dispersion of asbestos fibers into adjacent building areas, which may eventually settle onto building surfaces. OSHA's immediate interests in such a scenario are the potential for further disturbance of asbestos-containing debris and fibers and whether an employee could be exposed to airborne asbestos in excess of the PEL, which is an 8-hour time-weighted average (TWA) of 0.1 f/cc, or a 30-minute average excursion greater than the limit of 1 f/cc. 29 CFR 1926.1101(c). OSHA also requires that employers and building owners be aware of and make other people in their facilities aware of the presence of asbestos. 29 CFR 1926.1101(k).

In this scenario, OSHA's Asbestos standards would require employers to perform initial monitoring of employees who are, or may reasonably be expected to be exposed to airborne concentrations at or above the TWA permissible exposure limit and/or excursion limit, as required by paragraph 29 CFR 1910.1001(d)(2)(i). [See also, 29 CFR 1926.1101(f)(2)(i) and 29 CFR 1915.1001(f)(2)(i).] Objective data may be used by employers as a substitute for initial exposure assessments under all three of OSHA's Asbestos standards: for construction, 29 CFR 1926.1101; for general industry, 29 CFR 1910.1001; and for shipyards, 29 CFR 1915.1001. Specifically, paragraph 29 CFR 1910.1001(d)(2)(iii) states, "Where the employer has relied upon objective data that demonstrate that asbestos is not capable of being released in airborne concentrations at or above the TWA permissible exposure limit and/or excursion limit under the expected conditions of processing, use, or handling, then no initial monitoring is required." Similar provisions are in the construction standard, 29 CFR 1926.1101(f)(2)(iii)(A), and in the maritime standard, 29 CFR 1915.1001(f)(2)(iii)(A).

In the preamble to OSHA's 1986 final rule for asbestos, OSHA stated that objective data must demonstrate that the asbestos-containing product or material cannot cause exposures above 0.1 f/cc (the then action level) under "worst-case release conditions."3 In the preamble to the 1994 final rule amending the Asbestos standard, OSHA stated that objective data "must demonstrate that under the work conditions having the greatest potential for releasing asbestos, an activity coupled with a specific material, simply cannot result in excessive concentrations."4

Your sampling and evaluation protocol does not meet the OSHA requirements for exposure monitoring, including initial monitoring and negative exposure assessment. 29 CFR 1926.1101(f). OSHA exposure assessments are based upon breathing zone air samples that are representative of the 8-hour TWA and 30-minute short-term exposures of each employee, not area samples. 29 CFR 1926.1101(f)(1)(ii). In addition, your proposed sampling method does not replicate any work conditions having the greatest potential for releasing asbestos; samples are collected with quiescent air conditions which will minimize any estimate of exposure during a work activity.

Your protocol also proposes to use a vacuum sampling technique to determine the concentration of fibers collected on a filter from a 100 cm2 area, which is then used to estimate potential air concentrations. Sampling dust from a surface by scrape sample, tape-lift, wipe, or micro-vacuuming are common methods used to determine the presence of asbestos on surfaces. The results may be useful to employers to determine if asbestos is present in a building. However, interpretation of surface dust sampling results must be conducted on a case-by-case basis due to the wide spectrum of potential circumstances. Any potential for airborne exposure depends upon what operation will be performed and on the potential for fiber release. The basic premise for assessing airborne exposure using surface dust samples is to determine the number of fibers on the surface and from that assume a uniform dispersion of fibers in a volume above the surface. Such estimates have ranged from 6 feet, to the full ceiling height (10 feet as specified in your protocol).

This approach may be used for relative comparison, but it cannot be used to relate to actual occupational exposures. Uniform concentration in a floor to ceiling column is not an appropriate model for dispersion of dust from a surface. Concentrations are higher close to the point of disturbance and fall off as the distance increases in all directions. This has been demonstrated in a number of EPA activity-based sampling studies, which have included activities such as vacuuming, dusting, and general office work.

Furthermore, the collection of material from surfaces by the vacuum sampler does not uniformly replicate the release of fiber from the surface in aggressive activities. In addition, ASTM D5755 is an indirect preparation technique that is assumed to alter the fiber distribution of the collected sample. At paragraph 1.4.1, the method states that the preparation method "...disperses the aggregated asbestos into fundamental fibrils, fiber bundles, clusters or matrices that can be more accurately quantified by transmission electron microscopy. However, as with all indirect sample preparation techniques, the asbestos observed for quantification may not represent the physical form of the asbestos as sampled." In other words, fiber concentrations collected using vacuum sampling cannot be used to estimate air concentrations directly. ASTM D5755 has some value in estimating relative risk when evaluating similar situations. However, it is of limited value when used without reference to historical work and actual breathing zone air samples.

In summary, your sampling and evaluation protocol cannot be used for either objective data, or as a substitute for initial monitoring or a negative exposure assessment under OSHA's Asbestos standards.

Thank you for your interest in occupational safety and health. We hope you find this information helpful. OSHA's requirements are set by statute, standards, and regulations. Our letters of interpretation do not create new or additional requirements but rather explain these requirements and how they apply to particular circumstances. This letter constitutes OSHA's interpretation of the requirements discussed. From time to time, letters are affected when the Agency updates a standard, a legal decision impacts a standard, or changes in technology affect the interpretation. To assure that you are using the correct information and guidance, please consult OSHA's website at www.osha.gov. If you have further questions, please feel free to contact the Office of Health Enforcement at (202) 693-2190.


Thomas Galassi, Director
Directorate of Enforcement Programs


1One additional sample is collected for every 5,000 square feet above the initial 5,000 square feet.
2ASTM D5755-09(2014)E1, Standard Test Method for Microvacuum Sampling and Indirect Analysis of Dust by Transmission Electron Microscopy for Asbestos Structure Number Surface Loading, April 1, 2014.
3OSHA Final Rule, Occupational Exposure to Asbestos, Tremolite, Anthophyllite, and Actinolite, 51 Fed. Reg. 22612-22790, June 20, 1986; see p. 22712.
4OSHA Final Rule, Occupational Exposure to Asbestos, 59 Fed. Reg. 40964-41162, August 10, 1994; see p. 40983.