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.



August 19, 1993

Mr. Skip Elliott
1019 Bankton Drive
Charleston, South Carolina 29406

Dear Mr. Elliott:

This is in response to your request for an evaluation of an asbestos sampler, the Bellmouth cassette. We have reviewed the materials you submitted to Mr. Daniel Crane of my staff.

The Occupational Safety and Health Administration (OSHA) is a regulatory agency responsible for assuring safe and healthful conditions in the workplace. OSHA does not test, endorse, or promote goods and services of any kind. OSHA [standard] 29 CFR 1910.1001(d)(6)(ii) and 29 CFR 1926.58(f)(5)(ii) require[s] that exposure monitoring requirements be evaluated using the OSHA Reference Method (ORM) specified in Appendix A of the standards. 29 CFR 1910.1001(d)(6)(iii) and 29 CFR 1926.58(f)(5)(iii) require[s] that if an equivalent method to the ORM is used, the employer shall ensure that the method meets the following criteria:



  1. Replicate exposure data used to establish equivalency are collected in side-by-side field and laboratory comparisons;
  2. The comparison indicates that 90% of the samples collected in the range 0.5 to 2.0 times permissible limit have an accuracy range of plus or minus 25 percent of the ORM results with a 95% confidence level as demonstrated by a statistically valid protocol; and
  3. The equivalent method is documented and the results of the comparison testing are maintained.



Based on the evaluation of the test submitted, the Bellmouth cassette sampler has met the criteria of 29 CFR 1910.1001(d)(6)(iii) and 29 CFR 1926.58(f)(5)(iii) for the conditions it was tested. Should the sampler be used in other conditions, equivalency per the above standards must be demonstrated.

This response is not an approval or endorsement of the Bellmouth asbestos sampler.


Patricia K. Clark, Director
[Directorate of Science, Technology, and Medicine]

[This document was edited on 12/01/2001 to strike information that no longer reflects current OSHA policy.]

[Corrected 6/2/2005]