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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 20, 1987

Mr. David Borgan
Project Manager
Amaral & Neumeyer Incorporated
55th and A.V.R.R.
Pittsburgh, Pennsylvania 15201

Dear Mr. Borgan,

This is in response to you recent letter regarding the Occupational Safety and Health Administration's (OSHA) asbestos standard for the construction industry, [29 CFR 1926.1101]. We apologize for the delay in responding to your inquiry.

Your first question concerns the definition of the term "statistically reliable measurements" as used in paragraph [29 CFR 1926.1101(f)(4)(i)]. Paragraph [29 CFR 1926.1101(f)(4)(i)] states:

[If the periodic monitoring required by paragraph (f)(3) of this section reveals that employee exposures, as indicated by statistically reliable measurements, are below the permissible exposure limit and excursion limit the employer may discontinue monitoring for those employees whose exposures are represented by such monitoring.]

[Corrected 12/1/2001]

In the context of this paragraph "statistically reliable measurements" means that accepted statistical procedures must be applied to the daily monitoring data in order to demonstrate that employee exposures are not likely to be equal to or greater than the action level, and thus, that the daily monitoring can be suspended.

Your second question is, whether or not three days of sampling is enough to demonstrate that employee exposures will not exceed the action level. A standard number of samples required to show that employee exposures will not exceed the action level cannot be established.

The number of samples required is dependent on the variability of the data, and therefore must be determined on a case by case basis.

If we may be of further assistance regarding this matter, feel free to contact us.


Thomas J. Shepich, Director
[Directorate of Enforcement Programs]

[Corrected 6/2/2005]