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.



May 4, 1990

Larry Lockard
Westinghouse Electric
1234 Columbia Dr. SE
Richland, WA 99352

Dear Larry,

You ask regarding when blanks are necessary. Simply, internally, OSHA requires blanks to be taken for all asbestos samples regardless of purpose. The regulations require that a minimum of 2 and at least 10% blanks be taken for any set of samples for any purpose under the OSHA standards.

In general, whenever either of the major asbestos methods are used, blanks are required to be used. That is, whenever either OSHA ID 160 or NIOSH 7400 are used, a minimum of two and at least10% blanks must be taken and included in the analysis. The methods do not require laboratory blanks and these field blanks are required to assure that the medium is uncontaminated either in the field or from the manufacturer. If these guidelines are not followed, the analyzing laboratory may not say that they have followed either, NIOSH or OSHA guidelines.

If you have any further questions, do not hesitate to call.


Daniel T. Crane
Supervisory Physical Scientist

[Corrected 6/2/2005]



April 26, 1990

Mr. Dan Crane
P.O. Box 15200
Salt Lake City, UT 84115

Dear Mr. Crane:

I am writing in regards to our conversation on 4/26/90 concerning the necessity of collecting Phase Contrast Microscopy (PCM) field blanks with pre-abatement (baseline) samples. Mycontention is that failure to take blanks with pre-abatement samples introduces an unwanted and unwarranted bias into the procedure.

Thank you for your assistance. I am looking forward to your response on this subject.


Larry D. Lockard