November 8, 2011

Ms. Deborah Dietrich
Mr. Saulius Trakumas
SKC, Inc.
863 Valley View Road
Eighty Four, PA 15330

Dear Ms. Dietrich and Mr. Trakumas:

Thank you for your letter to the Occupational Safety and Health Administration's (OSHA) Directorate of Enforcement Programs concerning air sampling methods for dust. This letter constitutes OSHA's interpretation only of the requirements herein, and may not be applicable to any situation not delineated within your original correspondence.  You have a rebuttal to an OSHA letter of interpretation, January 30, 2007, entitled,"Use of the IOM sampler for inhalable dust and compliance with the PNOR requirements of 29 CFR 1910.1000."  Your position is stated below, followed by OSHA's reply.  We apologize for the delay in responding to your request.

Rebuttal:  The OSHA letter to Mr. Jesse Finney, dated January 30, 2007, contains a statement contrary to information published in peer-reviewed scientific literature.  Specifically, the OSHA letter makes the following assertion regarding dust sampling cassettes containing 37-mm filters vs. Institute of Occupational Medicine (IOM) Samplers: "Side-by-side samples collected using the two sampling methods will usually show lower results with the IOM Sampler.  This is especially apparent when an atmosphere has a greater concentration of larger particles."

Reply:  Upon review of the scientific literature regarding the use of an IOM Sample¹ compared to the OSHA sampling method using a 37-mm cassette for sampling total dust² we agree that the IOM Sampler is more efficient than the 37-mm cassette in sampling small and large particles.  The IOM Sampler is designed for sampling inhalable particles of up to 100 micrometers (µm) aerodynamic diameter.  OSHA's Salt Lake Technical Center agrees that the IOM Sampler should provide higher results than a 37-mm cassette, especially where large particles are involved.  Additionally, a 37-mm cassette and the IOM Sampler should provide very similar results up to about 20 µm in particle size.  Thus, a Total Dust measurement collected with an IOM Sampler may be used as an equivalent method when measuring an employee's exposure to particulates not otherwise regulated (PNOR), and to determine whether exposure exceeds the PNOR permissible exposure limit (PEL) in 29 CFR 1910.1000.  Therefore, OSHA's letter of interpretation to Mr. Finney, dated January 30, 2007, has been withdrawn.

Thank you for your interest in occupational safety and health.  We hope you find this information helpful.  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 continue to consult OSHA's website at http://www.osha.gov.  If you have any further questions, please feel free to contact our Office of Health Enforcement at 202-693-2190.

Sincerely,



Thomas Galassi, Director
Directorate of Enforcement Programs

cc:  Mr. Jesse L. Finney

¹  The IOM Sampler is a patented sampling cassette that houses a 25-mm reusable filter.  It was developed by J.H. Vincent and D. Mark at the Institute of Occupational Medicine (IOM) in Scotland.  See, Mark, D. and Vincent, J.H.,"A New Personal Sampler for Airborne Total Dust in Workplaces," Ann. Occup. Hyg. Vol. 30, 1986, pp. 89-102   [Return to Text]

²  See OSHA Analytical Method, OSHA PV2121, Gravimetric Determination, March 2003, for sampling particulates not otherwise regulated (PNOR), using a tared 37-mm diameter, low ash polyvinyl chloride filter, within a closed-face cassette.   [Return to Text]