December 18, 2017Ms. Brenda Finter, CIH, CSPB2 Environmental4503 S 90th StreetOmaha, Nebraska 68154 Dear Ms. Finter: Thank you for your August 16, 2017, letter to the Occupational Safety and Health Administration (OSHA). Your letter was referred to OSHA's Directorate of Enforcement Programs for a response. You have a question related to the acceptability of a sampler not specifically identified in OSHA's new Respirable Crystalline Silica standards. This letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any question not delineated within your original correspondence. Your paraphrased question and our response are below. Background: You state that the new Respirable Crystalline Silica standards specifically identify cyclones as acceptable particle-size-selective samplers, but do not mention if impactors can also be used for sampling for respirable crystalline silica. You have included the specifications for a commercially available parallel particle impactor (PPI) that you are interested in using to sample for respirable crystalline silica. Question: If a selective-size sampler meets the ISO standard, 7708:1995: Air Quality – Particle Size Fraction Definitions for Health-Related Sampling, but is not mentioned as an acceptable sampler in Appendix A of the Respirable Crystalline Silica standards, is it acceptable to use it for respirable crystalline silica sampling? Response: Yes. The silica standards, 29 CFR 1910.1053 and 29 CFR 1926.1153, define respirable crystalline silica as "quartz, cristobalite, and/or tridymite contained in airborne particles that are determined to be respirable by a sampling device designed to meet the characteristics for respirable-particle-size-selective samplers specified in the International Organization for Standardization (ISO) 7708:1995: Air Quality – Particle Size Fraction Definitions for Health-Related Sampling." In its final rule for respirable crystalline silica, OSHA noted that, in addition to cyclone samplers, personal impactors are available for use at flow rates from 2 to 8 L/min that have been shown to conform closely to the ISO/CEN convention (81 FR 16439, March 25, 2016). Therefore, a PPI or any sampling device that meets the ISO/CEN particle-size-selective criteria for respirable dust samplers would be acceptable for respirable crystalline silica sampling by employers, even if it is not mentioned as an acceptable sampler in Appendix A to the silica standards. The employer must also maintain an accurate record of all exposure measurements taken to assess employee exposure to respirable crystalline silica, which must include information on the sampling and analytical methods used, and the identity of the laboratory that performed the analysis, as required under 29 CFR 1910.1053(k)(1) and 29 CFR 1926.1153(j)(1). With regard to the specific PPI model that you have mentioned in your letter, note that OSHA does not approve or endorse products or equipment. 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 any further questions, please feel free to contact the Office of Health Enforcement at (202) 693-2190. Sincerely, Thomas Galassi, DirectorDirectorate of Enforcement Programs