Can impactors be used for sampling for respirable crystalline silica?

Yes. The silica standard, 29 CFR 1926.1153, defines 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.

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 1926.1153(j)(1).