• The selection of N-, R-, and P-series filters depends on the presence or absence of oil particles, as follows:

    • If no oil particles are present in the work environment, use a filter of any series (i.e., N-, R-, or P-series).
    • If oil particles (e.g., lubricants, cutting fluids, glycerine, etc.) are present, use an R- or P-series filter. Note: N-series filters cannot be used if oil particles are present.
    • If oil particles are present and the filter is to be used for more than one work shift, use only a P-series filter.

    Note: To help you remember the filter series, use the following guide:

  • Selection of filter efficiency [Respirator efficiency] (i.e., 95%, 99%, or 99.97%) depends on how much filter leakage can be accepted. Higher filter efficiency means lower filter leakage.

  • The choice of facepiece depends on the level of protection needed–that is, the assigned protection factor (APF) needed.

(“NIOSH Guide to the Selection and Use of Particulate Respirators Certified under 42 CFR 84.” 2020), formatting mine

Respirator for crystalline silica

NIOSH recommends the use of half-facepiece particulate respirators with N95 or better filters for airborne exposures to crystalline silica at concentrations less than or equal to 0.5 mg/m3.


The NIOSH recommended exposure limit (REL) remains 50 μg/m3 today.


The improved filtering efficiency characteristics of the particulate filters certified according to 42 CFR 84, compared to DM filters, result in filter ef- ficiencies of at least 95% for all sizes of silica dust; consequently, 100-rated filter efficiency (99.97%) is not required to achieve an APF of 10 in a properly fitted half-facepiece particulate respirator for crystalline silica exposures.

(“NIOSH Policy Statement: Respiratory Protection Recommendations for Airborne Exposures to Crystalline Silica.” 2008)