Particulate filters remove aerosols suspended in the air that you breathe (e.g., dust, mist, fog, smoke). Particulate filters DO NOT remove gases or vapors. The pesticide label specifies N, R, and/or P filters for non-powered air-purifying respirators (APRs), and HE for powered air-purifying respirators (PAPRs).
Particulate filters for non-powered air-purifying respirators are rated for both oil resistance and filter efficiency to remove particles. This is because oil mists will affect the filter efficiency. NIOSH-approved filters come in three grades of oil resistance: N-series, R-series, and P-series.
N-series filters are not oil-resistant; R-series filters are oil-resistant for up to 8 hours; and P-series filters are oil-proof. Each of the three grades of filters (N, R, and P) are available in three levels of filter efficiency (95, 99, and 100). These ratings are determined by the efficiency of a filter to remove the most penetrating particle size (as opposed to the smallest size particle).
Non-powered APR with Particulate Filtering Elements: clockwise from bottom: disposable N95 FFR; elastomeric full facepiece APR with dual replaceable P100 filters; silicon half facepiece APR with dual replaceable P100 filters; half facepiece APR with replaceable N95 filter (photo Rutgers University).
The 9 classes of particulate filters for non-powered APR and gas masks are:
Not oil-resistant
N95: moderate filtering efficiency (95%)
N99: high filtering efficiency (99%)
N100: highest filtering efficiency (99.97%)
Oil-resistant (somewhat resistant to oil)
R95: moderate filtering efficiency (95%)
R99: high filtering efficiency (99%)
R100: highest filtering efficiency (99.97%)
Oil-proof (strongly resistant to oil)
P95: moderate filtering efficiency (95%)
P99: high filtering efficiency (99%)
P100: highest filtering efficiency (99.97%)
Non-powered air-purifying respirators and gas masks are configured with replaceable particulate filters. Filtering facepiece respirators (FFRs) are typically single use; however, FFRs with replaceable filters are available (see figure above right). The class of the filter (such as N95) will be clearly marked on the filter, filter package, or respirator box.
Source: Respiratory Protection for Occupational Users of Pesticides. Patricia D. Hastings, Coordinator, Rutgers Pesticide Safety Education Program.