The first part of the filter’s classification uses the letters N, R, or P to indicate its ability to function when exposed to oils.
These filters are restricted to use in those atmospheres free of oil aerosols. They may be used for any solid or liquid airborne particulate hazard that does not contain oil. Generally, these filters should be used and reused subject only to considerations of hygiene, damage, and increased breathing resistance.
Filters intended for removal of any particle including oil-based liquid aerosol. They may be used for any solid or liquid airborne particulate hazard. If the atmosphere contains oil, the R-series filter should be used only for a single shift (or up to 8 hours continuous or intermittent use).
Intended for removal of any particle including oil-based liquid aerosols. They may be used for any solid or liquid particulate airborne hazard. NIOSH recommends that respirator manufacturers establish time use limitations for all P-series filters.
P-Series filters should be used and reused for no more than 40 hours of use or 30 days, whichever occurs first, in atmospheres that contain oil aerosols unless the filter needs to be changed for hygiene reasons, is damaged, or becomes difficult to breathe through before the time limit is reached.
When used in atmospheres containing non-oil aerosol, P-series filters should be used and reused subject to conditions of hygiene, damaged, and increased breathing resistance.
The numbers 95 and 100 indicate the percentages of particles the filters remove.
The 95 means the filter removes at least 95% and the 100 means the filter removes at least 99.97%. Therefore, an N95 filter is not resistant to oil and removes at least 95% of the most penetrating particles. And the P100 filter is oil-proof and removes at least 99.97% of the most penetrating particles.