42 CFR 84.170 - Non-powered air-purifying particulate respirators; description.
(a) Non-powered air-purifying particulate respirators utilize the wearer's negative inhalation pressure to draw the ambient air through the air-purifying filter elements (filters) to remove particulates from the ambient air. They are designed for use as respiratory protection against atmospheres with particulate contaminants (e.g., dusts, fumes, mists) that are not immediately dangerous to life or health and that contain adequate oxygen to support life.
(b) Non-powered air-purifying particulate respirators are classified into three series, N-, R-, and P-series. The N-series filters are restricted to use in those workplaces free of oil aerosols. The R- and P-series filters are intended for removal of any particulate that includes oil-based liquid particulates.
(c) Non-powered air-purifying particulate respirators are classified according to the efficiency level of the filter(s) as tested according to the requirements of this part.
(1) N100, R100, and P100 filters shall demonstrate a minimum efficiency level of 99.97 percent.
(2) N99, R99, and P99 filters shall demonstrate a minimum efficiency level of 99 percent.
(3) N95, R95, and P95 filters shall demonstrate a minimum efficiency level of 95 percent.