The certification and approval process for respiratory protective devices is governed by Part 84 of Title 42 of the Code of Federal Regulations (42 CFR 84).

The NIOSH-provided classifications only cover the filtration of particles or aerosols, not the air-purifying respirator's ability to remove chemical gasses and vapors from air, which is regulated under 42 CFR 84 Subpart L. For chemical cartridge classifications, NIOSH, under 42 CFR 84, partially defers to American National Standard ANSI K13.1-1973.

It is illegal in the United States to use filtration terms coined under 42 CFR 84, or mark masks with the word 'NIOSH' without the approval of NIOSH.

An example of an early respirator standard, Type A, established in 1926, was intended to protect against mechanically generated dusts produced in mines.

However, prior to the Hawks Nest Tunnel Disaster, these standards were merely advisory, as the USBM had no enforcement power at the time.

Non-powered respirator filters were classified based on their design against a contaminant, including substances like Dusts, Fumes, Mists, radionuclides, and asbestos.

The most popular respirator filters were often referred to as DM (Dust/Mist) or DFM (Dust/Fume/Mist) in CDC and NIOSH literature as shorthand.

[C1][11] In 1973, the Los Alamos National Laboratory (LANL) recommended NIOSH use NaCl aerosol to test DM and DFM filters.

[N2] The standard for N95 respirators includes, but is not limited to, a filtration of at least 95% under a 0.3 micrometer[C4] 200 milligram test load of sodium chloride.

When tested according to the protocol established by NIOSH each filter classification must demonstrate the minimum efficiency level indicated below.

[ND2] 42 CFR 84 Subsection L describes seven types of chemical cartridge respirators with maximum use concentrations and penetration, noting that colors and markings are definitively based on ANSI K13.1-1973.

[CF2] A TB guide, published by NIOSH in 1999, describes 13 combinations of contaminants with unique color markings.

[19] The definitive guide from ANSI, who, since the passage of 42 CFR 84 in 1995, has published a 2001 revision of K13.1-1973, named Z88.7-2001, describes 14 combinations of contaminants with unique color markings, based on 13 out of the 28 NIOSH Protection Designations.

In addition, the 2001 revision to ANSI K13.1-1973 provides exclusive colors to be used for non-P100 cartridge filters, in two categories: oil-resistant (remaining R- and P- NIOSH ratings), and non-oil resistant (all N-ratings).

[27] 42 CFR 84 (until 2020) did not change regulation regarding powered-air purifying particulate respirators, so have continued under TC-21C approval, with four digits, in the form TC-21C-####.