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A HEPA filter respirator is an air-purifying respirator whose particulate filter meets the HEPA benchmark: at least 99.97% efficiency against 0.3 micrometre particles. OSHA’s respiratory protection standard names N100, R100 and P100 as the equivalent NIOSH filters, so those three labels are how “HEPA” translates to a NIOSH-certified respirator. This page is for clinic and laboratory staff, safety officers, buyers and students who need to check a “HEPA” listing against the US rules. After reading it you should know which filter classes OSHA equates with HEPA, which respirator types use them, and what the word does not tell you.
This page describes products and general use; it is not medical advice.
Who uses it: employees whose employer requires respiratory protection against airborne particles (for example in laboratories or clinics), and the safety officers and buyers who specify filters for them.
What a HEPA filter respirator is
29 CFR 1910.134(b) defines a HEPA filter as “a filter that is at least 99.97% efficient in removing monodisperse particles of 0.3 micrometers in diameter” and adds: “The equivalent NIOSH 42 CFR 84 particulate filters are the N100, R100, and P100 filters.” The same section defines an air-purifying respirator as “a respirator with an air-purifying filter, cartridge, or canister that removes specific air contaminants by passing ambient air through the air-purifying element.” A HEPA filter respirator is therefore an air-purifying respirator whose element is a HEPA-class particulate filter. “HEPA” describes a filter performance level, not a respirator model.
Paragraph (d)(3)(iv) keeps the older wording next to the current rule. For particulates, an employer may provide an atmosphere-supplying respirator, or an air-purifying respirator with a filter certified by NIOSH under 30 CFR part 11 as a HEPA filter, or one with a filter certified for particulates by NIOSH under 42 CFR part 84. The standard therefore names both the HEPA wording and the current Part 84 classes.
How it is built
The standard defines the parts of a respirator separately. The respiratory inlet covering is “that portion of a respirator that forms the protective barrier between the user’s respiratory tract and an air-purifying device or breathing air source, or both”; it may be a facepiece, helmet, hood or suit. In a powered air-purifying respirator (PAPR), a blower forces the ambient air through the air-purifying elements to the inlet covering. A filtering facepiece is “a negative pressure particulate respirator with a filter as an integral part of the facepiece or with the entire facepiece composed of the filtering medium.”
Types and variants
| Type | What the standard says | Key difference |
|---|---|---|
| Filtering facepiece with an N100, R100 or P100 filter | Filtering facepiece: filter is an integral part of the facepiece or the whole facepiece is the filtering medium | Falls in the half-mask row of Table 1 (APF 10); the filter label does not change that row |
| Half mask with an elastomeric facepiece | Table 1 footnote 3: the air-purifying half-mask category “includes filtering facepieces, and half masks with elastomeric facepieces” | Same APF row (10) as a filtering facepiece; reused respirators fall under the cleaning intervals in paragraph (h) |
| Air-purifying full facepiece | Table 1: air-purifying respirator, full facepiece | APF 50 instead of 10 |
| PAPR with HE filters | PAPR: an air-purifying respirator that uses a blower to force ambient air through air-purifying elements | APF 50 (half mask), 1,000 (full facepiece), 25 or 1,000 (helmet or hood, see footnote 4), 25 (loose-fitting facepiece) |
Table 1 footnote 2 limits every APF: the values are “only effective when the employer implements a continuing, effective respirator program,” including training, fit testing, maintenance and use requirements. For the full APF table see respirator levels and protection factors; for the hood and helmet rule see PAPR hood.
Specifications that matter
| Item | Value | Source |
|---|---|---|
| HEPA definition | At least 99.97% efficient against monodisperse 0.3 µm particles | 29 CFR 1910.134(b) |
| NIOSH non-powered classes equal to HEPA | N100, R100, P100: minimum efficiency ≥99.97% | 42 CFR 84.174(i) |
| Lower non-powered classes | N99, R99, P99: ≥99%; N95, R95, P95: ≥95% | 42 CFR 84.174(i) |
| N-series test aerosol | Solid sodium chloride, count median diameter 0.075 ± 0.020 µm | 42 CFR 84.174(f)(1), (g) |
| R- and P-series test aerosol | Dioctyl phthalate (DOP) or equivalent oil aerosol, count median diameter 0.185 ± 0.020 µm | 42 CFR 84.174(f)(2), (g) |
| Non-powered test airflow | 85 ± 4 L/min for a single filter; 42.5 ± 2 L/min through each of a pair | 42 CFR 84.174(e) |
| PAPR filters (series HE, PAPR100-N, PAPR100-P) | DOP aerosol at 100 mg/m³ for 5 to 10 seconds; 115 L/min (tight-fitting) or 170 L/min (loose-fitting); total efficiency ≥99.97% | 42 CFR 84.175 |
The HEPA definition and the NIOSH tests use different test particles, but the standard treats the N100, R100 and P100 filters as the equivalent of a HEPA filter.
How to choose
Each criterion below is stated in 29 CFR 1910.134.
| Criterion | What the standard says | Paragraph |
|---|---|---|
| Start from the hazard | Select a respirator based on the respiratory hazard and on workplace and user factors; evaluate the hazard, including a reasonable estimate of exposure and the contaminant’s chemical state and physical form | (d)(1)(i), (d)(1)(iii) |
| Certification | Select a NIOSH-certified respirator and use it in compliance with the conditions of its certification | (d)(1)(ii) |
| Particulate filter route | An atmosphere-supplying respirator, or an air-purifying respirator with a HEPA (30 CFR part 11) or Part 84 particulate filter; for particles with a mass median aerodynamic diameter of at least 2 micrometres, any NIOSH-certified particulate filter | (d)(3)(iv) |
| Protection level | Use the Table 1 APF to select a respirator that meets or exceeds the required protection; MUC = APF × the OSHA exposure limit | (d)(3)(i)(A), (b) |
| Models and sizes | Select from enough models and sizes that the respirator is acceptable to, and correctly fits, the user | (d)(1)(iv) |
The third row shows that OSHA does not require a HEPA-class filter for every particulate hazard; paragraph (d)(3)(iv)(C) allows any NIOSH-certified particulate filter where the particles are mainly 2 micrometres or larger.
Safe use and handling basics
- Medical evaluation first: the employer provides a medical evaluation “before the employee is fit tested or required to use the respirator in the workplace” (paragraph (e)(1)).
- Fit testing: an employee using a tight-fitting facepiece respirator must pass a qualitative or quantitative fit test before initial use, whenever a different facepiece is used, and at least annually (paragraph (f)(2)). The test is with the same make, model, style and size that will be worn. See OSHA respirator fit test.
- Facial hair: tight-fitting respirators may not be worn by employees with facial hair that comes between the sealing surface of the facepiece and the face, or that interferes with valve function (paragraph (g)(1)(i)(A)).
- Cleaning: a respirator issued to one employee is cleaned and disinfected as often as necessary to keep it sanitary; one issued to more than one employee is cleaned and disinfected before a different person wears it (paragraph (h)(1)).
- Program context: the written program, training and records are covered in respiratory protection program for laboratories.
Where HEPA appears in the fit-test rules: Appendix A to 1910.134 says a respirator tested with the irritant smoke (stannic chloride) protocol “shall be equipped with high efficiency particulate air (HEPA) or P100 series filter(s),” and the generated aerosol quantitative protocol replaces the normal filter or cartridge element of an air-purifying respirator with a HEPA or P100 series filter supplied by the same manufacturer.
Common mistakes
- Treating “HEPA” as the certification. The selection rule asks for a NIOSH-certified respirator used within its certification (paragraph (d)(1)(ii)). The HEPA wording describes filter efficiency.
- Expecting a HEPA-class filter to handle gases or vapors. The standard sets separate rules for gases and vapors in paragraph (d)(3)(iii), which allows an air-purifying respirator only with a NIOSH-certified end-of-service-life indicator or a change schedule. See respirator cartridges.
- Reading the filter label as the protection factor. The APF comes from the respirator type in Table 1, and only within a continuing program.
- Mixing up efficiency levels. N95, R95 and P95 are ≥95%; only N100, R100 and P100 are ≥99.97% (42 CFR 84.174(i)).
HEPA respirator variants: N95, reusable, brand filters and fumes
HEPA filter respirator vs N95
The difference is the minimum filter efficiency: an N95 filter must reach at least 95% and an N100 at least 99.97% under 42 CFR 84.174(i). Both a filtering facepiece with an N95 filter and one with an N100 filter sit in the half-mask row of Table 1 (APF 10), so the facepiece type, not the filter label, sets the APF. For the N100 comparison see N95 vs N100.
Reusable HEPA filter respirators
Table 1 footnote 3 places half masks with elastomeric facepieces in the same APF row as filtering facepieces. A reused respirator is covered by the cleaning, disinfecting and storage requirements in paragraph (h), including cleaning before a different person wears it.
3M and other brand filter lines
Brand names do not change the regulatory test. For any manufacturer’s filter, the questions the standard supports are: is the respirator NIOSH-certified and used within its certification; is the filter class N100, R100 or P100 (or a PAPR HE or PAPR100 filter) rather than a 95 or 99 class; and does the wearer pass a fit test on the same make, model, style and size.
Respirator mask for chemical fumes
Fumes and vapors fall under paragraph (d)(3)(iii), not the particulate rule in (d)(3)(iv). A HEPA-class filter is a particulate filter; for gases and vapors the standard calls for an atmosphere-supplying respirator or an air-purifying respirator with an ESLI or change schedule. See respirator cartridges for the cartridge types.
Sources
- OSHA, 29 CFR 1910.134 Respiratory protection, including Table 1 and Appendix A (read 2026-11-07): law.cornell.edu/cfr/text/29/1910.134
- NIOSH, 42 CFR 84.174 Filter efficiency level determination test, non-powered series N, R and P filtration (read 2026-11-07): law.cornell.edu/cfr/text/42/84.174
- NIOSH, 42 CFR 84.175 Instantaneous filter efficiency level determination test, PAPR series HE, PAPR100-N and PAPR100-P (read 2026-11-07): law.cornell.edu/cfr/text/42/84.175
