Written and maintained by CASRAI Editorial Board
Last updated
This page describes products and general use; it is not medical advice.
“Respirator levels” is used for three different things: the filter class printed on a particulate respirator (N95, P100), the assigned protection factor (APF) that OSHA gives each type of respirator, and the hazmat suit levels A to D. The APF is the one that says how much protection a respirator type is expected to give, and it depends on the type of respirator and its facepiece, not on the filter label. This guide sets out OSHA’s APF values by respirator type and then the NIOSH filter classes. It is written for safety officers, clinic and laboratory staff, buyers and students who need to tell respirator types apart.
What is a respirator?
A respirator is protective equipment worn over the face to reduce the wearer’s inhalation of airborne contaminants. OSHA’s respiratory protection standard (29 CFR 1910.134) splits respirators into two families. An air-purifying respirator is “a respirator with an air-purifying filter, cartridge, or canister that removes specific air contaminants.” An atmosphere-supplying respirator “supplies the respirator user with breathing air from a source independent of the ambient atmosphere.” Filtering facepiece respirators, the disposable kind, are air-purifying: NIOSH describes them as respirators that “filter out particles such as dust, mist, and fumes.”
Who uses them: workers covered by an employer respiratory protection program, including health care, laboratory, construction and emergency-response staff.
Respirator levels explained: three meanings
| Meaning of “level” | What it describes | Where it comes from |
|---|---|---|
| Filter class (N95, R99, P100) | How efficiently a particulate filter captures particles, and its oil resistance | NIOSH certification of filters |
| Assigned protection factor (APF) | The workplace level of protection a type of respirator is expected to provide | OSHA 29 CFR 1910.134, Table 1 |
| Hazmat Level A to D | Combined suit and breathing-apparatus ensembles; not covered here, see hazmat suit types | Emergency-response practice |
Respirator types and assigned protection factors
OSHA defines the APF as “the workplace level of respiratory protection that a respirator or class of respirators is expected to provide.” The higher the number, the greater the expected protection. Table 1 of 1910.134 gives these values (read 2026-10-30):
| Respirator type | Facepiece | APF |
|---|---|---|
| Air-purifying (negative pressure) | Quarter mask | 5 |
| Air-purifying (includes filtering facepieces and elastomeric half masks) | Half mask | 10 |
| Air-purifying | Full facepiece | 50 |
| Powered air-purifying (PAPR) | Half mask | 50 |
| PAPR | Full facepiece | 1,000 |
| PAPR | Helmet or hood | 25 / 1,000 (see note) |
| PAPR | Loose-fitting facepiece | 25 |
| Supplied-air (airline), demand mode | Half mask / full facepiece | 10 / 50 |
| Supplied-air, continuous flow | Half mask / full facepiece / hood / loose-fitting | 50 / 1,000 / 25 or 1,000 / 25 |
| Supplied-air, pressure demand | Half mask / full facepiece | 50 / 1,000 |
| SCBA, demand | Half mask / full facepiece / helmet or hood | 10 / 50 / 50 |
| SCBA, pressure demand | Full facepiece / helmet or hood | 10,000 / 10,000 |
Source: OSHA, 29 CFR 1910.134, Table 1 (read 2026-10-30).
Footnotes that change how the table is read
- A filtering facepiece such as an N95 falls in the half-mask row, APF 10.
- A respirator with a higher APF may be used at lower concentrations.
- APFs are effective only within a continuing, effective respirator program that includes training, fit testing and maintenance.
- A helmet or hood PAPR or supplied-air respirator gets the 1,000 value only when the manufacturer has test evidence for it; otherwise it is treated as loose-fitting, APF 25.
- APFs do not apply to escape-only respirators.
How maximum use concentration works
OSHA defines the maximum use concentration (MUC) as “the maximum atmospheric concentration of a hazardous substance from which an employee can be expected to be protected.” It is the APF multiplied by the applicable OSHA exposure limit. Where no OSHA limit exists, the employer determines it from available information and judgment.
Illustration with a hypothetical limit of 0.5 mg/m³ (not a real substance): a half mask (APF 10) gives an MUC of 5 mg/m³, and an air-purifying full facepiece (APF 50) gives 25 mg/m³. The arithmetic shows why the facepiece type matters as much as the filter.
What does 1910.134 say about choosing a respirator?
- Respirators must be NIOSH-certified and used within their certification.
- For an atmosphere that is immediately dangerous to life or health (IDLH), the standard calls for a full-facepiece pressure-demand SCBA rated for at least 30 minutes, or a pressure-demand supplied-air respirator with auxiliary SCBA. Oxygen below 19.5% is generally treated as IDLH, and so is any exposure that cannot be estimated.
- For gases and vapors, the standard calls for an atmosphere-supplying respirator, or an air-purifying one with an end-of-service-life indicator or a justified cartridge change schedule. See respirator cartridges.
- For particulates, the standard calls for an atmosphere-supplying respirator or an air-purifying one with a HEPA filter or a NIOSH 42 CFR part 84 filter. Where the particle mass median aerodynamic diameter is 2 micrometers or more, any NIOSH-certified particulate filter may be used.
- The employer must offer a sufficient range of models and sizes.
NIOSH filter classes, including P100
NIOSH certifies nine particulate filter classes: three series by three efficiencies. The efficiencies are at least 95%, at least 99% and at least 99.97% of airborne particles (the last is labelled 100). The series letter is about oil: N is “Not resistant to oil,” R is “Somewhat resistant to oil,” and P is “Strongly resistant to oil” (NIOSH, Filtering Facepiece Respirators, read 2026-10-30).
What is a P100 respirator?
P100 is the top efficiency (at least 99.97%) in the oil-proof P series. The filter class says nothing by itself about the APF: a P100 filtering facepiece is still a half-mask type with APF 10, and an elastomeric half mask with P100 filters is also APF 10. For the class-by-class comparison see respirator cartridges, N95 vs N100 and what is an N95 respirator.
How to use and wear a respirator
Under 1910.134 a respirator is used inside a program: a medical evaluation, a fit test for tight-fitting types, training and maintenance. The APF values above hold only when that program is in place. Requirements for the program are in respiratory protection programs in the laboratory and respirator fit testing requirements. For the filtering facepiece type specifically, see how to wear an N95 mask.
When to use a respirator
1910.134 ties respirator use to the hazard: the chosen type must suit the contaminant, its concentration and whether the atmosphere is IDLH, as set out in the selection rules above. Where the concentration or the contaminant cannot be estimated, the standard treats the atmosphere as IDLH.
Common mistakes
- Reading the filter class as the level of protection. N95 and P100 filtering facepieces both fall in the half-mask APF of 10.
- Applying an APF without a respirator program (training, fit testing, maintenance).
- Treating a hood or helmet PAPR as APF 1,000 without manufacturer test evidence; the default is 25.
- Applying APFs to escape-only respirators, which are excluded.
- Mixing up filter classes with hazmat Levels A to D.
Frequently asked questions
How to use a respirator?
Use it within a respirator program: medical evaluation, fit test for tight-fitting types, training and maintenance, as 1910.134 requires.
How to wear a respirator?
Tight-fitting types must seal against the face, which is why fit testing is required before use. Manufacturer instructions apply to each model; the N95 case is covered in the linked wearing guide.
What is a P100 respirator?
A respirator with a P-series (strongly oil-resistant) filter of the highest efficiency class, at least 99.97% of airborne particles.
What is a respirator?
Protective equipment worn over the face to reduce inhalation of airborne contaminants, either by filtering the air (air-purifying) or supplying separate breathing air (atmosphere-supplying).
When to use a respirator?
When the hazard calls for it under the selection rules of 1910.134: contaminant, concentration, and whether the atmosphere is IDLH.
Sources
- OSHA, 29 CFR 1910.134 Respiratory Protection: osha.gov/laws-regs/regulations/standardnumber/1910/1910.134 (read 2026-10-30).
- CDC NIOSH, Filtering Facepiece Respirators: cdc.gov/niosh/ppe/respirators/ffr.html (read 2026-10-30).
