Respirator guide
N95 assigned protection factor (APF)
An N95 is a NIOSH-approved filtering facepiece respirator that captures at least 95% of airborne non-oil particulates. Because it is a half-mask air-purifying respirator, OSHA assigns it an APF of 10 in 29 CFR 1910.134, Table 1 — the same as an elastomeric half-mask APR.
What APF 10 means in practice
An APF of 10 means a properly fitted N95, used in a complete respiratory-protection program, is expected to reduce the wearer’s exposure tenfold. So its maximum use concentration is MUC = 10 × OEL. An N95 is adequate only when the hazard ratio (measured concentration ÷ exposure limit) is 10 or less.
Critical limit: particulates only
An N95 protects against particulates (dusts, mists, fumes, bioaerosols) — not gases or vapors. For gases and vapors (for example ammonia, solvents, or chlorine) you need a respirator with the correct chemical cartridge, or an air-supplied respirator. An N95 also may not be used in IDLH or oxygen-deficient atmospheres.
N95 vs other options
- N95 / N99 / N100, R- and P-series — filtering facepieces, all APF 10 as half masks; the letter/number is filter efficiency and oil resistance, not protection factor.
- Elastomeric half mask (APR) — also APF 10, but reusable and available with gas/vapor cartridges.
- Full-facepiece APR — APF 50.
- PAPR — APF 25–1,000 depending on facepiece.
Check whether an N95 (APF 10) is adequate for your exposure with the respirator calculator, or browse selection by substance. Reference only — verify with a qualified professional.
Common questions
What is the assigned protection factor (APF) of an N95?
An N95 filtering facepiece is a half-mask air-purifying respirator, so under OSHA 29 CFR 1910.134 Table 1 its assigned protection factor is 10. It is expected to reduce a wearer’s exposure to airborne particulates by a factor of about ten when used in a complete respiratory-protection program with fit testing.
What is the maximum use concentration for an N95?
The maximum use concentration (MUC) of an N95 is its APF times the exposure limit: MUC = 10 × OEL. For a substance with a 5 mg/m³ PEL, the N95 MUC is 50 mg/m³ — provided that value is below the IDLH and the contaminant is a particulate.
Does an N95 protect against gases and vapors?
No. An N95 filters particulates (at least 95% of non-oil airborne particles). It provides no protection against gases or vapors. For gases and vapors you need the correct chemical cartridge or an air-supplied respirator.
Is an N95 enough for my exposure?
An N95 (APF 10) is adequate only when the hazard ratio — concentration divided by the exposure limit — is 10 or less, the atmosphere is not IDLH or oxygen-deficient, and the contaminant is a particulate. Enter your numbers in the calculator to check.