Concept + reference
Assigned protection factor (APF)
An assigned protection factor (APF) is the level of respiratory protection a class of respirators is expected to provide. An APF of 10 means the respirator is expected to reduce a wearer’s exposure tenfold — so it can be used at up to 10× the exposure limit. OSHA sets APFs in 29 CFR 1910.134, Table 1, and they apply only within a complete respiratory-protection program (fit testing, training, maintenance).
How to use it
Compute the hazard ratio = measured concentration ÷ exposure limit. A respirator is adequate only when its APF ≥ the hazard ratio. The highest concentration it may be used at is its maximum use concentration: MUC = APF × OEL (capped at the IDLH).
Find the right APF for your exposure automatically:
Open the calculator →OSHA assigned protection factors — Table 1
Air-Purifying Respirator (APR)
| Facepiece | Mode | APF |
|---|---|---|
| Quarter mask | — | 5 |
| Half mask | — | 10 |
| Full facepiece | — | 50 |
Powered Air-Purifying Respirator (PAPR)
| Facepiece | Mode | APF |
|---|---|---|
| Half mask | — | 50 |
| Full facepiece | — | 1,000 |
| Helmet / hood | — | 25 |
| Loose-fitting facepiece | — | 25 |
Supplied-Air Respirator (SAR)
| Facepiece | Mode | APF |
|---|---|---|
| Half mask | Demand | 10 |
| Full facepiece | Demand | 50 |
| Half mask | Continuous flow | 50 |
| Full facepiece | Continuous flow | 1,000 |
| Helmet / hood | Continuous flow | 25 |
| Loose-fitting facepiece | Continuous flow | 25 |
| Half mask | Pressure-demand / positive-pressure | 50 |
| Full facepiece | Pressure-demand / positive-pressure | 1,000 |
Self-Contained Breathing Apparatus (SCBA)
| Facepiece | Mode | APF |
|---|---|---|
| Half mask | Demand | 10 |
| Full facepiece | Demand | 50 |
| Full facepiece | Pressure-demand / positive-pressure | 10,000 |
Common questions
What is an assigned protection factor (APF)?
An assigned protection factor is the workplace level of respiratory protection a respirator or class of respirators is expected to provide when used within an effective respiratory-protection program. OSHA lists APFs in 29 CFR 1910.134, Table 1.
What is the APF of an N95 / half mask / full facepiece?
An N95 or elastomeric half-mask air-purifying respirator has an APF of 10; a full-facepiece air-purifying respirator has an APF of 50. A full-facepiece pressure-demand SCBA has an APF of 10,000.
How do I use the APF to pick a respirator?
Divide the measured concentration by the exposure limit to get the hazard ratio. The respirator’s APF must meet or exceed that hazard ratio. For 150 ppm at a 50 ppm PEL, the hazard ratio is 3, so any respirator with an APF of at least 3 is adequate.
Related: Maximum Use Concentration (MUC) · N95 APF · APR vs PAPR vs SCBA. Reference only — verify with a qualified professional.