The Definition of Assigned Protection Factor (APF)

Definition of Assigned Protection Factor (APF)

An assigned protection factor (APF) is the level of workplace respiratory protection that a respirator, or class of respirators, is expected to provide to employees when the employer runs a continuing, effective respiratory protection program. OSHA lists APFs in Table 1 of 29 CFR 1910.134(d)(3)(i)(A). An APF of 10 means the respirator is expected to reduce the concentration a worker breathes to one-tenth of the concentration outside the facepiece.

Key Facts About Assigned Protection Factors

• Filtering facepiece or half-mask air-purifying respirator: APF 10
• Full-facepiece air-purifying respirator: APF 50
• Loose-fitting facepiece PAPR: APF 25
• Full-facepiece PAPR or pressure-demand supplied-air respirator: APF 1,000
• Pressure-demand full-facepiece SCBA: APF 10,000
• Maximum use concentration (MUC) equals the APF multiplied by the exposure limit for the contaminant.

Example of an Assigned Protection Factor

Air monitoring during paint removal shows lead exposure of 300 µg/m³ against a PEL of 50 µg/m³, so workers need a protection factor of at least 6. A half-mask respirator with P100 filters, APF 10, has an MUC of 500 µg/m³ and is adequate. When exposure on another task reaches 1,500 µg/m³, the required factor rises to 30, so workers switch to full-facepiece respirators with an APF of 50.

How to Use APFs to Select a Respirator

1. Measure the contaminant concentration with air monitoring.
2. Divide the measured concentration by the exposure limit to find the minimum protection factor needed.
3. Choose a respirator class with an APF equal to or greater than that value.
4. Confirm the MUC isn't above the IDLH level or any limit set by the cartridge manufacturer.
5. Fit test tight-fitting respirators and train workers so the APF is achieved in practice.

Related Terms

• Respiratory Protection
• Air-Purifying Respirator (APR)
• Fit Testing
• Exposure Limit

Frequently Asked Questions: Assigned Protection Factor

What is the difference between an APF and a fit factor?

An APF is a fixed value assigned to a class of respirators. A fit factor is the individual result of a quantitative fit test. OSHA requires a fit factor of at least 100 for half masks and 500 for full facepieces to pass, which is higher than the APF to allow a safety margin in real work.

Can I use a higher APF than the OSHA table if the manufacturer claims better performance?

No. Employers must use the APFs in OSHA's table, except where a substance-specific standard sets different requirements, which take precedence.

What if the required protection exceeds the IDLH level?

When concentrations are at or above IDLH, the respirator must be a full-facepiece pressure-demand SCBA or a combination supplied-air respirator with an auxiliary self-contained air supply, regardless of the calculated MUC.