Fit Testing
Quantitative Respirator Fit Testing (QNFT): A Complete Guide
Kevin Rittger, MD, FACEP, Founder and Medical DirectorUpdated 
Quantitative Fit Testing (QNFT) is the OSHA-approved fit-test protocol that uses calibrated equipment to numerically measure leakage into a respirator. QNFT is required whenever the worker must achieve a fit factor greater than 100, including all full-facepiece negative-pressure respirators. QNFT can be used for any tight-fitting respirator. Reference: 29 CFR 1910.134 Appendix A.
Key Requirement. QNFT must be used for any tight-fitting respirator that must achieve a fit factor greater than 100, including all full-facepiece negative-pressure respirators. Reference: 29 CFR 1910.134 Appendix A.
Key Takeaways
- QNFT produces a numeric fit factor, not a pass/fail call.
- QNFT is required for respirators that need a fit factor over 100 (full-face APRs, fit factor 500).
- Three approved methods: CNC (PortaCount), CNP (Quantifit), Generated Aerosol Quantitative.
- QNFT can be used for any tight-fitting respirator, but the CNC method destroys N95s.
- PLHCP medical clearance under 29 CFR 1910.134(e) is a prerequisite to QNFT.
What is QNFT?
OSHA defines a quantitative fit test as an assessment of respirator fit by numerically measuring leakage into the respirator. QNFT is the most objective method available because it does not depend on the worker's sense of smell or taste; the equipment counts particles directly.
The three OSHA-approved QNFT methods
| Method | Equipment | How it works |
|---|---|---|
| Ambient Aerosol Condensation Nuclei Counter (CNC) | TSI PortaCount | Compares ambient particle count to in-mask count |
| Controlled Negative Pressure (CNP) | OHD Quantifit | Measures leak rate at controlled negative pressure |
| Generated Aerosol Quantitative | Test chamber | Worker breathes in a chamber filled with a test aerosol |
The CNC protocol using PortaCount is the most common in practice. The equipment is versatile and supports multiple modes and respirator types.
When QNFT is required
QNFT must be used in these situations:
- Negative-pressure air-purifying respirators when the contaminant level exceeds 10 times the PEL
- Required fit factor greater than 100 for half-facepiece respirators
- Required fit factor of 500 or greater for full-facepiece respirators
- Supplied-air respirator (SAR) or SCBA used in demand mode (uncommon, mostly for escape)
- SCBA facepieces for structural firefighting under NFPA 1500 Chapter 15
Key terms
Assigned Protection Factor (APF): Estimate of the protection a properly used respirator provides. APF determines whether QNFT is required.
Fit Factor: A numeric measurement of the fit of a particular respirator to a particular individual, produced by the QNFT equipment. If the worker cannot achieve the required fit factor, the respirator does not fit and another must be tried.
Prerequisites for QNFT
Every worker who participates in QNFT must have completed a PLHCP-reviewed Medical Evaluation Questionnaire under 29 CFR 1910.134(e) before the test. VestMed handles MEQs 100% online with PLHCP review.
When QNFT is not the best choice
QNFT can be used for any tight-fitting respirator, but the CNC method is destructive for reusable N95 respirators. The PortaCount sample line punctures the facepiece, making the respirator unusable after the test. During N95 shortages (such as the early COVID-19 pandemic), many hospitals shifted to QLFT to preserve supply.
Equipment
The two dominant QNFT systems:
- TSI PortaCount (CNC protocol) - tsi.com
- OHD Quantifit (CNP protocol) - ohdusa.com
VestMed does not endorse either manufacturer; the references are for information only.
Equipment must be calibrated and maintained per manufacturer specifications. Calibration records are part of the respiratory protection program documentation.
Where to find protocols
The required minimum fit testing procedures are published in 29 CFR 1910.134 Appendix A. Manufacturer training videos are available on YouTube and on each manufacturer's site.
Trainer certification
OSHA does not require a specific certification for the fit tester. The fit tester must be competent in QNFT protocols and the specific equipment being used, and the program administrator must be qualified by training or experience commensurate with program complexity. Reference: 29 CFR 1910.134(c)(3).
What if a worker fails a QNFT?
Common reasons a worker fails:
- Wrong size of respirator
- Mask brand or model does not fit the worker's face
- Facial hair or features that interfere with the seal
- Damaged respirator
- Worker did not follow test instructions
- Fit tester error or protocol deviation
Re-check size, offer an alternative make or model, and rerun the test. If QNFT fails repeatedly and a respirator with a lower fit factor requirement would be adequate for the actual exposure, QLFT may be appropriate.
Recordkeeping
Every QNFT record must include:
- Worker name or identifier
- Type of fit test performed
- Specific make, model, style, and size of respirator
- Date of the test
- Results including fit factor and strip chart recording (where applicable)
Plus calibration records for the QNFT equipment.
Records must be retained until the next fit test at minimum, normally within 12 months.
Cost considerations
QNFT equipment is expensive to acquire and maintain. Two ways to reduce cost:
- Rent equipment for short-duration testing events
- Hire an external vendor to come on-site and run multiple tests in a single visit
Implementation Best Practices
| Step | What to do |
|---|---|
| 1. Clear every wearer through a PLHCP MEQ | Required before any fit test |
| 2. Determine if QNFT is required | Based on respirator type and required fit factor |
| 3. Choose protocol and equipment | CNC for most situations, CNP for some |
| 4. Calibrate the equipment | Per manufacturer schedule |
| 5. Train the fit tester | Hands-on course on the specific equipment |
| 6. Stock multiple makes and sizes | First failure usually means wrong respirator |
| 7. Document every test | Worker, respirator, date, fit factor, strip chart |
| 8. Re-fit annually | And on health, job, or respirator change |
Conclusion
QNFT is the most objective fit-testing protocol available and is required for full-face APRs, high-APF respirators, and certain SCBA and SAR configurations. Pair QNFT with PLHCP medical clearance for every wearer under 29 CFR 1910.134(e). VestMed handles the clearance side of the program through 100% online digital MEQs reviewed by our PLHCPs.
Frequently Asked Questions
Q: When is QNFT required?
A: For any tight-fitting respirator that must achieve a fit factor greater than 100, including all full-facepiece negative-pressure respirators (fit factor 500). QNFT is also required for SAR or SCBA used in demand mode and SCBA facepieces used in structural firefighting under NFPA 1500. Reference: 29 CFR 1910.134 Appendix A.
Q: What are the three QNFT methods?
A: Ambient Aerosol Condensation Nuclei Counter (CNC, PortaCount), Controlled Negative Pressure (CNP, Quantifit), and Generated Aerosol Quantitative. The CNC method using PortaCount is the most common.
Q: Does QNFT destroy N95 respirators?
A: The CNC method does, because the sample line punctures the facepiece. The CNP method is non-destructive. During shortages, employers should shift to QLFT for N95 fit testing where the respirator's required fit factor is 100 or less.
Q: Do workers need medical clearance before a QNFT?
A: Yes. 29 CFR 1910.134(e) requires PLHCP medical clearance before any fit test. The PLHCP reviews a Medical Evaluation Questionnaire to determine whether the worker can safely wear a respirator.
Q: What records must we keep for a QNFT?
A: Worker identifier, type of fit test, specific make, model, style, and size of respirator, date of the test, fit factor result, and strip chart recording where applicable. Plus equipment calibration records. Maintain until the next fit test at minimum.
Sources
- 29 CFR 1910.134 - Respiratory Protection
- 29 CFR 1910.134 Appendix A - Fit Testing Procedures
- TSI PortaCount Product Page
- OHD Quantifit Product Page
The information on this page is meant to be informative and is not a substitute for professional or legal advice.
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Kevin Rittger
MD, FACEP, Founder and Medical Director