The Definition of Quantitative Fit Test (QNFT)

Definition of Quantitative Fit Test (QNFT)

A quantitative fit test measures how well a tight-fitting respirator seals to a worker's face using an instrument rather than the worker's senses. The test produces a fit factor, which compares the concentration of particles or air pressure outside the respirator with the amount that gets inside. A higher fit factor means less leakage.

OSHA's Respiratory Protection Standard (29 CFR 1910.134, Appendix A) accepts several quantitative methods, including the ambient aerosol condensation nuclei counter (CNC) method, the generated aerosol method and controlled negative pressure (CNP) methods. Because the result is measured, QNFT can be used for any tight-fitting respirator, including full facepieces that need high fit factors.

Key Facts About Quantitative Fit Testing

• To pass, a tight-fitting half facepiece needs a fit factor of at least 100 and a tight-fitting full facepiece needs at least 500.
• QNFT is required for full facepiece negative-pressure respirators used in atmospheres that need more protection than a fit factor of 100 provides.
• Like qualitative testing, QNFT must be done before first use, at least annually and when the respirator or the worker's face changes.
• The test runs through a set of exercises, such as breathing, head movement, talking, grimacing and bending, while the instrument records leakage.
• QNFT gives an objective, documented number, which many employers prefer for consistency and audit records.

Example of a Quantitative Fit Test

A refinery maintenance technician will wear a full facepiece respirator during tank cleaning. The tester connects a sampling probe on the facepiece to a condensation nuclei counter. As the technician performs each exercise, the instrument measures particles inside and outside the mask. His overall fit factor is 1,800, well above the 500 needed for a full facepiece, so he passes.

How to Run a Quantitative Fit Test Program

1. Specify QNFT in your written respiratory protection program for respirators that require it.
2. Confirm medical clearance and that the worker is clean-shaven in the seal area.
3. Use a calibrated instrument and an OSHA-accepted protocol, with probed or adapted facepieces.
4. Run the full exercise sequence and record the overall fit factor.
5. Keep records of each test and track annual retest dates for every worker.

Related Terms

• Qualitative Fit Test (QLFT)
• Fit Testing
• Assigned Protection Factor (APF)
• Air-Purifying Respirator (APR)
• Respiratory Protection

Quantitative Fit Test Frequently Asked Questions

What is a fit factor?

A fit factor is a number that shows how well a respirator seals, calculated by comparing the concentration of a test agent outside the respirator with the concentration inside during the test. A fit factor of 100 means about 1% of the outside concentration leaked in.

Is a fit factor the same as an assigned protection factor?

No. The fit factor is the result of an individual's fit test. The assigned protection factor is the level of protection a class of respirator is expected to provide when the program is properly run.

Can quantitative fit testing be used for N95s?

Yes. N95 filtering facepieces can be tested quantitatively using an instrument with the appropriate adapter or mode, which some employers prefer to qualitative testing.

How long does a quantitative fit test take?

Most tests take around 10 to 20 minutes per respirator, including donning and the exercise sequence, depending on the protocol used.