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Quantitative Fit Test (QNFT)

Last updated: June 21, 2022

What Does Quantitative Fit Test (QNFT) Mean?

A quantitative fit test (QNFT) is a type of respirator fitting test that numerically evaluates respirator fit, measuring the leakage into the respirator. It compares the respirator leakage with ambient concentrations of the test agent. This test is used where higher respirator fit factors are essential for safety.

Safeopedia Explains Quantitative Fit Test (QNFT)

The advantages of QNFT are that there is no limit of protection-factor, numerical results can be documented and there is no chance of user deception. The disadvantages are that it requires expensive equipment, a probe adapter and regular calibration.

During the test, a challenge agent is administered outside the face piece and the presence of the agent is detected and counted by an instrument.

There are three types of QNFT:

  • Generated Aerosol: Uses corn oil and a photometer-based aerosol detector.
  • Ambient Aerosol Nuclei Count: Uses laser technology to measure aerosol concentration inside and outside the respirator.
  • Controlled Negative Pressure: Creates a vacuum in the mask and calculates airflow.


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