A quantitative fit test (QNFT) can be used to fit-test any tight-fitting respirator. It involves using an instrument to measure leakage around the face seal and produces a numerical result called a “fit factor.” There are three OSHA-accepted QNFT test protocols:
- Generated aerosol uses a non-hazardous aerosol such as corn oil generated in a test chamber.
- Condensation nuclei counter (CNC) uses ambient aerosol and doesn’t require a test chamber.
- Controlled negative pressure (CNP) uses a test that creates a vacuum by temporarily cutting off air. (There is also a fourth method, which is an abbreviated version of this one.)
QNFTs use the same seven exercises as QLFTs, plus an additional “grimace” test where the subject smiles or frowns for 15 seconds.
A fit factor of at least 100 is required for half-mask respirators and a minimum fit factor of 500 for a full facepiece negative-pressure respirator.