Three Approved Methods for QNFT

  1. Generated Aerosol Booth System QNFT utilizes an aerosol mixture (commonly corn oil) administered in a test chamber or booth. The subject being tested stands inside the booth or chamber and performs a series of exercises as the instrument samples how much challenge agent leaks into the respirator. This system is not widely used due to the high maintenance required to clean the equipment and the relatively large size of the system.

  2. Ambient Aerosol QNFT instruments measure aerosol concentrations inside and outside the test respirator and compute the fit factor. The challenge agents used in this test is ambient microscopic dust in the air and other aerosols. Ambient aerosol fit testers use a technology referred to as condensation nuclei counting (CNC) or condensation particle counting (CPC). These testers use laser technology to count particles. The respirator used in the test is equipped with P100 (HEPA) filters that prevent the ambient particles from passing into the respirator. Accessories are also available to conduct a QNFT on lower class filters, such as the 95 class filters, commonly found in the disposable filtering face piece respirators. One of the more common ambient aerosol fit testers is the TSI Portacount.

  3. Controlled Negative Pressure (CNP) QNFT involves the instrument pulling affixed vacuum on the respirator and the instrument measuring the airflow, or leak rate, needed to maintain the vacuum. The instrument then computes an estimated or equivalent fit factor. Two shortcomings of this type of testing are the person being tested must hold their breath during the measurement and remain motionless, and CNP testing can not be performed with filtering face piece respirators.

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