Determinations of known respirator leakage using controlled negative pressure and ambient aerosol QNFT systems

During comparative studies, controlled negative-pressure fittest systems have consistently reported lower fit factors and more respirator leakage than aerosol-based systems. This study was designed to assess how well a controlled negative pressure and an ambient aerosol fit test system could measure known sources of leakage introduced into respirators worn by human subjects. The basic study design involved conducting a sequential pair of fit tests with the same system. A fixed source of leakage (leak needle) was uncapped after the first test, so that the difference between the pair of fit tests reflected the introduction of the known leak source into the respirator. A second pair of fit tests was then completed with the second fittest system in the same manner. In repeated (N=15) measurements of respirator fit for five subjects, the controlled negative pressure system's measurements of known leak sources averaged 105% of the known leakage rate, with a mean coefficient of variation of 10%. The ambient aero...