Effect of Facial-seal Leaks on Protection Provided by Half-mask Respirators

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Abstract
Applications are presented of a computer model that gives the performance (overall protection factor including filter penetration and facial-seal leakage) of half-mask respirators for protection against aerosols. Input variables for the model are type of filter used, work rate of the wearer, QNFT-measured fit factor, and size distribution of the exposure aerosol. Based on the model, measurement errors due to loss of particles in leaks during qualitative fit testing (QNFT) measurements with current equipment are estimated to be less than 5 percent, but the change from high efficiency test filters to regular dust, fume, and mist (DFM) filters in use can reduce protection significantly. Overall protection factors are predicted for 33 industrial exposures based on assumed QNFT fit factors of 20 and 50. In these examples, DFM respirators with a QNFT fit factor of 50 have predicted protection factors from 21 to 2900, depending on aerosol size distribution. Overall protection factors for disposable and DFM filter respirators having a given facial-seal leak are presented graphically for a wide range of aerosol size distributions and two work rates. Also given is a contour chart showing the QNFT fit factor required to achieve an overall protection factor of 20 or 50 for a wide range of aerosol size distributions. For an unknown aerosol size distribution and average respirator performance (half-mask with DFM filters), a QNFT fit factor of 15 or more is required to ensure an overall protection factor of at least 10.