RESPIRATORY LEAK DETECTION BY ULTRAFINE AEROSOLS - A PREDICTIVE MODELAND EXPERIMENTAL-STUDY

The leak performance of half-mask, maintenance-free respirators was st udied theoretically and experimentally. A predictive model for the the oretical protection factor and leakage flow has been developed that us es the equation of particle conservation inside and outside the respir ator. An experimental study was conducted using NaCl particles of 10 n m in diameter and a condensation nucleus counter as the particle detec tor. A respirator fitted with controlled leak holes of 20-3000 mum in diameter was tested at steady How rates of 10, 32, and 100 L/min. Resu lts showed that the aerosol penetration into a respirator was strongly influenced by the filter efficiency, leak hole size, and How rate thr ough the respirator. The results are in good agreement with theory, bu t some discrepancy has been noted at lower flow rates and smaller leak hole sizes. For the dust/mist respirators, the experimental protectio n factor for ultrafine 0.01-mum NaCl particles ranged from 3145 to as low as 3. For the high efficiency dust/mist/fume/radionuclide respirat or, a protection factor as high as 4.1 x 10(9) was measured on the ult rafine aerosol. For all respirators, the protection factors decreased rapidly with increasing leak hole size and increased as flow rate decr eased. The result of the study shows that with ultrafine aerosols, the particle penetration through the respirator filter can be reduced to a small, and in some instances, negligible value. The resulting protec tion factor is then due almost entirely to aerosol penetration through the leak hole. The ultrafine aerosol test can thus be used to study t he characteristics of the face seal leakage, without the complication of the aerosol penetration through the respirator filter.