Evaluation of particle penetration and breathing resistance of N95 filtering face-piece respirators and uncertified dust masks

摘要

The research presented in this doctoral dissertation strived to increase knowledge with respect to respirators performance in the workplace by evaluating particle penetration and breathing resistance (BR) of N95 filtering face-piece respirators (FFRs) under simulated air environmental conditions, determining maximum particle penetration of uncertified dust masks (UDMs) against sodium chloride (NaCl) and BR of UDMs and FFRs when challenged against Arizona road dust (ARD), and evaluating BR of FFRs while performing power washing in swine rooms.A novel test system was used to measure particle penetration and BR of two N95 FFRs under modified environmental conditions. NaCl particle penetration through the FFR was measured before and after the BR test using a scanning mobility particle sizer. BR of the FFR was measured by mimicking inhalation and exhalation breathing, while relative humidity and temperature were modified. BR was evaluated for 120 min under cyclic flow and four temperature and relative humidity air conditions. The BR of the FFRs was found to increase significantly with increasing relative humidity and lowering temperature upstream the FFR (p u3c 0.001). Measured particle penetration was not influenced by the simulated air environmental conditions. Differences in BR was observed between FFRs indicating that FFRs filtering media may perform differently under high relative humidity in air.In the second study, the maximum particle penetration of five commercially available UDMs was evaluated against NaCl aerosol. Particle penetration was carried out as specified by National Institute for Occupational Safety and Health (NIOSH) to certify N95 FFRs (42 CFR Part 84). Particle penetration was found to vary between 3% and 75% at the most penetrating particle size. In addition, the effect of mass loading on BR of UDMs and FFRs over time was evaluated. ARD was used as the loading dust and BR was measured for 120 min on UDMs and FFRs. BR was found to increase differently between the tested UDMs and FFRs. Further analysis of the UDMs and FFRs external layer suggest that the development of the particle dust cake during mass loading may be influenced by differences of the external layer.In the third study, field research was conducted to evaluate BR of two N95 FFRs while performing power washing in swine rooms. A member of the research team wore the FFR while power washing swine rooms. Every 30 min the team member stopped power washing, BR was measured and power washing continued. At the end of the 120 min trial, the FFR model was switched and the team member continued to power wash the rest of the room. Results demonstrated that BR of the tested FFRs did not increased during power washing in swine rooms (FFR 1, p = 0.40; FFR 2, p = 0.86). Power washing was found to have an effect in the temperature and relative humidity inside the rooms. Based on this study, FFR wearer should expect no increase in BR over 8 hr of power washing, decrease health risk by wearing the FFR and no need to replace the FFR during the power washing task.