Date of Degree
PhD (Doctor of Philosophy)
Occupational and Environmental Health
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 < 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.
This study evaluated two properties of commercially available respirators and dust masks: particle penetration and breathing resistance. Particle penetration describe the fraction of particle passing through the respirator and dust mask. Breathing resistance describe how difficult is to breathe through when using the respirator or dust mask.
An equipment setup was constructed to measure the particle penetration and breathing resistance of respirators and dust masks. Particle penetration of respirators and dust masks was evaluated against sodium chloride aerosol. Breathing resistance of two respirators was evaluated in simulated air temperature and relative humidity conditions. Also, Arizona road dust was used to evaluate the breathing resistance of respirators and dust masks. Finally, breathing resistance of two respirators was evaluated while power washing swine rooms.
Breathing resistance of respirators increased with increasing relative humidity and low temperature outside the respirators. Particle penetration did not changed under simulated temperature and relative humidity conditions. Particle penetration through dust masks varied greatly against sodium chloride aerosol. Arizona road dust affected the breathing resistance differently of all the tested respirators and dust masks. The breathing resistance of two respirators was unaffected during the power washing task in swine rooms.
Overall differences were observed in particle penetration and breathing resistance in the tested respirators and dust masks. However, further research is needed with additional respirators and dust masks to observe if differences are encounter in multiples respirator and dust mask models.
xi, 88 pages
Includes bibliographical references (pages 83-88).
Copyright 2015 Joel A. Ramirez