10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Low-Cost Particle Sensor for Monitoring Real-Time Protection of Respirators
BINGBING WU, Maija Leppänen, Jonathan Corey, Michael Yermakov, Yan Liu, Sergey A. Grinshpun, University of Cincinnati
Abstract Number: 188 Working Group: Low-Cost and Portable Sensors
Abstract Elastomeric particulate half- and full-facepiece respirators equipped with HEPA filters generally provide a high level of protection against various aerosol particles. Penetration of relatively large particles (approximately 0.5 μm and above) through a typical HEPA filter is extraordinarily low and usually undetectable. If these large particles penetrate an elastomeric respirator in any significant quantity, one could reasonably expect that this occurred due to a failure in respirator fit. Respators are prone to faceseal leakage, which often represents the primary penetration pathway. Therefore, it would be useful to monitor the aerosol concentration inside the respirator during work activities with a portable sensor capable of detecting relatively large aerosol particles in real time. If detected, one may conclude that the face seal integrity is compromised. Recent developments in aerosol instrumentation have led to low-cost, ultra-small optical particle sensors. In this study, a low-cost, portable Respirator Seal Integrity Monitor (ReSIM) was developed and evaluated.
The ReSIM prototype is based on a low-cost optical particle sensor (PPD60PV-T2, Shinyei, Kobe, Japan). It is designed to perform continuous air sampling inside a respirator, process all particle detection events over every 30-second interval and identify sudden particle concentration increases corresponding to faceseal leakage. ReSIM was first evaluated using a respirator-wearing manikin set-up and thereafter tested with firefighters engaging in simulated workplace activities in a 24.3-m3 laboratory exposure chamber. Two challenges, NaCl aerosol and combustion aerosol, were generated in the chamber during the manikin study. Only NaCl aerosol was generated when testing ReSIM on human subjects (firefighters). The tests in the manikin-based set-up were performed at three breathing flow rates: 30, 60 and 85 L/min.
While ReSIM performed in-mask air sampling from the respirator donned either on a manikin or on a subject, an operator intermediately induced leaks using a solenoid control valve and closed the valve to maintain a tight faceseal. Additional leaks were established by each human subject slightly repositioning the respirator on his/her faces, which commonly occurs in practice. A reference optical aerosol spectrometer (OAS, Model 1.108, Grimm Technologies) was connected to the same sampling probe as ReSIM. Its role was to confirm that a faceseal leakage was successfully established. It also verified that no large particles (within the optical range) penetrated while the respirator was fully sealed.
The leak detection performance of ReSIM was evaluated in terms of sensitivity and specificity. Sensitivity is defined as the probability of correct identification of the intervals with leaks, whereas specificity refers to the probability of correct identification of the intervals with no leaks.
When tested on the manikin, the ReSIM provided leak detection sensitivities of 71.8% and 98.4% when challenged with NaCl and combustion aerosol, respectively. The specificity was 99.8% for both aerosols. A lower sensitivity (58.0%) was obtained when testing with human subjects and NaCl; however, it should be higher for combustion aerosols based on the manikin-based study findings. When tested on firefighters, ReSIM demonstrated a specificity of 96.1%. Lower sensitivity and specificity values obtained with subjects compared to the manikin-generated data could be primarily attributed to the effect of moisture on the particle sensor, variability among subjects, and in-mask sampling bias.
In summary, ReSIM demonstrated its ability to assess the real-time respirator performance during actual use with sufficient sensitivity and rather high specificity. With an integrated alarm system, this response would trigger an alarm signaling the wearer that he/she can be overexposed to aerosol hazards.