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Volume: 33 | Article ID: art00020
Optical determination of filter effectiveness in potentially aerosol contaminated classrooms during the COVID-19 pandemic
  DOI :  10.2352/ISSN.2470-1173.2021.3.MOBMU-144  Published OnlineJune 2021

Increasing COVID-19 infections are reason of concern for all the inside workplaces where physical presence is necessary for collaborating. Classrooms are one of the suspected places, where usually students are closely placed to learn together as in times before the pandemic. To reduce the infection rate in classrooms, an air purifier was designed around a commercial filter which removes 99,9% of particles with 3μm. A baseline optical study of air purification was carried out to ensure effectiveness of the purifier during operation in closed environment. With conclusive evidence of microscopic images, breathing tests and aerosol penetration test using oil, the filter effectiveness was recorded. Optical values for suspended particle counts are recorded for variations in air flow rates of the air purifier and the gradual change is helping to understand the filter performance. Already around 70% minimum effectiveness of one flattened tissue layer removed from the filter was recorded during the tests, where the functional filter is folded in zigzags and 25 times thicker than a single layer. Furthermore, microscopic images showed solids deposited on the filter fabric and fuzzy spots on the tissue could indicate possible dried aerosol spots. This could be the hint supporting the hypothesis that aerosols can be effectively filtered reducing the virus load thus also risk of super-spreading of potential infection risk to an acceptable level. Beyond this research, and with the same group, measurements were made finding out the degree of reduction in potential aerosols particles in a classroom with a continuously aerosol emitting person. On that basis from this and the other optical studies, it was concluded that the spread of COVID-19 virus can be mitigated through effective air purification systems in classrooms and students can continue learning smoothly during the ongoing pandemic.

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Thomas Pfeiffer, Domínguez Téllez Batcheva, Khadse Himanshu Dilip, Bum-Ki Choi, Gesa Beck, Michael Hartmann, "Optical determination of filter effectiveness in potentially aerosol contaminated classrooms during the COVID-19 pandemicin Proc. IS&T Int’l. Symp. on Electronic Imaging: Mobile Devices and Multimedia: Technologies, Algorithms & Applications,  2021,  pp 144-1 - 144-11,

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