Special Issue on COVID-19 Aerosol Drivers, Impacts and Mitigation (XIV)

Audrey J. Dang1, Benjamin M. Kumfer1, J. Tyler Bertroche2, Jane Olson Glidden3, Christopher R. Oxford1, Udayabhanu Jammalamadaka4, Mary Ruppert-Stroescu5, Alexander R. Scott6, Jason A. Morris6, Connie Gan6, Jesse Hu6, Bradley King7, David I.A. Dhanraj1, Shruti Choudhary1, Pratim Biswas1,8, Richard L. Axelbaum1, Kathleen W. Meacham9, Brent J. Williams  1 

1 Center for Aerosol Science and Engineering, Department of Energy, Environmental and Chemical Engineering, Washington University in St Louis, Saint Louis, MO 63130, USA
2 Department of Otolaryngology-Head & Neck Surgery, Washington University School of Medicine, St. Louis, MO 63110, USA
3 Weavers' Guild of St. Louis, Missouri, USA
4 Mallinckrodt Institute of Radiology, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA
5 Sam Fox School of Design and Visual Arts, Washington University in St. Louis, Saint Louis, MO 63130, USA
6 Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA
7 Division of Environmental Health & Safety, Washington University in St. Louis, St. Louis, MO 63110, USA
8 College of Engineering, University of Miami, Coral Gables, FL 33146, USA
9 Department of Anesthesiology, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, USA


Received: November 13, 2020
Revised: January 30, 2021
Accepted: February 6, 2021

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.


Download Citation: ||https://doi.org/10.4209/aaqr.200629  


Cite this article:

Dang, A.J., Kumfer, B.M., Bertroche, J.T., Glidden, J.O., Oxford, C.R., Jammalamadaka, U., Ruppert-Stroescu, M., Scott, A.R., Morris, J.A., Gan, C., Hu, J., King, B., Dhanraj, D.I.A., Choudhary, S., Biswas, P., Axelbaum, R.L., Meacham, K.W., Williams, B.J.  (2021). Challenges in Predicting the Filtration Performance of a Novel Sewn Mask: Scale-up from Filter Holder to Mannequin Measurements. Aerosol Air Qual. Res. 21, 200629. https://doi.org/10.4209/aaqr.200629


HIGHLIGHTS 

  • A novel sewn mask filters 85 ± 1% of 136 nm particles (at 85 L min–1).
  • The design passes quantitative fit testing for 4 of 6 volunteers.
  • Material filtration efficiency measurements overpredict mask performance.
  • Test conditions are critical for interpreting filtration test results.
 

ABSTRACT


Novel designs and materials for filtering face-piece respirators (FFRs) have been disseminated in response to shortages during the COVID-19 pandemic. Since filtration efficiency depends on particle diameter and air face velocity, the relevance of material filtration or prototype fit data depends on test conditions. We investigate whether characterizing a material in a filter holder at a range of face velocities enabled precise prediction of the filtration performance of a novel sewn mask design. While larger particles (> 500 nm) are more relevant for inhalation exposure to respiratory emissions, we compare this mask and a N95 FFR (as a control) with smaller particles more similar to those in the N95 test method. Sewn from sterilization wrap, our mask (sealed to a mannequin head with silicone) filters 85 ± 1% of 136 nm particles (NaCl, 85 L min–1) and passes quantitative fit tests for 4 of 6 volunteers, representing intermediate protection between a surgical mask and N95 FFR. Filter holder material measurements overpredict the sewn mask’s filtration efficiency by 8.2% (95% CI 7.4–9.1%) (136 or 200 nm). While testing flat material in a filter holder enables comparison between materials, filtration performance does not precisely scale-up from filter holder to mannequin tests. Testing full prototypes at relevant conditions is crucial if an improvised design is intended as a substitute for a commercial surgical mask or FFR.


Keywords: Respirator, Filtration, Face velocity, COVID-19, Mask




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