Challenges in predicting the filtration performance of a novel sewn mask: Scale-up from filter holder to mannequin measurements

Audrey J. Dang, Benjamin M. Kumfer, J. Tyler Bertroche, Jane Olson Glidden, Christopher R. Oxford, Udayabhanu Jammalamadaka, Mary Ruppert-Stroescu, Alexander R. Scott, Jason A. Morris, Connie Gan, Jesse Hu, Bradley King, David I.A. Dhanraj, Shruti Choudhary, Pratim Biswas, Richard L. Axelbaum, Kathleen W. Meacham, Brent J. Williams

Research output: Contribution to journalArticlepeer-review

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.

Original languageEnglish (US)
Article number200629
JournalAerosol and Air Quality Research
Volume21
Issue number6
DOIs
StatePublished - Jun 2021

Keywords

  • COVID-19
  • Face velocity
  • Filtration
  • Mask
  • Respirator

ASJC Scopus subject areas

  • Environmental Chemistry
  • Pollution

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