Protection levels of N95-level respirator substitutes proposed during the COVID-19 pandemic: Safety concerns and quantitative evaluation procedures

David H. Ballard, Audrey J. Dang, Benjamin M. Kumfer, Patricia B. Weisensee, J. Mark Meacham, Alex R. Scott, Mary Ruppert-Stroescu, Broc A. Burke, Jason Morris, Connie Gan, Jesse Hu, Bradley King, Udayabhanu Jammalamadaka, Sena Sayood, Stephen Liang, Shruti Choudhary, David Dhanraj, Bruno Maranhao, Christine Millar, J. Tyler BertrocheNirah Shomer, Pamela K. Woodard, Pratim Biswas, Richard Axelbaum, Guy Genin, Brent J. Williams, Kathleen Meacham

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4 Scopus citations


Objective The COVID-19 pandemic has precipitated widespread shortages of filtering facepiece respirators (FFRs) and the creation and sharing of proposed substitutes (novel designs, repurposed materials) with limited testing against regulatory standards. We aimed to categorically test the efficacy and fit of potential N95 respirator substitutes using protocols that can be replicated in university laboratories. Setting Academic medical centre with occupational health-supervised fit testing along with laboratory studies. Participants Seven adult volunteers who passed quantitative fit testing for small-sized (n=2) and regular-sized (n=5) commercial N95 respirators. Methods Five open-source potential N95 respirator substitutes were evaluated and compared with commercial National Institute for Occupational Safety and Health (NIOSH)-Approved N95 respirators as controls. Fit testing using the 7-minute standardised Occupational Safety and Health Administration fit test was performed. In addition, protocols that can be performed in university laboratories for materials testing (filtration efficiency, air resistance and fluid resistance) were developed to evaluate alternate filtration materials. Results Among five open-source, improvised substitutes evaluated in this study, only one (which included a commercial elastomeric mask and commercial HEPA filter) passed a standard quantitative fit test. The four alternative materials evaluated for filtration efficiency (67%-89%) failed to meet the 95% threshold at a face velocity (7.6 cm/s) equivalent to that of a NIOSH particle filtration test for the control N95 FFR. In addition, for all but one material, the small surface area of two 3D-printed substitutes resulted in air resistance that was above the maximum in the NIOSH standard. Conclusions Testing protocols such as those described here are essential to evaluate proposed improvised respiratory protection substitutes, and our testing platform could be replicated by teams with similar cross-disciplinary research capacity. Healthcare professionals should be cautious of claims associated with improvised respirators when suggested as FFR substitutes.

Original languageEnglish (US)
Article numbere045557
JournalBMJ open
Issue number9
StatePublished - Sep 2 2021
Externally publishedYes

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  • COVID-19
  • adult anaesthesia
  • health & safety
  • occupational & industrial medicine
  • preventive medicine


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