Heat and Humidity for Bioburden Reduction of N95 Filtering Facepiece Respirators

Loïc Anderegg; John Doyle; Margaret L Gardel; Amit Gupta; Christian Hallas; Yuri Lensky; Nancy G Love; Bronwyn A Lucas; Edward Mazenc; Cole Meisenhelder; Ajay Pillarisetti; Daniel Ranard; Allison H Squires; Jessica Vechakul; Nathaniel B Vilas; Stuart Williams; Daniel Wilson; Tyler N Chen

doi:10.1089/apb.20.0053

Heat and Humidity for Bioburden Reduction of N95 Filtering Facepiece Respirators

Appl Biosaf. 2021 Jun 1;26(2):80-89. doi: 10.1089/apb.20.0053. Epub 2021 Jun 2.

Authors

Loïc Anderegg^{1

2}, John Doyle^{1

2}, Margaret L Gardel^{3

4}, Amit Gupta⁵, Christian Hallas^{1

2}, Yuri Lensky⁶, Nancy G Love⁷, Bronwyn A Lucas⁸, Edward Mazenc⁶, Cole Meisenhelder^{1

2}, Ajay Pillarisetti^{8

9}, Daniel Ranard⁶, Allison H Squires³, Jessica Vechakul⁸, Nathaniel B Vilas^{1

2}, Stuart Williams¹⁰, Daniel Wilson⁸, Tyler N Chen¹¹

Affiliations

¹ Department of Physics, Harvard University, Cambridge, Massachusetts, USA.
² Harvard/MIT Center for Ultracold Atoms, Cambridge, Massachusetts, USA.
³ Pritzker School of Molecular Engineering, The University of Chicago, Chicago, Illinois, USA.
⁴ Department of Physics, The University of Chicago, Chicago, Illinois, USA.
⁵ Consolidated Sterilizer Systems, Billerica, Massachusetts, USA.
⁶ Department of Physics, Stanford University, Stanford, California, USA.
⁷ Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan, USA.
⁸ PPE Sanitizer Group, Vallejo, California, USA.
⁹ Gangarosa Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, Georgia, USA.
¹⁰ University of Louisville, Louisville, Kentucky, USA.
¹¹ Department of Bioengineering, Stanford University, Stanford, California, USA.

Abstract

Introduction: The coronavirus disease 2019 (COVID-19) pandemic has caused a global shortage of single-use N95 filtering facepiece respirators (FFRs). A combination of heat and humidity is a promising method for N95 FFR decontamination in crisis-capacity conditions; however, an understanding of its effect on viral inactivation and N95 respirator function is crucial to achieving effective decontamination. Objective: We reviewed the scientific literature on heat-based methods for decontamination of N95 FFRs contaminated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and viral analogues. We identified key parameters for SARS-CoV-2 bioburden reduction while preserving N95 fit and filtration, as well as methods that are likely ineffective. Key Findings: Viral inactivation by humid heat is highly sensitive to temperature, humidity, duration of exposure, and the local microenvironment (e.g., dried saliva). A process that achieves temperatures of 70-85°C and relative humidity >50% for at least 30 min is likely to inactivate SARS-CoV-2 (>3-log reduction) on N95 respirators while maintaining fit and filtration efficiency for three to five cycles. Dry heat is significantly less effective. Microwave-generated steam is another promising approach, although less studied, whereas 121°C autoclave treatments may damage some N95 FFRs. Humid heat will not inactivate all microorganisms, so reprocessed N95 respirators should be reused only by the original user. Conclusions: Effective bioburden reduction on N95 FFRs during the COVID-19 pandemic requires inactivation of SARS-CoV-2 and preservation of N95 fit and filtration. The literature suggests that humid heat protocols can achieve effective bioburden reduction. Proper industrial hygiene, biosafety controls, and clear protocols are required to reduce the risks of N95 reprocessing and reuse.

Keywords: N95; decontamination; heat; humidity; respirator; steam.

Publication types

Review