Controlled Heat and Humidity-Based Treatment for the Reuse of Personal Protective Equipment: A Pragmatic Proof-of-Concept to Address the Mass Shortage of Surgical Masks and N95/FFP2 Respirators and to Prevent the SARS-CoV2 Transmission

Abstract

Background: The coronavirus infectious disease-2019 (COVID-19) pandemic has led to an unprecedented shortage of healthcare resources, primarily personal protective equipment like surgical masks, and N95/filtering face piece type 2 (FFP2) respirators. Objective: Reuse of surgical masks and N95/FFP2 respirators may circumvent the supply chain constraints and thus overcome mass shortage. Methods, design, setting, and measurement: Herein, we tested the effects of dry- and moist-air controlled heating treatment on structure and chemical integrity, decontamination yield, and filtration performance of surgical masks and FFP2 respirators. Results: We found that treatment in a climate chamber at 70°C during 1 h with 75% humidity rate was adequate for enabling substantial decontamination of both respiratory viruses, oropharyngeal bacteria, and model animal coronaviuses, while maintaining a satisfying filtering capacity. Limitations: Further studies are now required to confirm the feasibility of the whole process during routine practice. Conclusion: Our findings provide compelling evidence for the recycling of pre-used surgical masks and N95/FFP2 respirators in case of imminent mass shortfall.

Keywords: COVID-19; FFP2/N95; SARS–CoV-2; coronavirus; facemask; heating; recyclibility; surgical face masks.

Figure 1

(A) Observation through scanning electron microscopy of the middle layer of surgical masks and filtering face piece type 2 (FFP2) respirators whether untreated or treated by moist-air heating at 70°C (75% humidity rate (HR) during 1 h) in the climate chamber. The inner panels show the correct structural integrity of polypropylene nanofibers at higher magnification. (B) Assessment of the molecular modifications of FFP2 respirators treated by moist-air heating at 70°C (75% HR during 1 h) in the climate chamber compared to untreated FFP2, as observed through Fourier-transform infrared attenduated total reflection (FTIR-ATR) (left panel) and thermal desorption–gas chromatography–mass spectrometry (TD-GC-MS) (right panel). The FFP2 respirator layers were confirmed as composed of polypropylene only, except for the mid-layer of treated/untreated FFP2 respirators that also presented four additional bands centered at 3,295, 1,640, 1,565, and 1,530 cm⁻¹, which probably correspond to a molecule of the amide family; this hypothesis is supported by the fact that this kind of molecule is known to be an effective process agent during the melt-blown process of the polypropylene fibers (22). The left panel shows only the internal and mid-layer as examples. The chromatogram displayed in the upper right panel showed the four layers of the untreated FFP2 respirators altogether. It indicated a low quantity of molecules: most of them were linear and branched alkanes. The two main peaks at 14 min represented butylated hydroxytoluene (BHT), i.e., a very well-known antioxidant, and 2-ethylhexanoic acid. In the lower right panel is superimposed the chromatogram of the treated FFP2 respirators to the untreated ones. Only two very weak new peaks were observed: the first one corresponds to benzoic acid, the second one being unidentified. a.u., arbitrary units; cm⁻¹, per centimeter; min, minute.

Figure 2

(A) Decontamination yields obtained after dry- or moist-air heating treatment for influenza A H3N2/Scotland/20/74 virus and oropharyngeal bacteria. (B) Decontamination yields obtained after moist-air heating treatment for swine porcine epidemic diarrhea virus [(PEDV) left panel] and avian infectious bronchitis virus of chicken [(IBV) right panel] coronaviruses. Lack of virus re-isolation was arbitrarily indicated in the figure as a titer equal to the lower limit of detection (LLOD) of the re-isolation process. (C) Filtration properties of surgical masks (upper panel) and filtering face piece type 2 (FFP2) respirators (lower panel) for the influenza A H3N2/Scotland/20/74 virus strain and for Staphylococcus aureus ATCC 6538 (on surgical masks only for the latter as specified by EN 14683 guidelines). (D) Measurement of inspiratory resistance for surgical masks (left panel) and FFP2 respirators (right panel). All results are expressed as mean ± SEM. CFU, colony-forming unit; ΔP, differential of pressure; L/min, liter per minute; ND, not determined; Pa/cm², Pascal per square centimeter; PFU, particle-forming unit; SEM, standard error of the mean.