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COVID-19 Decontamination and Reuse of Filtering Facepiece Respirators

Vaporous hydrogen peroxide, ultraviolet germicidal irradiation, and moist heat are the most promising decontamination methods. If FFR decontamination is considered, these methods do not appear to break down filtration or compromise the FFR; however, many of these methods can only be used for limited times.

Vaporous hydrogen peroxide (VHP)

Investigations into VHP decontamination of FFRs provide evidence of minimal effect to filtration and fit while demonstrating 99.9999% efficiency in killing bacterial spores. VHP did not reduce the filtration performance of ten N95 FFR models tested while showing a 6-log reduction in Geobacillus stearothermophilus spores [2-4].

In a report prepared by Battelle Memorial Institute, the 3M 1860 FFR was shown to maintain filtration performance for 50 treatment cycles of VHP, also referred to as HPV by some decontamination system manufacturers, using the Clarus® R HPV generator form Bioquell (utilizing 30% H2O2). Additionally, FFR fit was shown to be unaffected for up to 20 VHP treatments cycles using NPPTL’s Static Advanced Headform [4, 5]. Strap degradation occurred after 20 treatment cycles. Kenney et al. co-contaminated 3M 1870 FFRs with three bacteriophages, T1, T7, and Phi 6, and decontaminated the FFRs using VHP generated from the Bioquell’s BQ-50 system. The VHP treatment was shown to inactivate >99.999% of all phages which was below the limit of detection [6].

Viscusi et al. found that 9 FFR models (three particulate N95, three surgical N95 FFRs and three P100) exposed to one cycle of VHP treatment using the STERRAD 100S H2O2 Gas Plasma Sterilizer (Advanced Sterilization Products, Irvine, CA) had filter aerosol penetration and filter airflow resistance levels similar to untreated models; however, Bergman et al. found that three cycles of VHP treatment using the STERRAD 100S H2O2 Gas Plasma Sterilizer negatively affected filtration performance [2, 3].

Bergman et al. measured acceptable filtration performance for six FFR models (three particulate and three surgical FFRs) that received three cycles of VHP treatment using the Clarus® R HPV generator (utilizing 30% H2O2) [3]. VHP is a promising method with a potential for high capacity throughput, but certain VHP systems, such as the Clarus® R HPV generator, may be more suitable for FFR decontamination.

Ultraviolet germicidal irradiation (UVGI)

UVGI is a promising method but the disinfection efficacy is dependent on dose. Not all UV lamps provide the same intensity thus treatment times would have to be adjusted accordingly. Moreover, UVGI is unlikely to kill all the viruses and bacteria on an FFR due to shadow effects produced by the multiple layers of the FFR’s construction.

Acceptable filtration performance was recorded for eleven FFR models exposed to various UV doses ranging from roughly 0.5–950 J/cm2 and UVGI was shown to have minimal effect on fit [2, 3, 7, 8, 9, 10]. Heimbuch et al. tested filtration and fit of 15 FFRs and found no adverse effects to FFR performance [11]. Lindsley et al. reported a reduction of the durability of materials of the FFRs for doses ranging from 120–950 J/cm2; however, an approximate inactivation of 99.9% of bacteriophage MS2, a non-enveloped virus, and H1N1 influenza A/PR/8/34 were achieved with much lower doses of approximately 1 J/cm2 [12–14]. Heimbuch et al. tested the performance of 1 J/cm2 of UVGI against Influenza A (H1N1), Avian influenza A virus (H5N1), Influenza A (H7N9) A/Anhui/1/2013, Influenza A (H7N9) A/Shanghai/1/2013, MERS-CoV, and SARS-CoV and reported virus inactivation from 99.9% to greater than 99.999% [11].

UVGI is harmful. Proper precautions are required to avoid UVGI exposure to skin or the eyes.

Moist heat

Moist heat, consisting of 60°C and 80% relative humidity (RH) caused minimal degradation in the filtration and fit performance of the tested FFRs [3, 9, 10]. Heimbuch et al. disinfected FFRs contaminated with H1N1 influenza using moist heat, of 65°C and 85% RH, and achieved a minimum of 99.99% reduction in virus [14].

One limitation of the moist heat method is the uncertainty of the disinfection efficacy for various pathogens.

Steam treatment

Steam treatment may be a suitable approach for decontaminating FFRs. The limited number of studies for steam report minimal effect on FFR filtration and fit performance and a minimum of 99.9% reduction in H1N1 influenza and bacteriophage MS2 [14, 15].

Fisher et al. used microwave steam bags, designed for disinfecting infant feeding equipment, to decontaminate six FFR models and achieved 99.9% inactivation of MS2 bacteriophage. Filtration performance of all tested FFRs scored above NIOSH certification requirements. Three FFRs were further evaluated for three cycles of steam exposure and demonstrated no change in filtration performance [15]. Bergman et al. also demonstrated acceptable filtration performance after three cycles of exposure to microwave generated steam [3]. Microwave generated steam had little effect on FFR fit after exposure to up to three cycles of steam [9, 10].

Using microwaves to produce steam to decontaminate FFRs is not without limitations. Not all microwaves are constructed the same and some are more powerful than others. The effect of higher power microwaves on FFRs is unknown. Furthermore, the metal nosebands of FFRs may cause arcing, sparks inside the microwave oven, during exposure to microwaves.

Liquid hydrogen peroxide

Liquid hydrogen peroxide showed no effect on FFR filtration performance [3, 7]. Bergman et al. evaluated six FFRs for filtration performance after a 30-minute submersion in 6% hydrogen peroxide. All six FFR models tested demonstrated no changes in filter performance after three cycles of decontamination. FFR fit and disinfection efficacy were not assessed for this method.

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