Evaluation of Regeneration Processes for Filtering Facepiece Respirators in Terms of the Bacteria Inactivation Efficiency and Influences on Filtration Performance

Abstract

The regeneration of filtering facepiece respirators (FFRs) is of critical importance because of the severe shortage of FFRs during large-scale outbreaks of respiratory epidemics, such as COVID-19. Comprehensive experiments regarding FFR regeneration were performed in this study with model bacteria to illustrate the decontamination performance of the regeneration processes. The results showed that it is dangerous to use a contaminated FFR without any microbe inactivation treatment because the bacteria can live for more than 8 h. The filtration efficiency and surface electrostatic potential of 75% ethanoltreated FFRs were significantly reduced, and a most penetrating particle size of 200 nm was observed. Steam and microwave irradiation (MWI) showed promising decontamination performances, achieving 100% inactivation in 90 and 30 min, respectively. The filtration efficiencies of steam-treated FFRs for 50 and 100 nm particles decreased from 98.86% and 99.51% to 97.58% and 98.79%, respectively. Ultraviolet irradiation (UVI) effectively inactivated the surface bacteria with a short treatment of 5 min and did not affect the filtration performance. However, the UV dose reaching different layers of the FFP2 mask sample gradually decreased from the outermost layer to the innermost layer, while the model bacteria on the second and third layers could not be killed completely. UVI+MWI and steam were recommended to effectively decontaminate the used respirators and still maintain the respirators' filtration efficiency. The present work provides a comprehensive evaluation for FFR regeneration in terms of the filtration efficiencies for 50−500 nm particles, the electrostatic properties, mechanical properties, and decontamination effects.

Disinfection Treatments of Disposable Respirators Influencing the Bactericidal/Bacteria Removal Efficiency, Filtration Performance, and Structural Integrity

“…In the 2.5 cm × 2.5 cm designated area of each web, non-treated samples showed 1.46 × 10 6 and~2.53 × 10 6 CFUs on the coverweb and stiffener, respectively. Microwaving, oven-dry, and UV treatment showed similar bactericidal effect up to about 82%; in fact, this is inconsistent with previous studies [18,20], where 99.99% inactivation efficiency was achieved. This discrepancy can be attributed to the different treatment conditions, such as irradiation intensity, treatment time, and amount of bacteria loaded.…”

“…Complete bactericidal efficiency of S. aureus [20] Microwaving No particle filtration efficiency drop for 2 min exposure NA [10] No particle filtration efficiency drop for 2.5 min exposure >4-log 10 reduction of E. coli for 2.5 min exposure with 500 W power [18] UV irradiation NA Complete bactericidal efficiency to B. subtilis spores [12] No particle filtration efficiency drop NA [7,10,12,17] Complete bactericidal efficiency of S. subtilis and E. coli [18] Small decrease in particle filtration efficiency (up to 1.25%) NA [16] Chlorinated disinfectant No drop in particle filtration efficiency after using hypochlorite wipe About 1-log 10 attenuation in S. aureus after using hypochlorite wipe [13] Decrease in particle filtration with increased pressure drop (up to 18.3%) NA [11] No effect on aerosol penetration efficiency NA [10,14] Ethanol Drastic decrease in filtration efficiency (up to 18%)…”

“…Complete suppression of bacterial growth after 5 min immersion [22] NA [7,19] Complete bactericidal efficiency of S. subtilis and E. coli [18] Isopropanol Decrease in particle filtration efficiency (over 5%) NA [11,17] Significant drop in oily aerosol filtration efficiency after 2 min immersion (up to around 40%) NA [9] Detergent -laundering Significant drop in particle filtration efficiency after soap solution soaking for 2 min (up to around 39%) NA [15] The particle filtration of an electret media is attributed to the mechanical capture and the electrostatic attraction of particles [31,32]. Many previous studies associated the deteriorated performance of disinfection-treated respirators with the loss of electrostatic charges [7,9,11,15,[17][18][19]22,25], yet the direct evidence of charge deterioration was often missing. Additionally, it has hardly been examined for the effect of treatment on the structural integrity of the filter media, which may affect the resistance of respirators.…”

“…This discrepancy can be attributed to the different treatment conditions, such as irradiation intensity, treatment time, and amount of bacteria loaded. In a previous study, 1.0 × 10 6 CFU of bacteria was loaded on the respirator with a nebulizer; and the UV irradiation (wavelength; 254 nm, 5 min) and microwaving (400 W, 10 min) resulted in complete inactivation of cells [18]. The case of an oven-dry treatment (100 • C, 15 min) also achieved 99.99% inactivation efficiency, when 5.0 × 10 4 CFU of bacteria was dropped onto the surface of the respirator [20].…”

“…As a contingency strategy for the capacity crisis of disposable respirators, the Centers for Disease Control and Prevention and the National Institute of Occupational Safety and Health announced the guidelines of potential disinfection methods for the reuse of disposable respirators, which include the application of ultraviolet (UV) germicidal irradiation, vaporous hydrogen peroxide (VHP), and moist heat [5]. Table 1 shows the summary of previous studies on respirator disinfection methods [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. As for the bactericidal efficiency, autoclaving, UV irradiation, and chemical solvent treatments using bleach, ethanol, and VHP showed up to a 99% reduction of tested bacteria or virus [21,[25][26][27][28][29][30].…”