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| Methodology | Key results | Study |
| UVGI |
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| 15 N95 FFR models (3M 1860, 3M1870, 3M VFlex 1805, Alpha Protech 695, Gerson 1730, Kimberly-Clark PFR, Moldex 1512, Moldex 1712, Moldex EZ-22, Precept 65–3395, Prestige Ameritech RP88020, Sperian HC-NB095, Sperian HC-NB295, U.S Safety AD2N95 A, and U.S Safety AD4N95) contaminated with H1N1 influenza and covered with a soiling agent (artificial saliva or artificial skin oil) were placed in a custom UV device made of polished aluminum and irradiated with UV dose of 1 J/cm2 in ∼1 min. | Significant reductions (≥3 log) in influenza viability for both soiling conditions were observed on facepieces of 12 of 15 FFR models and straps from 7 of 15 FFR models. | Mills et al., 2018 [12] |
| 3 N95 models of N95 were placed into a UV sterilizer cabinet (CHS-208A), with a 254 nm, 8 W lamp, and 475 cm2 internal area. Samples were irradiated for 30 minutes and left to stand under ambient conditions for 10 minutes per cycle for 10 cycles. | After 10 cycles of UV treatment, the meltblown filtration efficiency and pressure drop remained constant. | Liao et al., 2020 [13] |
| 4 models of N95 (3M 1860, 3M 9210, Gerson 1730, and Kimberly-Clark 46727) were exposed to UVGI doses (UV-C) from 120 j/cm2 to 950 j/cm2 in a custom-made 91 cm × 31 cm × 64 cm high chamber. | UVGI exposure led to a small increase in particle penetration (up to 1.25%) and a little effect on the flow resistance. Some degradation of elastic straps was noted on exposure to higher UV levels | Lindsley et al., 2015 [14] |
| 1 model of N95 was placed on the working surface of a laminar flow hood, Sterilgard III, (The Baker Company, Sanford, ME) fitted with a 40 W ultraviolet light. | No visible changes were observed. Various parts, e.g., straps, nose clips, and exhalation valves remained intact. Average penetration was not altered significantly. Filtration efficiency was good. | Viscusi et al., 2007 [15] |
| Using 126 (L) % 15.2 (W) % 10.8 cm (H), dual-bulb, 15-W UV-C (254 nm wavelength) lamp (Ultraviolet Products, Upland, CA, USA) was placed in a Labgard class II, type A2, laminar flow cabinet (NuAire, Inc., Plymouth, MN, USA), 3M 1860 and 3M 1870 were decontaminated subjected to treatment for 15 min at a UV-C wavelength dose of 18 kJ m2. | Reduction of virus load by > 4 log median tissue culture infective dose (>10,000-fold reduction in H5N1) for both FFRs was observed. | Lore et al., 2012 [16] |
| 6 N95 FFRs (N95-A, N95-B, and N95-C, SN95-D, SN95-E, and SN95-F) were placed on the working surface of a Sterilgard III laminar flow cabinet (The Baker Company, Sanford, ME) fitted with a 40-WUV-C light with 176–181 mJ cm−2 exposure to each side of the FFR, for a total time of 30 minutes. | UVGI treatment did not affect filtration aerosol penetration, filter airflow resistance, and physical appearance of FFRs. | Viscusi, et al. 2009 [17] |
| FFRs (3M 8000, 3M 8210, Moldex 2200, 3M 1860, 3M 1870, and Kimberly-Clark PFR95–270) were placed in a Sterilgard III laminar flow cabinet (The Baker Company, Sanford, Maine) fitted with a 40W UV-C bulb, intensity 1.8 mW/cm2 measured with a UVX Digital Radiometer with a MODEL UVX-25 sensor (254 nm filter). The total exposure time was 30 min (15 min each FFR side). | No significant changes in fit, comfort, or donning difficulty were noted. | Viscusi, et al., 2011 [18] |
| 6 models of N95 (N95-A, N95-B, and N95-C and SN95-D, SN95-E, and SN95-F) were decontaminated using a UV bench lamp (UV-C, 254 nm, 40 W), Model XX-40S (UVP, LLC, Upland, CA). 45 minute exposure at intensity 1.8 mW/cm2 was given. | All models had expected levels of both filter aerosol penetration and filter airflow resistance with no visible physical changes. | Bergman et al., 2010 [19] |
| 15 N95 FFR models (3M 1870, 3M 1860, Kimberly-Clark PFR, Moldex 1512, Precept 65–3395, Gerson 1730, Sperian HC-NB 095, U.S Safety AD2 N95 A, Moldex 1712, US Safety 4 N95, 3M VFlex 1805, Alpha Protech 695, Prestige Ameritech RP 88020, Sperian HC-NB295 F and Moldex EZ-22) were placed 25 cm below of a 120 cm, 80 Watts UV-C lamp (Mineralight XX-20S 20-W UV bench lamp) for a total of 15 min exposure. | Average log reduction of 4.69, virus reduced to values below the detection limit. No significant physical changes or changes in odor were observed. | Heimbuch et al., 2011 [20] |
| The relative survival of Bacillus subtilis spores was determined by loading onto N95 models (8210, 3M, St. Paul, and MN) after UVGI (UVA 365 nm and UVC 254 nm) decontamination under 37°C and relative humidity of 95%. FFRs was placed 10 cm below a 6 W handheld UV lamp (model UVGL-58, VUP LLC, Upland, CA) that emitted a wavelength of 254 nm (UV-C, 18.9 mW/cm2) or 365 nm (UVA, 31.2 mW/cm2) | No colony was recovered after exposure to UV-C for as little as 5 minutes. Relative survival remained above 20% after 20 minutes of irradiation by UVA, exponentially decaying with increased exposure time. | Lin et al., 2018 [21] |
| N95 respirators (8210, Cardinal N95-ML, Wilson SAF-T-FIT, 3M 1860, 3M 1870, and Kimberly-Clark PFR95–174) exposed to aerosolized particles containing MS2 coliphage were treated with internal filtering medium- (IFM-) specific UV-C doses ranging from 38 J m-2 to 4707 J m-2 using a biological safety cabinet (SterilGARD® III Advance; The Baker Company, Sanford, ME, USA). | Models exposed to a minimum IFM dose of 1000 J m−2 demonstrated at least a 3 log reduction in viable MS2. Model‐specific exposure times to achieve this IFM dose ranged from 2 to 266 min. | Fisher et al., 2010 [22] |
| 3 models of N95 respirators (3M 1860, 3M 1870, and Kimberly-Clark PFR95-270 (46767) were placed on a laboratory stand inside a Sterilgard III laminar flow cabinet (The Baker Company, Sanford, ME) fitted with a 40 W UV-C bulb for 15 minutes. | Respirator fit was preserved through 3 decontamination cycles alternating with 4 donning/doffing cycles. No physical degradation of FFRs was observed. | Bergman et al., 2011 [23] |
| N95 FFR (model N1105) loaded with MS2 coliphage was decontaminated by a UV germicidal lamp in a biological safety cabinet (SterilGARD III model SG403 A; Baker Company, Sanford, ME) using low doses of 4.32–5.76 J/cm2 and high doses ≥ 7.20 J/cm2 with a 5-hour irradiation time. | Low UVGI dose resulted in 3.00- to 3.16-log reductions, and high doses resulted in no detectable MS2 virus. | Vo et al., 2009 [24] |
| Ethylene oxide (EtO) |
| One model of N95 subjected to two treatments: EtO 3M Steri-Vac 4XL sterilizer at 55°C and 883 mg/L ethylene oxide gas and EtO 3M Steri-Vac 5XL sterilizer at 55°C and 725 mg/L ethylene oxide gas. All samples underwent 1 h exposure followed by 4 h aeration. | No negative effect on filtration performance. Average penetration of masks was slightly increased but not beyond their respective NIOSH certification criteria. | Viscusi et al., 2007 [15] |
| Steri-Vac 5XL 100% ethylene oxide sterilizer at 55°C; 1 h exposure (725 mg/L) followed by 4 h aeration. Six models of N95 (N95-A, N95-B, N95-C, SN95-D, SN95-E, and SN95-F) were evaluated. | EtO treatment did not affect the filter aerosol penetration, filter airflow resistance, or physical appearance of FFRs. | Viscusi et al., 2009 [17] |
| Amsco Eagle 3017 100% ethylene oxide sterilizer at 55°C; 1 h exposure (736.4 mg/L) followed by 12-h aeration. Six models of N95 (N95-A, N95-B, N95-C, SN95-D, SN95-E, and SN95) were utilized. | No visible physical changes to the appearance of FFRs or effect on filtration performance. | Bergman et al., 2010 [19] |
| Using Amsco Eagle 3017 sterilizer, the amount of residual EtO on six models of FFRs (S1, S2, S3, P1, P2, and P3) was measured. Headspace solid-phase microextraction (HSSPME) analysis using gas chromatography-mass spectrometry (GC-MS) was performed. | No residual EtO was detected in any of the respirators or respirator components tested. | Salter et al., 2010 [25] |
| Hydrogen peroxide vapor (HPV) |
| N95 FFRs (model 1860) inoculated with Geobacillus stearothermophilus spores were subjected to 50 repeated aerosol inoculation/decontamination cycles using a Bioquell Clarus C HPV generator. The 8-hour HPV cycle included a 10 min conditioning phase, 20 min gassing phase at 2 g/min, 150 min dwell phase at 0.5 g/min, and 300 min of aeration. | Decontamination of the respirator can be carried out for up to 50 cycles with >95% efficiency. After 30 HPV cycles, the elastic material in the straps split when stretched affecting respirator fit. | Battelle, 2016 [26] |
| Clarus C system (Bioquell, Horsham, PA), 3M 1870 N95 respirators (3M, St. Paul, MN) with 3 aerosolized bacteriophages; T1, T7, and Pseudomonas phage phi-6. Sterilization was performed with BQ-50 using a 10 min conditioning phase, 30–40 min gassing phase (varies with humidity and room size) at 16 g/min, 25 min dwell phase, and a 150 min aeration phase. | Single cycle resulted in complete eradication of phage from masks. After 5 cycles, the respirators appeared similar to new with no deformity. | Viscusi et al., 2007 [15] |
| 3M 1870 N95 respirators inoculated with 3 aerosolized bacteriophages (T1, T7, and Pseudomonas phage phi-6) were suspended by their elastic on racks in 33 m3 room and sterilized with the BQ-50 system (Bioquell, Horsham, PA) using the 10 min conditioning phase, 30–40 min gassing phase at 16 g/min, 25 min dwell phase, and a 150 min aeration phase. Half of the respirators underwent steam sterilization at 275°F for 5 min. | Single HPV cycle resulted in complete eradication of phage from masks. After 5 HPV cycles, the respirators had no deformity. Steam sterilization degraded the respirators with no additional virucidal activity. | Kenney et al., 2020 [27] |
| 3M1860 N95 FFRs loaded with Geobacillus stearothermophilus spores were decontaminated using Bioquell Z vaporizer (Andover, United Kingdom) utilizing 30% hydrogen peroxide solution programmed to gas for 20 min at 10 g/min, reaching ∼500 peak ppm followed by aeration of 4 hours. | Nonstatistical significant degradation of mask components. No physical or performance degradation and no noticeable odor. | Schwartz et al., 2020 [28] |
| Liquid hydrogen peroxide |
| Submersion of samples of one type of N95 in a dishpan containing 3–5 liters of 3% hydrogen peroxide for 30 min and 6% hydrogen peroxide for 30 min. Respirators were hung on a pegboard and air-dried for 72 h. | Use of 3% hydrogen peroxide exhibited no visible changes. Use of 6% solution slightly faded label ink on the fabric of the respirator. Average penetration did not significantly change for the N95 respirator and remained well below the NIOSH 5% criteria. | Viscusi et al., 2007 [15] |
| 30 min submersion of six N95 models (N95-A, N-95 B, N-95 C, SN-95 D, SN-95 E, and SN-95-f) in 6% solution of hydrogen peroxide over three cycle processing. FFRs were hung on a laboratory peg board and dried for a minimum of 16 h using a fan. | All models demonstrated no changes in filter performance after three cycles of decontamination. Staples oxidized to varying degrees in models with staples, i.e., N95-B, N95-C, SN95-E, and SN95-F. | Bergman et al., 2010 [19] |
| Hydrogen peroxide gas plasma (HPGP) |
| Six models (N95-A, N95-B, N95-C, SN95-D, SN95-E, and SN95-F) were sterilized using STERRAD® 100S H2O2 Gas Plasma Sterilizer (Advanced Sterilization Products, Irvine, CA, USA) with a 55-minute standard cycle | Aerosol penetration and filter airflow resistance of the respirators were not significantly affected. | Viscusi et al. 2009 [17] |
| Six models (N95-A, N95-B, and N95-C, SN95-D, SN95-E, and SN95-F) were sterilized using STERRAD® 100S H2O2 Gas Plasma Sterilizer (Advanced Sterilization Products, Irvine, CA) with 59% H2O2 and cycle time ∼55 min at 45°C–50°C. Samples were packaged in Steris Vis-U-All low temperature Tyvek®/polypropylene–polyethylene Heat Seal Sterilization pouches. | FFR filtration and the fit test were passed. No physical changes in masks were observed. No significant changes in aerosol penetration | Bergman et al. 2010 [19] |
| Hot air oven |
| N95 level meltblown filtration fabric and N95 respirators were kept in a hot air oven at 75°C for 30 minutes and variable humidity (up to 100% relative humidity) | 50 cycles of heat treatment did not deteriorate filtration efficiency. No visible mechanical damage, and ear straps retained elasticity. | Liao et al., 2020 [13] |
| 50 μl of 105 58 TCID50/mL of SARS-CoV-2 was applied on N95 fabric and stainless steel and exposed to 70°C dry heat | Heat caused more rapid inactivation on N95 than on steel. Filtration performance was unaffected after one decontamination round but subsequent rounds significantly reduced filtration ability. | Fischer et al., 2020 [29] |
| Moist heat incubation (MHI) |
| Six N95 models (N95-A, N95-B, N95-C, SN95-D, SN95-E, and SN95-F) were processed over 3 cycles for 30 min incubation at 60°C and 80% RH in the Caron model 6010 incubator | All models filtered >95% of 300 nm particulate after 3 cycles. Mean % is P < 4.01%, which is similar to penetration levels found in untreated fabric. SN95-E exhibited partial separation of the inner foam nose cushion from the FFR. | Bergman et al., 2010 [19] |
| Three N95 models (3M 1860, 3M 1870, and KC PFR95- 270) underwent incubation at 60°C for 15 min and 80% RH in the Caron model 6010 incubator for up to three cycles | Respirator fit was maintained throughout three cycles alternating with four donning/doffing cycles. Slight separation of the inner foam nose cushion was observed in 3M 1870. Face seal leakage value was below 1%. | Bergman et al., 2011 [23] |
| Six N95 models (M 8000, 3M 8210, Moldex 2200, 3M 1860, 3M 1870, and Kimberly-Clark PFR95–270) were decontaminated in a Caron model 6010 laboratory incubator (Marietta, Ohio) at 60°C for 30 min at 80% relative humidity | No significant changes in fit, odor detection, comfort, or donning difficulty were noted for any model | Viscusi et al., 2011 [18] |
| Six models contaminated with H1N1 influenza virus were subjected to 30 min of MHI at 65°C and 85% relative humidity | A >4-log reduction of viable H1N1 virus was noted. | Heimbuch et al., 2011 [20] |
| N95 FFRs (3M models 1860s and 1870) contaminated with H5N1 placed in a 6 L sealable container with 1 L of tap water was heated to 65 ± 5°C for 3 hours in an oven | Reduction of virus load by > 4 log median tissue culture infective dose (>10,000-fold reduction in H5N1). All FFRs displayed <5% penetration by 300-nm particles with no significant reduction in filtration performance. | Lore et al., 2012 [16] |
| Microwave steam bags (MSB) |
| N95 masks (3M 1860, 3M 8210, Cardinal Health N95, 3M 1870, Kimberly-Clark PFR 95, and Moldex 2200) contaminated with bacteriophage MS2 were exposed to steam treatment thrice | Tested steam bags were found to be 99.9% effective for inactivating MS2 on FFRs. Filtration efficiency was above 95%. | Fisher et al., 2011 [30] |
| Microwave-generated steam (MGS) |
| Two N95 models (3M 1860 and 3M 1870) contaminated with influenza (A/H5N1) virus were placed above a plastic box filled with 50 ml room temperature tap water, and the top of the box perforated with 96 holes (7 mm diameter). FFRs were irradiated for 2 min at full power in a 1250-W (2450 MHz) commercially available microwave oven (Panasonic corp., Secaucus, NJ, USA) | An absolute reduction of >4 log was achieved | Lore et al., 2012 [16] |
| Mean penetration at 300 nm was <5% for both models with no significant degradation of filter performance |
| Six FFR models contaminated with H1N1 influenza virus were exposed to MGS at 1250 W for 2 minutes | More than 4-log reduction of viable H1N1 virus was noted | Heimbuch et al., 2011 [20] |
| Six models (N95-A, N95-B, N95-C, SN95-D, SN95-E, and SN95-F) were processed in the commercially available 2450-MHz, Sharp Model R–305KS (Sharp Electronics, Mahwah, NJ) microwave oven; 750 W/ft3 experimentally measured; 2 min total exposure duration at maximum power. Two pipette tip boxes placed side-by-side were filled with 50 mL room-temperature tap water. | No change in filter performance after three cycles. SN95-E samples experienced partial separation of the inner foam nose cushion and slight melting of head straps of two SN95-Ds following the first 2 min cycle. The mean initial filter penetration was ≤4.01%. | Bergman et al., 2010 [19] |
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