On This Page On This Page PURCHASE WITH CONFIDENCE Discover the 17 questions you need to ask before buying your next autoclave. Get the Guide Decontaminating N95 Masks with Steam Sterilization Written by: Amit Gupta MS Mechanical Engineering, Vice President of Engineering Can N95 Masks be steam sterilized for reuse? This article attempts to answer this question by giving a review of the current literature and taking a closer look at N95 filter types and materials of construction. The ability to autoclave N95 masks would be ideal because autoclaving is a proven sterilization process and existing autoclave infrastructure is ubiquitous in labs, hospitals, dental offices, and many other types of facilities. While data from studies performed in years past suggested that steam autoclaves were ineffective for the reprocessing of used N95 masks, newer data suggests that the earlier studies did not necessarily paint the whole picture, and in instances where technologies like Hydrogen Peroxide vapor and UV-C are not available, supplies of N95 respirators may be stretched through the use of autoclave decontamination. Background Leading into the coronavirus pandemic, there was widespread concern regarding shortage of personal protective equipment (PPE) – specifically N95 masks. Over the past few months, there has been much research conducted into various ways to decontaminate N95 masks to allow them to be safely reused. As we discussed in our previous post, Hydrogen Peroxide vapor and UV-C light decontamination are popular methods for N95 decontamination. Unfortunately, in many areas of the US and around the world, these technologies are either not available, too expensive or too complicated to be implemented. N95 Filter Type – Electrostatic vs. Pleated N95 masks typically employ one of two different filtering techniques. The first category of N95 mask uses a melt-blown polymer fiber that is imbued with an electrostatic charge, this filtration layer is called the electret. As particles pass through this electrostatically charged filter, they get trapped by the electro-magnetic fields. These types of masks are also referred to as cup masks. The second category of N95 uses a pleated fiber filter similar to a HEPA filter. The pleated filters rely on the closely packed density of the fibers to mechanically prevent the passage of particles – similar to how a screen works, but on a microscopic scale. These types of masks are also referred to as flat fold or folded masks. Data published by co-inventor of the electrostatic N95 mask Peter Tsai stated that steam and condensate may have little effect on the electret. In “Performance and the Protection against COVID-19 and Their Efficiency Degradation by Sterilization to Reuse the Masks” (4) Tsai found that the charge on the electret filtration element used in N95 masks showed no noticeable loss after exposure to steam at typical sterilization temperature of 250⁰F (121⁰C) for 3 minutes. However, data collected by the Texas Department of Medicine (11) found that one full 30-60 minute steam decontamination cycle in a prevacuum autoclave degraded the filtration efficiency of the 3M 1860 (mask with an electret) to below 95%. Pleated style filters don’t have an electret. Studies on pleated style N95 masks were published by Anand Kumar et. al (4). Kumar analyzed the impact of steam decontamination in a laboratory autoclave analogous to a Consolidated model 3AV-X1. The cycle was set to a sterilization temperature of 250⁰F (121⁰C) with a sterilization time of 15 minutes. All four models of masks used (3M 1860, 3M 1870, 3M VFlex 1805 and AO Safety 1054S) were able to withstand autoclave treatment at these parameters and successfully pass quantitative fit tests. Kumar showed that the three pleated filter N95 masks could withstand at least 10 autoclave sterilization cycles before failing fit tests and the popular 3M 1860, which uses an electrostatic filter, was only able to withstand one autoclave cycle before showing unacceptable degradation. A Texas study by Nathan Bopp et al. (11) found that 3M models 1805 and 1870 could pass fit testing after 3 autoclave cycles. The degradation of filter integrity was tested after 3 cycles at 250⁰F (121⁰C) for 30m and 239⁰F (115⁰C) for 60m. Results indicated that the lower-temperature 60 minute decontamination cycle degraded filtration integrity less than the higher-temperature shorter cycle. However, all masks showed filtration efficiency dropped below 95% even after 1 cycle of processing. Mask Construction – Materials and Glues An earlier study (8) had shown that the high temperatures of 250⁰F (121⁰C) involved in typical steam sterilization cycles deformed the materials used in the construction of certain models of masks. Unfortunately, this study did not list what model N95 was used and this result was interpreted by many as applying equally to all models of N95 masks. Further, a different study (1) showed that steam sterilization at an even higher temperature of 273⁰F (134⁰C, time was not reported) damaged the 3M 8822 type mask. Studies performed by de Man (9) and van Statren (10) showed that the 3M 1862+ N95 mask was able to withstand standard steam sterilization cycles at temperatures of 250⁰F (121⁰C) for 15 minutes for up to five cycles prior to unacceptable loss of filtration efficiency. Additionally, these masks passed pressure drop and fit testing based on the author’s standards. They also showed that while processing masks at 250⁰F (121⁰C) was successful, processing at 273⁰F (134⁰C) was not. The 3M 1862+ mask used in these experiments has an electrostatic filter element. As of May 2020, the 3M corporation still does not recommend the use of high temperature, autoclaving or steam heat to disinfect 3M N95 masks (2). However, 3M’s latest technical bulletin outlines parameters employing temperatures between 60-70C and 50-80% relative humidity for 30 minutes to decontaminate certain models of N95 masks. It is important to note that this temperature range may not inactivate all organisms. Organisms that are more difficult to inactivate like fungus and bacterial spores may survive. As such, the mask may not be sterile but rather have a reduced population of contaminating organisms. 3M model 1870 N95 Respirator (Pleated Fabric Design) 3M 1860 N95 Respirator (Rigid Design) SARS-CoV-2 Viral Inactivation Kumar’s study also included tests on viral inactivation of SARS-CoV-2, the virus that causes COVID-19. Kumar inoculated masks prior to autoclaving and compared viral growth with unprocessed control masks. On all four models of mask, sterilization by autoclaving resulted in a total inactivation up to detection limits of SARS-CoV-2 viral particles. It is worth noting that while the masks were only inoculated with 5.0 Log TCID50 of SARS-CoV-2 so a 6 Log reduction was impossible to show. However, after processing, no virus was recovered. Conclusion Experiments performed on various methods of decontamination on N95 masks have shown a great need to validate the method on the specific mask to be used. Even popular methods like hydrogen peroxide vapor cannot be used on masks that contain cellulose. Similarly, the use of high temperature steam for autoclaving N95s cannot be categorically accepted nor rejected. While initial results appear to allow greater reuse of pleated/folded style masks, some tests have shown loss of filtration efficiency (11). There have also been some successful and some unsuccessful tests on electrostatic/cup style masks. In terms of N95 mask fit and filtration performance, the most repeatable moist heat data points towards the use of temperatures below 100C at an elevated relative humidity. Best practice would suggest performing an autoclave test using the specific make and model N95 mask worn prior to determining whether steam sterilization is appropriate. For reference, here are some commonly available models of N95 masks with references to studies that tested them. Manufacturer Model (Line) Filter Type Known Autoclave Studies # of Reuses per Study 3M 1804 (VFlex) Pleated/Folded (2) – 65C & RH (3) – 121C 10 10 3M 1805 (VFlex) Pleated/Folded (11) – 121C 1 3M 1860 Electrostatic/Cup (2) – 65C & RH (3) – 121C 10 1 3M 1862+ Electrostatic/Cup (9) – 121C 5 3M 1870 (Aura) 1870+ (Aura) Pleated/Folded (3) – 121C (11) – 115C (2) – 65C & RH 10 1 10 3M 8210 Electrostatic/Cup (2) – 65C & RH (3) – 121C 10 1 3M 9210 (Aura) Pleated/Folded (3) – 121C 10 Aearo 1054S (Pleats Plus) Pleated/Folded Yes – 121C 10 References: 1) https://www.rivm.nl/en/documenten/reuse-of-ffp2-masks 2) https://multimedia.3m.com/mws/media/1824869O/decontamination-methods-for-3m-n95-respirators-technical-bulletin.pdf 3) https://www.medrxiv.org/content/10.1101/2020.04.05.20049346v1 4) https://utrf.tennessee.edu/information-faqs-performance-protection-sterilization-of-face-mask-materials/ 5) Fisher, E.M., J.L. Williams, and R.E. Shaffer, Evaluation of microwave steam bags for the decontamination of filtering facepiece respirators. PLoS One, 2011. 6) https://www.cdc.gov/coronavirus/2019-ncov/hcp/ppe-strategy/decontamination-reuse-respirators.html 7) https://www.nebraskamed.com/covid 8) Viscusi DJ, King WP, Shaffer RE. Effect of decontamination on the filtration efficiency of two filtering facepiece respirator models. J Int Soc Respir Prot. 2007;24:93–107. 9) http://resolver.tudelft.nl/uuid:f048c853-7e1d-4715-b73d-3b506b274a30 10) http://resolver.tudelft.nl/uuid:078a3733-84d6-4d4a-81e6-74210c7fed78 11) Bopp, Nathen & Bouyer, Donald & Gibbs, Christopher & Nichols, Joan & Ntiforo, Corrie & Grimaldo, Miguel. (2020). Multicycle Autoclave Decontamination of N95 Filtering Facepiece Respirators. Applied Biosafety. 153567602092417. 10.1177/1535676020924171. 12) https://www.medrxiv.org/content/10.1101/2020.04.01.20050443v2 DISCLAIMER: IN RECOGNITION OF THE COVID-19 CRISIS, CONSOLIDATED STERILIZER SYSTEMS IS ONLY SHARING INFORMATION PROVIDED FROM PUBLICLY AVAILABLE RESOURCES. CSS MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED ABOUT THE EFFICACY, COMPLETENESS, ACCURACY, RELIABILITY, SAFETY OR SUITABILITY WITH RESPECT TO THE INFORMATION SHARED HERE. THE USE OF SPECIFIC METHODOLOGIES OR TECHNOLOGIES TO DECONTAMINATE PPE OR FFP MATERIALS HAS NOT BEEN SCIENTIFICALLY EVALUATED BY CSS. THE DECISION TO USE ANY METHOD FOR THE APPLICATION OF PPE OR FFR DECONTAMINATION SHOULD BE DONE SO ONLY AT THE SOLE DISCRETION OF QUALIFIED MEDICAL PERSONNEL. INFORMATION CONTAINED HERE DOES NOT REPRESENT MEDICAL ADVICE NOR IS IT A SUBSTITUTE FOR REGULATORY GUIDANCE AND/OR REQUIREMENTS. USE OF THIS INFORMATION IS AT YOUR SOLE RISK. Don't Buy An Autoclave Until You Read This Find out the 17 questions you need to ask before buying your next autoclave. Download eBook Tweet Like Share
Decontaminating N95 Masks with Steam Sterilization Written by: Amit Gupta MS Mechanical Engineering, Vice President of Engineering Can N95 Masks be steam sterilized for reuse? This article attempts to answer this question by giving a review of the current literature and taking a closer look at N95 filter types and materials of construction. The ability to autoclave N95 masks would be ideal because autoclaving is a proven sterilization process and existing autoclave infrastructure is ubiquitous in labs, hospitals, dental offices, and many other types of facilities. While data from studies performed in years past suggested that steam autoclaves were ineffective for the reprocessing of used N95 masks, newer data suggests that the earlier studies did not necessarily paint the whole picture, and in instances where technologies like Hydrogen Peroxide vapor and UV-C are not available, supplies of N95 respirators may be stretched through the use of autoclave decontamination. Background Leading into the coronavirus pandemic, there was widespread concern regarding shortage of personal protective equipment (PPE) – specifically N95 masks. Over the past few months, there has been much research conducted into various ways to decontaminate N95 masks to allow them to be safely reused. As we discussed in our previous post, Hydrogen Peroxide vapor and UV-C light decontamination are popular methods for N95 decontamination. Unfortunately, in many areas of the US and around the world, these technologies are either not available, too expensive or too complicated to be implemented. N95 Filter Type – Electrostatic vs. Pleated N95 masks typically employ one of two different filtering techniques. The first category of N95 mask uses a melt-blown polymer fiber that is imbued with an electrostatic charge, this filtration layer is called the electret. As particles pass through this electrostatically charged filter, they get trapped by the electro-magnetic fields. These types of masks are also referred to as cup masks. The second category of N95 uses a pleated fiber filter similar to a HEPA filter. The pleated filters rely on the closely packed density of the fibers to mechanically prevent the passage of particles – similar to how a screen works, but on a microscopic scale. These types of masks are also referred to as flat fold or folded masks. Data published by co-inventor of the electrostatic N95 mask Peter Tsai stated that steam and condensate may have little effect on the electret. In “Performance and the Protection against COVID-19 and Their Efficiency Degradation by Sterilization to Reuse the Masks” (4) Tsai found that the charge on the electret filtration element used in N95 masks showed no noticeable loss after exposure to steam at typical sterilization temperature of 250⁰F (121⁰C) for 3 minutes. However, data collected by the Texas Department of Medicine (11) found that one full 30-60 minute steam decontamination cycle in a prevacuum autoclave degraded the filtration efficiency of the 3M 1860 (mask with an electret) to below 95%. Pleated style filters don’t have an electret. Studies on pleated style N95 masks were published by Anand Kumar et. al (4). Kumar analyzed the impact of steam decontamination in a laboratory autoclave analogous to a Consolidated model 3AV-X1. The cycle was set to a sterilization temperature of 250⁰F (121⁰C) with a sterilization time of 15 minutes. All four models of masks used (3M 1860, 3M 1870, 3M VFlex 1805 and AO Safety 1054S) were able to withstand autoclave treatment at these parameters and successfully pass quantitative fit tests. Kumar showed that the three pleated filter N95 masks could withstand at least 10 autoclave sterilization cycles before failing fit tests and the popular 3M 1860, which uses an electrostatic filter, was only able to withstand one autoclave cycle before showing unacceptable degradation. A Texas study by Nathan Bopp et al. (11) found that 3M models 1805 and 1870 could pass fit testing after 3 autoclave cycles. The degradation of filter integrity was tested after 3 cycles at 250⁰F (121⁰C) for 30m and 239⁰F (115⁰C) for 60m. Results indicated that the lower-temperature 60 minute decontamination cycle degraded filtration integrity less than the higher-temperature shorter cycle. However, all masks showed filtration efficiency dropped below 95% even after 1 cycle of processing. Mask Construction – Materials and Glues An earlier study (8) had shown that the high temperatures of 250⁰F (121⁰C) involved in typical steam sterilization cycles deformed the materials used in the construction of certain models of masks. Unfortunately, this study did not list what model N95 was used and this result was interpreted by many as applying equally to all models of N95 masks. Further, a different study (1) showed that steam sterilization at an even higher temperature of 273⁰F (134⁰C, time was not reported) damaged the 3M 8822 type mask. Studies performed by de Man (9) and van Statren (10) showed that the 3M 1862+ N95 mask was able to withstand standard steam sterilization cycles at temperatures of 250⁰F (121⁰C) for 15 minutes for up to five cycles prior to unacceptable loss of filtration efficiency. Additionally, these masks passed pressure drop and fit testing based on the author’s standards. They also showed that while processing masks at 250⁰F (121⁰C) was successful, processing at 273⁰F (134⁰C) was not. The 3M 1862+ mask used in these experiments has an electrostatic filter element. As of May 2020, the 3M corporation still does not recommend the use of high temperature, autoclaving or steam heat to disinfect 3M N95 masks (2). However, 3M’s latest technical bulletin outlines parameters employing temperatures between 60-70C and 50-80% relative humidity for 30 minutes to decontaminate certain models of N95 masks. It is important to note that this temperature range may not inactivate all organisms. Organisms that are more difficult to inactivate like fungus and bacterial spores may survive. As such, the mask may not be sterile but rather have a reduced population of contaminating organisms. 3M model 1870 N95 Respirator (Pleated Fabric Design) 3M 1860 N95 Respirator (Rigid Design) SARS-CoV-2 Viral Inactivation Kumar’s study also included tests on viral inactivation of SARS-CoV-2, the virus that causes COVID-19. Kumar inoculated masks prior to autoclaving and compared viral growth with unprocessed control masks. On all four models of mask, sterilization by autoclaving resulted in a total inactivation up to detection limits of SARS-CoV-2 viral particles. It is worth noting that while the masks were only inoculated with 5.0 Log TCID50 of SARS-CoV-2 so a 6 Log reduction was impossible to show. However, after processing, no virus was recovered. Conclusion Experiments performed on various methods of decontamination on N95 masks have shown a great need to validate the method on the specific mask to be used. Even popular methods like hydrogen peroxide vapor cannot be used on masks that contain cellulose. Similarly, the use of high temperature steam for autoclaving N95s cannot be categorically accepted nor rejected. While initial results appear to allow greater reuse of pleated/folded style masks, some tests have shown loss of filtration efficiency (11). There have also been some successful and some unsuccessful tests on electrostatic/cup style masks. In terms of N95 mask fit and filtration performance, the most repeatable moist heat data points towards the use of temperatures below 100C at an elevated relative humidity. Best practice would suggest performing an autoclave test using the specific make and model N95 mask worn prior to determining whether steam sterilization is appropriate. For reference, here are some commonly available models of N95 masks with references to studies that tested them. Manufacturer Model (Line) Filter Type Known Autoclave Studies # of Reuses per Study 3M 1804 (VFlex) Pleated/Folded (2) – 65C & RH (3) – 121C 10 10 3M 1805 (VFlex) Pleated/Folded (11) – 121C 1 3M 1860 Electrostatic/Cup (2) – 65C & RH (3) – 121C 10 1 3M 1862+ Electrostatic/Cup (9) – 121C 5 3M 1870 (Aura) 1870+ (Aura) Pleated/Folded (3) – 121C (11) – 115C (2) – 65C & RH 10 1 10 3M 8210 Electrostatic/Cup (2) – 65C & RH (3) – 121C 10 1 3M 9210 (Aura) Pleated/Folded (3) – 121C 10 Aearo 1054S (Pleats Plus) Pleated/Folded Yes – 121C 10 References: 1) https://www.rivm.nl/en/documenten/reuse-of-ffp2-masks 2) https://multimedia.3m.com/mws/media/1824869O/decontamination-methods-for-3m-n95-respirators-technical-bulletin.pdf 3) https://www.medrxiv.org/content/10.1101/2020.04.05.20049346v1 4) https://utrf.tennessee.edu/information-faqs-performance-protection-sterilization-of-face-mask-materials/ 5) Fisher, E.M., J.L. Williams, and R.E. Shaffer, Evaluation of microwave steam bags for the decontamination of filtering facepiece respirators. PLoS One, 2011. 6) https://www.cdc.gov/coronavirus/2019-ncov/hcp/ppe-strategy/decontamination-reuse-respirators.html 7) https://www.nebraskamed.com/covid 8) Viscusi DJ, King WP, Shaffer RE. Effect of decontamination on the filtration efficiency of two filtering facepiece respirator models. J Int Soc Respir Prot. 2007;24:93–107. 9) http://resolver.tudelft.nl/uuid:f048c853-7e1d-4715-b73d-3b506b274a30 10) http://resolver.tudelft.nl/uuid:078a3733-84d6-4d4a-81e6-74210c7fed78 11) Bopp, Nathen & Bouyer, Donald & Gibbs, Christopher & Nichols, Joan & Ntiforo, Corrie & Grimaldo, Miguel. (2020). Multicycle Autoclave Decontamination of N95 Filtering Facepiece Respirators. Applied Biosafety. 153567602092417. 10.1177/1535676020924171. 12) https://www.medrxiv.org/content/10.1101/2020.04.01.20050443v2 DISCLAIMER: IN RECOGNITION OF THE COVID-19 CRISIS, CONSOLIDATED STERILIZER SYSTEMS IS ONLY SHARING INFORMATION PROVIDED FROM PUBLICLY AVAILABLE RESOURCES. CSS MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED ABOUT THE EFFICACY, COMPLETENESS, ACCURACY, RELIABILITY, SAFETY OR SUITABILITY WITH RESPECT TO THE INFORMATION SHARED HERE. THE USE OF SPECIFIC METHODOLOGIES OR TECHNOLOGIES TO DECONTAMINATE PPE OR FFP MATERIALS HAS NOT BEEN SCIENTIFICALLY EVALUATED BY CSS. THE DECISION TO USE ANY METHOD FOR THE APPLICATION OF PPE OR FFR DECONTAMINATION SHOULD BE DONE SO ONLY AT THE SOLE DISCRETION OF QUALIFIED MEDICAL PERSONNEL. INFORMATION CONTAINED HERE DOES NOT REPRESENT MEDICAL ADVICE NOR IS IT A SUBSTITUTE FOR REGULATORY GUIDANCE AND/OR REQUIREMENTS. USE OF THIS INFORMATION IS AT YOUR SOLE RISK. Don't Buy An Autoclave Until You Read This Find out the 17 questions you need to ask before buying your next autoclave. Download eBook Tweet Like Share
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