Abstract: 24 As the prevalence of COVID-19 in all the area of China and continuous spread to 25 many other countries, it is in urgent need of medical mask for community people. We 26 have reported a simple method to inactivate artificially influenza virus-contaminated 27 medical mask without affecting the filterability of mask by heating with hair dryer for 28 30min. In this study, we extended our studies to optimize our protocols and evaluate 29 the filterability of mask after several-rounds of heat treatment. We found that baking 30 at 70℃ for 30min almost completely inactivated virus as hair dryer treatment for 31 30min described before. One-round of heat treatment with hair dryer for 30min or 32 baking at 70℃ for 30min did not affect filterability of mask whilst two-rounds of 33 treatment slightly but significantly reduced filterability of mask. Thus, heating with 34 hair dryer for 30min or baking at 70℃ for 30min can inactive contaminated medical 35 mask and the treated mask can be reused at least once.
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The copyright holder for this preprint this version posted July 6, 2020. . https://doi.org/10.1101/2020.07.01.20144527 doi: medRxiv preprint 3 38 Introduction: 39 Since the outbreak of COVID-19 in Wuhan China, it was endemic to all over the 40 China within less than one month, causing over 80000 cases and over 3000 mortalities 41 in China. It is artificially contaminated by influenza virus via heating with hair dryer for 30min 58 without affecting its filterability 8 , which can be easily adapted by public. In this study, 59 All rights reserved. No reuse allowed without permission.
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The copyright holder for this preprint this version posted July 6, 2020. . https://doi.org/10.1101/2020.07.01.20144527 doi: medRxiv preprint we extended our studies to optimize our protocols by shortening treatment intervals 60 with hair dryer and baking mask at different temperatures. We demonstrated that hair 61 dryer treatment for 15 min did not effectively inactivate influenza virus (IVA) on 62 medical mask compared with 30 min as described before. And that baking at 70℃ for 63 30 min effectively inactivated IVA on mask whereas baking at 65℃ for 30 min did 64 not. We also evaluated the filterability of mask after several-rounds of heat treatment. 65 Our results reveal that two-rounds of treatment with hair dryer for 30min or baking at 66 70℃ for 30min significantly reduced filterability of mask but one-round of treatment 67 did not affect filterability of mask. Thus, we provided a simple method for reuse of 68 disposable medical mask, which may help tackle the urgent need of medical mask 69 during COVID-19 prevalence.
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The copyright holder for this preprint this version posted July 6, 2020. One-round use + baking group (masks are used under normal condition for 4 hours 115 and then baked in oven at 70℃ for 30min); 3). Two-round use+ baking group (masks 116 All rights reserved. No reuse allowed without permission.
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The copyright holder for this preprint this version posted July 6, 2020. . https://doi.org/10.1101/2020.07.01.20144527 doi: medRxiv preprint are used under normal condition for 8 hours, with incubation in oven at 70℃ for 117 30min every 4 hours); 4). One-round use + hair dryer group (masks are used under 118 normal condition for 4 hours and then heat treated by hair dryer for 30min as 119 described above); 5). Two-round use + hair dryer group (masks are used under normal 120 condition for 8 hours, with heat treatment by air dryer for 30min every 4 hours). (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
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Heat inactivation of IVA on mock-contaminated medical mask 129 In our previous study, baking at 56℃ for 30 min only partially inactivated IVA 130 on medical mask, with a 1-3 log reduction of viral RNA level, comparing to 6 log 131 reduction of viral RNA level after hair dryer treatment for 30 min 8 . In the present 132 study, we first increased baking temperature and treated IVA mock-contaminated (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted July 6, 2020. . https://doi.org/10.1101/2020.07.01.20144527 doi: medRxiv preprint 9 PM 2.5 filterability of medical masks after heat treatment 152 We assessed protective function of medical mask by measuring the filterability 153 of medical masks to ambient PM 2.5 after similar heat treatment as described before 8 .
To evaluate the recycle times of the medical mask, masks were subjected to several Figure 2B ).
However, after being used and heat-treated twice (by baking or hair dryer), their 165 filtration efficiency was significantly reduced as shown in Figure 2B . Our results 166 indicate that heat inactivation by baking or hair dryer for 30 min may serve as an 167 effective way for reuse of disposable medical masks, but this method is not 168 encouraged to be used for more than once.
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The copyright holder for this preprint this version posted July 6, 2020. heat treatment with hair dryer and baking that are easily to be adapted by community 180 people. We found that baking at 70℃ for 30min almost completely inactivated virus 181 as hair dryer treatment for 30min described before 8 . But baking at 56℃ and 65℃ 182 for 30min could not effectively activate virus 8 (Fig. 1A) . Incubating at 56℃ for 183 30min is a widely used protocol to inactivate influenza virus or coronavirus in 184 solution. The incomplete inactivation by baking at this temperature and at 65℃ 185 indicates that baking a surface has less efficiency than incubating in solution.
Maintaining the filter function of medical mask during usage is critical for preventing 187 virus infection. We demonstrated that one-round of heat treatment did not affect 188 filterability of mask whilst two-rounds of treatment slightly but significantly reduced 189 filterability of mask. Thus, we provided a simple method for reuse of medical mask 190 by heating with hair dryer for 30min or baking at 70℃ for 30min and the treated 191 mask can be reused at least once.
192 All rights reserved. No reuse allowed without permission.
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The copyright holder for this preprint this version posted July 6, 2020. 
The authors declare no conflict of interest.
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The copyright holder for this preprint this version posted July 6, 2020. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted July 6, 2020. . https://doi.org/10.1101/2020.07.01.20144527 doi: medRxiv preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted July 6, 2020. . https://doi.org/10.1101/2020.07.01.20144527 doi: medRxiv preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
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