Thursday, March 5, 2020

Disinfection and reuse of face masks

There is one topic related to the coronavirus outbreak but rarely covered in English: how to reuse face masks in the midst of their severe shortage in all stores, online or brick-and-mortar. Reusing masks for non-medical professionals is recommended and important. But I have not found any article in English about how to disinfect slightly infected masks in order for reuse.[note] Articles in Chinese however do abound. One written by a non-specialist, 好不容易买来的N95口罩,这么做就废了!!!(N95可重复利用方法) (Doing this to N95 masks you managed to buy would trash them!!! (Methods of reusing N95)), appears to make good sense. This February 8 article is posted by 澎湃新闻, a reputable news outlet. They claim the original author is a person by the Wechat ID 远方青木 or YFqingmu, whose article list around the date, however, does not include this article.

The main points of the article that I find most interesting are as follows (my translations in the parentheses):
KN95(口罩)能拥有这么强的防护能力,核心秘密在于静电吸附原理...静电最怕的就是水...消毒的重点有两个,第一个高温,第二个无水。可靠的消毒办法总共有三种,分别是: (The secret that KN95 (masks) can have such a strong protective ability lies in the principle of electrostatic adsorption ... What static electricity most fears is water ... The keys to disinfection is twofold, the first being high temperature, the second being lack of water. There are three reliable methods of disinfection:)
1、紫外线杀菌 (Ultraviolet sterilization)
2、干式烘烤 (Dry baking)
3、土法消毒 (DIY disinfection)
...酒精含水,能杀病毒没错,但口罩也废了 (Alcohol contains water. It sure can kill viruses, but masks also become useless)

While strong UV radiation works well, most households don't have such equipment. Dry baking or heating is good. But don't put the masks in a microwave because of the metal pieces in the masks. Many Chinese use alcohol to disinfect the masks. But it's said that the masks filter mainly by electrostatic adsorption of viruses instead of, as most people believe, through the tiny air passageways. Any amount of water, including that in alcohol in high concentration, much less 75% rubbing alcohol, disables the static adsorption capability. The article suggests putting the mask in a small jar, seal the jar and throw it in boiling water.

I personally find that a coffee mug warmer you would use in office can do the work too. If the warmer is at least 20w in wattage (no USB type), the surface temperature can be as high as 140F. Contact with the outer side of the mask for a few minutes should be enough for disinfection. You need to rotate the mask once in a while so the whole surface has a chance to touch the mug warmer surface.

Some people suggest using a hair dryer to blow on masks. It should work because the temperature is high enough to inactivate the viruses. The only caution to take is that this should be done outdoors, and the air should be blown away toward nobody, in case some inactivated viruses may fly into air.

Lastly, regarding reusing masks, we may also take the strategy of using multiple of them in turn. For example, you use a new mask on day 1, another one mask on day 2, but back to the first one on day 3, and so on. You can also rotate every 3 days. The reason for setting aside the mask to be reused at least 1 day after is that the viruses may be inactivated simply by loss of contact with their hosts. (The inactivated viruses might actually serve as vaccines!) You may disinfect the mask after you take it off. But leaving it aside for tens of hours alone is also a good way to "disinfect" it.

According to the research led by an Academy of Chinese Sciences academician posted on the web on February 27 titled 用电吹风给口罩“充电” ("Recharge" face mask with a hair dryer), the electrostatic of the masks can be recharged, as follows (my translations in the parentheses)

1.将用过的一次性医用无纺布口罩置于大于56℃热水中浸泡30分钟(56℃ 30分钟可有效灭活病毒),通常沸水与室温水(按20℃算)1:1混合后约为60度,为提高灭毒杀菌效果,可适当提高沸水比例;(Put the used disposable medical non-woven masks in hot water with a temperature of higher than 56℃ for 30 minutes (at 56℃ for 30 minutes the virus can be effectively inactivated). Usually, boiling water and room-temperature water (assumed to be of 20℃) mixed at a 1:1 ratio reaches about 60 degrees. In order to improve disinfection and sterilization, the proportion of boiling water can be somewhat increased;)
2.将口罩从水中取出,甩掉表面液滴,平放在干燥的绝缘材质表面(如桌布、床单等),用电吹风机吹烘约10分钟吹干并荷电,或用普通电风扇吹口罩约15分钟,或用普通家用电子点火器对口罩进行全面覆盖的“电击”,通过口罩内部纤维的摩擦或外部放电等,使口罩材料重新荷电。(Remove the mask from the water, shake off the surface droplets, and lay it flat on a dry surface of insulating material (such as tablecloths, sheets, etc.), blow dry with a hair dryer for about 10 minutes to recharge, or blow the mask with a regular electric fan for about 15 minutes, or "shock" the mask with a general household electronic igniter. Recharge the mask materials through friction of the fiber inside the mask or external discharge.)

The video on the webpage shows exactly how this is done. Impressive! The same content of the article is also published on the Ministry of Industry and Information Technology webpage.

[note] 2020-04-07 Update: CDC just published an article Decontamination and Reuse of Filtering Facepiece Respirators. Interestingly, they recommend "vaporous hydrogen peroxide (VHP), and moist heat" instead of dry heat. There is no mention of electrostatic property of the face masks.

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