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Doctors scramble for best practices on reusing medical masks during shortage

A man is shown wearing an N95 respirator mask, which is not intended to be reused.
A man is shown wearing an N95 respirator mask, which is not intended to be reused.
(Image: © Shutterstock)

Very little is known about how to properly reuse medical masks to fight infectious diseases. No method is confirmed to work. Still, in a report to doctors, which has yet to be peer reviewed, some researchers are beginning to point to the best options for decontaminating used masks.

Medical professionals are reusing single-use medical masks across the country right now, according to the news organization The Intercept and numerous other reports, as the COVID-19 pandemic is stressing the usual supply chains for the masks. Medical masks, including N95 masks, are intended to be single use and must be worn properly to be effective. According to a new article released by researchers at Stanford University's School of Medicine's COVID-19 Evidence Service today (March 24), however, there are some methods that doctors can use that do seem to be better than others. (Their communications particularly targeted anesthesiologists.) 

"We do not advocate or advise specific treatments or approaches," the researchers began. "The COVID-19 Evidence Service aims to share the best available evidence to address questions for clinical anesthesiologists and the anesthesiology community. We recommend that hospital policy and procedures be respected and adhered to."

Related: 13 coronavirus myths busted by science

Referring to a paper published in the journal Annals of Occupational Hygiene in 2009, among others, the researchers compared and contrasted these different methods for sterilizing N95 masks, many of which were ineffective:

  • Heat in an oven for 30 minutes at 158 degrees Fahrenheit (70 degrees Celsius)
  • Use ultraviolet light for 30 minutes
  • Soak the mask in 75% ethyl alcohol, then let it dry
  • Clean the mask with liquid or vapor hydrogen peroxide
  • Clean the mask with bleach
  • Steam the mask with hot vapor from boiling water
  • Microwave the mask
  • Use extreme heat in an oven or autoclave
  • Soak in soap and water

"To be useful, a decontamination method must eliminate the viral threat, be harmless to end-users and retain respirator integrity," they wrote.

All of the methods used were believed effective for destroying coronaviruses, they wrote, but not all of them were good ideas.

"DO NOT use alcohol and chlorine [bleach]-based disinfection methods," they wrote. "These will remove the static charge in the microfibers in N95 facial masks, reducing filtration efficiency. In addition, chlorine also retains gas after de-contamination, and these fumes may be harmful."

Microwaves tended to melt the masks and render them useless.

Hydrogen peroxide and ultraviolet radiation appeared to be at least somewhat more effective, they wrote, "but it is not known if they would retain filtration, material strength and airflow integrity with repeated use."

Autoclaves, 320 F [160 C] ovens, and soap and water soaking, all appeared ineffective, they wrote.

However, they wrote, "70 C / 158 F heating in a kitchen-type of oven for 30 min, or hot water vapor from boiling water for 10 min, are additional effective decontamination methods."

The CDC still does not recommend reusing masks, and the researchers encouraged doctors to follow guidelines in their clinics. If you are not a medical professional, the best way to avoid getting sick isn't using a mask (new or reused), but staying at home. If you must go out, homemade cloth masks are an imperfect but better-than-nothing option, as Live Science has reported. However, a mask is much more likely to help you avoid spreading the illness if you are sick than it is to protect you from the illness, as Live Science has also reported.

Again, if you can, stay at home.

Coronavirus science and news

Originally published on Live Science. 

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  • jones1347
    There's a bit of a typo in the story. In one spot, the required temperature is given as 58 degrees F, not 158.
    Reply
  • Richard Harpster
    I have sleep apnea. I currently use a SoClean machine that uses ozone to clean my mask. Based on what I have read, Ozone has been proven to kill the SARs Coronavirus. I have bought a second machine and modified it slightly so it is a completely closed unit that bathes the contents in Ozone for 7 minutes. The unit makes you wait about two hours for the ozone to be changed back to oxygen before opening the cleaner. I run the mask through two cleaning cycles.

    Based on what I have read, a study is going to be published that shows Ozone kills the COVID-19 virus. Why don't the hospitals build ozone chambers to decontaminated the masks after use. Ozone generators are very cheap.
    Reply
  • Brash54
    We recently purchased reusable N95 - N99 masks. These masks have a mesh shell that can be washed in soapy water, and a replaceable filter insert with an active carbon component. We also happen to have devices that use UV light to clean cell phones (Phone Soap). I will be using this device to sanitize our mask's filter inserts, hoping to extend their longevity (replacements are out of stock and should go to health workers when available again). Hopefully those with the means can report on the effectiveness of these devices, or the effectiveness of exposing used masks to strong sunlight.
    Reply
  • James
    Drying, especially in sunlight would seem to be effective...
    https://smartairfilters.com/en/blog/disinfect-clean-n95-mask-virus-coronavirus/ideally you would have a few days supply and rotate through them giving them time to sterilise.
    Reply
  • GaryFulcher
    Fact Checking:

    Rafi says that Annals of Occupational Hygiene states that:
    "70 C / 158 F heating in a kitchen-type of oven for 30 min, or hot water vapor from boiling water for 10 min, are additional effective decontamination methods."

    I read the article in Annals of Occupational Hygiene and can not find the quote.

    Could someone give me a link to that quote. I do not want to distribute this quote if it is not true


    Thanks

    Gary
    Reply
  • Steve Erickson
    Richard Harpster said:
    I have sleep apnea. I currently use a SoClean machine that uses ozone to clean my mask. Based on what I have read, Ozone has been proven to kill the SARs Coronavirus. I have bought a second machine and modified it slightly so it is a completely closed unit that bathes the contents in Ozone for 7 minutes. The unit makes you wait about two hours for the ozone to be changed back to oxygen before opening the cleaner. I run the mask through two cleaning cycles.

    Based on what I have read, a study is going to be published that shows Ozone kills the COVID-19 virus. Why don't the hospitals build ozone chambers to decontaminated the masks after use. Ozone generators are very cheap.
    Ozone is going to degrade the material. I would keep a close eye on whether there seems to be any change in the pressure needed to respire.
    Reply
  • Steve Erickson
    admin said:
    Very little is known about how to properly reuse medical masks to fight infectious diseases, but some best practices are starting to emerge.

    Doctors scramble for best practices on reusing medical masks during shortage : Read more

    Since the SARS and MERS epidemics, there is a fair amount of scientific literature looking at the need to sterilize standard N95 respirators in the event of a pandemic. Two US government studies from that time period posited that the US alone would need 90 or 360 million masks in the event of an influenza pandemic. Well, here we are.

    The most realistic method I've seen that can be done on a small scale - or scaled up for larger use without a lot of resources- is steam sterilization in Microwaveable Steam Bags. See:
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3078131/
    Basically, masks and respirators are sterilized by microwaving in the microwaveable bags that are readily available for sterilizing baby bottles and breast pumps. These are preferred to the bags made for food because they are multi-use, whereas the food bags are single use.

    This method could be easily scaled up. Imagine a process where mask users place used masks in these bags. The bags are taken to a room set up with negative air pressure (for infectious agent containment), water available to fill the bags, and standard consumer grade microwave ovens. The ovens are arranged so that they are run from a single switch outside the room (to reduce potential worker exposure to microwave scatter). The bags have the requisite amount of water added, are loaded into the ovens, the worker exits the room and triggers the ovens. The worker then re-enters, removes the bags from the ovens, takes them to another room set up with screens on racks and forced warm air for drying. The masks are taken from the bags and placed on the screens for drying. They are then placed back out for users. Since the entire sterilization process (including drying) could be set up for 6-15 cycles/hour and racks of ovens take relatively little room, it should be possible to set up for processing 100s to 1000s of masks per hour, all with off the shelf equipment.
    Reply
  • Brash54
    Here’s a link to an article discussing the use of vaporized hydrogen peroxide to disinfect N95 masks:

    https://techcrunch.com/2020/03/27/duke-university-uses-vaporized-hydrogen-peroxide-to-clean-n95-face-masks-for-reuse/
    It is reported as an effective disinfectant method. Perhaps hospitals without the units specifically designed for this disinfecting method could jury-rig one as follows:
    Place a benchtop isolation chamber in a hood.
    Place a cool mist ultrasonic humidifier filled with hydrogen peroxide in the isolation chamber.
    Place the masks to be disinfected in the isolation chamber, hung in some fashion to expose the entire surface.
    Seal the isolation chamber and turn on the humidifier.
    When the disinfecting cycle is completed (TBD empirically), vent the isolation chamber in the hood.Testing would be required to determine if this method could achieve the vapor concentrations needed to be effective.
    Please don’t try this at home! Breathing hydrogen peroxide vapor is dangerous!
    Reply
  • Richard Harpster
    Steve Erickson said:
    Ozone is going to degrade the material. I would keep a close eye on whether there seems to be any change in the pressure needed to respire.
    Steve,

    The Ozone exposure is very short. My CPAP machine has probably through 700 cleaning cycles. What type of deterioration do you expect to see in the materials.

    Thanks for you help,
    Rich
    Reply
  • Steve Erickson
    I expect the filter media (generally a non-woven fabric) to be degraded. Basically, you're trying to oxidize the pathogen, but other materials exposed to the ozone will be affected. We've got an ozone generator we use to remove smoke and mold odors from books, but also inside musty motor vehicles. One hour in a closed vehicle is enough to make rubber bands brittle and easily breakable. So, the effect on the filter material may be similar, reducing its filtration effectiveness. You could try it and see if there is ay detectable change in the pressure required for inhalation and exhalation. If the needed pressure changes that could indicate the material is "clogging" (possibly from small pieces that have disintegrated) or (the reverse) been removed so filtration is reduced. The wiggle here is that the test sensitivity (your subjective breathing experience) may not be sensitive enough to detect changes in airflow. Multiple ozone exposures over time may be eve more difficult to detect because your comparing with the very last time you used the filter, not its initial condition. I hope that makes sense.
    But if its a choice between the ozone and nothing . . .
    Still, if you've got a microwave oven the wet steam in a bag method has some testing behind it.
    Reply