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Please forgive the obvious question.

H2O2 vapor sterilization is deadly for the layperson but should be workable for hospitals. I can't find the small Chinese study I read the other day about it. Here are two more quickly googled sources.

  1. https://www.fda.gov/emergency-preparedness-and-response/mcm-regulatory-science/investigating-decontamination-and-reuse-respirators-public-health-emergencies

http://wayback.archive-it.org/7993/20170113034232/http://www.fda.gov/downloads/EmergencyPreparedness/Counterterrorism/MedicalCountermeasures/MCMRegulatoryScience/UCM516998.pdf

2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781738/

  • People in the USA are now spraying their respirators with bleach to use again the next day as there is an extreme shortage. – Graham Chiu Mar 22 at 3:31
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    Could you clarify who "we" are? – Carey Gregory Mar 22 at 4:19
  • @GrahamChiu: frankly that seems unsafe as bleach sometimes leaves a solid residue. I know this from my own experience with using large quantities on some (not wearable) item. A quick search shows that's not a unique experinece quora.com/… – SX welcomes ageist gossip Mar 22 at 8:40
  • @GrahamChiu: from the Sciencemag article you linked in another recent question "an October 2019 study in JAMA Network Open found that nurses who regularly used disinfectants to clean surfaces were at higher risk of chronic obstructive pulmonary disease. A 2017 study linked exposure to disinfectants to asthma to adults in Germany. Both of those studies dealt with yearslong exposure to disinfectants." Still putting them on your mask sounds like a substantial increase in exposure... – SX welcomes ageist gossip Mar 22 at 8:51
  • Well, I guess they're not aware of this. But long term COPD seems less imminent than death by covid-19. – Graham Chiu Mar 22 at 9:05
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Dr. Peter Tsai, the INVENTOR of the filtration fabric in the N95 mask. N95 masks are made of polypropylene material and are designed to tightly fit over your face with little leakage around the edge of the mask.

method 1

When reusing N95 masks, leave a used respirator in dry, atmosphere air for 3-4 days to dry it out. Polypropylene in N95 masks is hydrophobic and contains zero moisture. COVID-19 needs a host to survive–it can survive on a metal surface for up to 48 hours, on plastic for 72 hours, and on cardboard for 24 hours. When the respirator is dry in 3-4 days, the virus will not have survived.

Take four N95 masks, and number them (#1-4).

On day 1, use mask #1, then let it dry it out for 3-4 days.

On day 2, use mask #2, then let it dry out for 3-4 days.

Same for day 3, and day 4…

method 2

You can also sterilize the N95 mask by hanging it in the oven (without contacting metal) at 70C (158F) for 30 minutes-it is reported that COVID-19 cannot survive at 65C (149F) for 30 minutes.

Use a wood clip to hang the respirator in the kitchen oven to do the sterilization.

Experimentally though this time is much less when incubating virus in transport media

With the incubation temperature increased to 70°C, the time for virus inactivation was reduced to 5 mins.

UV light

When sterilizing N95 masks, be wary of using UV light–keep N95 masks away from UV light / sunlight. N95 masks are degraded by UV light because it damages the electrostatic charges in the polypropylene material. It is unclear how long the masks can be exposed to UV light before they are ineffective.

Read more details at the link

https://www.sages.org/n-95-re-use-instructions/

We do have more data now on UV and what levels are safe to use

Ultraviolet germicidal irradiation 

UVGI disinfection involves placing respirators in direct line with UV-C lamps. Any exposed surface of the mask will be disinfected. This process generally requires the masks to be flipped after some period to ensure both sides of a mask are disinfected or requires a setup involving two UV-C lamps on either side of the respirator.

For samples of FFR filters treated with SARS (severe acute respiratory syndrome) and MERS (Middle East respiratory syndrome) viruses, no viable virus was found following a dose of 1 joule per square centimeter (J/cm2) of short wavelength (254 nanometers) UV-C light, even in the presence of artificial skin oil and saliva.11 Researchers found no impact of doses ranging from 3 to 20 J/cm2 on filter performance.9-12

A similar dose range did not compromise fit on three N95 FFRs worn by 10 volunteers.12 Doses ranging from 3 to 6.5 J/cm2 did not alter fit performance on human subjects; doses up to 20 J/cm2 did not significantly change fit performance on respirators mounted on a static head form connected to a breathing machine.11

Lindsley et al13 tested the impact of much higher doses, ranging from 120 to 950 J/cm2, on respirator filter samples and 590 to 2,360 J/cm2 on respirator straps. For most samples, filter efficiency decreased after UVGI treatment but remained above 95% at all dose levels for the four tested respirator models. Strength of the different layers decreased at all doses, with more layers showing decreased strength with increasing dose. The breaking strength of straps also decreased at all doses, ranging from a loss of 10% to 21% at the lowest dose of 590 J/cm2 and 20% to 51% at the highest dose of 2,360 J/cm2. Respirators treated with a single decontamination of UVGI showed no significant difference from untreated respirators in odor, donning ease, comfort, and respirator fit.9

Altogether, these data suggest that respirators could be decontaminated by UVGI for up to 20 cycles at a dose of 1 J/cm2 per cycle, if the fit performance data from Heimbuch and Harnish11 using a static head form are representative of fit on humans. Limited human data on a small number of N95 FFR models suggest that 3 cycles at this dose will not degrade fit.

While respirator filter performance (and perhaps fit) were not adversely affected at the higher doses studied by Lindsley et al,13 because the lowest dose level of 120 J/cm2 caused a loss of strength of at least one filter layer, extending UVGI treatment beyond 20 cycles does not seem appropriate at this time.

https://www.cidrap.umn.edu/news-perspective/2020/04/commentary-respirators-can-be-reused-decontamination-not-well-studied

https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(20)30003-3/fulltext

https://utrf.tennessee.edu/information-faqs-performance-protection-sterilization-of-face-mask-materials/

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  • If you trace this back to the original source, these are untested suggestions on how a mask might be prepared for re-use. – Mark Mar 31 at 21:51
  • This is advice from the inventor of the mask filter so we call that expert advice, or level 5 evidence. It was an interview so he didn't provide his references. And I see your answer has no reference at all. – Graham Chiu Mar 31 at 22:04
  • They're untested suggestions from an expert, so there's a fair chance they'll work out, but they're still untested suggestions. – Mark Mar 31 at 22:17
  • it's based on scientific principles. Is that something you don't understand? – Graham Chiu Mar 31 at 22:23
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    I'm an engineer, not a scientist. I've got plenty of experience telling me that scientific principles tend to run up against cold, hard reality in unexpected ways from time to time. – Mark Mar 31 at 22:25
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Some hospitals are sanitizing (not sterilizing) their N95 respirators (not masks) already.

Coronavirus Update: Massive N95 Mask Sterilizing Machines Now Running on Long Island

Doylestown Hospital has solution to coronavirus mask shortage - WHYY

As others have pointed out, for an item that is usually $2-3 at most, the time and effort involved had not previously been worth even investigating sanitization and re-use until now. Quite literally, in some areas even up to last month people used to use one of these respirators for 3 minutes and throw it out.

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Some hospitals are experimenting with using UV light to decontaminate respirator masks that are to be reused:

https://www.nytimes.com/2020/03/20/health/coronavirus-masks-reuse.html

EDIT enter image description here To follow up on RudyB's answer, Battelle has been awarded a contract to use H2O2 vapor (sources: NYtimes, Reuters)

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The main reason is that we don't know how.

For something like an N95 mask, a sterilization process needs to be designed so that it (a) kills any contaminating microbes, and (b) doesn't compromise the effectiveness of the mask.

UV sterilization may not be able to light up every contaminated surface of the mask, or it might damage the filter material or the straps that hold the mask in place.

Hydrogen peroxide vapor might not penetrate the filter material sufficiently, or residual hydrogen peroxide might remain in the filter to harm the user.

Heat-based sterilization could warp the edges of the mask or the outflow valve so they no longer provide a tight seal, and superheated steam might also collapse the filter material into an air-tight barrier -- or expand it into a fluff that viruses have no trouble passing through.

Any sterilization method needs to be tested for safety and effectiveness, and historically, it's been faster and cheaper to simply discard a contaminated mask and use a new one.

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From {1}:

  • It is unknown how wearing the same mask multiple times effects the fit of N95 masks [NIOSH]
  • NIOSH states “there is no way of determining the maximum possible number of safe reuses for an N95 respirator as a generic number to be applied in all cases” and advise to “discard N95 respirators following use during aerosol generating procedures.”
  • Some methods of N95 mask disinfection can maintain filtration efficiency. Their effect on mask fit is unknown, and these methods are not approved by NIOSH.

Their summary on sanitizing methods:

In summary bleach and microwaves were failures at point of care because the bleach gases (skin and respiratory irritants) remained after multiple strategies were used to remove them, the microwave melted the masks and soaking them first led to reduced filtration. EtO, UVGI, and hydrogen peroxide decontamination were safe and effective in the models tested but it is not known if they would retain filtration, material strength, and airflow integrity with repeated use. EtO, UVGI, and hydrogen peroxide limitations include time from decontamination to reuse and available space and materials to decontaminate in an OR setting. 70C /158F heating in an oven (not your home oven) for 30min, or hot water vapor from boiling water for 10 min, are additional effective decontamination methods.

Also, from https://techcrunch.com/2020/03/27/duke-university-uses-vaporized-hydrogen-peroxide-to-clean-n95-face-masks-for-reuse/ (mirror):

Duke University thinks it has found a solution using vaporized hydrogen peroxide to decontaminate the masks.

The process uses specialized equipment to vaporize hydrogen peroxide, which can then infuse all the layers of the mask to kill germs (including viruses) without degrading mask material.

This Google Document goes over several papers on mask disinfection: https://docs.google.com/document/d/1YJ2MXeMSSIpm8Wxk8vN7zQ5SQJK9ukOh3wa-UhCJ6ZU/edit


References:

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