[SirLuxuryYacht]

This[0] article goes over recommendations for extended use, reuse, and risks. It also has a healthy list of references, some of which are by Fisher et al., the author of the paper you linked.

Most masks have a metal tab bending over the bridge of the nose, as well as metal staples for the elastic bands, which would prevent you from microwaving. Cartridge type filters would work though.

[0]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3373043/#!po=12...

[doodlebugging]

I had considered the metal parts of the mask to be a potential problem. In the worst case scenario it should be relatively simple for mask owners to remove the metal tab from the nose and the staples holding the elastic bands before microwaving.

Once they are done in the microwave the bands could be stapled in place with your ordinary stapler and the band reattached with hot glue. Those who have a needle and thread could also stitch a sleeve onto the nose piece that is open at one end and just reinsert the metal nose piece once it is out of the microwave. The thin metal should withstand several bend cycles before needing to be replaced and it can be replaced with any thin aluminum strip which one could obtain from lots of places around the house or at the hardware store.

The bands and straps could be washed in ordinary soap to sterilize them before reuse.

Just thinking outside the box here. What do you think?

[tim333]

Apparently salt on the mask kills viruses https://www.sciencedaily.com/releases/2017/01/170105160228.h... https://www.businessinsider.com/mask-coated-in-salt-neutrali...

I was going to DIY. Soak in brine then dry the thing.

[doodlebugging]

I read about this option. The potential problem that I see is that coating the mask with salt or another substance, especially if part of a DIY project, is likely to leave you with a mask that is unusable since you have no way to control salt crystal size, nucleation points, etc.

The crystals will inevitably grow on the treated surface and block the filter media so that you start with an N95 rated mask and end up with an N99 or higher rated mask that can only be used for a few minutes before it leaves the user gasping for breath. Preserving the filter ability should be the goal in the sterilization process. I don't see a way to accomplish that without specialized equipment that allows the user to limit crystal size and nucleation sites.

That is why microwaving or UV sterilization seem the most viable to me. UV sterilizers require the user to follow specific guidelines to avoid health negative consequences and it seems unlikely that everyone could or would take steps to protect themselves from the UV damage.

Microwaves are nearly ubiquitous, though I personally don't own one and haven't since I had my wife get rid of ours once our son was done with bottle feeding. People know how to follow directions for using microwaves. It just seems easier to me to accomplish the objective with something that is a common or easily obtained household item that people are already familiar with.

[Engineering-MD]

I believe it also recommends the addition of a surfactant to make small crystals and a more even coating

[doodlebugging]

I read the same thing. Glad to see others investigating their options.

I'm not sure a DIYer could accomplish this without compromising the filter media unless there were kits available or a crystal clear guide for the task.

I realize that you can just wash the mask to remove the salt and surfactant and in the process any pathogens will be killed by the salt and soap. However, if you have to wait on this to dry between uses since the washing will fill some percentage of the pore spaces with water then you haven't accomplished as much as you could have if you had simply microwaved the mask in a boil-in bag allowing the steam to do the same work. As a bonus, people already know how to use microwaves and most have them at home.

I'm not trying to say that salt and surfactant doesn't work, only to say that this is better accomplished in a controlled environment with equipment that can insure that crystal size is controlled and filter media is relatively unaffected.

[mattkrause]

You probably want to avoid manipulating the mask a lot, both because it may be contaminated and to avoid punctures.

[doodlebugging]

I agree that the mask could be contaminated. In fact, I would hope that the person wearing the mask has a good reason to wear it, either someone in their household is sick and they are protecting themselves or they are sick and they are protecting everyone else who is home with them. I think it is a bad idea for everyone to wear a mask when there is no threat to their health. With people furloughed home it is likely that many of us can avoid contact with an infected person and therefore we don't need masks.

But if the user has paid close enough attention these last few weeks, then they are probably already washing hands anyway so as long as they wash up after putting the mask in the microwave and before they touch their face they should be good.

If the mask is punctured that creates a much larger path for droplets to get behind the mask or if the user is the infected one, to get past the mask into the clean air on the other side. To mitigate that situation, there is no reason that I can see where coating the puncture with elmer's glue, hot glue, etc doesn't solve that issue.

Bending the mask will probably create permeability that could allow larger particles to pass anyway. The plastic filaments they talk about are not likely to hold up to much flexing and it is a decrease in the tortuosity of the path through the media that creates the risk. Therefore, breakage along clearly defined planes creates an easy path through the media even if the mask is perfectly fitted to spec. I think bending the mask is the easiest way to send it out of spec so like you say, manipulating the mask creates a situation where it may no longer be effective against the particles sizes that it should protect against.

[paulmd]

While I suppose it’s an interesting academic discussion, frankly the idea of being able to safely contain an aerosolized upper respiratory disease at home is ludicrous to begin with, so it doesn’t really matter.

The simple truth of the matter is that if you are in a home or apartment with an infected person, and you remain present during their period of high viral shedding, you’re practically certain to contract it as well. You don’t have a negative pressure containment room, your home furnace is going to drag it all over the house. Normal airflow as you open the door will probably drag it out.

It’s perfectly valid to stay and care for grandpa, just don’t have any illusions that you’re not going to get it as well. You 100% will. Doctors who are trained in cleanliness and with access to real, non-makeshift gear are getting it.

That’s fine if you’re not a senior yourself. Severe reactions are fairly rare for anyone under 60 or so. And it can’t really be helped without abandoning grandpa.

[doodlebugging]

I am going to use recent personal experience to disagree with your conclusion that uninfected people in a house with someone who is infected cannot protect themselves and will end up sick.

This past December, in the week before Christmas, my wife had surgery that required an overnight stay. She was released with instructions to avoid laughing, coughing, no physical activity, etc. for several weeks. A couple days after she was home our son came down with an infection that turned into a deep, dry, raspy cough with sudden fever over 102*F. Since she needed to avoid any sort of infection and he was getting worse by the hour I took him to ER where he had a test for flu since people at his school had been down with it in the weeks prior.

The ER doctor told us it was a viral infection but the flu test was negative meaning that we either got there before there was enough viral material for a positive test or that it was something else causing it besides flu.

It became my job to keep his infection from spreading to my wife. To manage that I used sanitation instructions from my sister, a nurse, and I kept him isolated in his bedroom and my wife in our bedroom. I prepared all meals, etc. and cleaned the house, etc. I slept in a spare bedroom in case I was infected. I bought some cheap face masks, not hospital grade, just over-the-ear masks and made sure that she wore one every time she left her room and he wore one every time he left his room. I also wore one every time he left his room. Once he returned to his room I went along behind him and wiped every knob, switch, flat surface, etc that he could've contacted and put his used glasses and utensils in the dishwasher. Then I washed my own hands.

My son's fever broke after 4 days on Motrin and his cough went away too.

My wife never got sick and neither did I. We were all in the same house sharing the same air on days when the heater ran regularly due to a strong cold front.

No one wore a mask all the time. We wore them only when we had the opportunity to have contact with each other.

When the stories started breaking in China about this, I started following it all here on HN. I understood the challenges they would face having just faced similar challenges myself.

I found myself with part of a container of lysol wipes, a few cheap face masks that hadn't been used, some hand sanitizer for each bedroom, and the knowledge that one could beat something like this if they were diligent.

I realize that this is just my story but it is all true. Isolating the infected person, using PPE, sanitizing everything diligently can prevent everyone in the house from being infected if someone in your family does come down with an airborne infection.

My house is cluttered and disinfecting was potentially a chore but I made it easier by following each person along and watching carefully everything that they did while they were out "in public". Once they were isolated, I retraced their steps wiping everything down. I hope you don't have to share my experience but you can rest easier knowing that there is hope.

[aaavl2821]

All of the things you've said about mask functionality, reusability and sterilization are very interesting. As is your experience with in-home caregiving.

Is there a quick, effective and easy sanitizing protocol for N95 masks that you think would work for hospitals that are short on masks?

[chuckledog]

Agreed. The use case I am hoping to help solve for is health care workers (eg. Nursing home aides) who have a very limited supply of N95 masks that they wind up having to re-use for multiple days / weeks at a stretch. If they have access to a quick affective way to sterilize them without ruining them (I like the microwave idea too) then they can stay healthier, and their patients can stay healthier.

[doodlebugging]

I have given this a lot of thought.

A filter mask becomes more efficient as time passes due to blockage of infiltration/exfiltration paths. In this fashion, an N95 mask degrades to an N99 level mask and it becomes more difficult for the user to get enough air across the filter media to support life so they end up needing a new mask that has less restriction.

As the user wears the mask, most of the blockage and increase in filtering efficiency will occur on the face side of the mask and will be a result of condensation of droplets from the user's respiration. The filter media will become blocked from the inside out. There will be little if any measurable restriction added by the pathogen load of the unfiltered air on the outside of the mask. The distribution of pathogens in the air or the dust load would need to be pretty high for the outside of the mask to ever cause the mask to be restricted.

The main problem with the outside of the mask will be one of accumulation of pathogens on the outside.

I believe that this is the case for use of a mask by an uninfected person.

If the mask user is infected then the mask still becomes blocked on the face side of the mask, increasing its filtering efficiency, but that side also contains the pathogen load that that mask needs to prevent escaping into the room air.

Since the blockage in any case will be mainly from condensation and not from any biological load or dust load then it should be a simple matter to sterilize the masks in a microwave with a small amount of water to create steam. It may even be that the breath condensed on the mask will be sufficient.

I doubt in any case that a pathogen can pass through a mask and I will tell you why.

The path of infection for most people wearing a mask is mostly likely to be infection due to an ill-fitted mask that allows air movement with no filtering such as through hair, or in small spots where a good seal is not possible.

Now the why - filter media must have porosity and permeability. It is designed to create a tortuous path through the media so that anything moving in the connected air spaces has a high probably of being trapped in a void. If there are lots of twists and turns the resistance to flow increases (geologists call it the formation factor - a measure of the tortuosity of the path through the media) and turbulence causes an increase in the likelihood that a particle will contact the inside of the pore path and become trapped. Think of it like water in a river. As the river winds across the landscape, there are points in the stream where flow is weaker and the particle load settles out to form sandbars. There are also points in the stream where the current is faster and larger particles can pass.

The path through filter media is the same. When something encounters an area of low air velocity it becomes stuck. When turbulence increases it becomes more likely to collide with the sides and become stuck. Most of the pathogen load will likely be found very close to the source side. I don't expect much to be able to penetrate to the center of the mask.

That is also why condensation ends up rendering the mask useless. Water droplets coalesce and eventually you have blocked too many of the potential paths through the filter media.

Anyway, this got long winded. Sorry.

I hope some of this makes sense and if anyone has anything to add or discuss hit me up.

[doodlebugging]

I thought about this a lot last night trying to get to sleep.

Using what we know about the lifetime of the virus on various surfaces can we exploit that to allow reuse of masks that have been exposed to the virus but that still retain their filtering ability because they were only used for the time period necessary to treat one patient and then were discarded so as not to carry the virus into clean areas?

I wonder whether masks that have been used once could be bagged and set aside long enough for the virus to die after which time they could be reused. One could speed the process by placing the masks in a humidity controlled environment so that air circulates around them allowing any water film from the user's breath to quickly evaporate. Obviously it would be critical to avoid any situation where you created an opportunity for mold growth.

In this model, the masks are collected as they are discarded. Then they are held out of service for at least double the known time necessary for them to die on the mask surface. This requires someone to determine how long it is viable on a mask. That seems easy enough to determine.

This may be an option for places where ordinary disinfection is problematic. Sounds extreme and potentially dangerous and that is why it should be thoroughly vetted before anyone attempts it. Don't try this at home!

I also wondered about how health care workers are being infected and after seeing a number of posts with pictures of workers showing their faces marked by the masks I have a question.

Is it possible that the health care workers are infecting themselves by creating an environment on their skin that is conducive to infection? There are pictures showing deep marks that to me suggest that the masks have been made to fit around noses but in the process, the fit across the rest of the face is compromised.

The model for this comes from my own experience repairing cars, plumbing, etc. in any situation where a gasket is used to create a seal.

The user needs to avoid over-torquing the connections being joined because that over-torquing deforms the gasket enough to compromise the seal thus creating a leak.

I know that the average mask does not fit many people's faces. It seems that a more effective seal can be accomplished if one had a gasket kit with the mask that would effect a seal without the need to tightly compress across the nose. The gasket could be applied directly to the edge of the mask and would adhere to the mask using a peel-n-stick gasket.

I know from using masks in my own shop that leakage around the nose is the biggest problem with masks. The second biggest in my experience is leakage on the cheeks due to facial hair since I have a mustache that grows wild on my own lip and I am unlikely to trim or shave it.

If health workers don't clean their faces when they put on a new mask they may be allowing virus to infect them in the damaged skin areas.

Thinking out loud here. It just seems stupid to throw away an effective filter that has been used once for a few minutes when it has been demonstrated that virus has a finite lifespan that we can nail down by testing. If we simply wait for time to do its job, the masks can be reused multiple times with no opportunity for chemical or mechanical degradation of the filter media.

Probably a monumentally stupid idea like all those ideas you get just before you slip into unconsciousness.

tl:dr - For those workers with no sterilization options can they just set the used masks aside out of service long enough for the virus to die before returning them to service?

Obviously this a question for someone with the facilities available to determine viability on mask media so no one should consider this to be an option at this time.

[roel_v]

"as well as metal staples for the elastic bands, which would prevent you from microwaving"

My microwave works fine with metal inside. Would only be a problem for some people.

[doodlebugging]

Thanks for this information. Very useful.

[doodlebugging]

BTW, I think you hit the mother lode on links about potential decontamination methods. I need to read some of this for future reference. Thanks!