[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.