[ Question ]

Alternative mask materials

by Dmitry Vaintrob2 min read27th Mar 2020No comments



Posting for the first time -- please LMK if this is the wrong format for a question.

I like Elizabeth's idea that we are still in the "throw things against the wall and see what sticks" phase of coronavirus response, so even very messy and non-expert questions can be helpful.

So here's a question. Tl:dr version: what are possible mask alternatives that are more easily scalable than standard N95 masks and have better coronavirus protection than surgical masks? If promising materials do exist, what are good ways to test promising materials without endangering doctors? Long version below.

I have been reading about the shortage of PPE (personal protective equipment) for doctors: hospitals are planning for re-using masks, substituting the more effective N95 masks for much less effective surgical masks (SSC compares effectiveness here https://slatestarcodex.com/2020/03/23/face-masks-much-more-than-you-wanted-to-know/). I have friends who are doctors or work with doctors and are absolutely miserable about this, and this strikes me as one of the biggest short-term problems we'll be facing.

Many companies and individuals have donated their stock of N95 masks, but there simply doesn't seem to be enough to go around. To be safe a medical professional needs to put on a fresh N95 mask for each shift that might involve coronavirus exposure. For most doctors and nurses in affected wards, this corresponds to (bare minimum) two masks per day, which will most likely mean 2-4 million masks per day for the US alone in the coming months.

From what I understand, this kind of production is nigh-impossible in the short term, because of the shortage of melt-blown fabric. From this NPR source

making a single machine line takes at least five to six months.

(Though the same source discusses Chinese factories that have gotten around this time limit.)

So a reasonable next question is to ask whether there are alternative materials/designs for masks that do not use melt-blown fabric or other difficult-to-scale materials and offer better protection against n-CoV exposure than flimsy fabric or surgical masks. A cursory literature search shows a bit of promise:

  • This nature article claims that adding a layer to a mask which is coated in dried salt significantly improves H1N1 flu virus filtration. The article has problems, and its *in vivo* mouse section strikes me as mostly garbage (sample size is too small, and they test by incubating virus on the mask rather than filtering through it), but the approach seems promising.
  • There is a plethora of different materials with filtration properties that are effective at removing virus aerosols. This handbook mentions that certain glass fiber materials in (non-wearable) air filters reduce virus levels by 9 orders of magnitude, and has this tantalizing, though unfortunately reference-less quote:
It is normally intended that very fine ('absolute') air cleaning filters should remove bacteria and viruses by direct filtration, so that air can be sterilized by such action. However, there is now a growing range of combination media where the fibres have been treated in some way with a range of anti-bacterial coatings, to provide an alternative (or supplementary) means of pathogen removal. These treatments may work by physical action (damaging the impinging cells) or chemical destruction on the pathogen particles, and may be 178 Handbook of Filter Media 'permanent' or have a definite active life, after which the filter is discarded or retreated.

BTW, a curious fact from the same handbook, probably not very applicable: old filters from WW2 and Russian early cold-war filters achieved particle filtration approaching the virus level using asbestos filters. This is obviously not a good idea in modern times (old Soviet asbestos-based gas masks are weirdly available to buy on the internet, but keep in mind if an outer filter layer is damaged they will result in you breathing asbestos, which is probably worse than getting coronavirus). Still, this can be taken as a datapoint that other cheap materials (which are not asbestos) with decent virus filtration properties might exist.

The big problem I see with trying new materials is that there do not seem to be that many good studies measuring viral filtration qualities of different materials for viral material in general, and, worse, studies for n-CoV filtration specifically are non-existent and probably not very realistic for the time scales involved.

So here are some specific questions that seem to me like they have a chance of being useful:

  • What are the most promising and quickly scalable materials one could test as alternatives for mask filtration?
  • What are fast-track ways of determining efficiency of different materials in filtering n-CoV particles? Are there any useful natural experiments that have happened or will happen, and ways to carefully gather data about them? Are there other quick preliminary ways to find promising candidates which do not involve endangering doctors?


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