Masks are not magic

[dreamshark]

This country seems to have settled into two camps: those who believe that coronavirus masks are nonsense and those who believe that they are magic talismans that would stop the virus in its tracks if everyone wore them. Neither is true.

I make really good masks, but I have never been under the delusion that particles do not pass through them. One way I know this is that when I pass the chicken rotisserie in the supermarket or the spice rack in the coop I can smell all that goodness.

This suggested a way to compare my various masks. Voila! My mask test station!


The winner! 3 layers of delicate silk, one layer of mid-weight cotton, and a felt filter. This one blocked the cinnamon and vanilla and substantially muted the molasses. Nothing could stand against the vinegar. There were actually a few other masks of similar construction that performed about as well, all of them pleated masks with felt filters.


The loser: a standard surgical mask. A small 2-layer mask with no filter performed similarly. Even the cinnamon was clearly detectable, although muted. Not saying that the less effective masks are useless. Certainly, all of the smells were much less detectable through any of the masks. But there were definitely differences in performance. 

Comments

[laramie]

I admire your scientific approach to mask-making. I have not yet checked out how the mask you gave me holds up after laundering. Perhaps I should have hand-washed. I'll let you know if it's still a good fit.

[dreamshark]

There are no materials in that mask that are likely to shrink, but you definitely should not put the silk in the dryer.

[marahmarie]

I washed mine in Dawn and left it to air dry. What is the silk mask's filter made from, again? Just a few uses and it got stained around the mouth so it looks like it needs replacing.

[dreamshark]

I think that's the safest approach. The biggest problem with machine washing seems to be that the pipe cleaner in the top gets twisted.

According to my notes, that mask has a polypropylene filter cut from a reusable shopping bag. If it's getting stained I guess that means it is doing its job. Not necessarily stopping viruses, but maybe just plain dust or smoke or something.

Polypropylene is perfectly washable, so try that first. Or you can make filters out of anything that makes sense to you, cutting them to fit. I've been doing a lot of experimenting with filters, and now usually cut them with rounded shoulders and a "nose piece" sticking up to fit better into the mask.

Polypropylene shopping bags are commonly recommended for filters. Just make sure they haven't been coated with a waterproofing material. If you can breathe through it, it's fine. Felt is great, and gives some shape to the mask, so it's my current favorite. Apparently denim makes a good washable filter. Also pieces of Pellon interfacing.

If you really are breathing in a lot of dust, disposable filters might be a better idea. Some people use coffee filters or even folded paper towels. Cotton cosmetic cleansing pads or Swiffer pads cut to size are very absorbent and last a little longer.

[marahmarie]

Hmmm, OK: I have paper towels and coffee filters, and a bag of polyfill but kind of thinking it's not Pellon, so maybe not the right thing, though now I'm curious how that might work out. I have no felt , denim, cotton or Swiffer pads to spare though, atm. I have a ton of shopping bags made of all different materials but I don't know how to tell if any of them are polypropylene (I'm thinking most if not all of them aren't, since none of them are as stiff as the filter was).

Thanks for giving me all these ideas.

[dreamshark]

Most reusable shopping bags that aren't obviously made of paper or cloth are polypropylene. You know, recycled plastic? Surprisingly, surgical masks are usually made out of polypropylene, but spun in a different pattern.

Actually, the polyfill might work. Ideally, the filter layer should be a non-woven material, kind of a mish-mash of fibers that mechanically traps particles. But denim is woven and they say that's good, so who knows?

[marahmarie]

Def going to give the polyfill a try, if only to see if it suffocates me as fast as I think it will, or if it just works. The denim is good to keep in mind but I clean out my closet Kondo-style a few times a year so just got rid of all my spare denim not too long ago. Good to keep in mind, though - and thanks again.

[davidwilford]

What masks do is lower the odds of either exhaling or inhaling enough virus particles to either infect someone else or be infected yourself. That's why I support a mandate for their use in public places. I now have several masks primarily made of layers of cotton, two with an additional layer of polyester. The rule of thumb I've heard about their effectiveness is that if you can blow out a birthday candle while wearing it, it's not a good mask and to get another that's better.

[dreamshark]

Blow out a candle? That's a pretty low bar! If you can put it over your eyes and still see well enough to drive it's probably not a very effective mask either.

[marahmarie]

I need to try this with my surgical masks. Never thought of testing them this way ("If I can see well enough to walk", even...).

[davidwilford]

I liked it as a basic test that everyone can relate to, and if it helps people use masks that aren't crappy that's a bit of a win at least.

[pameladean]

Scent molecules are way way way smaller than any virus, though.

P.

[dreamshark]

Really? I didn't think there was much of anything smaller than a naked virus particle.

I'm not sure how odors work, tbh. Certainly smoke consists of particles of various sizes, including some that are large enough to see. I would have thought that the smell of spices comes from tiny little bits of the spice in question. Pepper certainly seems to release clouds of pepper dust.

[quadong]

Acetic acid molecules (vinegar) are certainly smaller than viruses. For your other three test substances, I have no idea how we smell them and what size particles are involved.

[dreamshark]

Well, there was absolutely no stopping that vinegar smell, so that tracks. Perhaps spices are a better choice for this test than liquids. The cinnamon was easiest to block. Sage was more penetrating than cinnamon, but heavily reduced by the better masks.

[pameladean]

Okay, this is what I recall from a research rabbit hole that I went down for a story that didn't end up using it.

First, bear in mind that a virus is really small for a living or quasi-living thing, but it's a mechanism for reproducing itself and it's composed of at least tens of thousands of molecules.

Scent molecules are chemical compounds. The smell of any given substance can be made up of a lot of different kinds of molecules, but what our olfactory system responds to is on the molecular level. We can pecrcive some scents from a very small sample of the molecule in question. Molecules have to be in a gaseous state for us to perceive them -- they have to evaporate or sublimate out of the pepper dust or whatever. You don't have to breathe in pepper dust to smell the pepper.

This is about the limit of my knowledge, and it certainly may not be adequate to address the situation.

P.

[marahmarie]

Ha! TIL

[minnehaha]

I adore everything about this.

K.

[dreamshark]

Well, except that it may be wrong-headed if odor molecules are really way smaller than viruses as Pamela commented. The masks definitely do filter out quite a lot of the odor, however. And there do seem to be differences among the masks.

[pameladean]

I feel that the information about the differences is very likely useful regardless of the size of scent molecules compared to viruses. I'm just not persuaded that scent molecules are a good proxy for viruses.

P.

[dreamshark]

You are probably correct. That's reassuring, actually, because one certainly can smell things through all of these masks and I would like to think that they work a little better than that on viruses. But from what little research I have found, even the best cloth masks are probably at best 75% effective. Way better than nothing, but outmatched by the air in a crowded bar or church service.

[pameladean]

That's why they keep telling us that masks are not a substitute for social distancing. Though I think the 75% figure is just for one person wearing a mask, and if everybody is wearing one the effect is cumulative?

Regardless, you're sure not finding me in any crowded indoor setting until things are very different all over than they are now. I wish we had a functioning government that would not put people who have to work in such settings in danger and would provide for their survival instead.

P.

[dreamshark]

Good points.

[ckd]

As I understand it, while a virus particule by itself is very small the droplets of moisture (even the smaller "aerosol" droplets that linger rather than the large "ballistic" droplets) that carry the virus are not nearly so small.

https://tinyurl.com/FAQ-aerosols says:
"""
While the size of an individual SARS-CoV-2 virus is very small (120 nm or 0.12 microns), the aerosol in which respiratory viruses are contained are larger, albeit still small enough to remain suspended in air for long periods. A widely held misconception is that the virus is naked in the air, perhaps with some water. This has been propagated by graphics in major medical journals such as JAMA. Our best guess is that the most common aerosol size is a few microns, where the viruses comprise a very small fraction of the aerosol, as exemplified in the figure below. Aerosol size has major implications for the ability of masks and filters to remove it from the air, how deeply it will penetrate the lungs, and determines the loss rate due to gravitational settling in indoor spaces.
"""

[dreamshark]

FANTASTIC link! Thanks!

[quadong]

I've always been befuddled by people attempting to block odors with scarves or their shirts or whatnot. I just assumed that it didn't work at all because all the relevant molecules would easily pass through cloth. Obviously I never did the experiment, so thanks for correcting my misconception. I guess part of what I had wrong must be as you said elsewhere, that some smells are carried by particles and not gasses.

On the two camps that you note, I think this has got to be one of the biggest problems with trying to have rational arguments in this country. It seems that 3/4 of everyone can't conceive that anything could be *somewhat* useful, or that maybe there are situations with tradeoffs that need to be balanced.

[dreamshark]

I must admit that none of the masks had much effect on that damn vinegar, which must be pumping out its odor bearing compounds at the molecular level. But the molasses, which also has a very strong odor, was noticeably reduced. The vanilla was interesting in that some of the masks blocked the recognizably vanilla odor but let the alcohol smell through.

But don't take my word for it - try your own experiments. Probably a fun project to do with kids.

[marahmarie]

How do you get the smells strong enough to smell through a mask? I envision myself tossing vinegar and cinnamon all over the floors and walls and counters to make sure there's enough of everything to smell.

[dreamshark]

I just take the top off the bottle, hold it up to the mask, and inhale. I suppose this whole thing is dependent on having a reasonably strong sense of smell. But if you can't smell an open bottle of vinegar you can't smell anything.

[marahmarie]

Good point (and a lot less messy! *flings flour around to see if I can smell it through the mask*)