So, masks have been in the news a lot recently for some strange reason. Probably most interesting; in the Czech Republic masks were made mandatory, but as there wasn’t enough existing masks in the supply chain, people had to create their own. Their president is crediting the widespread use masks as one of the main reasons they’re doing so well right now.
There are a number of organizations online that have provided instructions on how to make your own mask, and, in areas which are much more severely affected, some hospitals have been requesting people produce homemade masks for them to use. Thankfully, there’s groups of volunteers around the world which have been stepping up and making them en masse. (This whole situation is something that we likely would have considered ludicrously implausible just 6 months ago)
Luckily, here in Australia the supply for medical professionals seems to be holding out, and I haven’t heard of any hospitals which need the public to make stuff for them.
But masks as a whole seem like a great idea, and they are certainly easy to make. So, my friend Kate and I decided to stitch up a bunch of masks for ourselves and others.
Making the mask:
We used the pattern and instructions from here:
and made the following modification so that you get a much better fit:
First, grab some 1.6 mm diameter armature wire . (This is the sort of thing they use inside clay puppets so they can hold position while being filmed for stop-motion animation.)
We cut 190 mm of wire, and put it in inside the mask, at the bridge of the nose, with a stitch underneath to keep it held in place.
After assembly, here’s what it looks like:
The fit is very comfortable. As a test, I wore my one for several hours straight while we were cutting and stitching the others, and I had no issues.
Also, the armature wire in the nose is a godsend. When I put the mask on, I can press down and ensure shape the wire so the top part of the mask sits tight against my face. Most importantly, no matter how hard I exhale, I can’t fog my glasses. I don’t think I’ve ever had a mask that I could easily wear glasses with before. (This probably just means I’ve been wearing dust masks incorrectly for years, but hey)
Some tips I’d recommend if you make your own:
- If you’re using ribbons and not elastic to hold it on, then use fairly thick ribbons, (~10-20 mm?). The thin ones we made (~6mm) have a tendency to be hard to tie in a bow, and tricky to undo if stuck. (I ended up with one double-knotted behind my head and needed another pair of hands to rescue me, which kind of defeats the point of social distancing with a mask)
- Use two different colours of fabric, with a boring fabric inside, so it’s obvious how to put it on.
- Some sources say to use non-absorbent material such as (polyester or poly-cotton blend) for the outside of the mask, and absorbent material (such as pure cotton) for the inside. Others don’t specify, or just use the same material for all layers. If you have a choice of materials maybe do non-absorbent on the outside.
- Make more masks than you think you’ll need, and that way you can give (a washed) one away or have spares if needed.
Do they work?
There’s the question of whether homemade masks work. I’ve seen some people say that masks for uninfected people are a bad idea, and other say they’re great, and everyone should be wearing them. My inner [socratic dialog/shower thoughts/ shoulder angels discussion] ran something like this;
A: Now I’m confused. Hmm… What do we think?
B: Well, the argument is that while a mask might intercept an incoming droplet from someone else, in doing do it then traps the virus right next to your mouth, where you’ll just breathe it in later
A: That logic seems weird to me. I think surely more would still be stopped than make it through? I mean, how can the steady state be worse than the no-mask case?
B: Hmm… good point. But then there’s the effect that the mask stays warm with exhaled breath, so is that giving trapped particles a boost? Like a mini incubator?
A: But what about touching your face? We’ve all learned recently just how often everyone does that. A mask completely stops you touching your mouth and nose. And makes you more aware if you try and touch your eyes.
B: So in a sense, a mask makes your hand washing more effective?
A: I’d wager so. But what about that ‘incubator’ idea? Is it a real effect? And if so, does it cancel out the benefits?
B: Hmm… How the hell would we test that?
And I just got tied up in knots trying to imagine stuff I don’t have enough experience to predict well. But thankfully we don’t have to mentally simulate everything from first principles to find the likely answer. For example, this study:
did a randomised controlled trial of just under three thousand doctors that interacted with patients with influenza. The doctors were issued at random either an:
- N95 mask (roughly equivlant to a ‘P2’)
- These are specially designed to stop aerosolized particles, have a material with guaranteed effectiveness stopping particles of a certain size & are tested rigorously
- Are a pain to fit properly. You can be ruled out from wearing particular sized masks because of your head shape, or if you have a beard.
- Depending on your area, may periodically require special procedures for a Fit Test, involving wearing the mask while an aerosolized chemical is sprayed directly at your face. If you can’t smell it at all, while vigorously breathing in and out, (you can’t cheat by holding your breath, they make you read out loud long sections from a book), then your mask fits.
- Surgical mask
- These aren’t remotely air tight, they’re designed to be comfortable and easy to use
These have no special requirements relevant to stopping viruses. (at least for the couple of models I looked at). The only specs and standards I saw were: BFE > 98% – this only applies to bacterial filtration ability, not relevant to much smaller viruses like coronavirus EAN14683: Type II – this specifies that : It has a low differential pressure. I.e. it’s easy to breathe through, and specifically not required to have any splash resistance, and specifically not required to have any sub-micron particulate filtering ability
- The particular surgical masks used in the study were better than ordinary cloth masks, however.
- They had fluid resistance ratings of 160 mmHg, indicating it needs approx 1/5th of an atmosphere pressure difference to force liquid through,
- They had particulate filtering ability at 0.1um of 98% (this is about the size of coronavirus particles)
So the study describes a comparison between basically a ‘gold standard’ mask and a quite good mask, but which is not guaranteed to be airtight , tested by people wearing them whenever they were:
“routinely positioned within 6 feet (1.83m) of patients”.
And they found no significant difference in the number of doctors contracting influenza.
Of course, the influenza-A & B from the study obviously isn’t the same as coronavirus, so perhaps it might turn out that there’s a true difference in PPE effectiveness. But, I mean, they’re pretty similar. Both are small, airborne, viruses made of RNA, and if significant amounts could traverse an improperly fitted mask so easily, then we would probably have seen that reflected in the study, which we didn’t.
The study follows 1607 healthcare workers in Hanoi who used either:
- locally produced cloth masks,
- locally produced surgical masks,
- or their normal procedures (which would likely have some form of surgical mask).
The study covers a four week period, and covers seventy four wards of varying types (including emergency & infectious/respiratory disease wards) specifically selected because they were high-risk.
Looking at the results of the study, at first glance the Relative Risk level of 13 to 1 seems terrible. i.e. wearing a cloth mask is 13 times more risky than wearing a surgical mask, as far as Influenza Like Illnesses goes.
But when you look at the actual outcomes, the numbers don’t look so scary:
- Surgical mask: 580 people, 1 got Influenza-Like-Illnesses
- Cloth masks: 569 people, 13 got Influenza-Like-Illnesses
[Edit: Screw it, I decided the picture from the journal article didn’t convey it well enough, so here’s my own plot instead. Edit2: I removed the ‘control arm’ section as it was confusing and not relevant as it was their old procedure. The numbers here just show surgical masks vs cloth masks]
When you consider that these numbers are specifically selected from front line healthcare workers, in high-risk areas, and still indicate that you can wearing cloth masks for a month and still only have a 7.6% chance of catching a CRI, or 2.3% chance of ILI, that would seem to indicate cloth masks are still pretty fuckin’ awesome.
Don’t get me wrong, I’m sure surgical masks are better, (and they should be mandated in any countries that haven’t yet), and if you’re a healthcare worker you should absolutely use them if you have access. But it looks like we’re talking about fairly subtle differences in safety here. If it were a car, it’d be the difference between having airbags with extra side-impact cushions, and just regular airbags. Whatever you have, it’s far better than nothing.
Now pretty much none of the extreme scenarios in either of those studies apply to me, or anyone likely to get a mask from me. I’m not the worst-case of someone spending all day next to a contagious patient, I’m just some schmuck making a quick trip to the shops. Or getting drive-through. I just want a little more protection when I have some short interactions with others, and that’s that.
I can then carefully take off the mask (without touching the outside), stick it in a plastic bag and boil it when I get home. And I have a couple of masks ready so I’m still covered in case I have another errand later.
So as far as effectiveness of homemade masks goes, it looks cautiously encouraging. But at any rate, I’m working on the assumption that:
it’s a mask, not a magic wand:
- Wearing it does not grant me magical powers. I will not assume that I am in any way immune to infection because of my stylish facewear
- I’m still going to keep social distancing, and not do any extra errands which I wouldn’t have done anyway.
- I’m going to be careful taking it off, making sure I don’t touch the outside
- I’m still going to wash my hands with soap and water, or hand sanitizer, as normal
- If I do unknowingly have the virus, I’ve probably made it less likely for others to get it off me. Win!
- If I do run across someone that unknowingly has the virus, I have probably made it a bit harder for them to infect me. Win!
If you’ve got a sewing machine, why not make your own? If nothing else, it’s an excuse to use up those fat-quarters of unmatched fabric you’ve had laying around for years…