In this post, I propose to rate masks on their ability to filter out cigarette smoke. The particles in cigarette smoke are roughly the same size as virus/aerosol particles. (Although their chemistry is quite different.) I am going to use those second-hand smoke particles as my best proxy for human aerosol emissions. The basic idea being that if a particle-filtering mask is good at removing something as small as cigarette smoke particles, it probably does a pretty good job at filtering aerosols in general.
I’m announcing the full scope of the test ahead of time because that’s good science. This way, I can’t just bury the results if they turn out unfavorable. (AKA, toss them in the circular file.) In some sense, it’s as important to know this doesn’t work, as it is to know that it does work, as a way to test masks.
The test is pretty straightforward: Light a cigarette, hold it under your face, and rate how strongly you can smell cigarette smoke while breathing through the mask. Less is better.
A cigarette is ideal for several reasons. One, it provides a consistent burn, meaning, a consistent concentration of smoke particles from one mask to the next. Two, it’s a readily-available and easily-repeatable standard. Three, the smoke has been well-characterized. Four, there is no risk (as with incense) that the material has been doused with molecules meant to volatilize as the base product is burned. If you smell tobacco smoke, you are smelling smoke particles. if you smell incense, it’s not clear what you are smelling.
I’m going to start with these five scenarios, hoping to establish some sort of scale:
- 3M N95 respirator (new old stock, should be true N95 filtration)
- Dust mask with two layers of Filtrete 1900 fabric (~ N85)
- Dust Mask with one layer of Filtrete 1900 fabric (~N60)
- Plain dust/surgical mask (N low).
- No mask (N00)
The first problem is, I still have to manufacture items 2 and 3. I did a bunch of #3 masks for friends, early in on this pandemic. I need to make some more, document that, and then go on to make #2 masks. These should provide known filtration standards below N95.
Then I’ll rate the following six masks on that scale. These are the masks whose performance I am trying to judge. Starting with the beat-to-heck 3M dust mask that I have been wearing since the start of the pandemic, that I hope is still working well. And then some other alternatives that are readily available to the US public.
- 3M N95 dust mask (extremely well-used)
- “KN95” mask #1, from Twins Ace Hardware in Fairfax
- “KN95” Mask #2, from Twins Ace Hardware in Fairfax
- Generic single-use “surgical-style” mask #1.
- Generic single-use “surgical-style” mask #2.
- Plain-vanilla single layer cloth mask.
The point is to say whether or not you would materially improve your protection from aerosol-sized particles by swapping a plain-vanilla cloth mask for a typical generic, non-certified “KN95” mask offered as an impulse item at our local Ace Hardware.
Background and Caveats
The need for this test, and the theory behind it, were developed in Post #747.
Briefly: In all likelihood, despite what the WHO says (Post #748 and many others stretching back some months), the evidence suggests that COVID-19 can spread through aerosol (airborne) transmission. That is, via tiny (under-five-micron) particles that can remain suspended in the air for a considerable length of time, and that are poorly filtered by cloth masks.
The possibility of significant aerosol (airborne) transmission of COVID-19 has some fairly strong implications for how you should behave. When you are in an indoor space (or, possibly, a crowded outdoor space) with people other than your family, you should ideally wear a mask capable of filtering out aerosol particles. Whether or not you are properly “social distancing”.
Filtering such small particles is what an N95 respirator does. If it is fit perfectly to your face, with no leaks, it filters out 95% of particles that are 0.3 microns in diameter. (That size is chosen for the test because it is the most difficult particle size to filter out.) In practice, an N95 respirator will filter less than that, because all masks (and mask-style respirators) leak around the edges to some extent, and what you breathe is some mix of filtered and unfiltered air.
But you can’t buy proper (e.g., 3M) N95 respirators. Not in any mainstream retail outlet. And I do keep checking from time to time, to see if I can buy a standard 3M valved dust mask in any of the local hardware stores, or on Amazon. And at present, the answer remains no. All N95 production is, in theory, being reserved for health care workers. (You can, of course, roll the dice on Ebay, but in any case, there would not be enough such under-the-counter masks to supply any significant portion of the US population.)
That said, at some point, I’d expect the manufacturing base to crack, on this exact point of not selling N95s to the public. For the simple reason that you can make a buck doing it. At present, this is the only indication I have seen that this has started to occur. Fore sure, 3M ain’t doing that. But if this becomes commonplace, then there is no need for any of the rest of this posting. Just buy a proper, certified N95.
So, for now, it looks like generic non-certified “KN95” masks are the only mass-produced alternative to cloth masks for widespread use by the public. If we’re going to upgrade our protection, at present, that seems to be the sole alternative.
But “KN95” has no legal meaning in the US (see Post #747). Formally, KN95 is a Chinese filtration standard equivalent to the US N95 standard. In practice, in the US, “KN95” is now being used to refer to a style of mask, without regard to the mask’s ability to filter out fine (aerosol) particles.
And so, the point of this test will be a) to see whether or not I can establish a scale (part I), and then b) see how specific masks perform on that scale (part II).
More to follow, once I make the masks and set up the experiment.