Post #747: Can Kents clarify KN95 chaos? Updated

Posted on July 7, 2020


Update 2:  This didn’t work, at all.  Not even a little bit.  See Post #790 for details.  You can’t use the odor of cigarette smoke to test mask filtration.

Update:  See postscript at bottom.  The ability of genuine N95 masks to filter smoke particles is well known and well documented.  In that light, my proposed “sniff test” for KN95 masks looks fairly promising.  To the extent that a mask reduces the odor of cigarette smoke, then it is filtering out virus-sized particles.

In Post #740, I noted that my local convenience store had “KN95” masks for sale.    I’ve heard a rumor that one of the local hardware stores is also selling such masks.  (I plan to check that out soon.)  And I exchanged emails with  neighbor who is in the process of purchasing some KN95s, from a couple of different sources, for daily wear at work.

In theory, wearing a KN95 gives you the same protection as an N95 respirator.  So, in theory, upgrading from a cloth mask or similar to a KN95 is a smart thing to do.

In practice, not so fast.  I’ve started looking into the “KN95” mask market, and it is complete chaos.  I guess that’s no surprise.  That’s more-or-less of a piece with the entire Federal response to COVID-19.


To be clear, KN95 is a Chinese standard for respirator filtration.  Functionally, the KN95 standard is virtually identical to the US N95 standard.  It means that the mask filters out 95% of the hardest-to-filter particles, 0.3 microns in diameter.  That’s about twice the diameter of an individual virus particle.  (Or about 1/250th the width of an human hair.)

But in practice, “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.  It is being use to refer to any sort of mask that “looks like” a proper KN95 mask.  As with the mask above.  That’s marked “KN95”, but there is no guarantee that the mask will in fact filter out small particles.

In the USA, KN95 isn’t a filtration standard.  It has become more of a fashion statement.  Style, but not necessarily any substance.

For the informed buyer who is not a health care worker, deciding whether or not to use one of these masks is a surprisingly tough problem.  Just to encapsulate it, here’s a quick categorization of what you can find.

Source:  CDC

  1. Genuine NIOSH- and FDA-approved masks.  For health care workers, you need genuine NIOSH-approved KN95s that are listed on the FDA list of acceptable masks.  (NIOSH is the National Institute for Occupational Safety and Health).  CDC has a guide to checking out the markings on masks, to see that the markings indicate that the mask is, in fact, NIOSH-approved.  Then, within that, the FDA has a list of approved Chinese mask manufacturers and model numbers.   These masks will always have lots of stuff printed on the surface, per the illustration above, and will be on the US FDA’s list of approved KN95 respirators (Appendix A, here). 
  2. Sub-standard but genuine KN95 masks.  Then there are masks that are manufactured in China as KN95, but fail to meet the N95 standard when tested using US methods.  These are “sub-standard” KN95 masks.  These will have most or all the printing above, but the will not be on the US FDA’s list of approved respirators, or will be specifically noted as having been removed from that list.
  3. Knock-offs of NIOSH-approved masks.  And, of course, there are knock-offs that do not meet the KN95 standard, but the supplier is smart enough to print all or most of the right codes onto the mask.  The CDC has an entire page devoted to detecting knock-offs.  Problem is, these could, in theory, have all the right numbers on them anyway, and still not meet the N95 standard.
  4. “KN95” masks that are not NIOSH approved and are up front about it.   These typically will be plain, with no detailed printing on the mask.  The white mask above illustrates a non-NIOSH-approved KN95.
  5. “KN95” masks that don’t even mention NIOSH approval. Again, typically plain with no detailed printing on the mask.  The white mask above illustrates a non-NIOSH approved KN95.

Here’s the hard part.  From what I’ve read, my impression is that even the ones that aren’t NIOSH-approved may provide more protection that the typical cloth face mask.  At the minimum, they are structured to provide a reasonably tight seal against the face, reducing the amount of unfiltered air that bypasses the mask.  For another, most use (or claim to use) melt-blown cloth, which is substance used by proper medically-rated surgical masks to provide particulate filtration without producing a lot of back-pressure.  That’s key, because if there’s high back-pressure, you end up breathing around the mask, rather than through it, and so you end up breathing unfiltered air.

But how can you tell?  How can you tell that trading in your cloth mask for a store-bought “KN95” is an improvement?  You can’t (necessarily) trust the markings on the mask (though the lack of those is a sure indicator a mask is not NIOSH tested and approved.)  And each mask (on Amazon, say) seems to come from different supplier, under a different brand name that you’ve never heard of before, and never will again.  And despite what you may see on social media, there is no simple test to determine whether or not a mask is a “genuine” KN95 (i.e., actually meets the Chinese standard).

It just ain’t that simple.

Given the huge diversity of the “KN95” market, there’s no way that any central testing authority can do you any good.  Even if I could test a batch of so-and-so brand masks, that wouldn’t do you any good unless you could purchase a mask from that exact batch.  So centralized testing is fine for (e.g.) hospitals that buy batches of 10,000 masks.  Sure, send one off to be tested.  But for the average citizen, picking a generic “KN95” mask from the sin section of the local 7-11, that centralized testing is useless.

You literally need a way to test the mask that you bought.

If only there were some way to produce virus-sized particles that linger in the air.  Particles that you, the ordinary citizen, could somehow detect.  You could then test whether or not a mask is an upgrade by subjecting your current mask, and a proposed replacement, to some test based on those virus-sized particles.

After pondering this for a bit, two things turned up.  First, the particles in cigarette smoke are just about the right size.  They tend to average out to be somewhere around 0.2 microns — just shy of the 0.3 microns actually used for the N95 standard.  Second, there is good precedent for using the odor of cigarette smoke to test masks.  US infantry long ago figured out that a good field test of whether their gas masks were fitted and working was to see if they could smell cigarette smoke through the mask.  If yes, adjustments were needed.

These Chinese-made “KN95s” are cheap enough that most people can afford to take a gamble on buying a few.  So I am proposing, but have not yet tried out, a simple way to test your existing mask against a store-bought “KN95” mask:  See how well it filters out the odor of cigarette smoke.  The less you can smell it, the better the mask is at keeping virus-sized particles away from your nose.

Presumably, this test would also work for store-bought “PM2.5” masks.  These are masks that claim to filter out most particles around the size of 2.5 microns.  In the US, there is no standardized testing for these masks.  If you buy a “PM2.5” mask, you have no guarantees as to filtration ability.

The only one I haven’t quite figured out is activated charcoal filtering.  Here’s what I believe to be true.  These remove odors by “adsorbing” individual molecules to the porous activated charcoal surface.  So those are NOT particulate-filtering masks.  Those masks work based on the surface chemistry of activated charcoal, and are designed to trap specifically classes of molecules.  Masks that rely on activated charcoal will filter odors, but should NOT be used for protection against COVID-19. 

This cigarette-smoke test is a simultaneous test of mask fit and mask filtration ability.  What you smell is based on what comes around your mask (fit) and through your mask (filtration).  But that’s exactly what you want to test.  That’s really the bottom line.

Consider those cigarette smoke particles to be a proxy for COVID-19 aerosols.  Only, unlike the virus, you can smell them.

Note that perfume won’t do.  Perfume, flowers, peppermint oil, and a lot of other odors are from individual molecules.  Those are vastly smaller than viruses. No particulate filtering mask is going to (or is designed to) remove them.

You have to use combustion smoke of some sort, because you want to test ability to filter particles.   It’s not clear that tobacco smoke is uniquely the correct substance to use, but it has the advantage of having been widely studied.

Plausibly, anything that will put a lingering smoke into the air, when burned, will do.  The fact that the smoke lingers tells you that you are looking at aerosol-sized particles.  Possibly, anything that puts out a lingering smoke with a distinctive odor when burned — tobacco, wood chips for barbeque, incense — would provide a reasonable test.  But, again, the most widely-studied smoke in the world is tobacco smoke.

I’ve never bought cigarettes before.  So this will be a first.  But, in the name of science, I’m going to buy a pack and try this out.  The mask I have been wearing has finally broken down, and I need to switch to something.  I’m going to take this as an opportunity to see if this quick-and-dirty test is a useful way to sort through the chaos of the current KN95 market.

POSTSCRIPT:  In fact, before the pandemic, genuine N95s were recommended as a way to avoid second-hand cigarette smokeWhen tested, most N95s did an excellent job of filtering out cigarette smoke particles.  Californians apparently routinely wear them when the air is bad from forest fires.  (Also discussed here.)

When all is said and done, this is looking fairly plausible.  N95s do, in fact, filter out smoke particles.  Smoke particles are just about the right size for testing masks for filtration of aerosols.  And you can smell smoke.  To me, at the minimum, that adds up to a simple “sniff test” for any proposed mask replacement.  Does it reduce the smell of smoke (or incense) better than your existing mask?  If so, in all likelihood, it will do a better job at filtering out aerosol-sized particles.