Thread by @DavidLKeating

Important🧵 on the exponential power of #bettermasks against #COVID19 and #Delta -- please read & retweet.

Use of #Bettermasks causes infection risk to fall exponentially by the power of two.

#Bettermasks put the power of exponential risk reduction on our side.

That's how the virus spreads -- exponentially.

That's why we need exponential powers on our side, especially against #Delta, which is 2X more infectious.

If we all wear #bettermasks, we get better filtration of exhaled air from an infector AND better filtration of your inhaled air from the infector.

We get that multiplier working for US to beat the virus!

Now let's talk about mask effective filtration efficiency (EFE).

A good mask has good filtration AND good fit. You need BOTH. Don't focus too much on filtration efficiency.

EFE accounts for both air leakage around the mask AND how many particles could get through the filter.

If everyone wears 25% EFE masks, infection risk goes down by 1.8X. Not bad.

50% EFE, risk goes down by 4X.
75% EFE, risk goes down by 16X.
80% EFE, risk goes down by 25X.
85% EFE, risk goes down by 44X.
90% EFE, risk goes down by 100X.
95% EFE, risk goes down by 400X.

This risk reduction calculation -- it's based on this excellent peer-reviewed paper.
tandfonline.com/doi/full/10.10…

With a 90% EFE mask on all, "the conditional infection probability is reduced by a factor of 100. This is due to the 10× decrease in quanta emitted to the room combine[d] with the 10× decrease in quanta inhaled through a mask, resulting in a total reduction of a factor of 100."

The #Delta variant is the virus upping its game.

Now we have to up our mask game to win.

Cloth masks often have 25% EFE, but some do a lot better -- hard to say in most cases. I've seen some at 60%.

Surgical style "procedure" masks without a mask fitter, likely 30s EFE, it depends on how good the material and how it fits you. Real medical grade surgical masks with earloops, in the 40s EFE. Surgicals with headbands, in the low 70s.

The problem with the cloth masks is they often don't filter well. Surgical masks that meet the ASTM 2100 standard provide excellent filtration, over 95%. BUT they leak -- a lot -- around all the sides.

You can bump up the performance of the surgical masks a lot by double masking with a breathable tight-fitting cloth (wear the surgical under the cloth) or by using the knot hack. The knot hack seems to get EFE in the 60s. Earsavers do about as well.

Depending on how tight your cloth mask fits and how good your surgical mask, if we're all double masking we could probably get in the 70s EFE. It's believed the nylon stocking hack over the surgical can get in the low to mid-80s.

A quality surgical mask like the @armbrust_usa & @FixTheMask mask fitter gets EFE to 97.3%. That is stunning proof that fit matters! A LOT.

There are two new standards -- Workplace Performance and Workplace Performance PLUS. Excellent standards, rigorous.

Yay @CDCgov @NIOSH!

Kudos to @armbrust_usa & @FixTheMask and 3M for making the Workplace Performance Plus grade.

So far only these two are on the Workplace Performance Plus list. There are none yet that meet the less rigorous Workplace Performance standard.

Hopefully we'll see more soon on both lists.

Here's the list:
wwwn.cdc.gov/PPEInfo/RG/Fac…

Here's a link to the @armbrust_usa & @FixTheMask:
armbrustusa.com/products/the-b…

And a link to the 3M mask that made the cut (Target seems to carry it):
3m.com/3M/en_US/p/d/b…

Both made the list with lots of room to spare. Both appear to have N95 class performance.

Masks nerds who understand the CDC data understand those two masks giv N95 class protection. wwwn.cdc.gov/PPEInfo/RG/Fac…

But getting N95 certification is a long process.

The Workplace Perfomance and Workplace Perfomance Plus standards are based in part on the testing methods in the ASTM F3502-21 Barrier Face Covering Standard. Here's a good summary of the ASTM F3502-21.
blogs.cdc.gov/niosh-science-…

The basic ASTM 3502 Level 1 standard is pretty weak. I would NOT use a mask that meets it but such a mask is probably better than most cloth masks.

The Workplace Perfomance and Workplace Perfomance Plus standards are MUCH stronger than the ASTM 3502 standards.

At ASTM 3502 level 1 you only get 20%+ filtration.

Now to be fair, the test is very difficult -- "mass median aerodynamic diameter of 0.3 microns." A lot of virus laden particles you may encounter are bigger and easier to filter.

So it probably performs better in real-world conditions than it looks from the % number.

But the standard provides NO test data on fit, meaning leakage around the mask. All you get is a subjective assessment -- it's snug on a variety of faces.

There doesn't appear to be a nose wire requirement -- IMHO a must have.

Now with an ASTM 3502 Level 1 mask that just meets the standard, let's assume we're at effective filtration efficiency (EFE) of 20%.

If everyone is wearing a Level 1 mask, infection risk declines by at least 1.6x. Maybe better than that as most masks will clear the standard by a good margin.

Much better than no mask. But we need to do better against #Delta.

(We assume the virus is on the same size particles in the test, which is probably more challenging than the reality.) So the risk reduction could be more significantly than 1.6x.

At ASTM 3502 level 2, you get 50%+ filtration. But again, no info on fit, so you don't know EFE.

But if you had 50% EFE, then risk is cut by 4x compared to no mask. Even better.

Now here's where things get unnecessarily confusing.

A mask that meets the Workplace Performance standard must have over 50% filtration material and a fit leakage ratio of 5 or more (higher #s are better).

cdc.gov/niosh/topics/e…

This makes no sense because the fit leakage test accounts for BOTH material filtration effectiveness AND leakage. So you can ignore the filtration percentage #.

A ratio of 5, that translates to 80% EFE.

If everyone wears such a mask, your risk of infection falls by 25x!

A mask that meets the Workplace Performance PLUS standard must have over 80% filtration material and a fit leakage ratio of 10+.

A ratio of 10 translates to 90% EFE.

If everyone wears such a mask, your risk of infection falls by 100x!

Now we're talking fantastic protection.

But if everyone was wearing a mask like the @armbrust_usa + @FixTheMask or N95 class mask, then the risk of infection would fall by 400X.

Wow!!!

Moral of the story -- get the best filtration you can. BUT also get a tight fitting mask with proven low leakage data.

KF94s, a great option, can leak up to 8% (material and around the mask). That's an EFE of 92%. If everyone is wearing one, infection risk falls by about 150x.

BUT, and this is a big BUT. I've heard some disappointing fit test results with earloop KF94s.

It was a small sample of people but not close to 92% EFE.

So my advice is get a headband version if you can. Alternatively, use ear savers to get a tighter fit.

The KN95 standard is basically the same as the KF94.

However, there are so many KN95 fakes that don't meet the standard I can't recommend them. KF94s from Korea seem to have better quality control.

I prefer @FixTheMask mask fitter +@larmbrust surgical medical masks, N95s or N99s.

That's the best protection among disposable masks.

But if you get a KN95, the one with the best reputation is the Powecom, which is sold by @projectn95.

Again, to get good protection you must wear your better mask correctly.

Info on getting good fit in the Better Mask Options (at 6.3) linked below.

If you get any of the #bettermasks, remember that you will always get better protection with a headband version instead of earloops, though ear savers will usually help earloop performance.

And don't forget about elastomerics -- great fit, comfort, and it's possible to get close to EFE 99+ protection.

More info on #bettermasks here.
masks4all.co/faqs-on-better…