Thread by @ghhughes

How many times have you seen a mask worn like this, just thrown on without fitting it at all? Does it even do anything?

I did a quick check with a headform mask testing system. While the unfitted BYD surgical mask may block large exhaled droplets, the unfitted mask did not protect from inhaling aerosols:

It got 6.5% filtration.

It leaks 93.5%.

Fitting the nose wire of this BYD surgical mask to the headform increased the filtration efficiency to 36.1%. Still not great, but over 5x more protection.

Fit matters, even for leaky surgical masks.

The exact numbers vary from mask to mask and person to person, but you will always get more protection if conform mask to your face as well as possible.

And, of course, an N95 or other similar mask can give 95% filtration or better if it seals well on your face, much more protection than even the best fitted surgical mask can offer.

Just to be complete, I tried fitting the BYD surgical mask as best as possible to the testing headform by firmly pressing the custom molded mask fitter that comes with it to the headform during the duration of a test.

The best total filtration efficiency I could get from the BYD was 83%. I can't tell how much of that is from filter penetration vs. seal leakage due to the nature of the headform testing.

I'm able to get scores over 99% with some N95s using this same method of clamping. So, yes, N95s are better than surgicals, even if you clamp the surgical securely to your face, but in a pinch (such as early in the pandemic during the N95 shortage) a surgical mask held tightly with a mask fitter may be the best protection available.

(Speaking of mask fitters, I got a score of 81% using a Fix the Mask mask fitter over the mask in another test. Mask fitters are great tools to help many kinds of masks seal better, but can be hard to find these days. Not shown in the photos.)

My testing is generally single sample testing using ambient particles, so results should be considered approximate.

Testing made possible by a grant from #kanro.

All testing data dedicated to the public domain.

I should note that this doesn't mean surgicals were a bad thing early in the pandemic. They were not. And not all surgicals fit as poorly as the unfitted BYD in the example.

Surgicals were what was available, and they were primarily meant as *source control*, to reduce the spread of germs from an infected person. It is easier to filter respiratory droplets at the source when they are larger and haven't evaporated into smaller particles.

The CDC advocated wearing a tight fitting cloth mask over surgicals to help improve the fit, because the filter media of the surgicals can and does filter aerosols, even if typically not as well as N95s and other respirator grade filtering facepiece masks.

The conclusion should be that people should wear the best masks that are available and wear them well fitted, not that we should just throw our hands up and do nothing if perfect is not available given that it almost never is.

More education is needed to help people choose and wear masks well when needed.