[tzs]

Isn't the following simple experiment enough to show that wearing a mask should help?

1. Without a mask, I coughed while probing the space around my face with one of my hands, at a distance of maybe 9-12 inches away.

I could easily feel significant airflow from the cough in a cone in front of mouth. Nothing to the sides (for purposes of this discussion, "side" means significantly off-axis from from the line down the middle of the cone, so includes above and below the face, not just left and right).

2. Same test, with mask. I either did not detect any airflow or just detected a bare hint of some at the same test distance as unmasked. (I'd need an assistant to tell which, since I can't think of a good way to do a blind test alone).

There was definitely some airflow out the sides with the mask, as I could see by the coughs fogging my glasses, but it only seemed to be very close to my head.

3. I Repeated the above, but replacing "cough" with "blow as hard as I can". Same results.

How does one escape concluding from this that if I'm infectious wearing a mask will reduce the volume over which my releases of air containing virus laden droplets spread? Or that this means my chances of passing it on to someone I'm only spending a little time with (clerks helping with a purchase, people standing in the same line for something, etc) will be reduced?

[jfengel]

It shows that it might help, but it's not conclusive. It's clear that air molecules pass easily throught he mask, even if you can't feel the flow. So the fact that you can't feel the flow doesn't really tell you all that much about whether the air is moving.

It means that they're moving in a more diffuse fashion, so they may not spread quite as fast. But once in the air, they can still drift around.

That said, viruses are larger than air molecules, and the droplets that carry them are considerably larger than that. They're larger than the pores in N95 masks, in fact. So yes, there's good reason to expect that masks provide protection.

On the gripping hand, this study isn't really about any of that. It's about mask mandates, which has to factor in whether people comply, what materials they're using, how much noncompliance matters, etc.

So yes, you can take "Wearing a mask helps" for granted, even if you need to think a little deeper than "I can't feel the air". Each individual act on that. But more importantly, "Requiring people to wear a mask helps", which is an important action for legislatures, not just individuals.

[emerged]

To play devils advocate, masks could be ineffective if people tend to behave in more dangerous ways while comforted by wearing a mask. For example, by spending more time around people, frequently touching public objects, standing much closer to people, etc.

[ardy42]

> To play devils advocate, masks could be ineffective if people tend to behave in more dangerous ways while comforted by wearing a mask. For example, by spending more time around people, frequently touching public objects, standing much closer to people, etc.

I think that was one of the fears in the first place, and one reason why the CDC didn't initially recommend masks for the general population. However, experience has shown that many Americans will "tend to behave in more dangerous ways" during the pandemic even without a mask, so that fear was unfounded.

[ceejayoz]

Yep. For a more dramatic test of what you're describing, you can add fire. It's a pretty clear difference with the mask versus unmasked: https://www.youtube.com/watch?v=x6cTDGqcUpA

[Gys]

Seems to me that if you have the urge to cough, you better stay away from others anyway. So wearing a mask in that case makes no difference: nobody should be near you ;-)