[perl4ever]

>It can only stop fairly large droplets.

What is your basis for this statement?

If I wear a regular dust mask, without edge sealing, and glasses, my glasses fog up when I exhale. Seems to me suggestive evidence that anything at all deflects normally invisible breath that would travel outward onto the surroundings.

[thu2111]

Well, that's pretty well known. There are different tiers of mask. This article looks at the evidence for them:

https://www.cidrap.umn.edu/news-perspective/2020/04/commenta...

Some kinds of masks can stop much finer grained objects than droplets, e.g. gas masks, but the kinds of masks people are actually wearing are just regular cloth masks and there's no evidence they accomplish anything and plenty of evidence they don't: the article goes into this.

It's logical: your glasses fog up exactly because the hot air is exiting the mask and travelling outwards, that's why it's hitting the cold glass of your glasses.

But it's not sufficient to merely deflect a small amount of air from each breath in a different direction. That's not permanently trapping infected air; obviously it can't be because otherwise CO2 saturated air would build up inside your mask and suffocate you. The air has to be able to circulate. The mask is meant to let air through whilst blocking ... well, whilst blocking what? Virus particles? They're far too small. Water droplets that contain virus? Maybe, but only if you're actually spreading water droplets around and if you're asymptomatic then clearly you're not. Yet everyone is being forced to wear masks even if they're visibly healthy, on the basis that "you might be infected without realising it". The science behind this is garbled nonsense, being pushed on people because something must be done, this is something, therefore it must be done.

Stopping stuff travelling out is a different matter.

[DanBC]

The other thing that's being missed is even for proper masks there are time limits to their effectiveness. That doesn't matter so much for health care professionals who should be frequently replacing the masks, but it is relevant to members of the public walking around.

Either they're keeping the mask on all day and it stops being useful after an hour, or they're taking it off and putting it on as they go in and out of shops.

https://www.ijic.info/article/download/10788/7862/

> This study was conducted to check the efficacy of face masks in limiting bacterial dispersal when worn continuously in Operation Theater. A comparison was done to find out difference between fabric and two ply disposable masks. The first sample was collected prior to wearing the mask, using cough plate method holding a blood agar plate approximately 10 -12 centimeters away from the mouth. The personnel were asked to produce “ahh” phonation. Participants were then asked to don the face mask, continue routine work and report to the study center located inside the theater for further sample collections at designated intervals of 30, 60, 90, 120 and 150 minutes after wearing the fabric mask made of cotton. The study was replicated on immediate next day using two ply disposable mask keeping all the other conditions and personnel exactly the same. Bacterial counts before wearing the mask were 5.36±4.38 and 5.7±2.99 on day 1 and day 2 of study. Bacterial counts were 0.96±1.06 (P<0.001) and 0.7±0.87 (P<0.001) at 30 min; 2.33±1.42 (P<0.001) and 2.36±1.03 (P<0.001) at 60 min; 3.23±1.54 (P=0.007) and 4.16±1.78 (P=0.011) at 90 min; 5.63±4.02 (P=0.67) and 4.9±1.98 (P=0.161) at 120 min and 7.03±4.45 (P=0.019) and 5.6±2.21 (P=0.951) at 150min respectively for fabric and two ply disposable mask. Counts were near pre-wear level in about two hours irrespective of the type of mask. There was no significant difference between cotton fabric and two ply disposable masks. Face masks significantly decreased bacterial dispersal initially but became almost ineffective after two hours of use.