Masks with exhalation vents protect you but not others, and are not permitted under CDC guidelines.
Why is that so bad?
If I protect myself, I protect you by proxy. I can't infect you if I'm not infected. And a proper valved, sealed, FFP3 mask gives a really high level of protection, while a valveless N95 is moisture-saturated and useless in a matter of hours, and a simple face covering is no protection at all in enclosed spaces, in either direction.
This is why valves are not useful and not accepted.
If your mask gets moisture-saturated, just replace it.
Why? All of these measures are probabilistic.
P(infect others) = P(infected) * P(transmission)
Simple masks don't have much impact on P(infected), but substantially reduce P(transmission) under some circumstances. Valved FFP3 don't have much impact on P(transmission) [not zero], but vastly reduce P(infected) in virtually all circumstances. It's not clear to me even under this simplistic analysis that it is not superior. And in an enclosed space, the effect of simple masks on P(transmission) is almost wiped out.
>If your mask gets moisture-saturated, just replace it.
New mask every 2 hours?
In a public space there is simply no way of efficiently knowing and verifying everybodies P(infected), thus the only remaining measure is to reduce P(transmission).
And yes, if that‘s the time it takes for your mask to get wet, then it is time to replace it.
https://www.thelancet.com/journals/laninf/article/PIIS1473-3...
Mitigation measures should target what makes a disease particularly deadly and neutralize it, in order to be effective.
A recent study debunks that assertion and shows that they protect others more than standard surgical mask and cloth face coverings.