If you are wearing a mask and it has a valve, you are doing it wrong. Valves allow you to exhale without any inhibition — the air flows without being filtered. Industrial masks have valves (not medical masks) as the concern is not about making people sick — coal does not get sick.
goatinamoat:
And a clarification — industrial N95 masks have valves — medical N95s do not. I now return you to your regularly scheduled nudity.
“A foolish consistency is the hobgoblin of little minds, adored by little statesmen and philosophers and divines. With consistency a great soul has simply nothing to do. He may as well concern himself with his shadow on the wall. Speak what you think now in hard words, and to-morrow speak what to-morrow thinks in hard words again, though it contradict every thing you said to-day....
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matoushka:
:') Twain is excellent.