There is some level of misunderstanding about this. A mask is not verified or tested for both inhalation and exhalation on filtration efficiency. Mask is tested for inhalation and the exhalation efficiency could be much weaker. The job of the mask is to no. 1 protect the wearer and not others. Protecting others come as a consequences and not a requirement. Having an exhalation valve makes it easier to wear the mask longer. Also, not all exhalation comes through the valve. Now, if you are truly concerned about others, you need to insure that the exhalation as well as mask leak rate is the same both ways.
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