Yes you can work with a mask on but it absolutely needs an exhalation valve to allow moisture to escape.
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Most of you know that I have a portable sawmill and I saw 12 months a year. Yes, Winters are cold and Summers are hot. Eye and hearing protection, gloves, leather apron, steel toe boots, and of course the wearing of a 3M N95 mask. This picture was taken in 2010 and nothing has changed. I have always bought the masks in 6 boxes of 10 for the best price and no shipping charges.
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Humana just sent (two each) masks to my wife and myself for everyday use..