The little funny looking doctors type mask does not do the job. I wear glasses and when useing those, my glasses fog up bad. Get you the best dual cartridge you can afford. Especially haveing a beard, you need the best seal around you face you can get. I always wondered about Micheal Jackson, maybe he was a lot smarter than we gave credit for.
Just another note, if you can, do it outside with a large fan blowing everything away from you. Remember the hazzards of knapping inside? Its not the dust you can see that gets you, it's the micro carbons floating in the air that you breath. I have an exhaust fan over my grinder, a shop vac hooked to it, all in a 12X12 building. But even with that, there is no where for the micro carbons to go, even if you are not grinding. When you stop, they are still there, even if you stir the dust up again.
I stripped a few feathers last night getting ready to gind, and after about 1/2 hour, looked down at my chocolate colored shirt and it was white with dust and fibers. Doing nothing but splitting, and the hazzards are still there.
Take some advice everyone, use all the precautions you can, they are cheap compared to what it can cost you later,,,,trust me,,,, I know.