[Speedslug]

I will add that respirators should be the "second line of defense" after the action of a high volume ventilation system.

If you don't have really good ventilation then the particles that respirator is keeping out of you lungs for the moment will land on your tools, workbench and glass and will eventually wind up on your hands and that will lead to ingestion either from disturbed dust lofting back into the air or in your next meal.