A dust mask is a flexible paper pad held over the nose and mouth by elastic or rubber straps for personal comfort against non-toxic nuisance dusts. They are not intended to provide protection from toxic airborne hazards.
Are dust masks reusable?
In workplaces with low dust levels, a mask can be reused as long as it is not soiled, damaged, contaminated or creates breathing difficulties. In workplaces with high levels of dust, the mask should not be used for more than 8 hours. So it should be changed each working day.