The first thing to do if you are worried about dust is do NOT use air gun. All you do is spread it around for cleanup later.

Dust from sanded paint containing lead cadmium or chromates are probably the worst especially if you have young kids. If you are concerned about them GET RID of air gun. Paper type masks are about a waste of time and money if you want filtering. Best is air fed hood then a full face respirater then half face with the radionuclide labeling.
Dan Bentler