N95 masks are fine for dust as long as dust is all you're wanting to filter. And the style of N95 matters on your comfort level and whether or not you routinely wear glasses.

If you're being exposed to viruses, you would probably want an N99 or N100.

Here are some definitions for those masks, very basic:
http://infectiousdiseases.about.com/od/faqs/g/N95def.htm

Sue