The general wisdom is that any sand (or loose substrate of any kind) is a risk for beardies. The main risk is of course, impaction, but sand can also cause irritation if it gets into beardie's eyes. Additionally, loose substrates tend to harbor more bacteria than solid, not as easy to keep clean unless of course, you plan to change it out often.
Some do opt to use play sand (the ONLY recommended sand for beardies), that is well sifted and cleaned. And this, ONLY for adult dragons, 1 1/2 - 2 years and up. No sand whatsoever is recommended for babies and/or juveniles.
Safest substrates for beardies are repti-carpet, slate, tile, shelf liner, or just plain old paper towel. If you look into the "viv pics only" thread in the "enclosures" forum, you'll find some great examples of what people have done, in particular, with slate and tile... some really nice vivs and ideas.
Hope this helps!
Em