Do NOT use sand. In the course of my duties, I visit many sandblasting operations and nobody uses sand, even though everyone is suited, hooded and with a filtered fresh air supply. Commonly used media in commercial blasting includes coal slag (Black Diamond or Black Beauty), alum. oxide, steel shot, plastic beads and many other types as determined by the what the blaster is trying to accomplish (paint/rust removal, surface prep on new metal, etc). Please read
http://www.cdc.gov/niosh/docs/92-102/ before you decide what media to use.