I work as a sheet metal worker everyday of the week, i am grinding stainless steel and aluminium everyday.
I wear one of the cheap air masks to prevent inhaleation. At work we are constantly reminded to wear these.
Another thing you have to be careful of is noise, if your using angle grinders etc you NEED to wear ear protection, it only takes a couple of months grinding without ear protection for you to loose 15% of your total hearing!!!!
All metals when grinded are dangerous, they damage the walls of your breathing system which cant be good..... lol