Before we got smart, they used asbestos fibers in lots of things as a benign filler. Now we know it is not so benign. Not that it will kill you on contact or anything like that, but if you break the fibers into small bits and inhale them, your body can't get rid of them, and this can cause all sorts of issues, most of which are the result of long-term exposure. So, the last thing you want to do is sand something containing asbestos, or do anything that generates dust that contains it.