Dr;
Grinding dust is not to be taken lightly. Breathing it in can give you lung problems that are really serious. After getting a big dose of dust a few years ago and feeling like I had a case of pneumonia, I became a stromg advocate of wearing dust masks. 3M makes very good ones; they look a little like the hardware store variety and cost a little more but they WORK.
Regards, Neil Tucson, AZ