Back Respirator - 3M 6200
Like most hobbyists I know I have been using disposable face masks whenever I have been doing enough grinding to create an appreciable amount of dust in the air. The reason I don't use it for small jobs is basically because I don't like wearing them it just seems like too much effort to put it on for a few seconds of grinding.

The disposable masks really don't fit me well. I have never been able to get a good seal, especially around my nose where the air I breath drags the dust in with it.

Given the amount of dust I have breathed in over the years it might be a bit late in the day but I decided I would buy a proper respirator and give that a try. WOW! Why didn't I do that sooner. Unbelievably comfortable. Easy to breath with. While the seal is still not perfect (I have the devils own job finding a divers mask to fit as well) it is better than the disposables.

I found that is was so comfortable that I didn't bother taking it off when I had small jobs to do in between the grinding. That is really saying something because I usually can't wait to rip the disposables off.

If you are serious about protecting your lungs then I highly recommend getting a proper respirator.
Video review
Get your very own at one of the links below: (I recommend choosing one of the 7 in 1 options)
 3M 6200 Respirator on EBay AU  3M 6200 Respirator on EBay CA
 3M 6200 Respirator on EBay US  3M 6200 Respirator on EBay UK