I just read a "letter to the editor" in a woodworking magazine. If I
recall, the fellow worked at one of the companies that makes DCs. He said
that 1-10 microns are the dangerous size. He also got down on the idea of
trying to use an air cleaner to keep the air safe. It cleans the air after
it has been blowing around the room for you to breathe. Better to collect
it at the source.

I just noticed the Grizzly catalog sells 0.5 micron bags.