Don't you use a HEPA filter on your respirator? They block particles to .3 microns and are used for removing asbestos. I can't smell smoke wearing one, that's how efficient they are. I was an EPA certified asbestos inspector and management planner. Also got building inspection and Radon certs plus some OSHA certs too. Nice side jobs.
HEPA filters block bacteria too, but one thing is critical, you must fit the filter mask and this is usually done professionally using ammonia capsules by an OSHA certified expert (me
) who uses it around the typical weak points where a good seal is hard to attain. I have never had someone with a full beard pass the ammonia test, ever. Hate to tell you guys with beards, but the fine particles are getting through even though you don't feel it. You need a full face mask which doesn't require a test.
High Efficiency Particulate Absolute=HEPA filter, the violet or purple colored ones; I used to tape a layer of paper towel over mine to keep them from getting too clogged while grinding including ivory and I couldn't smell it or bone either and bone is disgusting. There is one catch and that is if your belts are getting dull or clogged up then you start to burn the ivory and make fumes, it's a particle filter, not a fume filter. I used a belt cleaner every minute when grinding bone or else it burns and I would start to smell it. darn stuff clogs belts in the finer grits quickly and I don't recommend going over 400 grit without a belt cleaner or silicone carbide wet belts. My 1x42 with 8" disk can run wet or dry and is easy to clean up wet grinding slurry, especially the disk which I can get high grits SC from lapidary suppliers. I don't have an exhaust since my grinding happens outside and my grinders are on a cart. Live in an apartment.