I use a half respirator with organic vapor cartridges while spraying (in a tent like Mark does). Works fine for epoxy and enamels (don't smell a thing), but the stain sprayed on my bed wood does make my eyes sting after just a bit. Keeping the tent open helps with that.
I wouldn't worry about overspray getting exhausted. It'll eventually coat the inside of the exhaust system with tiny dots of epoxy. Maybe after 20 years use it'll be uniformly coated.
