We changed our organic filters when there is resistance when inhaling or after 8 hours, which ever occurs first; the hepas were changed when we felt resistance. Now we have combination hepa and organic filters. We're fit tested every year after certain age, I use a full face respirator when I paint or sand; the half face works ok but the eye protection is so much better with a full face and you get 50 times the protection over a 1/2 face model.
