Respirator FOR CERTAIN. I've done demolition work in old houses for about 10+ years. I can tell you the Plaster Dust Alone is horrid.. but it is the 80 or 90 years of ash, dust, blown insulation that will kill you if you spend even 20 hours sucking it in!

If you run into Asbestos.. that's a tricky one. Technically you have to be certified in Asbestos removal to do it. If the property owner gets nailed disposing of it improperly he is in for one helluva fine!