The FDA lists both Propanol-2 and Ethanol as Class III solvents, with exactly the same residual limits of 5000 ppm or 50 mg/day. There is no question that Isopropyl (P-2) is more damaging in excess than ethanol, but the point is perspective. Neither was found damaging by the FDA hygiensts below 5000 ppm or 50 mg/day. Because of how many lives have been ruined by alcoholism, ethanol is one most closely studied of the alcohols, and the data will show it is responsible for any number of toxic effects, including cancer, when consumed toxic levels or chronically at sub-toxic levels. When Isopropyl is consumed at sub toxic levels, the person doesn't keel over like they were shot, but it does attack the central nervous system, especially the auditory nerves. Consider the conundrum of having the material available to extract cancer meds for a patient, but no access to any Class III solvent less damaging than Isopropyl. Should the patient be allowed to die, or should they take their best shot using a Class III solvent that can easily be removed below toxic levels??? Our central method of extracting cannabis meds is Butane or Ethanol, because both are considered GRAS (Generally Regarded As Safe) by the FDA, and suitable for inclusion in food stuff. Normal and Isobutane are both used as a food propellant, and ethanol available as drinking alcohol. If neither were available, we would move to the next available Class III solvent, with the least toxic effect, and would purge below toxic levels. We also have human sensory threshold working to our favor, to at least keep us out of the deep woods, but I will come back to a proviso on that in a moment. In the case of Isopropyl, it smells and tastes like Isopropyl at 5000 ppm, so head space GC tests aren't required to sense its presence at those levels but in general if you aren't in a position to verify your residual solvent levels, sticking with the least toxic GRAS solvents adds further levels of safety. Coming back to the sensory threshold thing. I judged concentrates at a cup that required a stiff entry fee, so each of the entries ostensibly thought they had the winner. About three of the 28 samples had retained Iso above both sensory and residual solvent limits. That implies ignorance, or inured senses. With constant exposure, our sensory perception thresholds raise.