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On pumped fuel gases: Point well taken, you're correct that it used to
be at least partly carbon monoxide. I think that industrial fuel gases were even purer CO at one time. I have a vague memory that it was produced by passing flue gases through heated iron pipes to convert CO2 to CO--is that correct? On helium solubility: Thanks for the note, I wasn't aware of Trimix. Similarly, I didn't know helium had a drug effect. Xenon must have the most of all the noble gases; it has good anesthetic effect at about 70 Torr and is currently being proposed for actual surgical anesthesia. It has the interesting problem of not being patentable, and therefore not worth any company's money to get through FDA approval, so it may never appear on the drug market. Of other small, nonpolar molecules, the one I'm sorry I missed (it was gone before I started my practice) is cyclopropane. It's similarly very blood insoluble and therefore fast-acting (more on that if anyone's interested). It has the problem of being not just inflammable like ether, but explosive. Spark suppression used to be a big deal in operating room design. Another interesting suicide-by-oxygen-dilution problem is automobile exhaust. Catalytic converters work well enough that running a car engine in a closed garage frequently produces anoxic brain damage (CO2 poisoning) rather than death (CO same). Perhaps that happens to some of the suicides who are unaware that fuel gas got swapped for methane. Things were quiet in the operating room today, and I had an hour to chat with the anesthesiology residents. I told them about this Usenet discussion and asked them to distinguish CO2 poisoning from that by CO. They didn't do very well. David Don W wrote: Hi David, David Kazdan wrote: Helium is almost exactly the dilutional asphyxiant that nitrogen is. It's used in deep-diving artificial atmospheres for two reasons: Nitrogen is a weak anesthetic gas, producing intoxication at several atmospheres pressure--(nitrogen narcosis"), and it's soluble enough in blood and other water-based body fluids to fizz out when the pressure is released suddenly (the bends, caisson worker's disease). "Helium has neither of these properties." snip David David Kazdan, MD, PhD Anesthesiologist Pilot I hesitate to enter this discussion since you are obviously well qualified, however, that is often how learning occurs and I still have a lot to learn. I agree with all of your excellent post with one minor exception. Helium _is_ absorbed into the bloodstream under high enough partial pressure and does release bubbles when the pressure is released too quickly. Heliox (Helium + O2) and Trimix (Helium + N + O2) are common gasses used in the technical diving community, and they both require decompression stops on the way back to the surface. Technical divers use these mixes for dives from 130' (~5 atmospheres) to as much as 1000' (~31 atmospheres). The O2 content of the mixes is reduced to avoid oxygen toxicity effects at high PPO2. I also would point out that helium at high PP--although not narcotic like Nitrogen--does produce some strange physiological effects including a "buzz" similar to having had a lot of caffein. Don Woodbridge P.E. Engineer Technical Diver Pilot |
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