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On Sat, 15 Jul 1995 UnderhillP@ao*.co* wrote, in response to my comments on hydrogen: > According to David Swatzky's chapter in the NSS-CDS Cave Diving handbook, > hydrogen is more narcotic than neon and less so than nitrogen. He also > claims that it has successfully been used for deep saturation diving. This > is obviously outside the realms of tech diving at this time. > > Do you know if any non-military, non-commercial (i.e. technical) divers have > ever used neon gas mixtures? If so, what are the advantages/disadvantages. > Are there any tables available for diving such mixtures? > > Regards: > > Philip > > PS If you can offer any information, this may start an interesting thread > (take a few peoples minds away from dead Nick whatsisname) so feel free to > post this and your reply. I'm posting this mainly because I know there are others far more qualified to answer this than I am. I'll comment on what I do know (at least what I think I know). According to Bennett in Bennett and Elliot, H2 gas has a relative narcotic potency of 1.83 (N2 is 1.0, Ne is 3.58, and He is 4.26; the higher the number the less narcotic). Thus it is indeed slightly less narcotic than N2 and somewhat more narcotic than Ne or He. HPNS is a neurological excitatory syndrome, which appears to result from increased ambient pressure (not, as some believe, from high PHe). Narcosis is a neurological depressive reaction to increased concentrations of certain dissolved gases. Peter Bennett wrote some articles discussing how adding a small amount of N2 to He-O2 mixtures (i.e., trimix) can reduce the severity of HPNS symptoms on exceptionally deep dives. It is believed that the depressive action of the nitrogen offsets the the excitatory response from the high ambient pressure (i.e., narcosis seems to counteract the effects of HPNS). Taking advanmtage of the narcotic potency of H2, COMEX began using He-H2-O2 trimix to achieve even greater depths than possible with He-N2-O2 trimixes. H2 has the advantage of being less dense than N2, and therefore causes less work of breathing at great depths. H2 has some serious risks associated with it; particularly the fact that it combusts in the presence of more than 4% O2 (evidenced by the Hindenburg disaster). Thus, it can't really be breathed safely at depths less than about 130 feet. Neon is an interesting molecule for breathing gases in diving because it has the combine characteristics of low narcotic potency, but high molecular weight (5x greater than He). Thus, it's not very useful for going extremely deep (too much breathing resistance), but may have some decompression advantages for short-duration dives to moderate depths (300-500 feet). I spent some time investigating the possibility of using raw Neon as a diluent for short duration rebreather dives (raw Neon is about 75% Ne and 25% He, and a lot less expensive than pure neon). Bill Hamilton suggested that it would have roughly the same decompression characteristics as N2. I did some simulations and decided that it wasn't worth it (saving 15 minutes off a 2-hour decompression schedule). Neon has been investigated as a constituent for deep breathing gases mainly because it is cheaper in some parts of the world than He. Neon has been used by a technical diver to a depth approaching 500' (there was a thread on techdiver a while back; I did a search of the archives but couldn't find the details, and I can't remember the details). Hope all that is mostly correct... Aloha, Rich
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