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ARGON Argon is definitely a better choice for dry suit insulation than air. The heat conductance of argon is .18 expressed as (Joules / second per square centimeter) times minus third power of 10. The value for nitrogen is .26 and oxygen is .27. Air is thus .262. For all practical purposes one can say that any nitrox (including air) gives the same insulation. Argon conducts heat 68.7 % as well as air - or put the other way around, is a 31.3 % better insulator. The gain of inflating a dry suit with argon rather than air (nitrox) means, roughly speaking, a reduction in heat loss of one third. Counterdiffusion problems do not seem to be manifest in anything short of sat diving; for ordinary diving one can safely breathe air (nitrox) and put argon in the dry suit. There is one operational hazard - by introducing a pure inert gas one runs the risk of accidentally breathing a gas that will not sustain life. Breathing argon would cause blackout without any warning. If one employs stage bottles and as well as bottles with argon for suit inflation, one could run the risk of mistaking them. One could by accident fill a stage bottle with argon or one could swop them at the dive site. I know that this should never be allowed to happen, but the remote possibility of such a disasterous mistake should be considered. We have been through the same discussion for air and nitrox, but this is a more serious one. If one should ever pick a wrong nitrox mix it will at any rate sustain life. Oxygen poisoning could be a killer, but the most likely outcome of violating oxygen limits is still no adverse effects whatsoever. If one does the opposite mistake, he could contract decompression sickness. Thus, it is all RCOULDSs, and even the RCOULDSs will have a good chance of survival / successful treatment. On the other hand, breathing pure argon WILL cause fainting within a minute! To eliminate this risk, I+ve considered to mix 15-20 % oxygen with argon. That will give a breathable mix without raising the heat conductance too much. The conductance of 15% oxygen, 85% argon is .194 as opposed to pure argon+s .18. This is still 25 % better insulation than air. This mix would sustain life perfectly, even at the surface. Any possible mistake would not be fatal - in fact, it wouldn+t cause any problems at all. Further, breathing an argon / oxygen mix at decompression stops would probably be as efficient as breathing pure oxygen. Argon diffuses somewhat slower than nitrogen (almost 20 % slower), due to its high molecular weight. (Rate of diffusion is inersely proportial to the square root of atomic weight. The atomic weight of argon is 39.95 while those of nitrogen and oxygen are 14.01 and 16.00 respectively. Since argon doesn+t combine while the two latter are present as diatomic molecules, we get 39.95 versus 28.02 and 32.00.) It has, on the other hand, a higher lipid solubility than nitrogen. That means it would take longer bottom times to require decompression while, ones stops are called for, more decompression time would ensue. However, all this is purely of academic interest since there+s absolutely no reason to dive an argon / oxygen mix. The only application as a breathing gas would be for shallow stops. One would eliminate nitrogen over a 100 % gradient without any appreciable acquisition of argon. With a possible exception for deep stops of a considerable duration, one could safely disregard the amount of argon being dissolved. Thus, one could even plan on using argox for decompression. For actual diving argon is unsuited since it is more narcotic than nitrogen. Also, due to high density, argox would be limited to a maximum of about 50 feet. That is of course not to say that it would be fatal at greater depths, but it would be as breathing air at an ambient pressure twice as high. From 50 feet to the surface, however, it would probably not feel much different from air at moderate depths. If argox is used for stops, and if it+s as efficient as oxygen in eliminating nitrogen, one could wash out nitrogen without worrying about UPTD (oxygen RclockS). Since argon is more expensive than oxygen, it does probably not make sense to let argox replace nitrox for decompression. Argon is also colder to breathe (this depends on heat capacity, not conductance) and the gain of improved insulation would be lost. In fact, the increase in respiratory heat loss would almost exactly cancel the gain in insulation. The total energy budget would be as for ordinary air drysuit diving. It would be interesting to learn whether my assumption that argox eliminates nitrogen as efficiently as oxygen does, could be verified. From looking at concentration gradients, this conclusion should be fairly obvious. Zero nitrogen in gives a 100 % gradient for nitrogen out. One could argue that the limited influx of argon would add to tissue nitrogen. There+s probably some synergistic effect of any two inert gases. However, slower rate of diffusion and shallow stops should cause negligible tensions of argon. One could also consider isobaric counterdiffusion. That should, however, be no different from switching from heliox to air which is a standard DCIEM procedure. That also implies switching from a RfasterS to a RslowerS gas. Generally speaking, isobaric counterdiffusion doesn+t present any problems unless the tissues are saturated at a high ambient pressure. In conclusion, if argon is being employed for suit inflation and is present in the first place, one could at least make sure that it constitutes a breathable back-up rather than constituting the risk of a fatal mistake. The fact that this contingency gas supply would also be well suited for driving nitrogen out of the system is definitely no drawback. Hans Petter Roverud, using Julius Loennechens mail account.
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