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Randy MyAss Milak: You can copy textbooks well. Too bad you can't remember what you copy, because if you did, you would note that my post has no errors in it at all. Now get your nose off the floor and pay attention. The original question was about the ideal breathing mix for shallow dives, assuming cost is no object. If heliox were used in a dry- suit, isobaric counterdiffusion and conductive heat loss become disadvantageous. Using Argon for inflation, and breathing heliox, as Ben Wiseley asks, gets my vote for the ideal setup at 60 feet. Wanna vote, or just rant somemore. Mike Black --- Randy Milak <milak@Di*.zz*.co*> wrote: > "Michael J. Black" wrote: > <snip a whole pile of shit> > > Here you go Black, this is a freebee lesson with citations for > you, so that you won't look like such a moron on your next 'helium' > post. > > A french astronomer, Pierre-Jules-C�sar Janssen, first obtained > evidence for the existence of helium during the solar eclipse of 1868 in > India when he detected new lines in the solar spectrum. No element at > that time was known to give these lines and so it was apparent that the > sun contained a new element. This initiated a search for the new > element on earth. In 1895, Sir William Ramsay discovered helium in > clevite, a uranium mineral. The identification of helium was left to > Sir William Crookes and Sir Norman Lockyer. It was discovered > independently in clevite by Cleve and Langley at about the same time. > Lockyer and Frankland suggested the name helium from the Greek word > "helios" meaning "sun" (1). > > Helium is a very light, inert, colourless gas element, having > the lowest known boiling and melting points. Helium is hypothesized to > be produced in the earth's crust by the radioactive decay of uranium and > other elements. It is also hypothesized that helium was produced during > the fusion of hydrogen when the earth was first formed. Either way, it > then gradually works its way into the atmosphere. Helium would be more > plentiful in air if not for the fact that its atoms are so light that > they keep escaping from the earth's gravitational field and moving off > into space. > > Concentration of helium in the atmosphere represents > approximately five parts per million. Due to low atmospheric > concentrations, commercial helium is obtained from natural gas deposits > which contain helium in concentrations above 0.03% by volume. > > Helium's main purpose as a diving gas, is to reduce the fraction > of nitrogen in a breathing mixture to reduce narcosis (2). Helium is > blended into a diver's mix to give a desired equivalent narcotic depth > compared to air. By reducing narcosis, a diver can retain motor skills > and mental concentration, thus adding safety to the bottom phase of a > dive. Adding helium (instead of nitrogen), also helps to reduce the > fraction of O2 in a divers' mix to make it surface hypoxic. At depth, > the diver will have less oxygen exposure. > > The best-known effect of breathing helium is its speech > distortion. The thinner gas passing across the vocal cords at > atmospheric pressure produce a comical high-pitched squeak reminiscent > of Donald Duck. The thinner gas affects the speed of sound as well as > flow turbulence (3). In fact, any change of air density can produce a > similar effect. Divers at a pressure of 40 m (132 ft) in a > recompression chamber will also produce distorted speech. Helium's > speech distortion is only relevant when through-water communications are > being used. Descramblers, called helium speech unscramblers/descramblers > (HSU or HSD) are commercially available to translate this distorted > speech (4-9). > > There is an apparent chilling during breathing. Dilutant gases, > such as helium or hydrogen, have low density but high specific heat > compared to nitrogen. This is again due to the thinner molecular > density of the gas, which transmits heat faster by direct conduction, > compared to air. The gas entering the diver's lungs will not conduct > heat out of the body as readily as air, there being fewer molecules to > warm up. Air by comparison is denser and may feel warmer when inhaled > at any given depth, but will transmit more heat out from the lungs (and > by that contribute more significantly to core heat loss) than helium > mixtures (10-14). The greatest contributor to convective respiratory > heat loss (Cr) is the temperature of inhaled gas more so than gas > density (15-17). Lung resistance (RL) increases are also linearly > related to cold-induced changes (18,19). > > Where helium-based mixtures can contribute significantly to heat > loss is when they are used as drysuit inflation gases, but overall the > use of trimix or heliox in drysuit inflation should be avoided at all > times. > > Helium's low molecular density has other practical advantages. > The thinner molecular structure of helium-based mixtures produces a > better regulator performance at depth by direct comparison with air. > Helium is less dense at 300 feet (91 meters) than nitrogen is at sea > level. The reduced density also makes breathing easier, and may help to > flush CO2 out of the lungs. CO2 has been implicated in deep water > blackouts (the Bohr Effect), and DCS. An increased partial pressure of > CO2 (PCO2) is dangerous. High levels can be reached in the lungs with > increasing depth, by improper breathing, increased gas density affecting > regulator, and pulmonary performance. Trimix/heliox can help reduce, > but not eliminate the problem (20). > > Some divers have a misconception that isobaric inert gas > counter-diffusion plays some adverse part when helium is used as a dry > suit inflation gas. Physical properties of skin as a diffusion barrier > for helium render such arguments void of merit. There are other more > pressing issues against helium's use in a drysuit. > > High pressure nervous syndrome (HPNS) is possibly the most > significant limitation to the use of helium as a diving gas. We do > know a little about HPNS, though the physiological process that creates > this syndrome is still not entirely understood. Helium has the lowest > lipid solubility and the lowest narcotic potency at 4.26. Xenon, which > has the highest narcotic potency at 0.039 is actually an anaesthetic at > atmospheric pressure, while krypton causes dizziness. > > Helium makes nerve cells "aggressive", which leads to HPNS, > nitrogen makes nerve cells "depressed" which leads to narcosis. Thus > trimix is created as a balanced or balancing gas. > > Pure helium should never be breathed during the blending > process, or at any other time. Irreversible asphyxiation may occur > because of the rapid diffusion of the gas into the lung tissues, > essentially blocking the passage of oxygen once the helium source is > removed. Helium can be breathed for months without tissue damage (21). > Helium for breathing purposes must be HP (hyper pure) or medical grade. > > I've invested 25 minutes in this, so I hope you appreciate it > Black. Before you disgrace the medical profession anymore with your > childish posts; try reading some of this research first. Man, I don't > know what medical school you went to, but I'm sure glad I got my > education somewhere else. > > -- > Randy F. Milak > Windsor, Ontario > > > (1) Lide DR, (ed.) in Chemical Rubber Company handbook of chemistry and > physics, CRC Press, Boca Raton, Florida, USA, 77th edition, 1996. > (2) Berghage TE, et al. Decompression advantages of trimix. Undersea > Biomed Res. 1978 Sep;5(3):233-42. > (3) Pasterkamp H, Sanchez I. Department of Pediatrics and Child Health, > University of Manitoba, Winnipeg, Effect of gas density on respiratory > sounds. Am J Respir Crit Care Med. 1996 Mar; 153(3):1087-92. > (4) Dejonckere P, et al. Mechanism of initiation of oscillatory motion > in human glottis. Arch Int Physiol Biochem. 1981 May;89(2):127-36. > (5) McGlone RE, et al. Vocal register "shift" identification in a > modified breathing atmosphere. J Acoust Soc Am. 1981 Feb;69(2):597-600. > (6) Rothman HB, et al. Speech intelligibility at high helium-oxygen > pressures. Undersea Biomed Res. 1980 Dec;7(4):265-75. > (7) Hollien H, et al. Voice fundamental frequency levels of divers in > helium-oxygen speaking environments. Undersea Biomed Res. 1977 Jun; > 4(2):199-207. > (8) Barry SJ, et al. Comparison of speech materials recorded in room > air at ground level and in a helium-oxygen mixture at a simulated > altitude of 18,000 feet. Aerosp Med. 1969 Apr;40(4):368-71. > (9) MacLean DJ. Analysis of speech in a helium-oxygen mixture under > pressure. J Acoust Soc Am. 1966 Sep;40(3):625-7. > (10) Hart JL. Salicylate hypothermia in rats exposed to hyperbaric air > and helium. J Appl Physiol. 1975 Oct; 39(4):575-9. > (11) Piantadosi CA, et al. Thermal responses in humans exposed to cold > hyperbaric helium-oxygen. J Appl Physiol. 1980 Dec;49(6):1099-106. > (12) Jammes Y, et al. Bronchomotor response to cold air or helium-oxygen > at normal and high ambient pressures. Undersea Biomed Res. 1988 > May;15(3):179-92. > (13) Naraki N, et al. Respiratory heat loss under hyperbaric > helium-oxygen environment (101 bar). Ann Physiol Anthropol. 1984 > Jul;3(3):227-36. > (14) Clarkson DP, et al. Thermal neutral temperature of rats in > helium-oxygen, argon-oxygen, and air. Am J Physiol. 1972 Jun; > 222(6):1494-8. > (15) Burnet H, et al. Relationship between inspired and expired gas > temperatures in a hyperbaric environment. Respir Physiol. 1992 > Dec;90(3):377-86. > (16) Brubakk AO, et al. Heat loss and tolerance time during cold > exposure in heliox atmosphere at 16 ATA. Undersea Biomed Res. 1982 > Jun;9(2):81-90. (17) Berezovskii VA, et al. Effect of helium on gas > exchange and tissue respiration. Fiziol Zh. 1982 May; 28(3):353-8. > Review. > (18) Jammes Y; Burnet H; Cosson P; Lucciano M. Bronchomotor response to > cold air or helium-oxygen at normal and high ambient pressures. > Laboratoire de Physiologie Hyperbare GS 15-CNRS, Facult�e de M�edecine, > Marseille, France. Undersea Biomed Res, 15(3):179-92 1988 May > (19) Burnet H, Lucciano M, Jammes Y. Respiratory effects of cold-gas > breathing in humans under hyperbaric environment. Respir Physiol. 1990 > Sep;81(3):413-23. > (20) Lanphier EH. (June 1958). Nitrogen-Oxygen Mixture Physiology, > Phases 4 and 6. Research Report 7-58. Navy Experimental Diving Unit. > Panama City, Florida 32407. > (21) Dejonckere P, et al. Mechanism of initiation of oscillatory motion > in human glottis. Arch Int Physiol Biochem. 1981 May;89(2):127-36. > -- > Randy F. Milak > Windsor, Ontario > ~Friends help you move; Real friends help you move bodies!~ > __________________________________________________ Do You Yahoo!? Talk to your friends online with Yahoo! Messenger. http://im.yahoo.com -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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