Posted by SLANG on October 10, 2000 at 17:15:41:
In Reply to: Re: Effect of Helium posted by Eins on October 09, 2000 at 22:43:39:
>>"One question though: what is the current status of knowledge on the effect of He to the human
I'm no expert, but this is what I do know. "He" has been used in connection with military / commercial / research diving for quite some time and its physiological effects have been well documented. In 1919, a guy named Elihu Thomson first theorized that helium might be able to be substituted in a diver's breathing mix to avoid the problems that were just then becoming known regarding the effects of nitrogen on divers. In 1924 the US Navy and the Bureau of Mines first sponsored experiments with helium-oxygen mixtures. Those first tests were conducted first on animal and then on human test subjects and the results showed no evidence of serious negative effects from the use of heli-ox, with reduced narcotic effects and significantly shortened decompression times.
Helium is a completely inert gas, which you probably already know means that its chemistry is such that it has little or no tendency or ability to react with other chemicals. This means that it can be used as a "filler" gas in a breathing mix to dilute oxygen to avoid the well-known negative effects of breathing pure oxygen under pressure. It also does not have the narcotic properties of nitrogen that become apparent when N2 is breathed under pressure.
Here is an excerpt from the US Navy dive Manual, §2-10.4:
"Helium (He) is a colorless, odorless, and tasteless gas, but it is monatomic (exists as a single atom in its free state). It is totally inert. Helium is a rare element, found in air only as a trace element of about 5 parts per million (ppm). Helium coexists with natural gas in certain wells in the southwestern United States, Canada, and Russia. These wells provide the world's supply. When used in diving to dilute oxygen in the breathing mixture, helium does not cause the same problems associated with nitrogen narcosis, but it does have unique disadvantages. Among these is the distortion of speech which takes place in a helium atmosphere. The "Donald Duck" effect is caused by the acoustic properties of helium and it impairs voice communication in deep diving. Another negative characteristic of helium is its high thermal conductivity which can cause rapid loss of body and respiratory heat."
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