Heliox Decompression and HPNS: one view, was Re: xenonauts

From: Michael M. Butler (butler@comp-lib.org)
Date: Thu Jul 05 2001 - 22:17:26 MDT

Excerpted from

http://www.mtsinai.org/pulmonary/books/scuba/sectionl.htm :

Heliox is a mixture of helium and oxygen used for very deep diving, usually to greater than 200 feet.
Helium's great advantage is that it does not lead to nitrogen narcosis. Helium diving requires as much
or more decompression time as nitrogen, so there is no saving there. Beyond 300 feet heliox may cause
the 'high pressure nervous syndrome', a shaking sensation that can be incapacitating. Another
disadvantage of helium is that it conducts heat about six times faster than nitrogen, so divers get colder
than with air diving. A third problem is caused by the fact that helium is much less dense than
nitrogen or air; as a result, the vocal cords vibrate much faster and divers sound like Donald Duck.
Professional divers can use voice unscramblers to make their speech intelligible.
Trimix is a mixture of oxygen, helium and nitrogen. Nitrogen, usually in a small percentage (e.g., 15%),
is added back to heliox to create trimix, in order to lessen the risk of the high pressure nervous syndrome seen with
helium breathing. Nitrogen slows down nerve conduction.

...I'm still working on the noble gas tox info.

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