Hi David,

David Kazdan wrote:
Helium is almost exactly the dilutional asphyxiant that nitrogen is.
It's used in deep-diving artificial atmospheres for two reasons:
Nitrogen is a weak anesthetic gas, producing intoxication at several
atmospheres pressure--(nitrogen narcosis"), and it's soluble enough in
blood and other water-based body fluids to fizz out when the pressure is
released suddenly (the bends, caisson worker's disease). "Helium has
neither of these properties."

snip

David


David Kazdan, MD, PhD
Anesthesiologist
Pilot

I hesitate to enter this discussion since you are obviously well
qualified, however, that is often how learning occurs and I still
have a lot to learn.

I agree with all of your excellent post with one minor exception.
Helium _is_ absorbed into the bloodstream under high enough partial
pressure and does release bubbles when the pressure is released
too quickly. Heliox (Helium + O2) and Trimix (Helium + N + O2) are
common gasses used in the technical diving community, and they both
require decompression stops on the way back to the surface. Technical
divers use these mixes for dives from 130' (~5 atmospheres) to as much
as 1000' (~31 atmospheres). The O2 content of the mixes is reduced to
avoid oxygen toxicity effects at high PPO2. I also would point out
that helium at high PP--although not narcotic like Nitrogen--does
produce some strange physiological effects including a "buzz" similar
to having had a lot of caffein.

Don Woodbridge P.E.
Engineer
Technical Diver
Pilot