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.

But breath helium in the absence of oxygen and, just like if you breath
nitrogen in similar circumstances, you will become unconscious, have an
anoxic seizure, and die. It's the same mechanism as used by the suicide
who surrounds himself with non-burning natural gas in an oven. The
people you've seen get away with a breath or two of it on the residual
oxygen in their lungs and blood. They can't get away with it for long,
and there are a few deaths per year in the US from people persisting in
breathing toy-balloon oxygen for voice games. There are also a few
deaths to nitrous oxide breathing for intoxication, also for anoxia.

As others have noted, carbon monoxide is a metabolic poison and causes
problems even in the presence of normally adequate oxygen. Carbon
dioxide in high concentrations is primarily a dilutional asphyxiant but,
again as others have noted, also has metabolic toxic effects.

David


David Kazdan, MD, PhD
Anesthesiologist
Pilot

Roger wrote:
On Sun, 05 Feb 2006 17:50:04 GMT, Richard Lamb
wrote:


Might we go a bit farther?

The reason I ask is that I've seen people take big lungfuls of Helium,
which (obviously) doesn't produce the same effect.


A really big lung full can make you light headed in a hurry, but
beyond that?


Can someone explain why N is such a disaster but He doesn't?


"I think" it has to do with the partial pressure of He compared to N,
but I really don't know. There are warnings about inhaling He, but
I've not heard of any reactions like those of N2. Still, He is used
as an N2 replacement in diving air at times to reduce the likely hood
of getting the bends on deep dives.

There *must* be some one who reads this group who knows.


(Should have paid more attention in chemistry classes!)


I should have gotten better grades!

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com



Richard