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Hans Petter Roverud wrote:
> 
> At 09:49 PM 9/28/98 -0700, Esat wrote:
> >> Oops, He chill factor.  I don't thnk so unless U R using it in suit
> >> (now tht qualifies as dumb).
> >>
> >> Once again: Heliox does not increase respiratory heat loss.
> >> Yes Joel that is a fact.
> >
> > John replied:
> >  Esat, try diving.  Their is tooo a chill factor even when you use a
> >light He mix.  I have noticed this while switching back to mix for my
> >breaks on O2 usually within 1 minute.  Its very noticable and you can
> >see for yourself once you put down the tech books and go diving.
> 
> Helium has a higher heat conductance and a lower heat capacity. This means,
> helium conducts heat faster but it costs less energy to heat. Whatever gas
> goes into your lungs will be heated to core temperature anyway, thus heat
> capacity is the relevant number. Esat is right, it costs less energy to
> heat the helium. However, John is right also in pointing out that there may
> be a perception of cold. This is because helium draws heat faster, from
> areas where you are able to feel it. Your mouth feels the heat loss while
> your lungs don't since there are few (if any) thermo-receptors in your lungs.
> 
> Helium equilibrates in your mouth/ upper respiratory airways while
> air/nitrox draws heat from the lungs. You feel the chill of helium while
> you lose more heat breathing air/nitrox, drawn from areas where you can't
> feel it. Any deep diving presents respiratory heat loss problems, however,
> air would have been even worse at great depths (and you sure wouldn't feel
> a thing!).
> 
> In sat diving there's a treacherous problem with heated hot water suits and
> unheated gas. As long as your peripheral tissues stay warm you'll feel
> warm, irrespective of your core temperature. Thus, you may go severely
> hypothermic without knowing. As for oxtox, the body is not designed to
> react to problems that never happen in normal life. On land, cooling
> affects the periphery first. There's no need to monitor lung temperature.
> As long as the skin stays warm the brain decides you're OK. Conversely,
> when you draw heat from any peripheral tissue, lips/mouth included, you
> sense the chill even when the cooling is insignificant.
> 
> regards,
> 
> Hans
> Norway

   Obviously I am no physisist(or english major)but what I've felt goes
beyond my lips and mouth.  I have felt this throughout my torso.  When I
first entered the trimix realm I was told that He was a thermal
convector only if used as an insulating gas. It sure seems to me that it
removes heat from my body, most noticably wene I switch back and forth
from O2-He-O2-He ect. on my deco's.  I first noticed this by accident
and the chill came on in about 1 minutes time.  

      Thanks for you imput,  John Walker
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