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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 -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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