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On Sat, 21 Oct 1995, Mark Caney wrote: > For several years now I have used chemical heat packs inside my drysuit for >.... i am not familiar with the packs you describe, but, if they rely on oxidation as a heat source, your observations seem consistent. certainly, the catalized eutectics, sold as active diver-heating systems, and enclosed in polyurithane, are not sensitive to suit gas though. as far as ambient pressure affecting the heat-generating liquid-solid phase transition in these packs, you would need to look at the phase diagram--or listen to field experience: the packs give off heat at diving pressures, so forget the chemistry.... the main concerns here should be physiology (and psychology!), rather than chemistry. diver warmth is the result of a sum of thermal pluses and minuses. if you add a bit of active heating to one area, what if your brain thinks that your whole body is "warm" and increases blood flow to poorly insulated extremities where cold water conducts away more heat than you put in? two excellent discussions of thermal issues in diving are: 1) Bob Stinton's (of DUI) talk at tek95: "Thermal Protection"-you can order a tape of his talk for $10 from aquaCOMIX 2) B. Aspacher's article in the iantd journal a year ago i've used the poly-u paks for 1 hr-long new-year's dives in lake tahoe in near near freezing water and stayed warm. but maybe it was the argon.... regards, em _____________________________________________________________.sig Eric Maiken email: eapg243@ea*.oa*.uc*.ed* Dept. of Physics o: 714 824-6621 U of California fax: 714 824 2175 Irvine, CA 92715-4575
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