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Kevin, I think you are quite right that Heliair isn't the "perfect" gas because it locks you into a very rigid set of mixtures as you pointed out in your chart. In some cases, however it might be a reasonable way to go. Try this on for size, unless my math is wrong (wouldn't be the first time :) I think the gas you suggested (12/40) would actually be quite suitable for use at 200 fsw. Correct me if I am wrong but I think the formula is: Atmospheres Absolute (ATA) X % (Percent of Gas in Mixture) = PP (Partial Pressure) If we want an equivalent nitrogen depth max of 100 fsw then we would be looking at a PP of 3.16. 4 (ATA) X .79 (%) = 3.16 (PP) Breathing 12.6 / 40 / 47.4 at 200 fsw you would have a N2 PP of 3.318 which would result in an END of 105.6 fsw. 7 (ATA) X 47.4 (%) = 3.318 (PP) 3.318 / .79 = 4.2 (ATA) ( 4.2 -1) X 33 = 105.6 fsw (END) You would have an O2 PP at this depth of .882 which would be fine. Remember your O2 PP at the surface breathing air is only .21 . On the other hand the 18/40 you mentioned would give you an O2 PP of 1.27 and if you strayed down to 220 it wold take you right to the edge for a working dive with a PP of 1.379. Remember air maxes out at 218 fsw as far as O2 PP goes. 7.6 (ATA) X .21 (%) = 1.59 PP ( O2 PP of 1.6 at rest considered the max ) One down side to the 12/40 mix is that this mix is hypoxic from the surface where your O2 PP would be only .126 until you got to about 20 fsw where it would increase to .20 . Consequently you need something else to breathe from 0 to 20 and from 20 to 0. Comments anyone??? Dave Dalton ----- Original Message ----- From: Kevin Connell <kevin@nw*.co*> To: <tgunther@co*.co*> Cc: <techdiver@aquanaut.com> Sent: Thursday, December 30, 1999 5:32 PM Subject: Re: HELIAIR > Heliar is DIW. There is only one depth that the heliar mix curve matches > PPO2 and END, and it's not anywhere under 200fsw. > > Here is a mix chart for heliar for a 3000psi tank (I think) > (ftp://ftp.nwls.com/pub/kevin/mixing.xls) > > He psi he% n2% o2% > 100 3.3% 76.4% 20.3% > 200 6.7% 73.7% 19.6% > 300 10.0% 71.1% 18.9% > 400 13.3% 68.5% 18.2% > 500 16.7% 65.8% 17.5% > 600 20.0% 63.2% 16.8% > 700 23.3% 60.6% 16.1% > 800 26.7% 57.9% 15.4% > 900 30.0% 55.3% 14.7% > 1000 33.3% 52.7% 14.0% > 1100 36.7% 50.0% 13.3% > 1200 40.0% 47.4% 12.6% > 1300 43.3% 44.8% 11.9% > 1400 46.7% 42.1% 11.2% > 1500 50.0% 39.5% 10.5% > > as you can see, none of these mixes make any sense. > > For example, a mix for 200fsw would be something like 18/40, and you can't > get the right combination here. You could dive 12/40, but that is a little > low on the O2, and unnecessarily hypoxic. > > > > At 01:26 PM 12/30/1999 -0800, you wrote: > >Team: > > > >I am told that many members create their own mixes using personal cascade > >systems. > > > >Because heliair would probably be the easiest introduction to this method, and > >also increase the safety of ones mix (only interested in < 200fsw at this > >point), I was wondering if anyone would like to share their experiences in > >this > >area. Pros, cons, concerns, applicability, etc. > > > >Thanks, > >Tod > > > > > >-- > >Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > >Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. > > > ---------------------------------- > Kevin Connell <kevin@nw*.co*> > > NW Labor Systems, Inc > http://www.nwls.com > > > ---------------------------------- > > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. > -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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