OP
impulse
Guest
No I know what you mean. But I ask about the descent gas consumption.
Determining Gas Supply - Question
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Descent gas is part of your bottom gas calc.
As noted above pretty much everyone assumes the descent is included in the bottom time. This is particularly true if you are using run times.
On ascent, agencies tend to vary with some recommending you use the same gas calculation as your max depth to pad things a bit while others want you to use the average depth between the bottom and the first deco stop and then include the deep stop. You could get real picky and figure each 3m/10' or use calculus to solve the rate/change problem, but no one does it that way in real life, at least manually - some gas planning programs do exactly that and if that is the case you need to be aware there may no longer be the pad you got used to.
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The deco schedule is clearly a stock US Navy air decompression schedule with long shallow stops and no deep stops, but I think that happens with a couple other agencies as well where they will do the academics and course materials with a "standard" table everyone will have (now and several years in the future) but then rely on the instructors to actually teach and use something a bit more modern and more appropriate to accellerated decompression procedures.
The important thing to realize here is that you would not use a straight US Navy air decompression table with 50% and 100% O2 without adjusting the stop times. If you used the normal stops, in particular the long 3m/10' and 6m/20' stops, with 100% O2 the oxygen toxicity issues and risks are far our of proportion to the benefits. In general, the 3m/10' and 6m/20' stops on an air decompression table will be about half the time if using 80-100% O2 for the deco gas.
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The air versus helium at 45m/150' issue to a great extent reflects the relative wealth in helium in the US versus most of Europe. and the rest of the world for that matter. We Americans tend to have the flaw of seeing ourselves as being the center of the universe and some among us make it worse and live up to the "ugly american" image by looking down their noses at those who may not agree with them.
It's not all bad news however as I assume that most of the GUE set, if they truly live the doctrine, will elect not to dive below 30m/100' in Europe when they can't get helium at all or at best only at outrageous prices, so the 45m/150' wrecks in Europe won't be very crowded with self-centered Americans.
On ascent, agencies tend to vary with some recommending you use the same gas calculation as your max depth to pad things a bit while others want you to use the average depth between the bottom and the first deco stop and then include the deep stop. You could get real picky and figure each 3m/10' or use calculus to solve the rate/change problem, but no one does it that way in real life, at least manually - some gas planning programs do exactly that and if that is the case you need to be aware there may no longer be the pad you got used to.
-----
The deco schedule is clearly a stock US Navy air decompression schedule with long shallow stops and no deep stops, but I think that happens with a couple other agencies as well where they will do the academics and course materials with a "standard" table everyone will have (now and several years in the future) but then rely on the instructors to actually teach and use something a bit more modern and more appropriate to accellerated decompression procedures.
The important thing to realize here is that you would not use a straight US Navy air decompression table with 50% and 100% O2 without adjusting the stop times. If you used the normal stops, in particular the long 3m/10' and 6m/20' stops, with 100% O2 the oxygen toxicity issues and risks are far our of proportion to the benefits. In general, the 3m/10' and 6m/20' stops on an air decompression table will be about half the time if using 80-100% O2 for the deco gas.
----
The air versus helium at 45m/150' issue to a great extent reflects the relative wealth in helium in the US versus most of Europe. and the rest of the world for that matter. We Americans tend to have the flaw of seeing ourselves as being the center of the universe and some among us make it worse and live up to the "ugly american" image by looking down their noses at those who may not agree with them.
It's not all bad news however as I assume that most of the GUE set, if they truly live the doctrine, will elect not to dive below 30m/100' in Europe when they can't get helium at all or at best only at outrageous prices, so the 45m/150' wrecks in Europe won't be very crowded with self-centered Americans.
Last edited:
OP
impulse
Guest
Thanks for all the answers. I really have a long way to go about Tec Diving.
Need to read books about maybe decompression rules, gas calculations etc...other thanthe PADI Tec Deep Diver manual....Any advice?
Need to read books about maybe decompression rules, gas calculations etc...other thanthe PADI Tec Deep Diver manual....Any advice?
PfcAJ
Contributor
Pick your reads carefully, there is a lot of nonsense floatin' about.
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