as a representative "math weenie" all i have to say is.... nope. gave him a starting point for a mathematical model that can at least reproduce IBCD on paper and he just completely ducked it. yapping about anything else is fairly worthless.
w0rd.
still not sure why if he wants to do these dives and he has it all figured out, that he's yapping on this forum when he clearly thinks he's brilliant and we're all idiots. apparently this is some kind of voodoo that if he insults enough people on scubaboard, he thinks he won't get bent or something....
he's also ducking going over to the GUE forum to have a talk with the people involved in the 1999 paper he quotes like gospel and the people who have the real experience at pushing this level...
The base mathematical "model" was posed in my original question Lamont (and it's a simple, relevant, & elementary arithmetic incongruity that you have failed to adequately answer with your meaningless rhetoric above):
Again, the simple logical means to an end --if you're trying to off-gas Nitrogen loading from your bottom mix, why are you switching to a intermediate "standardized deco gas" with significantly more Nitrogen than your bottom mix???
Wow, Kev, even had I the stomach to attempt to make any sense of that. I'd probably take me a week.
Still see you quoting percentages of a gas when PPN2 would actually make sense (I don't think my organs are that great with percentage calculations)
The simple fact is, for moderate exposures this stuff works fine, and for longer bottom times, adding extra He to the deco mixes (without adding O2 and incurring a PPO2 of 1.6 at depth) is a very easy step to take that still doesn't violate the standard gases model yet still works.
I honestly don't think this Trimix deco is quite as complex as you are attempting to make it as long as you stick to reasonable assumptions, calculations and procedures.
why not go out and do some dives in the ranges that require those deeper bottle switches and let us now how it goes, instead of (potentially mis-)quoting a bunch of theoretical papers.
In trying to solve a problem that for most dives is a non-problem, and for others can be easily overcome, you are sure introducing a lot of complexity.
And also, how do you bring along the best mix of gases for a multi-level dive ? Just did on to 200 yesterday where we spent say 10 mins at 200, 10 at 170 and 10 at 150. Do I now need 3 different sets of deco gases with different O2 and He percentages to make sure I'm not going to die .....
No Nick, you just bring whatever bottom mix you need for you MOD and accordingly plan your deco gases with decreasing inspired inert Helium & Nitrogen (and Oxygen tolerable to established ppO2 limits and practice).
The simplest practical rule of thumb is not letting your inspired ppN2 change by 0.5 bar or more at the switch from bottom mix to the intermediate deco trimix. Ross Hemingway does this in V-planner (refer to link
http://www.scubaboard.com/forums/ask-dr-decompression/366427-inner-ear-dcs-2.html#post5692197), but according to Mark Powell in Deco for Divers p.195, this value is a purely arbitrary value --and IMO "snap-shot" limit.
A very good valid & practical rule based on the deco properties of Helium and Nitrogen is discussed in Deco for Divers p.195:
A more recent approach suggested by Steven Burton attempts to put a limit on the relative changes in gas composition. The allowable changes are based on the physical properties of nitrogen and helium. As we have seen, Helium is a fast gas and will diffuse in and out of a tissue approximately 2.65 times faster than nitrogen; however nitrogen is approximately 4.5 times more soluble in lipid tissues than helium.
Burton's approach is based on the fact that the quantity of a dissolved gas in a fixed volume of a saturated tissue is equal to the current saturation pressure multiplied by the solubility factor in the medium. Obviously the total quantity of dissolved gas is the sum of the quantity of each of the inert gases present. When switching from a high helium mix to a high nitrogen mix, the higher solubility factor of Nitrogen offsets the decrease in pressure of Helium. This results in an increase in the total quantity of dissolved gas. As nitrogen is approximately 4.5 times more soluble than helium, Burton proposes that by increasing the nitrogen percentage by no more than 1/5th of the reduction in the helium percentage, then the total quantity of dissolved gas will not increase and hence an IBCD event can be avoided. The permissable percentage increase in nitrogen for a given percentage helium reduction is given in the table below:
[table00]
%He Gas reduction:|
Permissable %N2 increase:
10|2
20|4
30|6
40|8
50|10
60|12
70|14
80|16
90|18
[/table]
Again, the simple logical means to an end (and by the easy to use table above based on the physical deco properties of Helium & Nitrogen) --if you're trying to off-gas Nitrogen loading from your bottom mix, why are you switching to a intermediate "standardized deco gas" with significantly more Nitrogen than your bottom mix???
Why do you use an intermediate deco gas (21/35) that has a higher fN2 than your bottom mix (12/60 or 10/70 trimix in this case, a dive to 90m/300')???
---->(i.g. 12/60 or 10/70 bottom mix have a fN2 of 28% and 20% respectively, while 21/35 intermediate trimix deco gas has an fN2 of 44% --why are you switching to a deco gas that has more Nitrogen percentage wise, than that of your bottom mix???
Coming off a bottom mix of 12/60 or 10/70 to standard intermediate deco trimix 21/35 --look at the fraction of Helium: you have a concentration of either 60% (if using 12/60) or 70% (10/70), and upon switching to 21/35 on deco at 57m you have a Helium fraction now of 35%. You have now a decreasing concentration gradient, going from 60 or 70% Helium in the bottom mix to a lesser inspired gradient of 35% in the intermediate deco mix of 21/35, which is the proper tactic for off-gassing the Helium from tissues. That's a given, noted and understood . . .
---->By this tactic above for decreasing the inspired gradient of the inert Helium then, --why can't you do the same simultaneously with the inspired inert Nitrogen?
