no nitrogen breathing gas ?

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RumBum:
Rick - if you see something incorrect, rather than just saying it is incorrect maybe you could enlighten us? We learn nothing by just being told that something somewhere in this thread is wrong. :05:
It isn't worth it. For example, a discussion of Helium's specific heat and the relationship between that and mass vs mole in-lung (and therefore breathing) relative heat loss between breathing gasses with and without helium would (1) take too long and (2) yield results insignificant to the overall discussion at this level of detail. If anyone says anything dangerous and I see it I'll say so.
My point is that we're not going to teach a mixed gas class in this thread; if one is interested in the finer points then the course is where to find it. (Well, sort of... there are some rather egregious - for a phyics fanatic - errors in the texts I've seen, too, but not harmful ones.)
In diving we often measure with a micrometer, mark with chalk and cut with an ax.
Rick :)
 
Rick Murchison:
It isn't worth it.... there are some rather egregious - for a phyics fanatic - errors in the texts I've seen, too, but not harmful ones.)
Rick :)

Okay, I am not trying to learn how to dive mixes from this thread, but I totally find it interesting. I like the physics of diving, but I have no desire to go deep enough to use a trimix or heliox. I probably should read some books on it, but I find technical reading very difficult.

The original question for this thread was

caribou:
at recreational depth (say 120 feet), if we were to breath 21% oxygen, 79% helium (or any other inert gas, excluding nitrogen), asides from the problem of getting such a fill, would it eliminate NDL ?

Or would we see the same problem, i.e. the helium goes into solution in the bloodstream, and creates bubbles as the pressure decreases, prompting the need to create tables again...

if not then, since 21% oxygen isn't toxic at this depth (120 feet), what else could prevent us from staying down as long as the gas supply allows and then ascend slowly back up.

so (beginner disclaimer) the answer would be YES there are mixes of other types of gas that you can breath for diving. It not reasonable to dive helium at a depth of 120 feet due to the long deco time you would incur for a very brief dive. So helium has faster on-gassing and slower off-gassing properties than nitrogen? Nitrox mix, however does extend your NDL. Is there a table that shows the speed at which different gasses build up in tissue? Ox-tox is not an issue at recreational limits as long as you are breathing 21% O2; but you can survive with as low as 12%, right? I was just now trying to extrapolate the formula for oxygen partial pressure at depth, but got myself confused. I am probably trying to get too technical again for my current knowlege level. Like I said before, though, I just think this stuff is really interesting. I think I am ready to take Nitrox classes now. :D
 
RumBum:
Okay, I am not trying to learn how to dive mixes from this thread, but I totally find it interesting. I like the physics of diving, but I have no desire to go deep enough to use a trimix or heliox. I probably should read some books on it, but I find technical reading very difficult.
The original question for this thread was
caribou:
at recreational depth (say 120 feet), if we were to breath 21% oxygen, 79% helium (or any other inert gas, excluding nitrogen), asides from the problem of getting such a fill, would it eliminate NDL ?
Or would we see the same problem, i.e. the helium goes into solution in the bloodstream, and creates bubbles as the pressure decreases, prompting the need to create tables again...
if not then, since 21% oxygen isn't toxic at this depth (120 feet), what else could prevent us from staying down as long as the gas supply allows and then ascend slowly back up.
so (beginner disclaimer) the answer would be YES there are mixes of other types of gas that you can breath for diving. It not reasonable to dive helium at a depth of 120 feet due to the long deco time you would incur for a very brief dive.
Ok.... the answer to the first question, "would it eliminate NDL ?" is no.
The biggest reason to not use Heliox at recreational depths is more that the cost-to-benefit doesn't compute, as well as the impact on decompression time. As an example, using one currently popular decompression algorithm, a 20 minute bottom time at 120 feet on air would require stops totalling 17 minutes. Using Heliox at 21% Oxygen would add 12 more minutes - a total of 29.
But... let's look quickly at some other alternatives, both cheaper than Heliox-
With a PO2 max of 1.4 ATA, your best mix for such a dive using Nitrox would be EAN 30, and your required deco obligation would be 5 minutes.
And for the "best of all worlds" we could reduce our narcotic depth to about 75 feet (using the N2+O2 method) and reduce our deco requirement to 2 minutes (a normal safety stop would suffice) by using 30/30 Trimix (That's "Triox" for you NAUI trained folks).
RumBum:
So helium has faster on-gassing and slower off-gassing properties than nitrogen?
The "faster ongassing" common knowledge is, even as we type, undergoing research and revision, with the latest research showing some fascinating counter-intuitive results. The jury's still out but it may be that we'll have to do some major rethinking on Helium on and off-gas rates.
RumBum:
Nitrox mix, however does extend your NDL. Is there a table that shows the speed at which different gasses build up in tissue?
There are theoretical tissue models from which tables can be produced, but every real cell in a real living organism will have its own rate on any given day under any given set of circumstances - so a table isn't practical for real live tissue(s).
RumBum:
Ox-tox is not an issue at recreational limits as long as you are breathing 21% O2; but you can survive with as low as 12%, right?
At one atmosphere.. so you're really asking about survival at .12 ATA oxygen. The answer is "highly variable" - and there's a difference in survival and functioning. Most folks can function well down to about .16 with moderate exertion.
RumBum:
I was just now trying to extrapolate the formula for oxygen partial pressure at depth, but got myself confused.
Let's keep it simple. PPO2 is the fraction of oxygen (FO2) times the actual pressure in atmospheres (ATA). In feet, you get atmospheres with depth/33 + 1. So at 99 feet you have 99/33 +1 or 4 ATA, and with air you have PPO2 of .21X4=.84
RumBum:
I am probably trying to get too technical again for my current knowlege level. Like I said before, though, I just think this stuff is really interesting. I think I am ready to take Nitrox classes now. :D
It is fascinating. Have fun with it.
Rick :) (Make mine an Appleton's)
 
This is cool stuff, thank you! :D
 
RumBum:
I haven't taken any courses yet for air mixing, but let me take a stab at this and y'all tell me if I have it all wrong...

essentially, there is Nitrox, Heliox, and Trimix. They are used to extend NDL and/or to allow safety with deeper dives (depending on the mix). Each mix has its own set of tables. You are still loading on gasses that your body cannot metabolize so you have to have deco time to offgas before surfacing.

Correct me if I'm wrong...

The following inert gases have been used as a replacement for Nitrogen: helium, argon, hydrogen, neon. Could be some others. Hydrogen and O2 do not play nicely together if there is too much of either. Argon is wickedly narcotic. Neon can be a real drag from a re-compression standpoint if you get bent. Helium seems to be the most user friendly. But even HeliOx presents problems; like HPNS which ironically is somewhat softened by adding a bit of N2 to suppress your jangled nerves.
 
Green_Manelishi:
The following inert gases have been used as a replacement for Nitrogen: helium, argon, hydrogen, neon.
Hydrogen ain't inert. :)
Rick
 
Rick Murchison:
Hydrogen ain't inert. :)
Rick

Correct. I should not have included that rambunctuous element with true nobility.
Mea Culpa. Thanks for reminding me. And while we are at it, could you please tell others that "mil" is not the same as MM ;-)
 
Green_Manelishi:
The following inert gases have been used as a replacement for Nitrogen: helium, argon, hydrogen, neon. Could be some others. Hydrogen and O2 do not play nicely together if there is too much of either. Argon is wickedly narcotic. Neon can be a real drag from a re-compression standpoint if you get bent. Helium seems to be the most user friendly. But even HeliOx presents problems; like HPNS which ironically is somewhat softened by adding a bit of N2 to suppress your jangled nerves.

Heliox has its problems, like it is stated above: HPNS, cost, bad insulator in suits. 50/50 is a very good choice for deco.
Trimix counters HPNS, supposedly by getting you just narced enough so the helium excitement is no problem.
But by far the deepest dives have been conducted with hydrogen (Comex).

ciao, mart
 
Green_Manelishi:
could you please tell others that "mil" is not the same as MM ;-)
Well, sure, I could.... but it wouldn't do any good :)
Rick (45°/450Kts/4000AGL/107mils)
 

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