Nitrox for cold water diving

[alo100]

For cold water divers who maybe able to tell me more.
About the influence of low temperature over the gas mix, I'm not worrying about the max pressure allowance of a gas, but the min allowance... since the temp in water is lower; I'm thinking about the lower limit... min pressure allowance, the low temp makes the pressure lower than on land.
e.g. When we clac for the lower limit of a certain gas (e.g. Pmin of O2 in safety range and the corresponding depth) in gas mix, the decrease of temp in water can cause a lower pressure to happen... any hint?

 

[Thalassamania]

The change in temperature between hot (35 C) and cold (0 C) represents a change in pressure from 3000 PSI to about 2700. All gases in the mix change proportionately so the fractions do not change. What's your question?

 

[alo100]

Thanks! Did you just answer my question?
This is all new to me, I am just trying to figure out.
Let's say I calculated the range of depth I can use for a particular mix -- watching the PP02max = 1.6 and PP02min = 0.24 for 13 degree C.
Now I use the bottle for cold water, much colder, do I need to use something like:
P1/T1 = P2/T2 to figure out the new valid range of depth?

I think you have just stated that I can use T2/T1 and multiply on both sides of the Dalton's partial pressure formula. Is that right?
Or as long as we are warm enough this is not a concern (the gas we breath in would warm up in the body)?

 

[TSandM]

alo, you are thinking about the behavior of GASES with temperature, but what determines the pressure at depth is the behavior of WATER. Water is all but incompressible, and the pressure at 33 fsw is going to be 2 atmospheres regardless of water temperature, at least within any range of measurement accuracy with which a diver needs to concern himself.

So the answer is that no temperature correction is needed for calculating ppO2 or MOD.

 

[alo100]

Yes, tsandm, I was thinking about gases only, you are directing me to the right direction, now it's gases interfacing water, and even our lungs.

Let me show you what I am thinking... how depth and temperature influence the gas:

Let all of us sit besides a table inside a building, and you pull out an empty flask, the air inside is the same as outside approx 1 atm. He uses a plastic stopper and seals the opening. The air inside the flask is still approx 1 atm. Next step, all of us use a burner to heat the flask, "pop", the stopper flys away because the pressure within the flask builds up to something > 1 atm.

Then we go to the top of the 48 stories tall building. The pressure there is around 0.999....8 atm. Air pressure inside is 0.999....8 atm. We repeat the experiment, use a stopper to seal the flask, turn on the fire to heat the flask.... "pop".

If I said, please don't heat my tank up while I am diving, tsandm, I am tired of the "pop" sound.... you see what I mean, right?


Now something I am thinking..... the gas inside the tank we are diving with, in the sea, the temp and pressure outside then the temp and pressure inside the tank, and I take a breath, the gas go through 1st stage, 2nd stage, pressure and temperature now, and the gas enters my lung....

 

[matt_unique]

Water Temp is only a consideration for thermal protection, not for deco gasses or any other aspect of deco planning.

--Matt

 

[Xman]

alo100, you are making a question where there really isn't one. The temperature of the gases makes zero difference to calculations made regarding those gases, except when filling for maximum pressures (and, I guess for the fact that we then want to use the gas pressure once cooled to normal when calculating gas plan)

 

[PvilleStang]

Heat or cold won't change your PPO2 or PPN2, since its the Partial Pressure, in respect to the entire mix. You take a breath, and you ideally will inhale equal parts of each portion of the breathing mix, leaving you with the same mix you started with, just at a lower pressure.

 

[AquaHump]

The gas will expand with heat and compress under pressure. Also reduce in volume in cold but the property of the gas stays the same. There would be no partial pressure differences. Even as the gas worms from the cold tank to your worm lungs.

:h2o:

 

[alo100]

I posted the question mainly wanted to know if the cold water divers would do anything differently in caluculation and I think the answer I got is nothing much. No even a bigger margin for the max min pressures for O2 or N2.

About the pratial pressure, of course the partially pressure equation holds even the temp of the gas change -- the abosolute/total pressure (R.H.S of the formula) increased due to high temp, the corresponding partial pressures (L.H.S) increased correspondingly. I guess a lot of times, when we do this kind of calc. we assumed that the env is under a fixed given temp. Then like what TSandM mentioned, I pay attention only to the gases only, yes, I even asked a silly question to one of the gentleman here, "shall I concern the density of the water because of difference in temp?", for the L.H.S we deal with fsw, feet of salt water, or feet of fresh water... or in some high school exercise, mmHg....

I am sure eventually the gas come out from the tank, 1st stage, then 2nd stage would reach the same pressure as the outside env ... like in my example, after the gas got heated up (high pressure) and rushed out from the flask, eventually when its kinetic energy used up (another nerdy saying), the gas pressure got back to normal (a pressure corresponding to its particular altitude). The situation I am thinking is when the cold gas reached our lungs, the biological effect. Plus, I am not an expert on biology, including narcosis -- "intoxication at depth; occurs at any depth, but in most cases doesn't become noticeable until at deeper depths. The precise mechanism is not well understood, but it appears to be a direct effect of high nitrogen pressure on nerve transmission..... can happen when we are explosed to Ar, H2, N2..."

... and we give ourselves numbers for the max/min pressure of e.g. N2, not to reach these numbers ....