Rapid PO2 Change Theoretical Question

[NitrogenSweater]

Hello all,

I am NOT a technical diver (OW certified).. I am NOT doing technical diving, but I am playing around on pen and paper with planning deep technical diving and generating gas mixes (ALL ON PAPER).

I understand the limits on gas are determined by maintaining a PO2 in a tolerable range (~.21-1.4 ATA) and factoring in an equivalent narcotic depth of nitrogen (for my purposes (~.79-3.16 ATA).

In this theoretical dive, I would breathe compressed air down to 43 meters, where I would switch to 4/86/10 Trimix (of an ungodly price if this were a real dive). This mix would hopefully get me down to a whopping 300m (Po2=1.24, PN2=3.1). I would continue to breathe this mix on ascent until 43M, when I would switch back to compressed air.

My question is, would I THEORETICALLY run into issues changing mixes at 43M, going from a PO2 of ~1.1 to a PO2 of ~.21? Would a drastic change in PO2, even though both mixes should theoretically be safe, trigger physiological issues? What is the general way tech divers might deal with this?

Thanks for any input you might have. I am just messing around on paper here, math is not my strong suit, and I am NOT TRYING THIS.

 

[Whitrzac]

Step #1: Buy/read "deco for divers"

You would have deco stops deeper than 43m and run out of trimix long before switching to air.
And the PHE change would probobly give a nasty IBCD hit too

 

[inquis]

My experience is with dives shallower than 100 m, and even at that depth, the desire is for more efficient decompression than is afforded by the bottom mix. Your calculations are reasonable as far as ppO2 and equivalent narcotic depth go, but that's just the beginning of the things to consider. If you want to play with this hypothetically, pick a bottom time and see where your deco stops are in a planning application. Pick an intermediate gas mixture appropriate for that stop depth based on ppO2 and END. This figures into the amount of each gas you carry, which is the primary limiting factor on open-circuit. Even the relatively mundane aspect of staying warm has to be considered -- a drysuit for sure -- and the gas required to operate it.

I can only speculate about 300m, but rabbit holes you may wish to research: "High Pressure Neurological Syndrome" (though the little bit of nitrogen in your bottom mix helps in this regard) and "Isobaric Counter Diffusion" (though having intermediate deco gases based on ppO2/END/density helps here).

If you go down the tech path, you'll get plenty of opportunity to exercise your planning skills as part of the Advanced Nitrox / Deco Procedures and further certifications.

 

[lostsheep]

Step #1: Buy/read "deco for divers"


And the PHE change would probobly give a nasty IBCD hit too

Step #2: Buy "Deep into Deco" by Assar Salama

Your calculations are reasonable as far as ppO2 and equivalent narcotic depth go, but that's just the beginning of the things to consider.

I can only speculate about 300m, but rabbit holes you may wish to research: "High Pressure Neurological Syndrome" (though the little bit of nitrogen in your bottom mix helps in this regard) and "Isobaric Counter Diffusion" (though having intermediate deco gases based on ppO2/END/density helps here).

Sub'd

 

[NitrogenSweater]

Step #1: Buy/read "deco for divers"

You would have deco stops deeper than 43m and run out of trimix long before switching to air.
And the PHE change would probobly give a nasty IBCD hit too

Interesting. What would be the way to avoid IBCD in a deep dive like this. Could you cut out nitrogen altogether and exclusively use various heliox mixes throughout the dive?

Will get the above book and read through it. Thanks for the reply

 

[huwporter]

going from a PO2 of ~1.1 to a PO2 of ~.21? Would a drastic change in PO2, even though both mixes should theoretically be safe, trigger physiological issues? What is the general way tech divers might deal with this?

Answering, very specifically, ONLY the question about whether switching from a PO2 of 1.1 to 0.21 or vice versa would cause any issues - no, it would not. Technical divers routinely switch between mixes with greater differences of PO2 than this.

The PO2 change you describe is roughly equivalent to the PO2 change from going from breathing air to breathing oxygen on dry land - which people do for example every time they are 'put on oxygen' by a paramedic or whatever.

The diving scenario you outline to frame this question has an absolute host of other issues, but the jump in PO2 isn't one of them.

 

[jawaputih]

Interesting. What would be the way to avoid IBCD in a deep dive like this. Could you cut out nitrogen altogether and exclusively use various heliox mixes throughout the dive?

Will get the above book and read through it. Thanks for the reply

In regards to your question about Nitrogen, I'm not an expert, but I believe you need a bit of nitrogen too prevent something called HPNS (High Pressure Nervous Syndrome).

 

[inquis]

you need a bit of nitrogen too prevent something called HPNS (High Pressure Nervous Syndrome).

Or a VERY slow descent, one which is far too slow to not be on a tether (e.g., some Navy or commercial dives).