High altitude decompression diving

[inquis]

I emailed SW a couple days ago, just waiting to hear back.

 

[lostsheep]

I emailed SW a couple days ago, just waiting to hear back.

Excellent, I was going to do the same

 

[rjack321]

Mountain climbing acclimation for high mountains is not a few hours, it’s days to weeks and involves climbing and descending, or climbing, remaining overnight and descending again. You apparently become acclimatized mostly by your body making more red blood cells.

A chart sourced to the CDC has this:

From sea level, here is the average amount of time it takes to become FULLY acclimatized to altitude:​

• • 6,000 ft (1829 m) — 3 Weeks
• • 8,000 ft (2438 m) — 4 Weeks
• • 10,000 ft (3048 m) — 5 Weeks
• • 12,000 ft (3658 m) — 6 Weeks
• • 14,000 ft (4267 m) — 7 Weeks

Offgassing N2 from your sea level life doesnt take weeks. That's what most people are concerned about which is completely different than adapting to a lower ppO2 by enhanced red blood cell production. Once you start a dive you're not really limited by ppO2 anymore. Although... I am not generally anxious about breathing 15/55 at sea level for a minute on the surface (eg I never used another gas to get to the 1m minimum operating depth) I would not really want to do that at 8000+ft. But I also won't be doing an OC dive at 15/55 depths at 8000ft nowadays either - so its kinda irrelevant.

 

[lostsheep]

We should differentiate between OFF GASSING due to an increase in elevation vs ACCLIMATIZING to lower atmospheric pressure / PO2.

 

[inquis]

On the topic of tissue update during the drive to altitude (i.e., off-gassing/equalization) the Perdix AI and NERD2 manuals state:

Like the clock, the decompression tissue loading is saved every 16 seconds to permanent memory when on,
and every 5 minutes when off.

@J-Vo, was your computer on or off during the drive to Jefferson?

FWIW, Shearwater got back to me and said tissues are tracked/updated as long as the computer is on. The Teric is always on (even when the screen is dark). The Perdix/Petrel must be turned on before starting the drive up the mountain. This is contrary to the manual, so I'm inclined to think their emailed response is incorrect.

 

[J-Vo]

That's good information.

Do you notice any difference in SAC rates on those dives?

Hard to say since we are more bundled up than usual and the bottom is 38 degrees.

 

[J-Vo]

On the topic of tissue update during the drive to altitude (i.e., off-gassing/equalization) the Perdix AI and NERD2 manuals state:

@J-Vo, was your computer on or off during the drive to Jefferson?

FWIW, Shearwater got back to me and said tissues are tracked/updated as long as the computer is on. The Teric is always on (even when the screen is dark). The Perdix/Petrel must be turned on before starting the drive up the mountain. This is contrary to the manual, so I'm inclined to think their emailed response is incorrect.

Usually off. I don't take the batteries out.

 

[boulderjohn]

Hard to say since we are more bundled up than usual and the bottom is 38 degrees.

Yes, I remember my one dive there. I was actually warm in my old Whites MK3s.

I ask because an unusually high SAC rate was a major factor in the Peru dive.

 

[J-Vo]

Yes, I remember my one dive there. I was actually warm in my old Whites MK3s.

I ask because an unusually high SAC rate was a major factor in the Peru dive.

I don't remember it being "unusual", I certainly haven't been taken by surprise. Last time was on rebreathers, so it's been I while since doing it on OC.

 

[Fishdip]

Bumping this thread back up rather than starting a new one, sorry not sorry for the thread revival.

Does anybody have good resources for deco at elevation? I have targets in the 8000' (2500m) range and trying to further my understanding before going for it. I'm not aware of any altitude deco classes and resources are limited so I would appreciate any suggestions.

Some current questions:

What elevation range has Buhlman actually been tested to?

What changes if any to mixes and MODS do you make? I'm not asking for a class on nitrox here. I mean for a dive at 8000' , which roughly corresponds to an atmospheric pressure of .75atm, would you increase the MOD of 50% deco gas to 80' or would you bump up the FO2 to ~55% so the MOD remains the same? My gut tells me to not mess with mix or depths for consistency but wondering if anyone does this for optimization.

When do you start worrying about a travel gas taking into account decreased PO2 associated with decreased ambient pressure? At 8000', 21% is down to about the .16 PO2 range, 18/45 is about a 13.5 PO2 by my math. I'd be on CCR anyways but I feel like that should be considered.

I'm not a fan of just setting the shearwaters to auto and following them, need to understand a bit better. So I'll reiterate, what resources do you recommend?

I have only done 20 dives at 8000ALT and 9 of them had been deco dives with that said I followed the equivalent depth chart IE 60 feet is 80feet at 8000ALT so I did all my dives in multideco with that in mind. And had 0 issue I also was at that ALT for 48 before the dives and after