High altitude decompression diving

[boulderjohn]

I was just dong a little research, and as part of it, I programmed a deep decompression dive into V-Planner, putting in an altitude of 16,000 feet. I was surprised when it gave me a profile. I wonder what kind of data we have related to decompression diving at such high altitudes. I wonder how much confidence I would have in the profile it gave me. Does anyone have any information on this?

 

[shoredivr]

Huh. I know there was somebody from Denver area doing high altitude dives at 16,000ft IIRC in the Andes to shallower NDL depths for archeological work. He posted on here. Was it Rookers? Anyway he talked about padding those dives for conservatism IIRC.

Now I'll have to try my VPlanner.

---------- Post added September 3rd, 2014 at 08:34 PM ----------

Can only get the smartphone version to take me up to 10,000 ft.
Six minutes longer runtime on a 20 minute 160ft dive.

 

[Scott]

Yes it was Rookers.
Here is the link: http://www.scubaboard.com/forums/tek-trip-reports/463300-very-high-altitude-dives.html

 

[boulderjohn]

Yes, I know about that.

Things are not all that cool now.

 

[lostsheep]

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?

 

[inquis]

In my view, you've identified the two main considerations. I don't adjust deco mix/MOD (also for consistency) and reflect that when planning deco times & gas usage at altitude. (I use Subsurface, which allows me to override the switch depth.) ETA: in other words, I'll use 50% and switch at 70 ft.

On the travel gas: if you won't have a chance to acclimate, playing it safe at min PO2 of 0.15 wouldn't hurt (9000 ft equivalent). It's not uncommon for tourists here to have issues (blackouts) with the PO2 of 0.123 on top of Pike's Peak (14k ft).

I would have no qualms about setting the Shearwater to Auto, after making sure the surface pressure readout was reasonable. (Probably a good idea to verify that at any altitude. It actually mandates Auto if it thinks it's above about 1500 ft.) You could have it plan a square profile dive and compare the profile to a planner you trust that works at altitude for confirmation.

As to whether the model itself works well, I have only second-hand, anecdotal evidence at lakes just under 11k ft. Single-digit sample size. Resources are scarce. However, I would heed the current thinking about GFLow in the 50+ range.

Are there anyone in the team that is "local" or at least dived this site before?

 

[John C. Ratliff]

I attended an altitude diving conference sponsored by NAUI in 1975 (I think). I still have all my notes from that, along with the Cross Tables and tables for altitude corrections for depth gauges. I looked up on the DAN.org website, and found one article about diving at altitude which still references the Cross Tables. That article still had this to say:

Extreme Altitude​

Most altitude diving is conducted below 8,000 feet, altitudes generally well tolerated by healthy individuals. For higher altitudes, however, acclimatization to the reduced oxygen partial pressure may be an issue. Acute mountain sickness (AMS) can develop with sudden exposure to high altitude. Some of the highest altitude dives reported were made at 12,500 feet in Lake Titicaca on the border of Peru and Bolivia, initially in 1968 by Jacques Cousteau and later by others.

I’ll get you more information when I get to my main computer (I’m on my iPad right now).

SeaRat

 

[lostsheep]

Are there anyone in the team that is "local" or at least dived this site before?

I'm sure someone has done it but the "team" is me lol. I have buddies who go along with my odd ideas but the scheming is all me. My goal is most likely a giant waste of time and effort but I have to go have a look and won't know til I try.

 

[rjack321]

I've dove in Yellowstone Lake (~7,700ft). Not extensive deco, this predated widespread adoption of suit heat. I didnt change anything except was prepared for the extensive shallow stops. It's cold and a long way from help.

The biggest issue was actually the boat being O2 starved, the rated 60hp was more like 40hp at that elevation and it was way overpropped. That made scoping out our targets much slower than anticipated.

 

[John C. Ratliff]

Here are the notes and the articles from 1974 that perhaps you can use to help see what diving at 8;000 feet will do for the decompression tables, and the computer. I have no expertise on any of the computers and how they compute altitude. But do note that the depth may not be correct depending upon how the algorythm used compensates for both fresh water and altitude for depth. The one table showing depth gauges may be helpful in determining what the computer may be using, and perhaps building in some safety factors.

Here are more recent papers:

Diving at altitude: a review of decompression strategies.​

Egi SM 1,
Brubakk AO

Author information​

Undersea & Hyperbaric Medicine : Journal of the Undersea and Hyperbaric Medical Society, Inc, 01 Sep 1995, 22(3):281-300
PMID: 7580768
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Abstract​

---

Diving at altitude requires different tables from those at sea level due to the reduction in surface ambient pressure. Several algorithms extrapolating sea-level diving experimental data have been proposed to construct altitude diving tables. The rationale for these algorithms is reviewed together with the conservatism of the resulting tables and decompression computer outputs. All algorithms are based on the adaptation of critical tissue tensions to altitude. These are linear extrapolation (LEM), constant ratio translation (CRT), and constant ratio extrapolation (CRE) of maximum permissible tissue tensions (M values). Either new tables using the altitude-adapted M values were put forward or sea-level tables are to be used through an operation called correction. In this review it is shown that for a given set of M values, CRT and CRE give the same result for no-decompression-stop dives; they always yield more conservative results than LEM. When decompression stops are used, CRT is more conservative than CRE. When applied to different sets of M values, the conservatism becomes a function of bottom time, depth, and altitude. The analysis shows that the tables derived using CRT of U.S. Navy (USN) schedules and CRE Boni et al. tables give more conservative results than LEM Bühlmann tables for higher altitude, longer bottom time, and deeper dives. Aviation altitude exposure decompression sickness (DCS) data are also addressed to compare different model outputs. When applied to USN and Royal Navy tables, LEM yields an altitude DCS limit of 8,581 and 8,977 m, respectively. On the other hand, the altitude limit calculated using CRE applied to USN M values and LEM Bühlmann tables is found to be below 6,000 m.

Europe PMC

Europe PMC is an archive of life sciences journal literature.

europepmc.org

Here is a discussion in the Journal of Marine Medical Society of actual decompression sickness events and how they may be prevented.

https://www.researchgate.net/profile/Rohit-Verma-18/publication/232167569_DECOMPRESSION_SICKNESS_IN_HIGH_ALTITUDE_DIVING/links/0fcfd5077dfca6ce0c000000/DECOMPRESSION-SICKNESS-IN-HIGH-ALTITUDE-DIVING.pdf

One of the books referenced in the above link is the NOAA Diving Manual, 6th Edition. Here is a link to obtain one, free:

egp EMANG GUA PIKIRIN

egpegpsorry2aja-good.blogspot.de

SeaRat

PS, I just added my notes from the Altitude Diving Conference, which I had inadvertently left of when I originally posted.