Trivia Question: Where Would You Be At 1/2 Ata?

[Doppler]

Walter... you win the 16-inch pizza! Since you did the math and logic correctly...


However! I just wanna say that if we drove up the mountain to 18,000 feet, we'd all pass out and die while assembling our dive gear... since the ppO2 at 18,000 feet is 0.10 ATA! So my advice is use the EAN50 to breathe on the surface and leave the mountain diving until you have been at altitude for at least 3 months!

I'll drop you a line next time I'm in Florida dude!

 

[Charlie99]

Walter once bubbled...
First, from the NOAA manual, 4-26:

"DIVING AT ALTITUDES ABOVE 10,000 FEET IMPOSES SERIOUS STRESS ON THE BODY AND IS STRONGLY DISCOURAGED"

Assuming you ignored the above warning or sent the gauge down with a camera, you'd find the gauge would read 16.96 feet shallower than your actual depth. In this case, it would read 17 ft.

Keep in mind, you have totally ignored Sea Level Equivalent Depth. For decompression purposes, a dive to 80 ft at 10,000 ft (.688 ata) is equivalent to a dive to 120 ft at sea level.

You make the calculations WAAAAY too complicated Walter. GUE has the simplified method of calculating dives at altitude --- just ignore altitude!


To quote the GUE Rec Triox student that just posted a trip report on rec.scuba about their dives at Lake Tahoe: "120' on 30/30 triox. EAD for 120' on 30/30 is 120 * .8 = 96 feet. NDL for 100' on the air table is 20 minutes.
>
> Was there any consideration or discussion about NDL or depth adjustments for driving up and diving at 6,200' altitude?

Yes. Ignore the altitude. It doesn't matter.
------ Kevin Metcalfe"

 

[DeepTechScuba]

WALTER our Board Regulator noticed right away that you would need to be at 18,000 ft altitude for the ambient pressure to be 1/2 ata. The NOAA Diving Manual mentions this at Page 2-1 in their physics discussion on pressure.

Congrats, Walter!

"Up in the air" mentioned by ScottyK is not exactly right, because if you were up in the air in an aircraft, you would be in a pressurized cabin of a commercial aircraft or else in a military fighter jet breathing oxygen. So the military fighter jet angle is worth a consolation prize maybe!

DOPPLER was the most astute to recognize that there are so many peaks on the Earth of 18,000 ft or more, that we must take into consideration mountain ranges as well as mountains.

Congrats, Doppler!

Here is the list of mountain ranges and additional isolated mountains that I got from the World Almanac:

The McKinley Range in Alaska
The Yukon Range in Canada
The Andes Range in South America
The Himalaya Range in Asia

Then in addition to the above, there are 3 more isolated mountains of 18,000 ft altitude:

Pico de Orizaba in Mexico
Kilimanjaro in Africa and
Mt Elbrus in Russia.

I honestly do not know if it is possible to scuba at heights above 10,000 ft. And I do not know if anyone ever has.

The problem of diving at altitude is simply that since atmospheric pressure is lower, the dive itself is equivalent to a relatively deeper dive at sea level because the hydrostatic water pressure is effectively the same, as you go down into the fresh water lakes, at 34 ffw per ata. However when you return to the surface, you are now at such a lower ambient pressure that the charts and tables and dive computers no longer properly calculate your decompression obligation.

You cannot possibly ignor this, therefore you would need to do decompression calculations determined for the altitude you are intending to scuba dive at.

It could be that the decompression obligation from even merely a short exposure to compressed breathing gas underwater would make diving impossible, without an on-site recompression chamber available. But that is a topic for a different thread!

 

[Doppler]

That was good fun for all of us I think... nice to tease the brain sometimes... sitting here chained to a desk with the sun shining outside!

I also agree that diving at elevations at or around 18,000 would be a supreme challenge and I can't think of any articles or stories of people diving much above 8,000 feet.

Anyhow, have a great rest of friday folks

 

[cnidae]

CincyBengalsFan once bubbled...


The majority of the atmosphere is in the first 18,000 so I would guess .5 ATA would be closer to Everest or higher.

Yup it's not linear but 18,000 feet is half an atmosphere.

 

[cnidae]

Altitude Pressure Temp. Density -
(ft) (in. Hg) (F.) slugs per cubic foot
0 29.92 59.0 0.002378
1,000 28.86 55.4 0.002309
2,000 27.82 51.9 0.002242
3,000 26.82 48.3 0.002176
4,000 25.84 44.7 0.002112
5,000 24.89 41.2 0.002049
6,000 23.98 37.6 0.001988
7,000 23.09 34.0 0.001928
8,000 22.22 30.5 0.001869
9,000 21.38 26.9 0.001812
10,000 20.57 23.3 0.001756
11,000 19.79 19.8 0.001701
12,000 19.02 16.2 0.001648
13,000 18.29 12.6 0.001596
14,000 17.57 9.1 0.001545
15,000 16.88 5.5 0.001496
16,000 16.21 1.9 0.001448
17,000 15.56 -1.6 0.001401
18,000 14.94 -5.2 0.001355
19,000 14.33 -8.8 0.001310
20,000 13.74 -12.3 0.001267
25,000 11.10 -30.15
30,000 8.89 -47.98
35,000 7.04 -68.72
40,000 5.54 -69.70
45,000 4.35 -69.70
50,000 3.43 -69.70
55,000 2.69 -69.70
60,000 2.12 -69.70
65,000 1.67 -69.70
70,000 1.31 -69.70
75,000 1.03 -69.70
80,000 0.81 -69.70
85,000 0.64 -64.80
90,000 0.50 -56.57
95,000 0.40 -48.34
100,000 0.32 -40.11

 

[cnidae]

DeepTechScuba once bubbled...
The problem of diving at altitude is simply that since atmospheric pressure is lower, the dive itself is equivalent to a relatively deeper dive at sea level because the hydrostatic water pressure is effectively the same, as you go down into the fresh water lakes, at 34 ffw per ata. However when you return to the surface, you are now at such a lower ambient pressure that the charts and tables and dive computers no longer properly calculate your decompression obligation.

You cannot possibly ignor this, therefore you would need to do decompression calculations determined for the altitude you are intending to scuba dive at.

It could be that the decompression obligation from even merely a short exposure to compressed breathing gas underwater would make diving impossible, without an on-site recompression chamber available. But that is a topic for a different thread!

There you go again believing in those books. If your body reached an equilibrium with the pressure which it would and it would come close probably for how long it would take you to reach 18,000' the tables would still apply becuase they are generated from pressure, they have nothing to do with the atmosphere above you.

 

[Charlie99]

DeepTechScuba once bubbled...
The problem of diving at altitude is simply that since atmospheric pressure is lower, the dive itself is equivalent to a relatively deeper dive at sea level because the hydrostatic water pressure is effectively the same, as you go down into the fresh water lakes, at 34 ffw per ata. However when you return to the surface, you are now at such a lower ambient pressure that the charts and tables and dive computers no longer properly calculate your decompression obligation.

You cannot possibly ignore this, therefore you would need to do decompression calculations determined for the altitude you are intending to scuba dive at.

In spite of your statement that "you cannot possibly ignore this", it is clear that some divers do ignore even 6200' altitude as irrelevant.

It is not clear to me upon what basis GUE has made this decision to ignore altitude. George Irvine has also made the statement that the altitude at Lake Tahoe is irrelevant, but again, the reasons for this statement are unclear.

George Irvine's comments on altitude diving.

 

[Charlie99]

cnidae once bubbled...
<snipped a table of numbers>

I see that you recently took the GUE Rec Triox class that dove at Lake Tahoe. Although you didn't do those dives, can you educate us a bit on the reasoning behind how GUE handles altitude calculations?

Thanks in advance,

Charlie Allen

 

[cnidae]

Charlie99 once bubbled...
Although you didn't do those dives.

Charlie Allen

Huh?