Altitude Diving Lake Tahoe (Safety + Physics)

[TinFins]

Hi All,
I have some dive physics questions about Lake Tahoe. I have read a lot about altitude diving, I've even had a short course, but there are a couple questions I guess I just am not smart enough to clear up on my own.

1. My computer (Oceanic Atom 3.1) read 94 feet as my depth yesterday in Lake Tahoe. I understand that this is not the actual depth, but the equivalent amount of pressure to 94 feet of seawater at sea level.
-What was my actual depth?

2. When you ascend, 15 feet in Lake Tahoe is similar to +-15 feet in Monterey, but when you reach the surface you are suddenly at 6300' elevation.
-How is this different than diving Monterey and upon surfacing, getting in a helicopter and instantly flying up to 6300'?

Thanks in advance!

 

[boulderjohn]

You will find most of your answers in your computer's manual. It is on page 49 of this one: http://www.oceanicworldwide.com/us/media/wysiwyg/manuals/12-5216-r02_Eng.pdf

I would have pasted the information here, but it won't let me. The short answer is that your computer senses your altitude and makes adjustments both to the depth and to the ascent profile.

 

[tursiops]

1. About 3 ft deeper, because salt water weighs about 3% more than fresh water, for equal volumes. But, some computers allow you to set fresh/salt.
2. It is different in two ways:
(1) if you come to the surface in Monterey, the decompression models assume you have come from some depth to 1 atmosphere pressure, so the ascent rates and N2 management are based on that. But if you come to the surface at Lake Tahoe, you are going through more pressure change for the same amount of water, and the model needs to take that into account. If your dive is actually in Lake Tahoe, with everything taken into account, you'll be fine.
(2) If you instantly ascend in Monterey from the surface to 6300 ft, the last part of your "dive" is an extremely fast release of pressure, with possible N2 bubbles thus forming. So you need to make sure your helicopter doesn't ascend too fast. For reference, note that astronauts breathe pure O2 for a day prior to a shuttle launch so they don't get DCS during the launch.

So your altitude diving issues are that your gauges don't work right. and neither do your computer models. This is why you take a class, to learn how to manage all this!

 

[griffon]

Huh, learn something every day, the bit on the astronauts was news indeed.


Sent from my iPhone using Tapatalk

 

[tursiops]

Huh, learn something every day, the bit on the astronauts was news indeed.

Some of the launch information is at https://books.google.com/books?id=_... sickness in astronauts during launch&f=false.

Not only that, they need to dentrify prior to a spacewalk!
NASA - PREVENTING DECOMPRESSION SICKNESS ON SPACEWALKS

 

[boulderjohn]

By the way, the research on decompression sickness with astronauts and the research done on decompression sickness in divers was done by the same people. See Michael Powell, or just go to the ScubaBoard forum Ask Dr. Decompression and talk to him yourself.

There is, however, a big difference between astronauts zooming into space and people diving at relatively low altitudes like Lake Tahoe. The latter is pretty controversial, with some people claiming it is no big deal and requires no special attention. (I do not agree.) Diving at significantly higher elevations has not been adequately studied. A decompression program like V-Planner will spit out a decompression profile for a dive to 200 feet at 16,000 feet of altitude, but how on Earth do we know that profile is at all accurate? To my knowledge only two people have attempted a dive like that, and it did not turn out so well.

 

[descent]

Some friends and I jumped a CH-54 once that climbed to altitude at close to its maximum rate of climb.

The pilot warned us to get back to the deck quickly or we would likely get bent. We did not prebreathe O2 to flush nitrogen.

Probably playing with fire there.

 

[Eric Sedletzky]

Here is a chart from my old PADI AOW manual. You have to round up, so look at the 7000 ft column.
Don't forget they want you to wait at least 6 hours at altitude before you dive to allow yourself to off gas from the trip up. And they only want you to do 2 dives a day, however I am in the water a lot more than that but I'm only diving to 30 feet or less most of the time looking for goodies.
I'm going to be up there 7/6....Yay!!!
Crawdads, mmmm!!

 

[TinFins]

View attachment 211596
Here is a chart from my old PADI AOW manual. You have to round up, so look at the 7000 ft column.
Don't forget they want you to wait at least 6 hours at altitude before you dive to allow yourself to off gas from the trip up. And they only want you to do 2 dives a day, however I am in the water a lot more than that but I'm only diving to 30 feet or less most of the time looking for goodies.
I'm going to be up there 7/6....Yay!!!
Crawdads, mmmm!!

Nice! Rubicon wall was excellent last week.

 

[Eric Sedletzky]

Nice! Rubicon wall was excellent last week.

Have you ever tried the wall at Stateline on the north side? It's a great dive! it's a cascading wall with interesting structure and huge logs jambed into crevices down to about the deepest part of the lake. You can look out and see nothing but deep blue.
Right before stateline heading east on the north shore, take a right on Harbor drive and follow it down to Speed Boat Beach. If you get there early enough you can easily get a place to park. There's a porta-potty for convenience and beach access is free. I use a kayak to paddle the 1/4 mile or so over state line to the wall. Make sure you display a dive flag on your kayak.