Weird Question...

[Geek]

So I was checking out the ice diving video on TDS and it looked very cool... then I started to wonder, If your diving under ice thick ice, thin ice whatever, is the thickness of the ice calculated in your deco planning for depth? I mean, granted, I don't think I'll be diving under 200' of ice but if I were, would you count 200' in addition to your water depth? I was just wondering because the ice is floating on the water, so it follows that you would have the preasure of that ice..

I know, random questions that pop into my head first thing when I get to work.. anyone that has any idea's or guesstamations... or can make up a plausable answer?

[Joshua Smith]

So I was checking out the ice diving video on TDS and it looked very cool... then I started to wonder, If your diving under ice thick ice, thin ice whatever, is the thickness of the ice calculated in your deco planning for depth? I mean, granted, I don't think I'll be diving under 200' of ice but if I were, would you count 200' in addition to your water depth? I was just wondering because the ice is floating on the water, so it follows that you would have the preasure of that ice..

I know, random questions that pop into my head first thing when I get to work.. anyone that has any idea's or guesstamations... or can make up a plausable answer?

Decompression is based on pressure and time. Sea level is still sea level with or without ice.

[boydski]

then I started to wonder, If your diving under ice thick ice, thin ice whatever, is the thickness of the ice calculated in your deco planning for depth?

Water depth for deco is really equivalent to the pressure of the water on your body at depth (ATA's). Just like Cave Diving, it doesn't really matter how much or how thick the rock (or ice) is over your head, the depth (and deco obligation) is based on the height of the water column (and the pressure it creates on the diver).

We often do our deco in caves by finding a good spot near the entrance where the ceiling is 20' deep and then pin yourself to the ceiling while sucking on an Oxygen cylinder. It keeps you from silting while sitting in one place for so long.

[Geek]

I get it, for some reason I was just thinking ice overhead as vertical preasure coming down instead of total preasure on the water at sea level... I only had 3 cups of coffee so far this morning....

[Waynne Fowler]

In short Geek I think Josh and Scott are right.. but I do see your point.
The regulator use's ambient PSI to regulate the density of the gas we breathe.
The density of the gas we breathe is what determines our deco obligations

It 'seems' that all that ice sitting over the water would increase the ambient PSI, causing the regulator to increase the density of the gas therefore skewing the deco needed. That is a very good question and would be easy to dismiss out of hand as inconsequential. However when we start talking about 100's of feet of ice over 100's of feet of water, off the top of my head it seem's that one may need to take something more into account. As I type I'm thinking also that your depth gauge/computer would be taking the additional weight into it's calculations as they work on the weight of the water also.

I wouldn't dismiss the idea that one may need to adjust the deco when diving under thick (100's of feet) ice, but under the stuff we have around here I wouldn't even imagine it could have an affect.

i understand Scott's comment about the cave, the only difference may be that the rock of the cave is not supported by the water, the ice however is. Could this make a difference?????.. i dunno

Food for thought.
can anyone comment definitively one way or the other?

[boydski]

It 'seems' that all that ice sitting over the water would increase the ambient PSI, causing the regulator to increase the density of the gas therefore skewing the deco needed. That is a very good question and would be easy to dismiss out of hand as inconsequential. However when we start talking about 100's of feet of ice over 100's of feet of water, off the top of my head it seem's that one may need to take something more into account. As I type I'm thinking also that your depth gauge/computer would be taking the additional weight into it's calculations as they work on the weight of the water also.

Hi Waynne,

Remember Archimedes Principal. The Ice, even if 100' thick displaces a volume of water exactly equal to its weight, so it exerts the same weight/square inch that the water would have if present. So the 100' thick sheet of ice would float with about 88' below the surface. At 88' the ice sheet would exert the same 4.93 ATA's that the 88' column of seawater would have if still present (which is actually why it floats).

It's the same story in a cave, where the upward pressure created by the water helps hold up the ceilings of the caves. Many would collapse without the water being present.

[Geek]

I believe boydski has it correct, you can't compress water so any displacement would happen globaly, hense raising water when ice caps melt, in effect if I have it down correctly, even here in the sound we expierence the "pressure" of the polar ice on the ocean

[Waynne Fowler]

Doh!

Just like Jesus..... helping the blind see again!

Guess I shoulda had more coffee this morning too

[Burntchef]

9:13, Personal note: When I was a little kid my mother told me not to stare into the sun. So once when I was six I did. The doctors didn't know if my eyes would ever heal. I was terrified, alone in that darkness. Slowly, daylight crept in through the bandages, and I could see. But something else had changed inside of me. That day I had my first headache.


anyone??

[Burntchef]

My new hypothesis: If we're built from Spirals while living in a giant Spiral, then is it possible that everything we put our hands to is infused with the Spiral?

[Geek]

Ummmmm..............

[Dmitchell]

It 'seems' that all that ice sitting over the water would increase the ambient PSI, causing the regulator to increase the density of the gas therefore skewing the deco needed.

Density of the gas is based on atmospheric pressure. The regulator does not control the density only the flow. When the gas comes out of the 2nd stage it's at ambient pressure that's the pressure that your body is at.

The deco would be based on partial pressure which is based on the mix you are diving and the atmospheric pressure at depth and time. The mix won't change but the PP will increase or decrease based on your depth.

[citycatred]

9:13, Personal note: When I was a little kid my mother told me not to stare into the sun. So once when I was six I did. The doctors didn't know if my eyes would ever heal. I was terrified, alone in that darkness. Slowly, daylight crept in through the bandages, and I could see. But something else had changed inside of me. That day I had my first headache.


anyone??

Have you been ? LOL

[Kees]

Your depth gauge doesn't really measure depth, it measures pressure. Your gauge is really just an odd sort of pressure gauge that reads in ffw/fsw instead of psi (with unlabeled units, thanks a lot highschool science teachers). If you're under a layer of ice, a boat or a layer of pressurized air (like in a chamber) your gauge is not going to show you how far it is to the surface but how much pressure you have to go through to reach 1atm.

[Sounder]

Hey Geek - it's all about the pressure. I know nobody has mentioned that here yet, so I wanted to make sure it was clear. It's definitely the pressure.

[cardiver]

Hey Geek - it's all about the pressure. I know nobody has mentioned that here yet, so I wanted to make sure it was clear. It's definitely the pressure.

http://www.youtube.com/watch?v=YsSlNFTjxss