80cu Tank at 800 Feet ????

[Cave Diver]

Not that I would encourage something so fantastically stupid as Scuba to that depth on a single, but looking at apnea records makes the engineer in me say it is quite possible.

Odds are he could have made it to 480 on a single, but highly unlikely he would have returned to tell you about it.

A trained apnea diver, probably. Joe Diver on a single 80, not so much. It may be possible, but I think the odds would be stacked against them.

Even if they were to free dive to depth, and use the 80 to surface, once they take that first hit of gas the Narcotic effect would probably be overwhelming. If they used a gas that was sufficiently non-narcotic, the 02 content would likely be too low for breathing once they got shallower.

Then there is that whole "once you start breathing compressed gas under pressure and forcing inert gasses into your tissues you'll have to give it time to escape" thing...

But if the engineer in you thinks its possible and decides to test it, be sure someone videos it for the rest of us!

 

[Cave Diver]

480 is pushing it, but 440 is much more reasonable.

Wah Wah - SubAqua UK

(You probably dont want to try that at home )

Thank you! I've been looking for that article and the original hosting of it is no longer running!

 

[Cave Diver]

What are your emergency procedures if a couple of SPGs implode at 475'? Based on the observation I described in that thread, it would likely blow away the bourdon tube resulting in a couple of serious leaks (at that depth). Granted, it would not be such a big deal at 100' because of the flow restricting pinhole in the HP hose fitting.

Bend the hose back on itself and secure it with a spare double ender. I'd likely also start feathering the tank valve to conserve some air since that may not completely stop the leak.

It is however, fairly effective. I've tested low and high pressure hose failures on the surface and at depth before.

 

[Jax]

480 is pushing it, but 440 is much more reasonable.

Wah Wah - SubAqua UK

Another leading tech diving expert, who asked not to be identified, declared, "Natural selection is a slow process."

. . . . :lol:

 

[Akimbo]

I don't think the leak on a HP hose would be any faster at depth. If anything it would be slower due to the higher ambient pressure. (smaller pressure differential between tank and water)

Any volunteers?

(Agree that a LP leak will empty a tank faster at depth due to the actual IP being higher)

I suggest the fluid dynamics analysis misses the most important point. A small leak at that depth is hyper-critical because your backup options are so limited, especially if the failure occurs at the end of a dive. A saturation diver working out of a bell has to burn up a lot of backup gas supply options before resorting to the relatively minute amount of gas on their back. Keep in mind you're discussing this with a guy who thinks of gas supplies in terms of six-packs and tube trailers.

http://www.scubaboard.com/forums/te...ties/337376-use-heliox-commercial-divers.html

I can see one SPG implosion as manageable, but serious accidents usually involve two or three errors. How many SPGs do you carry at 475'?

The fluid dynamics analysis is pretty complex. The design of the "pin-hole" or orifice is critical along with the depth, gas density, Delta P (pressure differential which is a moving target), density of the media the gas escapes into, temperatures (also a moving target), and restrictions that may be left behind by the shattered bourdon tube(s).

 

[Akimbo]

... But if the engineer in you thinks its possible and decides to test it, be sure someone videos it for the rest of us!

I just put that on my "Things to do if I want to die list".

 

[ianr33]

If you are that worried about the SPGs why not take off/break the glass face before the dive? No way they could implode then and they will work fine for one dive. Might get expensive though if you are in the habit of hitting 800" every weekend.


I seem to remember in Exleys book that he deliberately flooded the spgs before a dive to stop them imploding.

 

[Cave Diver]

I can see one SPG implosion as manageable, but serious accidents usually involve two or three errors. How many SPGs do you carry at 475'?

Multiple.

There would be one on my backgas and then one on every one of my deco bottles.

Gas reserve planning would allow for the loss of small amounts of gas such as a HP leak. If necessary, feathering the valve would allow you to reduce the loss of gas further.

On such a dive it's not likely that you'd take all your tanks down with you, rather they would probably be staged on a line. IF you did take them all down, it's unlikely they would all implode at the same time. First failure means you call the dive, so you're still only dealing with one failure.

SPG is a nice feature to have, but it's not a necessity. Your deco schedule is going to run on a time factor and as you deco out either you have enough gas to do the deco or you dont. If your backgas SPG implodes, then your dive is ending sooner so you have even more sufficient deco reserves when you start back up.

If a deco SPG implodes, you complete your schedule til you run out of gas. At that point you either adjust the schedule and move up to your next deco gas, or you switch back to backgas until you can make your next deco switch.

Of course a good understanding of deco is imperative to making these on the fly adjustments.

I'd probably be more concerned about the concussive force and shock wave of an imploding SPG near my head at depth (from a clipped off deco bottle) than I would about the loss of gas.

 

[Akimbo]

Bend the hose back on itself and secure it with a spare double ender. I'd likely also start feathering the tank valve to conserve some air since that may not completely stop the leak.

It is however, fairly effective. I've tested low and high pressure hose failures on the surface and at depth before.

I am pleasantly surprised that it was even close to effective on an HP hose. Was your test on a Myflex or stock rubber hose?

In any case, this is useful information that may also be worth posting in that Operating Depth of SPG thread. However, I think I would put "head for the downline" first and deal with the hose along the way. I get really good at multi-tasking when it all starts swirling around the bowl.

 

[Cave Diver]

I am pleasantly surprised that it was even close to effective on an HP hose. Was your test on a Myflex or stock rubber hose?

In any case, this is useful information that may also be worth posting in that Operating Depth of SPG thread. However, I think I would put "head for the downline" first and deal with the hose along the way. I get really good at multi-tasking when it all starts swirling around the bowl.

Stock rubber hose. I've never used or tested a Myflex hose. And while it's not a perfect solution it is better than nothing.

And my test wasn't done at 475' either.