80cu Tank at 800 Feet ????

[Tigerman]

Thats why you can mix gases by weight to extreme accuracy

Edit: that was adressed to DSD rather than CD btw - and was more a side note really..

 

[Akimbo]

… 25.24 ATAs = 371.06 psi. At 372 psi, you'd no longer be able to draw a breath at that depth. 'Course, your pressure gauge wouldn't be reading 372 psi, since it's also relative - it'd be reading zero…

Rounding errors excepted, there is one major flaw in your analysis. Your SPG would have crushed like a grape between 3-500' and your reading would be... shall we say unreliable.

Unless you want to strap one of these babies to your side:

 

[Akimbo]

anyone know what the deco stops for a dive like that would look like ? how many how long and what depth and thanks rhone man and cave diver for all the info

No deco stops at all. You would be in a chamber, decompression would be continuous, you would be breathing Helium/Oxygen at .3 ATA, and you would be on deck in about 10 days. The good news is you probably would have been on the bottom for about a month and there would be a really nice check waiting for you!

Or did you mean making this dive on Scuba? In that case no stops are required either, being dead and all.

 

[Bossman]

Edit: Oops, looks like I was viewing an old, cached version of this thread, and the question's been long answered, with new ones asked and answered. My fault, sorry.

I was answering the question, "How to figure (ambient) pressure at that depth."



1 ATA = 14.7 psi, so...

25.24 ATAs = 371.06 psi. At 372 psi, you'd no longer be able to draw a breath at that depth. 'Course, your pressure gauge wouldn't be reading 372 psi, since it's also relative - it'd be reading zero.

The bottom line is that you'd have about 2628 psi of usable gas at that depth. Given that your average AL80 tank is actually 77.7 cubic feet of air, you're looking at about 68 cubic feet of usable gas, given a starting pressure of 3000 psi.

At a SAC (breathing) rate of .5 (average, skilled, and comfortable diver), one would use that in about 136 minutes at the surface.

Assuming nothing changes - stress level, exertion level, etc. - a diver with a SAC rate of .5 would burn through an AL80 in about 5.39 minutes (1/25.24*136=5.39), or about five minutes, 23 seconds.

This also assumes that the tank was not used to GET to 800 feet, and is thus full when you start breathing on it at 800 feet.

Interestingly, at the surface, the full AL80 would read 3000 psi. At depth, the full tank would read 2628 psi. The empty tank at depth would read zero psi, and the empty tank at the surface would read 372 psi.

Breathing air at 800 feet would almost certainly be lethal, by the way, so don't try it.

Thanks Math major. Interesting reading, and teaches some of us new guys a lot who actually have an interest in understanding the math and physics of diving.

 

[Akimbo]

Whew, I'm tired. I had to read that 3 times before I caught your meaning.

Isn't it normal for you guys to figure available gas in your calculations? Or was it just written badly?

 

[Deep South Divers]

Rounding errors excepted, there is one major flaw in your analysis. Your SPG would have crushed like a grape between 3-500' and your reading would be... shall we say unreliable.

Lol...

Dunno, the last time I dove to 800' I was doing it naked with Angelina Jolie and Jessica Alba and the creature from The Abyss. We were breathing water (no gear at all), so I didn't have a pressure gauge. I don't think I'd have had the attention span to check my gas supply anyway - I was pretty distracted.

...Then I woke up.

You sure that an SPG would crush? Pressurized internals wouldn't, 'cause they would be pressurized. Most of the rest of the internals are wet and pressure-neutral. Are you just talking about the actual gauge face itself? You could simply use a common oil-filled... Assuming that a standard brass & glass wouldn't handle 375 psi of pressure. I don't know if it would or not... I can tell you that I've seen them take a lot of abuse without cracking - tanks slamming down on them, heavy people stepping on them... And there's not a full cubic inch of space inside the face...

You don't think it'd take it, hunh? That'd be an interesting experiment...

 

[Cave Diver]

Isn't in normal for you guys to figure available gas in your calculations? Or was it just written badly?

I was just being dense and misreading this line:

If you could get 80 Ft³ out of an 80 Ft³ bottle at 800', you would have a negative pressure of 356 PSI. That's some pretty hard sucking.

 

[Deep South Divers]

Or did you mean making this dive on Scuba? In that case no stops are required either, being dead and all.

:rofl:

 

[Cave Diver]

You don't think it'd take it, hunh? That'd be an interesting experiment...

Seal the end and stick it on the end of a long fishing line.

 

[Deep South Divers]

Thanks Math major.

(Pushes taped-together glasses up against face with one finger.) You're welcome. (nerd smile)