Minimum gas I'd leave a cave with

[speleocrone]

Like many here, I think it really does depend on the cave, and the dive, and the tanks used.
A poke around in a small, no vis sump, with 3 lt tanks, alone, and I want pretty much close to half the start pressure at the end. I'm an air scaredy cat.

Dives in large, clearwater, complex systems, with a knowledgeable buddy that I don't know well (sort of trust me dive then??), and we do quite a few jumps. I want close to half again!

Long, complex system dives, with no silting, where I know the cave, and it's shallow, with a buddy, thirds rule.

Complex, depth, and some deco, better than thirds.

Any silty restrictions of more than a few metres length, better than thirds. Add complexity and length to the silt and I am back to halves.

As many are saying, it really depends on the circumstances of the dive. Many factors contributing. But I always err on the side of being cautious with turn pressures, as I see it anyway.

Apart from the EXTREMELY rare rock fall, ultimately only 1 thing kills a cave diver. Running out of air. This, if nothing else, is the ultimate in embarressment for a cave diver who wants to be seen as competent

Ok, DCI with depth can still do it too

[FW]

Thirds is the maximum I will dive to. I turn earlier for things like restrictions, new buddies, low visibility, things that might cause low visibility (deep silt, percolation, etc), solo, surveying, new cave (to me, or virgin), also more obvious things like syphons.

[Jack Hammer]

Essentially exiting with 1200psi (thirds) or more is what I'd like to say, it really depends on the size of the tanks i'm diving. We typically end a dive with much more than 1/3 remaining and often over 1/2, even if drills are practiced. My comfort level is different when I'm using doubled hp100's than it is with hp130's or lp120's. This becomes a major factor if we "recalculate" near the exit to explore or practice some skills. It's more about having a safe enough volume for the modified plan than the end pressure allowed, think along the lines of rock bottom.

[RN]

I usually exit the cave with 2000-2200 psi. But I also don't ever dive to full thirds. I always cut it back by 100-200 psi. Sheck stated in one of his books that thirds isn't conservative enough and I took that to heart. It's also what I teach. Sometimes I'll even cut it back by 300 psi so I'm effectively diving fourths. If I need more gas then I add stage cylinders. Besides, Faber cylinders trim out nasty when they get too low.

[Sludge]

I always (over the past eight years or so, at least) leave the cave will full backgas. The only exceptions are Galaxy Dives, which is pretty much the only time I breathe backgas.

[Garth]

I always (over the past eight years or so, at least) leave the cave will full backgas. The only exceptions are Galaxy Dives, which is pretty much the only time I breathe backgas.

You don't breathe the air in your tanks? How do I learn how to do that?


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[Pavão]

You don't breathe the air in your tanks? How do I learn how to do that?


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The key word you missed was backgas

[Garth]

The key word you missed was backgas

It was a joke. I know that he needs to be breathing from something.

Wouldn't that be cool though.




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[JCGoodwin]

I usually keep to the 1200 mark for MAX exit.
Rarely though do I go below that but have on occasion in cavern or pool working on skills or trying to drain tanks for fills.
I enjoy just putting around looking at things in the pool or cavern catching the right angles for pics.
My biggest reason for keeping a good reserve is for someone needing extra gas to deco or get out.

Like Forrest I rarely dive to the entire third turning most dives well before.
Variables factor into when I turn but it would be tough to make it out on 1/3's with a buddy who has lost all his or her gas.
Now that would take a drastic series of events but I plan for the worst hope for the best in my plan.
It seems when one failure announces itself there are more to follow.

I like the better safe than sorry rule no exceptions.
One compromise can be the last one you will make.
Its good to dive with buddies who understand each other in and out of the water!

JCG

[Garth]

How much gas are you comfortable planning to leave a cave with?

Another interesting discussion point may be for those who are doing considerable decompression and whether most plan on having a significant amount of backgas or non-deco gas to successfully complete deco in addition to having reserve gas on top of that.

I hadn't really considered oxygen a necessity for my diving as it's not very extreme but when considering the amount of decompression if I'm in a bailout scenario from my hammerhead it just made sense to start dropping a bottle of oxygen for dives greater than 2 hours for the typical 100ft or less cave that I dive in.

This is a great discussion and I enjoy hearing the variety.

Garth


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