How much gas are you comfortable planning to leave a cave with?
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How much gas are you comfortable planning to leave a cave with?
Other. Depends on the cave. I don't like to see less than 1000 psi, but that's nothing more than feeling too low.
depends on the cave and it depends on the tanks.
1000psi in AL80s is a different volume than 1000psi in 104s.
I marked 1200/1000 cavern but in reality, I normally exit the Florida caves with 1600 to 2000 on LP 85s or 95s. In the Mexican caves on AL80s, it is 1000+ On our last trip this year, we recalulated 1'3s on a couple of dives about 200 feet from OW. I think once I exited with less than 1000 and it was with 900.
Yeah, and not to mention when you finish your dive and there's this big ol' butt blocking your ability to get out of the cave, you have to reserve plenty of gas for that butt to get out of your way! :-DQuote:
Originally Posted by sandy
Whatever makes sense. Which Cave/Cavern? Cylinders? What was the fill (cooled or was it not even a cave fill)? What was the starting pressure? In reality, I'm way more worried about turn pressure. Risk falls with every foot closer to the exit that I travel. Is there deco? Do I have enough gas to deco out with lost deco gas? Buddy/Buddies? Heavily traveled like a busy day at Ginnie might all me to worry 10% less about triple failures, but also a MUST during the day/summer to plan for lost deco gas.
Just think it through; never plan for everything to go well, and plan for at least 2 failures and your buddy to be unreliable that day.
Have more than you need, not less, always.
Only takes a little groping to move it :)Quote:
Originally Posted by Squirrel Girl
definitely can't answer with anything but other. I dive PST HP120's most of the time, so the normal answer is 1200 unless I'm planning something. I.e. we are in a particularly nice cavern zone and want to dick around for a while and burn some gas, then I'll exit with generally about 500psi in both bottles, but I'm in the cavern zone, or at least beyond the sign, so not terribly worried about getting blocked in.
I also regularly dive LP72's, which means that I'm only starting with 2800psi max since I won't let them get filled higher than that, and they usually cool to 2600-2700. In that case, I expect to be leaving with around 900psi. I turn those at 1800psi regardless of fill, and I turn the 120's at 2500psi regardless of the fill, since Cathy doesn't give us over 3600 hardly ever, and 2500 is a nice number to see on the gauges. I am somewhat regularly the one with the lowest SAC and the smallest tanks unfortunately *this is compensated for gas matching*, and in the other scenario my buddy has a higher sac with HP100's, so he always hits turn pressure long before I do.
Can't put a number on it for all scenarios, but there's generalizations that tend to work. 1200 tends to be a good number, but with the springs flowing again, I don't think anyone has come out with 1200psi on a normal dive this year.
Groping? I need to dive with some more fun folks! Y'all sound like a fun group!Quote:
Originally Posted by sandy
Jokes aside, it really depends for me. "Minimum" for me is in the 800psi range, but it has to be a very unique set of circumstances. For example: I was practicing for Full Cave and reel work was my weak-point. I ran the line into and out of JB dozens of times. Exiting after a bunch of those with 800psi wouldn't have bothered me. If I had exited after a "real" dive I would've not been quite as happy. I've done planned exits as low as about 1000psi (penetrated to thirds, turned, then explored stuff MUCH closer to the exit in JB when the flow was still high).
Oh, indeed! We are a very fun group! :-) Block my way out of a cave, and I'm pretty much ready to grope almost anyone! :-)Quote:
Originally Posted by victorzamora
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:oops:.
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 :-D
Ok, DCI with depth can still do it too:roll:
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.
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.
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.
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.
Quote:
Originally Posted by Slüdge
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 backgasQuote:
Originally Posted by Garth
Quote:
Originally Posted by Pavão
It was a joke. I know that he needs to be breathing from something.
Wouldn't that be cool though. :-D
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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
Quote:
Originally Posted by Squirrel Girl
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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Eats lots of beans, oral inflator on drysuit.Quote:
Originally Posted by Garth
1800 because my gas consumption rarely gets below 2000 even on long dives. :-) I always have plenty of gas to spare for my buddies. AL 80 stage bottles I will breathe down to 1000 which saves back gas for emergencies
oh, another scenario, though it only happens once/year
Hydro/VIP time.... I'll keep my "reserve gas" in a bailout, and will run the main tanks down to 500psi, and just carry an AL80 for bailout. For something like this a nice big open cave is nice, JB etc, Orange Grove works as well because you can turn at a third then drop down to the deep cavern and burn the rest of the gas down there, but you run thirds on dive one, come out around half, then run in again to half of remaining plus 200, come out somewhere around 400-500psi or so. Keeps you from blowing off nitrox when they have to get broken down.
Certainly only something I do when it's time for the tanks to be broken down and it's easier to do in a cave than on a boat, and with a full AL80 I'm carrying right around the third I'd need if the 120's were full, and more than a third on any of the smaller tanks I use. Certainly the exception to the rule, but let the flaming begin.
What is this "psi" thing you talk of? Is it a bit like "vis"? We have neither of those here...
I wish we would switch over to bar.... I have a few bar spg's but don't use them because it confuses a lot of people during gas matching....
It depends on the type of dive. If solo I leave the cave with at least half of the gas I entered with, which means turning on thirds of my back gas carrying an equivalent third in a buddy bottle. With partner(s) I like to end up with 1/3 to 1/2 of what I started with. The tanks just get too light otherwise.
:clapperQuote:
Originally Posted by Duncan Price
Is there a photo of your setup? Sidemount with Doubles seems like a ton of tanks. Or are you on a Rebreather with bailouts on your back? Inquiring minds want to know!Quote:
Originally Posted by Slüdge
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Quote:
Originally Posted by AB8CD
I'm pretty sure from his past posts on the subject he is scootering with backgas and one or two stages and only breathing the stage.
ahh yes... Russell uses the scooter.
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