Discussion of best practices for advancing in cave diving (moved from A&I JB thread)

[nakatomi]

If you or your buddy have back gas you can take longer turns on the stage during restrictions. By the time you hit the second stage, your can each have one for yourself, swapping less often than every other breath.

If you understand the logic of diving half +200 psi on stages, you'll understand that the point is to use them up as much as possible on the way into the cave (and out for that matter). Then you factor that usage in and use less on your back gas to compensate, thus factoring it into your turn pressure.

Just assume this scenario as an example.
You use a bunch of stages going into the cave, lets say two 80s for simplicity, both breathed down by one third.
Then you switch to your back gas, also two 80s, breathe that gas down by one third as well, hitting overall thirds. Essentially you would now have used a third of all four 80s.
Let's say at this point you get into trouble. You may get lost, in zero vis off the line, stuck etc. Lets now assume you breathe the second third of your back gas in the process of fixing your issue.
What you now have left on you is only one third of your two back gas 80s, which is exactly what is left in those two stages you dropped earlier, meaning you need those two stages and no more delay or you will possibly not not make it out. You have essentially used up all of your reserves, sadly more than you have on you. You are now potentially in real trouble unless you find your stages.
So what if you passed a stage by accident during the zero vis issues? What if someone removed it?

A much better version would be, and this is only an example how I would do it, you breathed half +200 on each of your your two stages, subtract that from your total back gas, meaning you only count one of your 80s in the back gas for your consumption. That means, once you use a third of the other back gas tank (or a sixth in total of your two back gas 80s) it's time to turn.
This is being somewhat conservative but you'll now have all the gas you breathed in total (from your stages and your back gas), plus a little extra, on you. So even if you miss all your stages you would still make it out. If you had real trouble, a medical issue for example, you could opt to head straight out, maybe picking up a stage or both without switching to it, but you have way more options either way.

The whole point of all this is never to get into a situation where you may run out of gas. And if you do and have a buddy, you share gas using a long hose. That is what you learn and practice as a cave diver and it's also what you should do in an emergency.
It works through restrictions, it works in zero vis and it works great on a scooter.
Buddy breathing works with none of that.

The bottom line is, there is much you can do in preparation, planning and execution of a dive to never run out of gas. And you really shouldn't, it should absolutely never happen.

Not saying it is ideal, or what anyone should plan on. I don't have the experience or training to say what the right way is. I'm listening and asking questions to understand, so that I can be better prepared when I take the training. I much prefer to follow rules that I understand and internalize, rather than just following because I was told to.

That's good and trying to understand it all isn't always easy without having been in such a situation.
Buddy breathing happens in old movies, it was a thing back when people only had one regulator.
Nowadays every diver has two regulators for his back gas, plus one for each stage, plus maybe more for travel gas or O2. So no matter what breaks, you'll always find something to donate to your buddy that he can use. And that gets you the chance to fix and sort out problems, maybe even do a bit of underwater regulator fixing/service like my buddy @bamafan likes to do.

 

[L13]

If you understand the logic of diving half +200 psi on stages, you'll understand that the point is to use them up as much as possible on the way into the cave (and out for that matter). Then you factor that usage in and use less on your back gas to compensate, thus factoring it into your turn pressure.

Just assume this scenario as an example.
You use a bunch of stages going into the cave, lets say two 80s for simplicity, both breathed down by one third.
Then you switch to your back gas, also two 80s, breathe that gas down by one third as well, hitting overall thirds. Essentially you would now have used a third of all four 80s.
Let's say at this point you get into trouble. You may get lost, in zero vis off the line, stuck etc. Lets now assume you breathe the second third of your back gas in the process of fixing your issue.
What you now have left on you is only one third of your two back gas 80s, which is exactly what is left in those two stages you dropped earlier, meaning you need those two stages and no more delay or you will possibly not not make it out. You have essentially used up all of your reserves, sadly more than you have on you. You are now potentially in real trouble unless you find your stages.
So what if you passed a stage by accident during the zero vis issues? What if someone removed it?

A much better version would be, and this is only an example how I would do it, you breathed half +200 on each of your your two stages, subtract that from your total back gas, meaning you only count one of your 80s in the back gas for your consumption. That means, once you use a third of the other back gas tank (or a sixth in total of your two back gas 80s) it's time to turn.
This is being somewhat conservative but you'll now have all the gas you breathed in total (from your stages and your back gas), plus a little extra, on you. So even if you miss all your stages you would still make it out. If you had real trouble, a medical issue for example, you could opt to head straight out, maybe picking up a stage or both without switching to it, but you have way more options either way.

The whole point of all this is never to get into a situation where you may run out of gas. And if you do and have a buddy, you share gas using a long hose. That is what you learn and practice as a cave diver and it's also what you should do in an emergency.
It works through restrictions, it works in zero vis and it works great on a scooter.
Buddy breathing works with none of that.

The bottom line is, there is much you can do in preparation, planning and execution of a dive to never run out of gas. And you really shouldn't, it should absolutely never happen.



That's good and trying to understand it all isn't always easy without having been in such a situation.
Buddy breathing happens in old movies, it was a thing back when people only had one regulator.
Nowadays every diver has two regulators for his back gas, plus one for each stage, plus maybe more for travel gas or O2. So no matter what breaks, you'll always find something to donate to your buddy that he can use. And that gets you the chance to fix and sort out problems, maybe even do a bit of underwater regulator fixing/service like my buddy @bamafan likes to do.

Thank you for those examples, they really helped my inderstanding.

 

[Underwater Tourist]

@L13 ultimately all “gas rules” are just trade offs between how far you want to carry a stage.

Why drop it at all for example? Why not just swim with the stage forever and then switch only when it’s time to?

It’s just annoying to swim with one and it slows you down, so you are shooting yourself in the foot if you hold on to your stage for the full dive (more drag = slower speed = shorter penetration etc). That said, some people do carry their stage all the way, which is technically the safest way to dive because you always have your gas with you.

As long as you don’t violate your global rule of thirds (global meaning your 1/3 of your total gas, stage + main tanks), you can apply or create your own rules for dropping a stage that make sense given the dive.

For example, you can breath a stage for 1/3 and drop it.
Or do the half+ rule that essentially drops the stage further into the cave.
Or you can breather a stage for 1/3, switch to main tanks, swim a little, and then drop it.
Or a dozen of other combinations.



As for buddy breathing for BM there are some considerations how much gas you want to have in a stage vs BM tanks, but for example for SM it doesn’t matter as much. If it came to gas sharing in SM, it’s infinitely more efficient to just swap tanks with your buddy than to actually use a long hose.

 

[ginti]

As long as you don’t violate your global rule of thirds (global meaning your 1/3 of your total gas, stage + main tanks), you can apply or create your own rules for dropping a stage that make sense given the dive.

Great contribution! However, let me say that even the rule of thirds is usually not enough, so I would rephrase this sentence with "As long as you don’t violate the global gas consumption strategy more adequate for the dive."

We all know how the rule of thirds originated, but we also all know that, nowadays, the "third third" (sorry!) is not "to share" - it is "to solve problems." So very often, divers use more conservative approaches (in a team of two, I often use 1/4).

As cave divers, we should not give the impression that the rule of thirds is The Rule. It is just the limit, and it's crucial to be more conservative at any required time, which is more often than not.

 

[JonG1]

It's not uncommon to carry a safety/buddy bottle, I sometimes do this if solo or when guiding new divers, it doesn't get dropped and generally don't notice the extra drag enough for it to be an issue.

Pretty sure 3rds originated from solo and flow based cave diving, so naturally in the presence of a buddy or the absence of flow 3rds doesn't always cut it.

 

[ginti]

Pretty sure 3rds originated from solo and flow based cave diving

Not really. It actually generated from buddy diving; you can find a bit of it on Sheck Exley's blueprint for survival (page 12 here: https://nsscds.org/wp-content/uploads/2018/05/Blueprint-for-Survival.pdf)

A short part here:

 

[lermontov]

Working through your post maybe you can clarify some points for me that i may have overlooked -

I think the 1/2 rule is valuable for bottle management as youve rightly pointed out - im not sure what percentage of cave divers are utilising 3-4 stages in their dives but i imagine your doing it then youve accumulated a fair amount of experience. 2/3 is a more conservative approach - the down side is as someone has mentioned is not utilising the gas as well as it could be done.

If you understand the logic of diving half +200 psi on stages, you'll understand that the point is to use them up as much as possible on the way into the cave (and out for that matter). Then you factor that usage in and use less on your back gas to compensate, thus factoring it into your turn pressure.

your 1/2 plus 200 (14bar) is not that much difference than 2/3
200 bar tanks =100 plus 14 bar = 114 bar
200 bar tanks = 2/3 = 133 bar
obviously the more your tanks are filled the better the ratio is

Just assume this scenario as an example.
You use a bunch of stages going into the cave, lets say two 80s for simplicity, both breathed down by one third.
Then you switch to your back gas, also two 80s, breathe that gas down by one third as well, hitting overall thirds. Essentially you would now have used a third of all four 80s.

isnt this scenario the same risk as any dive that is not staged ?or do you use the principle of reserving one tank and keeping the second tank using rule of thirds for all dives?

Let's say at this point you get into trouble. You may get lost, in zero vis off the line, stuck etc. Lets now assume you breathe the second third of your back gas in the process of fixing your issue.
What you now have left on you is only one third of your two back gas 80s, which is exactly what is left in those two stages you dropped earlier,

no you have 4 /3 because you only used 1/3 on the way in - each tank has more gas in them than your 1/2 plus 200 (14Bar)

meaning you need those two stages and no more delay or you will possibly not not make it out. You have essentially used up all of your reserves, sadly more than you have on you. You are now potentially in real trouble unless you find your stages.
So what if you passed a stage by accident during the zero vis issues? What if someone removed it?

your suggesting your going to miss 4 tanks? two from you and two from your buddy? - for that to happen you'd have to silt a complete cave system

A much better version would be, and this is only an example how I would do it, you breathed half +200 on each of your your two stages, subtract that from your total back gas, meaning you only count one of your 80s in the back gas for your consumption. That means, once you use a third of the other back gas tank (or a sixth in total of your two back gas 80s) it's time to turn.
This is being somewhat conservative but you'll now have all the gas you breathed in total (from your stages and your back gas), plus a little extra, on you. So even if you miss all your stages you would still make it out. If you had real trouble, a medical issue for example, you could opt to head straight out, maybe picking up a stage or both without switching to it, but you have way more options either way.

I like this method but you can also adapt this system for the exploration after your last tank drop ie use one tank as reserve and use the second tank in the standard 1/3s rule- its no different. i dont think you have WAY more options. you have the same options.

thank you

 

[rjack321]

your suggesting your going to miss 4 tanks? two from you and two from your buddy? - for that to happen you'd have to silt a complete cave system

This has absolutely happened, multiple times too. In JB and Ginnie both, the flow carries the silt from the incident area EVERYWHERE downstream. Both the cave being completely blown out and people missing or not finding their stages - sometimes drowning practically next to them. Keeping your reserves on your person and not scattered in little bits in various stages is the way to go.

Why drop it at all for example? Why not just swim with the stage forever and then switch only when it’s time to?

It’s just annoying to swim with one and it slows you down, so you are shooting yourself in the foot if you hold on to your stage for the full dive (more drag = slower speed = shorter penetration etc). That said, some people do carry their stage all the way, which is technically the safest way to dive because you always have your gas with you.

If you are scootering it can be more efficient to just carry the darn thing. One of my local-ish caves (a mere 12 hrs away) when done on OC is best done as a 2 stage scooter dive. One stage in, one stage out, 100% of the backgas in reserve. Don't even bother to drop either of them, if you'll configured smooth and have a decent SAC rate you can hit the EOL with the one penetration stage (~1,500m p.)

 

[Underwater Tourist]

This has absolutely happened, multiple times too. In JB and Ginnie both, the flow carries the silt from the incident area EVERYWHERE downstream. Both the cave being completely blown out and people missing or not finding their stages - sometimes drowning practically next to them. Keeping your reserves on your person and not scattered in little bits in various stages is the way to go.

Shouldnt they have just grabbed onto the line when they arrived to a silt out, and then follow it until they literally bump into their stages?

If you are scootering it can be more efficient to just carry the darn thing. One of my local-ish caves (a mere 12 hrs away) when done on OC is best done as a 2 stage scooter dive. One stage in, one stage out, 100% of the backgas in reserve. Don't even bother to drop either of them, if you'll configured smooth and have a decent SAC rate you can hit the EOL with the one penetration stage (~1,500m p.)

Yep, scootering is a completely different beast. I haven't touched a dpv yet, but makes sense not to drop a stage since you are not actively swimming yourself.

 

[ginti]

your 1/2 plus 200 (14bar) is not that much difference than 2/3
200 bar tanks =100 plus 14 bar = 114 bar
200 bar tanks = 2/3 = 133 bar
obviously the more your tanks are filled the better the ratio is

They are not really similar.

Rule of thirds with a turning pressure of 133 bar:
Real turning pressure is 140 bar (you cannot read 3 bar on the SPG).
Gas used to enter the cave: 200-140=60 bar.
Gas used to exit the cave (in no-flow ideal conditions): 60 bar.
Gas you can use to manage problems: 200-60-60=70 bar, so you can both donate to your buddy during the entire exit or manage a big problem. This amount of gas is equivalent to 100% of the gas used to enter the cave (or more, depending on rounding numbers)

Rule of half+14 bar with a turning pressure of 114 bar:
Real turning pressure is 120 bar (you cannot read 4 bar on the SPG).
Gas used to enter the cave: 200-120=80 bar.
Gas used to exit the cave (in no-flow ideal conditions): 80 bar.
Gas you can use to manage problems: 200-80-80=40 bar, so you can NOT donate to your buddy during the entire exit nor manage very big problems. This amount of gas is equivalent to 50% of the gas used to enter the cave in this scenario - if you have more gas in the tanks, it will be even less than 50%!

With the rule of thirds, the reserve gas changes from 50% of the used gas (half+14) to 100% of the used gas in this case - this is a 100% proportional increase, not really a small difference...