Survey question rebreathers

[Greenwood_60]

Looking at reserves and bailout from the point of view of x times what I need to get out is simply wrong. It should be taught to plan to survive catastrophic failures. Fault tolerance: "Fault tolerance or graceful degradation is the property that enables a system to continue operating properly in the event of the failure of (or one or more faults within) some of its components. If its operating quality decreases at all, the decrease is proportional to the severity of the failure, as compared to a naïvely designed system in which even a small failure can cause total breakdown. Fault tolerance is particularly sought after in high-availability or life-critical systems." http://en.wikipedia.org/wiki/Fault_tolerance

With thirds in and a backmount team of two, you have 100% of the gas you need (in theory) to get out from a massive failure at max penetration. You may be able to save some of your gas by isolating... by your buddy may also fail to isolate. Either way, you play to survive that failure by both diving to thirds. With a SM pair of divers, you have 150% of what you need to exit with the same massive failure. With a pair of RB divers, and a massive failure, you have that same 150%. This is why some say it's OK to dive effectively half on a stage.

This of course says nothing for the failure rate of the individual systems, or the reliability of your buddy (both required for team BO and BM). It also says nothing for the increased probability of individual failures with the increase in the number of discrete systems.

[apitkin]

In the overhead environment how many bailout bottles? PO2 set points for 100' dive.

What a strange question to ask. Obviously it is impossible to answer. How fast are you going to survey? How much cave are you planning to survey? What grade - i.e. just a line survey or sketching, radials etc. What are the characteristics of the cave - silt, restrictions, flow, even variability in depth (which will use more diluent) all should be factored in.

I would hope that if you are sufficiently trained and experienced enough to survey in a cave on CCR you are able to synthesize an answer to your own question taking into account everything mentioned above.

Andy

Cue Rich Courtney: "If you have to ask, ya shouldn't be doing it."

[Draker]

I think the question was meant as a poll (taking a survey); not specifically about surveying on CCR in a cave.

[Draker]

Rick and I were having a discussion over a few beers last night about adequate BO. He doesn't CCR, but does occasionally dive in a mixed team. He and I have both observed on a number of occasions teams of CC divers who were probably not carrying enough BO given their dive plan.
I'm personally always amazed to see CCR cave divers only carrying one BO bottle. Or bottles that aren't sufficient enough to get out of the cave on given a truly sh*t hits the fan moment. I've also seen divers carrying BO that was not appropriate for the depth they are diving. ie, 21/35 at 250' depth in EN. (And no long hose on the lone BO bottle).
I have a have a hard time wrapping my head around the 1.5 rule. I'm a firm believer in two men enter, two men leave. This isn't Thunderdome...

[cloudboy55]

For the Hinkle, I'd personally plan to carry two 80's and drop a third along the way for rb bailout.

[CCRMichael]

I have been working on an article for my website with my thoughts about this. I guess this would be a good opportunity to post a rough draft.:

Many people teach that while diving a CCR in a cave a diver should carry twice as much bailout as needed to exit the cave. The purpose of this article is to apply the rule of thirds to CCR Cave bailout correctly. I do not want to talk anyone into carrying less bailout. I only hope to allow CCR Cave divers to better understand the rule of thirds and what it has to do with CCR Cave bailout and how to set up minimums.
First let's review traditional rule of thirds as it pertains to open circuit cave diving. With rule of thirds you use 1/3 to go in, 1/3 to go out and 1/3 for emergencies. It goes without saying that we need contingencies in cave diving and have to carry extra gas. The question is why 1/3 saved for emergencies. Without taking hours to convince you of all the possible scenarios where you could use this contingency gas lets look at why thirds became a minimum. If you were to have a catastrophic gas failure at the deepest point in the cave you should have exactly enough gas to get out. lets look at two possible scenarios.
A two person dive team where both divers have the same SAC rate enter the water wearing double 80s and swim into a cave for lets say 20 minutes. Their tanks were filled to 3,000 psi. After 20 minutes of swimming they turn the dive because they both reach 2,000 psi which is their turn pressure. That way they have used 1,000 psi entering the cave, and still have 1,000 psi to exit the cave upon which they will have 1,000 psi left in their tanks at the end of the dive that they did not use because they did not have an emergency.
Lets say diver 1 has a hose burst and is forced to shut down one tank. at the deepest penetration point where he is at 2,000psi. If he did this quickly he still has 2,000 psi, but half the volume of gas. So now he has Exactly the amount of gas needed to exit the cave. Upon exiting he will have 0 psi. Now thirds doesn't seem like so much extra gas does it. The diver would have enough to get out assuming nothing else went wrong on the way out and that it did not take him any longer to get out than it did for him to get in.
So why do we use such a low minimum as the standard rule for cave diving. Because this is the lowest amount of contingency gas someone could safely carry. If they want to carry more that is their choice. Rather than throwing random numbers out there divers can think well this amount is thirds and I will carry this much extra for this reason. Some of those reasons might be the flow of a cave, deco obligations, SAC rate of buddies, experience of buddies, familiarity with the cave, direction of flow, and many more. But they all plan based off of the minimum so they have an accurate understanding of how much they want to carry and how much beyond the minimum they want to carry as well as where to stage it if needed.
Lets analyze the rule of thirds and how it pertains to CCR Cave bailout. In open circuit diving if you do not have any emergency you have left in your tanks the exact amount of gas you would of needed to get out. If you carry enough bailout on your CCR to exit the cave from the deepest penetration then when you exit without any emergencies you will have the same "left" in your tanks, enough that you could have exited the cave.
If you were to use your redundant gas on open circuit from your turn point you would exit the cave and have 0 psi. On CCR Cave if you carry just enough bailout to exit and you had an emergency you would exit with 0 psi. So carrying just enough to get out is the same as diving the rule of thirds on open circuit. People who carry twice as much as needed to exit would be diving a "rule of fourths". There is nothing wrong with this and there are many great reasons to carry extra. However I strongly believe they should understand how much they are carrying and why. For this reason I suggest using a minimum (just like we do in Open Circuit rule of thirds diving) to plan and then add any extra beyond the minimum we would like.



80 v 2x 40s - I don't require it. Plus for deep diving I am not going to carry 2 bottles of deep mix, 2 bottles of travel mix and 2 bottles of deco mix.
In open Circuit diving you are using 1 regulator and the other is back-up. In CCR diving you are using your CCR and your bailout is your backup, it is no less redundancy than open circuit diving.


with 1/3rds in the event of an emergency you get out with just enough. That is why it is a MINIMUM standard, with CCR Cave if you carry twice as much bailout as needed to get out that is the equivalent of diving 6ths.

The only total failure that isn’t prevented with following the rules and a true pre-breath is torn loop and losing the group at the maximum penetration of the cave. That’s a bad day.

These are all minimums. They should be altered based on experience, cave environment, flow, definitely if diving a siphon, team size. Especially if solo diving.

[floridabob]

Great read, Michael. Succinct, specific and translates well to OC.

I don't have any issues with what people plan for their BO...as long as theirs is a plan shared and agreed. If we are on a team, then they need to understand MY plan does not involve sharing. We are same tide, same ocean for the type diving we are doing. That mean I won't help? No, It does not. It means plan Alpinist. Not buddy dependent.

Now, how much gas is a personal and logistical choice till it extends to a team. And is environment based: I plan differently for wrecks as much more is deco gas rather than bottom or penetration gas by mix rather than amount.

I am very comfortable having what I need to exit x 2. If I need 80 to exit, I take 160...which is a redneck thirds; if you figure if I need 80 to get out then I MUST have come to that point by using 80. I understand all the fancy stuff, I'm just using a broad brush: 80 in, 80 out, 80 reserve. The 80 in was supplied by the RB. Oversimplified, definitely. But clear enough, I think?

Now I have to say, if you don't do this stuff, easy on the declarative statements. Not a lot of credibility for non believers.

240 cf to exit from the Hinkle is a seiously bad day. I can swim out on a backup light on considerably less than an 80...done it. Not bragging but damn, 240 cf? I'd carry an extra backup light or two before I'd add a tank.

Just thinking out loud.

Remember, I'm an expert as I stayed at a Holiday Inn Express last night, drink Dos Equis and now have a whopping total of 87.5 hours on my RB....consider the source, boys and girls.

Bob

[floridabob]

Thunderdome! Love it!

[CCRMichael]

I am not saying people need to adopt the idea of team bail out but they also need to remember most tech diving principles came from cave diving and most cave diving principles came from exploration or expedition level cave diving. There gets a point where you go deep enough or enough penetration where carrying enough bail out for each person to exit on their own is more task loading then team bailout. The point where too many tanks is more dangerous is debatable and will vary but the point exists. Just as the point where a bail out breather becomes safer. The keyword being safer and not necessarily safe.

Even when I am carrying enough gas for me to personally get out I still teach to use team principles and gas swapping on the way out. Lets say one diver bails at maximum penetration and needs 80 ft3 to get out. The team begins the exit and they all have exactly enough OC BO to get out. Only one diver is actually using it. I breathe it down a 3rd and then swap it with a buddy. We have swam a third of the way out and the buddy I swapped the partially used cylinder would still have exactly enough to get out if he for some reason had to bail but I now have 1/3 extra. This doesn't put anyone at an added risk it just gives the diver who is actually in need extra gas without causing the rest of the team to not have enough. Everyone was carrying enough to get out on their own but that doesn't mean you can't still act like a team.

[floridabob]

Michael--I didnt think you were preaching Team Bailout. And I understand and respect the principles you are offering.

For me personally, I am anti-tank swapping. Not saying it wasnt taught and cant be done. Just that I wont use it as my go-to plan. I am not conducting high level exploration dives by any standard but hope to...and the plan for the group is generally different than what it sounds like you guys use.

Too much bailout can be complex, cumbersome and even counter-productive. I agree on that. There is a tipping point, as always.

And acting like a team is defined by the team. For instance: on one dive it was decided that, in the team of three all CC, if one has an issue he would peel off and the other two would continue. Gotta have my own gas in that scenario. I respect others would not want that plan and would go a different route. That was our advance decision and we were prepared accordingly.

I enjoy the interplay of ideas and different processes. One is not necessarily more right or better than the other. Usually, anyway.

Bob