Provocative talk yesterday at NSS-CDS: Toss out the rule of thirds?

[rjack321]

This is literally nothing new. I learned 3rds was flawed 15 years ago. I didn’t see the lecture. So maybe it’s innovative he has some data, but the underlying thought that thirds isn’t all it’s cracked up to be is far from new.

Not the first time old news has been repackaged with a flashy title

 

[jadairiii]

this is NOT a physiological problem of being "in shape," it's a psychological stress response. I'm a research psychologist, and he is right. We use physiological measures such as heart rate and respiratory response as dependent measures when studying stress and anxiety, because they skyrocket under stress - even if the person reports feeling calm. That is, you can feel calm and in control, and still find your respiratory rate increasing by upwards of (at the highest end) 700%.

I'm no expert, but ..... in shape or out of shape, the first moment the "Sh*t happens" in shape or out of shape, heart rate and respiratory response will go up. But the person in excellent shape can get their heart rate and respiratory response down fast, the person that is out of shape will often spiral out of control, never getting their heart rate and respiratory response under control. And a person in excellent shape should be able to control their to some degree.

I was a test subject for a psychological stress response test at UF back in my college days, when I was in psychology. I was in crazy good shape, they threw everything at me and my heart rate and respiratory response never fluctuated. The psychologist came in and told me they had to toss my test. To quote Rudyard Kipling: "If you can keep your head when all about you Are losing theirs and blaming it on you...."

 

[kensuf]

Stratis Kas addressed this at length in the talk - this is NOT a physiological problem of being "in shape," it's a psychological stress response. I'm a research psychologist, and he is right. We use physiological measures such as heart rate and respiratory response as dependent measures when studying stress and anxiety, because they skyrocket under stress - even if the person reports feeling calm. That is, you can feel calm and in control, and still find your respiratory rate increasing by upwards of (at the highest end) 700%.

Kas and colleagues have been modeling this and that was a large part of his talk, that you need to account for not only a stressed recipient, but also a stressed donor, both of whom are likely to be using far more than twice the gas they used to enter the cave on exit.

There's an excellent old post by Andrew Ainslie about the massive amount of gas he blew through during an incident at the back of Ginnie: How Much Gas is Enough? Running on Empty

Stress and anxiety can hit anyone under the right set of circumstances. And if you do this long enough, you'll have the right set of circumstances. Let me share one of my memoriable goof ups.

I was guiding someone in a relatively shallow system a few years ago. We were in a siphon, in a passage that I had not been in for a couple of years, so I was not as familiar with it as I probably should have been. Of course, due to the infrequent traffic in this passage, the passage was quite "dusty" and our exhaust knocked a bunch of organic debris off of the ceiling, reducing visibility to just a few feet.

At some point the arrows flipped, but due to the poor visibility, I missed seeing that happen at the midway point. The lines in this particular area of this particular cave are almost all 30-40 years old, #18 twist line, covered with years and years of dust and many side jumps are really close to this line, making an accidental blind jump a possibility. When I came across the first arrow that was pointing away from my known home, I took a deep gulp and turned the dive.

I kept my breathing under control, but I have to admit I had a solid 2-3 minutes of second guessing myself as we were working our way back along the way that I hoped would bring us out. I had thoughts ranging from "how could I have been so stupid to have gotten on a side passage" to "man, what kind of a moron am I for guiding someone in this system and getting them lost." Only once I came up to the back to back arrows did I really begin to feel better.

The one thing I can say is that knowing I had more than enough gas as well as the skills to solve the problem, made things easier and helped me keep my breathing under control. There was the deep gulp, and heart pounding in my ears, when I saw the first arrow pointing the wrong way, but after the initial shock of the situation I regained mental control.

The rule of thirds is really the most aggressive air management rule we can use in the overhead and it's really only applicable in the right set of circumstances (ex. 3 people, not a siphon). Obviously, an OOG situation is vastly different and the stress and anxiety could be overwhelming, but if you were out of gas and your entire team planned gas reserves properly, you should hopefully be able to regain your composure after a couple of minutes and realize there's plenty of gas to get you home.

BUT, and this is really critical, there really is no reason for someone to be OOG. I'm serious about this, there is absolutely no reason for a person to be out of gas without other issues.

Let's rehash the reasons why someone in a set of backmount doubles could potentially go out of gas:

1. Person was not paying attention to their gas and they simply ran out. This person should not be diving, period. If the situation was that they had their isolator or left post closed (roll off), hopefully they caught it when they realized their pressure gauge was not dropping. But let's say for the sake of argument that they were having a crappy day and that's why they didn't check their valves when their pressure gauge wasn't dropping, where was their buddy in this mix? Even if a person is oblivious to their gas consumption, their buddy should have hit their turn pressure well before anyone has run out of gas.

Whenever a single person in the team hits turn pressure, that's when it is time to go home. Even the worst gas hogs will rarely (if ever) breathe at a rate 3x their dive buddies. So let's say you've got two people diving thirds and starting with 3600. Even if one of them breathes their doubles beyond their turn pressure without noticing it, I'd bet their buddy hits 2400 before the first one runs out of gas.

However, if we've got two people in a dive team that are not monitoring their gas, that problem began before they ever got to the dive site...

2. A person knocked a valve into the ceiling and banged a first stage off. I know that sounds far fetched, but an old dive buddy from the 90s had that happen to his wife when they were a mile from home in Manatee Springs. Even though she knocked a reg off of her manifold, she was able to close the valve and nurse her way back home without running out of gas. Was it unpleasant and stressful? Sure. Did she run out of gas? No.

3. Burst disk fails. I won't wade into discussions about the pros/cons of burst disks/double disks/stainless plugs, but if a burst disk fails on you, you should be capable of isolating the manifold preserving some of your gas. If this happens at maximum penetration, yeah, you'll probably eventually run out of gas from your remaining cylinder on the exit, but it won't catch you by surprise. If you're the guy with the burst disk failure, I would put you in front of me (in a 2 person team), or in the middle (in a 3 person team) so when you run out of gas I can be sure you have a way to get it.

4. Reg failure (HP seat failure, LP hose rupture, etc). That's why we have two first stages. Shut the offending valve down and go from there. See the response for burst disk failure basic diver placement / procedure.

5. Manifold "spontaneously fails." This should never happen. I've had doubles fall off of benches and watched first stages break, but the manifold held. I think one guy in this thread even had a set of doubles go flying out of a truck bed, again the manifold held. The other Ken was rear ended not too long ago, a set of doubles went flying from his truck. Again, the manifold held. BUT, let's say it does fail against all odds, well that's where your buddies come in and their reserve gas is there for you.

So the odds of truly being out of gas in a cave are low, but it happens. But what I can tell you is that when it happens, it's because of some other series of events, such as getting lost (the guys with the cameras in Mexico, the intro divers at Manatee) and in those cases the rule of thirds wasn't the issue.

 

[rjack321]

The rule of thirds is really the most aggressive air management rule we can use in the overhead

In Caverns Measureless to Man, they're diving 1/2s plus 200, so 1/3rds is actually an improvement over that

 

[kensuf]

In Caverns Measureless to Man, they're diving 1/2s plus 200, so 1/3rds is actually an improvement over that

I dove with a J valve a few times. Anything's an improvement over the old ways.

I will say I miss the horsecollar BC with the CO2 cartridge. It was always freedive down to 30' and pop the cartridge at the end of a dive trip...

 

[rddvet]

What condition is causing a sudden OOG at max pen?

If something goes wrong on a cave dive (anything) and you don’t do anything about it, you’re going to drown. If your tanks are leaking and you just don’t address it, you’re cooked regardless of what your gas reserves are.

Everyone loves to blame manifold failures on doubles. Cause that happens all the time. Don't you know that's why sidemount is SOOOOOO much better?

 

[rddvet]

5. Manifold "spontaneously fails." This should never happen. I've had doubles fall off of benches and watched first stages break, but the manifold held.

Yep. Had same thing happen with old school tanks with the captured o-ring style valves. Landed straight on the manifold handwheel but only thing that broke was my reg

 

[scubadada]

...His research shows that RMV increases for both divers, but particularly for the out-of-gas diver, by a factor of as much as 6-10 times normal average...

Sorry, I am not a technical diver. How can one increase their RMV to that degree over any period of time?

Under extreme exertion and/or psychological stress, I have not been able to increase my RMV over a sustained period to more than 2-3 times my average RMV.

Thanks

 

[Capt Jim Wyatt]

I used 1/2+ 200 many many times at Little River, Devils' and Madison back in the 1970's. It was an acceptable gas rule long before the CDS existed.

I am not advocating for that rule now. But it worked and we had acceptable reserves when we surfaced.

 

[boulderjohn]

There was an OOA incident, ending near Grand Cenote near Tulum a couple years ago in which two people perished, and the details do suggest a highly increased RMV.

The two entered the cave using stages, dropped the stages, and continued on while dong a lot of videotaping. At some point they were returning, when they had a realization that they were in a gas shortage. The only clue is the notes they wrote in which they decided not to return to the entrance (and their stages) and decided to exit instead at another entrance, Grand Cenote. The last note (in German) was simply Rauss! (let's go!).

A look at a map suggests they may have been better off go back to the stages, but in any event, they ran out of gas roughly together. One guy got a little farther than the other, but but both computers showed the same dive times, suggesting they shared air. (IIRC, they were diving sidemount Toddy style, which makes air sharing interesting.)

I wrote a report on the incident for NSS, and in doing so I communicated extensively with the well-known divers who found the bodies and analyzed the dive. They took a long, long time looking at the gear, the computers, and the videotapes before finishing their study because it did not make sense. These were veteran divers who quite suddenly and without any apparent warning realized their gas supply was compromised. There was no sign of equipment problem. They then ran out of gas after completing a total distance that the investigators felt they should have been able to cover easily.

This is not on topic, but their exit ended in an area with no fixed guideline, nothing directing them to the relatively nearby exit. That is because there is a small cenote (not used) right there, so the guidelines to several directions of travels are missing because it is technically a cavern zone. They were very close to being able to reach that cenote, but, of course, there was no line showing the way. They may not have been able to reach it, but it was close.