When thirds are not enough....

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

From my understanding, at least one of them was lost and didn't find the main line right away. They were both in zero visibility during at least one part of the dive. The first one back to the main line looked and was about to exit when he saw his buddy's light coming down the main passage so he stayed to exit with him. If he hadn't waited for his buddy, he should have made it to his deco cylinder without running out of gas. I can't say I fault him for staying an extra minute when he saw his buddy's light. Had they both had an extra 300 psi in reserve, they would both have made it the last 300 feet to their deco cylinders. As it was, they both almost died.
Sounds like something with this story isn't being told-- I find it difficult to believe that two divers can't find the mainline in JB (run better than basically anywhere else in the state), and waste almost an hours worth of gas looking. Doesn't it sound like they're not telling the whole story to you, too?
 
From my understanding, the issue wasn't gas with those guys, it was failure to act as trained when there was a buddy separation. From what I heard, they were separated around kings canyon and wasted way too much gas looking for each other in a silt out. None of these gas plans work if you don't follow standard procedures. As a matter of fact, since these guys stuck around looking for each other until gas was critically low, I wonder if they had double the gas, would they have still been in the same situation? To my knowledge, no gear failure was involved in the situation.

I will say that I'm not entirely sure if my story is correct there, everyone seems to like to hint at this situation from a few months back and not put all the facts on the table.

Edit- I understand the logic behind -100 psi for spg error. That's what I was trying to get out of you-- the why.

If they "wasted too much time" only at King's Canyon they REALLY wasted too much time. Like all the way down to <1000psi remaining. I am not sure if I've only been in JB when the flow up or whatever, but non-stressed I estimate I could get from King's Canyon to 20ft on <40cf although that might require blowing through a few deep stops depending on the size of the cylinders and how much deco I'd racked up.
 
In fact, I've even compared SPGs and found as much as 500 psi difference in a couple (not mine).

That is a very good point to take into consideration, especially since some SPG's are more accurate within a certain range of pressure.
 
Sounds like something with this story isn't being told-- I find it difficult to believe that two divers can't find the mainline in JB (run better than basically anywhere else in the state), and waste almost an hours worth of gas looking. Doesn't it sound like they're not telling the whole story to you, too?


They scootered in a nasty silty area and probably got lost due to crashing a sit mound. I doubt they ever tell the whole story to anyone. Dont know if the scooters were dead or not but one of them couldnt get up the chimney from what i was told.

FWIW, I rarely dive 1/3rds at places like JB, seems the tourist caves are where we have most of the accidents and to make sure I dont get complacent I cut back.
 
Imo, diving a stage (as a proper stage, with reserves in your backgas) is better than a "buddy bottle", which is unsharable (for all practical purposes) and can be rendered somewhat useless by a simple failure.

I'll dive 1/3s in shallow no flow caves that I a) know relatively well and b) have a solid team with me. If we're going to be pokin around in tight areas, I'll back it off some, sure.

For more complex dives, I start to think less in terms of "thirds" or "quarters" and more in terms of "how much time do I have". Time becomes a real issue, especially in the deeper stuff. 10mins to sort out some snafu in 80ft uses a lot less gas (deco and bottom) than 10mins to sort out the same snafu in a 200' cave. Clearly, these simple rules of thumb break down, and different logic needs to be applied.

Agreed. Once you start getting far in a cave, you've also got to consider how much stress and fatigue is caused by carrying extra unneeded gas (and I use that term meaning it's not needed if things go as planned), and what the chances are that the extra task loading causes a problem that wouldn't exist without it. You and I discussed this yesterday via phone, and I don't think we see eye to eye on where the line is, but it's safe to see that we both agree there's a happy medium.
I'm hesitant about responding as its a touchy subject and one where people have in the past jumped to conclusions - and in fact those hasty conclusions are what results in what Marci is referring to in terms of getting beat with both ends of the stick.

Let me start with the fact that I agree that you need to consider the logistics and the effort rerquired to carry excess gas into a cave. The bigger the dive, the bigger the issue becomes. On the other hand, we all agree there are significant donwsides to diving thirds, and that diving on a two person team reduces the reserve gas available compared to three person team in the event of a total gas loss failure.

With that in mind, and applying it to Peacock, there are longer dives where we will use a stage and carry all of the reserve gas in the primary tanks (sidemount at this point). In that case we are not diving anywhere near thirds but are doing a dive that would either not be possible on thirds, would push thirds a bit too hard, or would leave no time to enjoy the dive. In that case, with the extra brought and used via the stage we are effectively not diving anywhere near thirds. The costs of that are the need to haul to more stages to the water and for each of us to carry them in the cave for a portion of the dive.

There are other dives we do that we may push close to thirds (to about 100 psi short of thirds) where neither of us are comfortable a) being that close to thirds on the dive, and b) not comfortable on a two person team without the reserve that a third team member may have offerred. In that case, one of us may carry a stage and then cache it 1500 ft or so into the cave as gas that is not figured in the plan but is just extra reserve gas. The cost of that is the need to carry one tank to the sink and for one of us to swim it in the cave for a portion of the dive.

It is true that the same dive could be staged instead, but the increased logistics of the dive argue against that. If we are not going to need the gas in the event a failure does not occur, then why have both of us carry and breathe stages?

If you extend that to 2 dives per day in the average 60-90 ft deep florida cave, by the end of the day we will have swam a stage upwards of 3000-4000', hauled 4 stages to and from the water, and will need to fill 4 stages at the end of the day. In contrast carrying a stage as a buddy bottle for additonal emergency gas not included in the gas plan reduces the distance a stage needs to be carried, reduces the number of stages needed in the vehicle by 1/4th and reduces the stages carried to the water by 1/2. And at the end of the day, no stages need to be filled.

So it's largely a matter of perspective, but you can't condem the practice and be on both the "be conservative" and "don't haul uneccesary gas" sides of the fence. The reality is that the practice is a compromise suited to specific dives where a stage is not required under normal circumstances, but where thirds, while do-able is less than optimum in terms of reserve gas. It is also true that a single stage is hard to share in an emergency, but the need to share a single remaining stage would assume a double failure and you can plan yourself right out of doing the dive if you go down that road.

Another thing I think people often forget, is how much deco gas do you have? I see an awful lot of people going to the far reaches of Ginnie (ie Heinkle Swim) with just an AL40, but backgas well within 1/3rds. There's also the risk of thinking that you're going to swim out of JB from EOL when the flow is down and deco out on a single AL40 with no redundancy. Also have heard of several cave divers skimping on deep deco bottles and not reserving enough backgas to get them to o2 if they had a true failure or delay at max penetration. That's something that's poorly taught at the full cave and even DPV specialty level. When we're doing long penetrations @ Manatee Springs, we'll carry an extra AL40 just so there's some redundant deco gas. You don't want to be buddy breathing a bottle for 30+ minutes.
I agree. When depth, and the steep deco penalties any delay imposes, comes into play the reserve needs to be increased, not just to allow more time at depth to resolve problems but also to handle the additional deco that may be needed, often even before the diver reaches the first deco bottle dropped in a cave.

I think you are absolutely correct that this is something that is not well addressed in the average full cave class, especially when the full cave candidate may not have already had AN/DP and ideally an extended range or a trimix course. Without that lead in training, the average full cave candidate is not well versed in lost gas and contigency planning.

The longer this discussion goes on, the more obvious it becomes-- these rules just don't hold up well outside of the common tourist caves. HOWEVER, history proves that they get most divers out of the cave safely until they gain experience and tackle dives where experience is needed to plan them. However, having said that, I think with the rise of side mount diving with new full cave divers, that we're over due for a few deaths in tight silty passages where these rules aren't conservative enough.
I think that is an accurate assessment. It's one thing when feeling your way out on the line is just a full cave drill, but it is something entirely different when exiting from a tight cave in low viz or no viz, in condtions where the low viz or no viz may persist for several hundred feet. If the diver is not prepared for that or planning for that, they can get themselves into a potentially lethal situation even before a failure occurs.
 
The problem with this idea is that it places a large reserve in the exact place you DON'T need it, and thats in the front of the cave. Having your reserve with you (in a sharable format) gives you much more options than a bottle that could be out of reach. There are at least two fatalities that come to mind where the diver did not reach their reserve gas in time.

Sucking it up and taking 1 more bottle and using it as a stage gives you that reserve in your backgas. You might be using the same total gas (drop stage at ~half, continue on backgas, turn when you complete your intended dive), but there is MUCH more gas on your person at max penetration. Plus, swimming a heavy bottle has got to be one of the most inefficient things in this entire discussion. Its even worse if you're trying to make an expeditious exit from the cave.

If you both carried a bottle and dropped it (like a safety bottle), then I could potentially see your point, but that's even a stretch on the dives you're talking about.
 
if you have a catastrophic gas loss at max penetration it's probably game over. let's be honest.

if you start going down these roads you can plan yourself right out of a dive. just something to think about

WOW, if I believe that, I would not be cave diving.
If you don't panic (and yes I've been in a real life situation to test this), there's lots you can do to cut down on consumption. Like skip breathing, re-cycling the air from your bc, etc.

Now, if there were two catastrophic gas losses at max penetration, it would really be scary, but I'd still try every trick in the book to make it.
 
WOW, if I believe that, I would not be cave diving.
If you don't panic (and yes I've been in a real life situation to test this), there's lots you can do to cut down on consumption. Like skip breathing, re-cycling the air from your bc, etc.

Now, if there were two catastrophic gas losses at max penetration, it would really be scary, but I'd still try every trick in the book to make it.

so would I.
but it's not likely
 
I've stashed a "safety bottle" not that far into JB when I was scootering there for the first time. IIRC we dropped it at the 2nd T when we dropped the scooters. We eventually swam to the trash room. No, not the far into the cave at all. But I was scootering there for the first time ever and bringing an extra 80cf along and leaving it at the point we started swimming was fine with me and covered some "new buddy" familarization/uncertainty as well.
 
WOW, if I believe that, I would not be cave diving.
If you don't panic (and yes I've been in a real life situation to test this), there's lots you can do to cut down on consumption. Like skip breathing, re-cycling the air from your bc, etc.

Now, if there were two catastrophic gas losses at max penetration, it would really be scary, but I'd still try every trick in the book to make it.
What real life situation have you been in involving a completely OOA situation?
 
https://www.shearwater.com/products/swift/
http://cavediveflorida.com/Rum_House.htm

Back
Top Bottom