Ginnie Springs diver missing - Florida

[boulderjohn]

As for a full report after a death in a cave...
Last year there were two german guys who passed away in a cave near Tulum. Lots of speculation on here and on cavediver.net. I understand that we (cave divers and others) want to understand what happened. It took about 1 year for a full report to be published and it was a very good detailed report. I took that report and printed it off - laid it out on my desk - and scrutinized it. ... My point is - a highly detailed and respectful report helps us cave divers understand what can happen and how we need to think to stay alive in a cave.

My NSS report on this incident was based on that excellent and highly detailed report as well as consultation with its author, during which we discussed possible scenarios. I can't figure it out, either.

That is partly what is maddening about writing such reports. You can be 95% sure about something, but....

A few people, including the former training director for the NACD, got on social media and said they could have saved the deceased. The deceased had over 60 minutes of mandatory deco and was 800' from the exit when he died; even if he could have been brought out, he couldn't have been revived before dying from explosive DCS.

...and that is what happens when you are sure of something but turn out to be wrong. You cause a Hell of a lot of trouble, so your wording has to be very, very careful

 

[Jeremy Williams]

On CCR 1.4 is a little high
1.3 is the default setpoint taught in MOD1

Longer cave dives are much lower, 1.0 or 1.1 is common. At 1.2 you hit 100% CNS in about 4 hours. 1.4 on a CCR cave dive is considered high but not cause for immediate concern. Hence the "just shut off the O2 and breathe it down" instruction, but this is a new phenomenon. Historically, seeing 1.4, would have been reason to dil flush.

MOD1 is only a course that theoretically exists. The actual TDI “Diving Rebreathers” student manual doesn’t say that 1.3 is the default. It’s been a while since I looked at the hot mess that is the IANTD CCR materials, but I’m pretty sure they don’t either.

Here is what the TDI book does say...

“For the above reasons, the oxygen setpoint on a closed-circuit rebreather should not exceed a maximum PO2 of 1.4 bar/ata, and the oxygen fraction of the supply gas for a semi-closed-circuit rebreather should not be less than 25 percent at normal workloads for the bottom phase of the dive. Whenever possible, lower setpoints on closed-circuit systems and more oxygen-rich gas supply mixtures on semi-closed-circuit systems should be used. Higher oxygen setpoints may be useful during decompression on certain dives. This must, however, be balanced against dive duration and workload.”

There is another passage that suggests that a setpoint below 1.0 is not advised. But the net result is that they don’t tell you what to use. Who’s material says that 1.3 is the ‘default’? I don’t dispute that your numbers are good advice, but I think that calling 1.3 the default is not accurate from my experience.

 

[boulderjohn]

Springboarding off of the need to be very careful when writing reports....

I have only written 2 reports in cases in which I was at least nearby. That means I have to rely upon multiple sources of information. In many cases, someone clearly made a mistake, and in cases where a number of people were involved, some of those people may be survivors. On more than one occasion, I was convinced the person I was interviewing was lying--but they were supposedly my best source of information. I am not a policeman, and I am not building a legal case. I consult with the NSS ACA editor, and we, of course, go with the most objective account possible, which may mean leaving out something I feel should be in there.

One thing that has become clear to me over the years is that the cave community has some strong antagonisms that extend well beyond geographical boundaries. I have felt those antagonisms that inspired skewed reports more than once.

All in all, there is a lot more involved in writing a fatality report than you might imagine.

 

[rjack321]

MOD1 is only a course that theoretically exists. The actual TDI “Diving Rebreathers” student manual doesn’t say that 1.3 is the default. It’s been a while since I looked at the hot mess that is the IANTD CCR materials, but I’m pretty sure they don’t either.

Here is what the TDI book does say...

“For the above reasons, the oxygen setpoint on a closed-circuit rebreather should not exceed a maximum PO2 of 1.4 bar/ata, and the oxygen fraction of the supply gas for a semi-closed-circuit rebreather should not be less than 25 percent at normal workloads for the bottom phase of the dive. Whenever possible, lower setpoints on closed-circuit systems and more oxygen-rich gas supply mixtures on semi-closed-circuit systems should be used. Higher oxygen setpoints may be useful during decompression on certain dives. This must, however, be balanced against dive duration and workload.”

There is another passage that suggests that a setpoint below 1.0 is not advised. But the net result is that they don’t tell you what to use. Who’s material says that 1.3 is the ‘default’? I don’t dispute that your numbers are good advice, but I think that calling 1.3 the default is not accurate from my experience.

Have never seen a manual but my TDI course slides talked about 1.3 so much it might as well been a "default". But you're right, that might be too strong a word. Especially for cave dives on a mCCR, people aren't swimming around for 30mins at 1.4 out of a 4 or 5 hour dive.

Historically the remedy would be to dil flush. Within the past few years a cadre of CCR instructors have advocated using an in-line shut-off on the O2 and "breathing it down". If you had proposed that on RBW 10 years ago you would have been ripped to shreds for teaching and adopting this practice. Yet here we are with more than a few mCCR divers being taught to shut off their O2 and at least one death due to resulting hypoxia. All to save a little dil.

 

[helodriver87]

Have never seen a manual but my TDI course slides talked about 1.3 so much it might as well been a "default". But you're right, that might be too strong a word. Especially for cave dives on a mCCR, people aren't swimming around for 30mins at 1.4 out of a 4 or 5 hour dive.

Historically the remedy would be to dil flush. Within the past few years a cadre of CCR instructors have advocated using an in-line shut-off on the O2 and "breathing it down". If you had proposed that on RBW 10 years ago you would have been ripped to shreds for teaching and adopting this practice. Yet here we are with more than a few mCCR divers being taught to shut off their O2 and at least one death due to resulting hypoxia. All to save a little dil.

I was taught to breathe down something minor like a 1.3, but that's on an eCCR with the parachute (solenoid) still in play. I actually didn't realize that was a technique that was taught on mCCR. Can't say I love the idea. I'm still chalking this most recent death up to lack of a HUD though. Lots of contributing factors at play, but ultimately, it was not paying attention to PO2 that lead here, and a HUD is such an easy way to catch an unsafe condition while it's still recoverable.

 

[tbone1004]

I was taught to breathe down something minor like a 1.3, but that's on an eCCR with the parachute (solenoid) still in play. I actually didn't realize that was a technique that was taught on mCCR. Can't say I love the idea. I'm still chalking this most recent death up to lack of a HUD though. Lots of contributing factors at play, but ultimately, it was not paying attention to PO2 that lead here, and a HUD is such an easy way to catch an unsafe condition while it's still recoverable.

cue one of the myriad of reasons that I think eCCR's are much safer. Parachute mode on eCCR is the bomb. I do not enjoy when my mCCR gets up to 1.5 or 1.6 and I have to wait to breathe it down with the O2 shut off. The needle valves don't make it any better because you still have to turn them back on. I've never been able to see an advantage of mCCR other than cheaper and easier to manufacture. I admittedly own two of them, but it's a big point of contention I have with them.

 

[helodriver87]

cue one of the myriad of reasons that I think eCCR's are much safer. Parachute mode on eCCR is the bomb. I do not enjoy when my mCCR gets up to 1.5 or 1.6 and I have to wait to breathe it down with the O2 shut off. The needle valves don't make it any better because you still have to turn them back on. I've never been able to see an advantage of mCCR other than cheaper and easier to manufacture. I admittedly own two of them, but it's a big point of contention I have with them.

One argument I hear is that buoyancy is a bit easier without the solenoid firing, but that's what MAVs are for. No reason you can't run setpoint 1.0 and manually fly at 1.2. Admittedly, I'm lazy and let the solenoid run the show on the bottom if it's not super shallow, but the solenoid should never fire from the moment I start my ascent to clearing deco. But it's nice to know it's there. eCCR is the only type of CCR that will actively prevent the loop from going hypoxic when it's in working order. Hypoxia scares the **** out of me, so I'll take a unit that will actively try to keep me alive any day.

 

[tbone1004]

One argument I hear is that buoyancy is a bit easier without the solenoid firing, but that's what MAVs are for. No reason you can't run setpoint 1.0 and manually fly at 1.2. Admittedly, I'm lazy and let the solenoid run the show on the bottom if it's not super shallow, but the solenoid should never fire from the moment I start my ascent to clearing deco. But it's nice to know it's there. eCCR is the only type of CCR that will actively prevent the loop from going hypoxic when it's in working order. Hypoxia scares the **** out of me, so I'll take a unit that will actively try to keep me alive any day.

eh, I haven't been able to tell a difference. I can go back and forth between my Meg and my KISS without noticing. If you are running min loop it doesn't add that much, it's when people don't run min loop that it just slows the buoyancy shift down.
Either way, if you're running min loop and running manual, it doesn't change all that much, so I'm going to call that argument BS.

I run parachute mode at 0.7. It makes me wake up when I hear the click because I apparently missed the flashy bit in my face with lots of red flashes. It admittedly has never gone off without me anticipating it *big ascents where I know I'm going to let it go way down before I stabilize*, but I don't like the solenoid running the show, it's no better than the leaky valve for that, but the solenoid gives me a lot more warm fuzzies than the leaky valve does

 

[helodriver87]

eh, I haven't been able to tell a difference. I can go back and forth between my Meg and my KISS without noticing. If you are running min loop it doesn't add that much, it's when people don't run min loop that it just slows the buoyancy shift down.
Either way, if you're running min loop and running manual, it doesn't change all that much, so I'm going to call that argument BS.

I run parachute mode at 0.7. It makes me wake up when I hear the click because I apparently missed the flashy bit in my face with lots of red flashes. It admittedly has never gone off without me anticipating it *big ascents where I know I'm going to let it go way down before I stabilize*, but I don't like the solenoid running the show, it's no better than the leaky valve for that, but the solenoid gives me a lot more warm fuzzies than the leaky valve does

I don't mind it on the bottom. It's nice to know it's working. Listen for the click, crosscheck PO2, move along. Like you said, min loop volume and it's not a big deal. You'll also notice if it's not firing that way since you'll start triggering the ADV or not get a full breath when you metabolize the O2 and it isn't replaced. But I take it out of the equation on ascents. It really is irritating there.

 

[rjack321]

I was taught to breathe down something minor like a 1.3, but that's on an eCCR with the parachute (solenoid) still in play. I actually didn't realize that was a technique that was taught on mCCR. Can't say I love the idea. I'm still chalking this most recent death up to lack of a HUD though. Lots of contributing factors at play, but ultimately, it was not paying attention to PO2 that lead here, and a HUD is such an easy way to catch an unsafe condition while it's still recoverable.

On mCCR with an orifice the only things bringing down a ppO2 of 1.4 in a reasonable time frame are: 1) ascending 2) adding dil 3) shutting down o2 and breathing it down.

At 100ft in the back of Ginnie your ppO2 of 1.4 is an fO2 of 35%. Assuming 8L of gas in the loop total that's 32L free gas @1 ata 8*4ata = 11.2L of o2 in the loop. At a consumption rate of 0.8lpm O2 that is 14mins to go from 1.4 to zero. So about 12 mins between little too high and "night night". Sounds like a long time, unless your attention is engaged in something else. 12 mins out of a 6 hour dive is chump change.

The lack of a HUD may have been part of the issue, we will never know if a HUD or NERD would have caught it. But not doing the initiating thing (shutting off O2) to breath down the loop instead of just adding dil would definitely avoid the cascade of events leading to hypoxia.