Two German divers drown at Gran Cenote Kalimba at Tulum

[lamont]

Pretty sure I've done single stage dives coming from Grand up the PDL line which have been over 120 minutes without violating thirds at all. I thought the average depth of the cave there was no deeper than 25 ft or so, which gives me a total runtime of 151 minutes on 2 Al80s consumed with a comfortable 0.60 cu/ft/min SAC, and a whole stage left in reserve. That kind of suggests to me that they weren't particularly fit or comfortable. If their Al80s were dropped on halves with 1300psi consumed (with a generous 400psi reserve) and the full 28 minutes used then their SAC rate at the entrance looks like 0.70. If they used 1500psi and 26 minutes with 2 minutes of switching and no reserve that would push it up to 0.87 for their "calm" SAC rate.

And given the 65-ish minutes from the stage drop to turn, and the 34-ish minutes from turn to fatality, it would seem they turned closer to halves than even thirds or fourths, and maybe even a bit beyond it. Even accounting for higher SAC rates at the end, 0.875 * 65 minutes * 1.6 ata = 91 cu ft in, and 1.26 * 34 * 1.6 = 68.5 cu ft which about accounts for it all and is 57% of their gas used before turn.

Those SAC rates seem so high I'm not certain I'm missing something though. Also I'd suggest the recovery team somehow missed a gas loss issue, but the high consumption in the stages is consistent with them just having high consumption.

 

[Norwegian Cave Diver]

I have read all of the posts and reread all of the posts. I have scrutinized the account of what happened and what may have happened. I have printed off the maps and marked them up to try and understand as best I can. About all I have left to do and dive the site to understand it better. And I’m not sure that even want to. I wish the family and friends and all those that knew them to be at peace. I’m sure they would say they are sorry if they could. It’s our role to learn. Not allow ourselves to be complacent. To always be wary.

 

[Izze]

Pretty sure I've done single stage dives coming from Grand up the PDL line which have been over 120 minutes without violating thirds at all. I thought the average depth of the cave there was no deeper than 25 ft or so, which gives me a total runtime of 151 minutes on 2 Al80s consumed with a comfortable 0.60 cu/ft/min SAC, and a whole stage left in reserve. That kind of suggests to me that they weren't particularly fit or comfortable. If their Al80s were dropped on halves with 1300psi consumed (with a generous 400psi reserve) and the full 28 minutes used then their SAC rate at the entrance looks like 0.70. If they used 1500psi and 26 minutes with 2 minutes of switching and no reserve that would push it up to 0.87 for their "calm" SAC rate.

And given the 65-ish minutes from the stage drop to turn, and the 34-ish minutes from turn to fatality, it would seem they turned closer to halves than even thirds or fourths, and maybe even a bit beyond it. Even accounting for higher SAC rates at the end, 0.875 * 65 minutes * 1.6 ata = 91 cu ft in, and 1.26 * 34 * 1.6 = 68.5 cu ft which about accounts for it all and is 57% of their gas used before turn.

Those SAC rates seem so high I'm not certain I'm missing something though. Also I'd suggest the recovery team somehow missed a gas loss issue, but the high consumption in the stages is consistent with them just having high consumption.

You have used incorrect time figures in your calculation. Stage drop to turn is around 47 minutes rather than 65 and turn to fatality is just over 50 minutes, not 34. The average depth is also deeper, especially in the first part of the cave coming from the Calimba side.

SAC for the stages works out to around 17 and 19 liters/minute which is in the higher ”normal” range. Nothing out of the ordinary, especially given the age of the divers. Filming probably added a little bit. Expected turn at thirds with that gas consumption would be around the 70-75 minute mark.

The reasoning for ruling out gas losses is detailed in the report. Let’s just say that it is unlikely.

 

[Bob DBF]

Filming probably added a little bit.

Depending on the quality of film they were working for it could add more than a little. Slowing down, to avoid the rapid video seen on YouTube, would add some, but in depth film in an area or reshooting can add up.


Bob

 

[kafkaland]

I’m still puzzled by the entire sequence of events. Where did the gas go? Even with the suspect gas planning and a SAC rate at the high end of normal, they should have had plenty of gas to get out at either exit if they indeed turned on thirds. I have to believe that at least one of the divers blew past thirds, didn’t look at his gauge when his buddy signaled turn pressure, and realized only how low he was when they got out of Much’s. Or something like that. It’s sad and also a bit scary how they apparently just whiled away their gas while filming until it was too late.

 

[Norwegian Cave Diver]

Look at the timeline and then plot it out on the second map. I appears they turned the dive back towards Kalimba and passed their first jump and then turned the dive again?? I think I am correct.

 

[Izze]

Look at the timeline and then plot it out on the second map. I appears they turned the dive back towards Kalimba and passed their first jump and then turned the dive again?? I think I am correct.

They took in the jump and likely grouped back together for the discussion just after the jump. They were technically turned towards Calimba but I doubt they swam any significant distance in that direction. The gap is less than six minutes and includes taking the jump back as well as deploying wetnotes and having a written discussion.

As for gas consumtion our belief is that stress played a significant part to increase it. Without a drastic increase in SAC there should have been enough to exit safely. A scenario where one diver turned a bit late and where both the time to swim back and gas used increases due to flow could easily lead to worryingly low reserves when the jump is taken in. It is entirely possible that the diver monitored gas levels for the way back and only notified his buddy when reaching critical levels.

 

[SapphireMind]

My understanding on this, and I am a novice and not a cave diver, just always seeking to understand: the rule of thirds is not always conservative enough, and a rule of fourths might be better? I don't fully understand the path since I'm not a cave diver, that part was confusing. They turned to go back, and then turned again to try and get to a different exit?

My OW instructor is an experienced cave diver and she taught me the rule of thirds, just for my regular recreational diving. It just gives an extra cushion for your trip, and if your SAC has dropped during the dive (as you settle in or whatever) you can dawdle more once you get close to your ascent area. But always better to have that time extra at the end of the dive, just in case.

 

[Big Eyes]

@ Izze: Is it correct that there was no video footage during the 39th - 64th minute and around the 75th minute? I ask because there is Assumption in the timeline at these times.

Could you perhaps explain that a little clearer? What exact distances or dive times are meant here?:
"You have used incorrect time figures in your calculation. Stage drop to turn is around 47 minutes rather than 65 and turn to fatality is just over 50 minutes, not 34. The average depth is also deeper, especially in the first part of the cave coming from the Calimba side."

 

[rjack321]

My understanding on this, and I am a novice and not a cave diver, just always seeking to understand: the rule of thirds is not always conservative enough, and a rule of fourths might be better? I don't fully understand the path since I'm not a cave diver, that part was confusing. They turned to go back, and then turned again to try and get to a different exit?

Its a low flow cave but there is some slight flow which adds up to increased consumption going up the Paso line or Much's towards Kalimba. 1/3rds is aggressive in a "no" flow cave but in this case they are actually diving a slight siphon, ie they started going downstream and had to swim into the flow however modest to get back to their entrance.

Yes the seem to have turned back towards Kalimba (going upstream) then decided to turn around again and head downstream and exit at Ho tul. The wetnotes suggest they realized the gas issue and were hoping the combination of downstream and wide open passage would be the fastest way out.