Rob Stewart and Third Dive

[sunnyboy]

If the actual diluent was 10/50, is there any scientific data or consensus on optimum ascent rate from these types of dives? I'm asking specifically about allowing time to get the He out of neurological tissues.

I know of at least one case of a severe neurological DCS from a 200ft bounce dive on 10/50 due to similar ascent rate.

Probably a question for Dr. Mitchell.

 

[justinthedeeps]

So they say you shouldn't do any freediving after SCUBA diving, because the very rapid depth changes of an extreme bounce to depth and back is like shaking up a carbonated beverage. More bubbles than you expected. Have heard accounts of this being real; has it killed anyone?

I guess some are seeing this third dive as tragic extension of that warning?

 

[Subfiend]

I am sure I have seen that when looking at the original documents, but I did not remember the 10/20 entered mix and the GF.
Hard to blame that on a typo when programming the SW, so I suppose the idea was to minimize the He penalty built in the deco algorithm? On top of a GF 90/90? And a 75 ft/mn ascent rate on a third dive?
What could possibly be wrong...

Stewart and Sotis had a conversation on camera where they both acknowledge they are programming the dive computers with the wrong gas mix specifically to avoid the Helium penalty. It was actually filmed twice, with all four divers and the dive boat captain present and participating. Keep in mind, the dive boat captain refilled the tanks between Days 1 and 2. He knew what mix they were breathing and what was programmed into the computers. So, the divers knew, the production company knew, and the dive boat captain knew, all before anybody went in the water on the first day.

 

[Subfiend]

The rapid ascent on the third dive was atypical. It seemed to have been caused by two factors:

1. Stewart was really, really, really afraid of being lost at sea and adrift. This was obvious from the first day's film. He did not want to do a "hot drop," so he made the boat go back to port to get an anchor because the boat was not set up with an anchor or sufficient rope on the first day. He spent a lot of time programming his personal locator device and making sure he and the Captain were on the same frequency.

2. The third dive on Day 2 was made a few minutes before dusk, in waning light. The divers went down to pull the hook and then do a free ascent. Stewart was above Sotis. Stewart ascended from roughly 200 ft. to 20 ft. at a rate of 75 fpm. It appears that Sotis chased him, and he ascended at 90 fpm.

 

[justinthedeeps]

On a recent Offgassing podcast Neal Pollock said something about younger people having fantastic skills, but reduced awareness of hidden dangers, especially decompression injury.


Freedive experience/training could exacerbate this, for someone who has built up habits for repetitive bounce diving, and ascending lines quickly.

Since you are trying to shave even more deco obligation, on top of the GF and the mix lies, just ascend faster so you absorb even less gas. Right?

Or was there a problem at depth?

 

[boulderjohn]

About the helium penalty:

Eliminating The Helium Penalty - Shearwater Research

Our understanding of decompression science has undergone dramatic revision in the last two years thanks to decompression physiologist David Doolette, Ph.D. and the team at the Navy Experimental Diving Unit (NEDU).

www.shearwater.com

An old SB thread:

Shearwater's take on the helium penalty

I was wondering if anybody else read this blog post. Eliminating The Helium Penalty - Shearwater Research Sounds like two major shifts will happen if this research holds out. 1) Pretty much all algorithms in use by modern computers will need to be updated...but there is currently no known...

scubaboard.com

Part of a post by Dr. Simon Mitchell in that thread:

The conundrum is in knowing how to practically apply these findings. Can we all tell our computers that we are diving air diluent when we are really diving trimix? The study does not answer that question unfortunately. Although it suggests that there is no evidence for treating helium and nitrogen differently (as reported by Doolette in animals) it is conceivable that the long held belief that helium needs more decompression has compensated for underestimation of required decompression (to achieve acceptable levels of risk) by the decompression algorithms we all use, and that we are doing the right amount of deco from very deep dives but probably for the wrong reason. I probably would not change much at this point.​

 

[justinthedeeps]

If the cause of injury were acute DCI due to an ascent from bottom that was too fast, how does this explain the apparently controlled deco stop in the dive profile?

Would you not need to assume then that the diver was already experiencing DCS on this deco hang, resulting from the ascent?

And what about hypoxic diluent entering the loop via either an accidental manual addition, or an automatic diluent valve (ADV)? Suppose the diver gets to the surface, over-vents the loop, and then the ADV injects in a lungful of 10% oxygen?

 

[Ez E]

How do you watch the documentary video on this? I cant find it anywhere.

 

[rjack321]

If the cause of injury were acute DCI due to an ascent from bottom that was too fast, how does this explain the apparently controlled deco stop in the dive profile?

Would you not need to assume then that the diver was already experiencing DCS on this deco hang, resulting from the ascent?

And what about hypoxic diluent entering the loop via either an accidental manual addition, or an automatic diluent valve (ADV)? Suppose the diver gets to the surface, over-vents the loop, and then the ADV injects in a lungful of 10% oxygen?

Rob's shearwater profile doesn't support hypoxia at all.

Acute (cerebral/ type 2) DCI is really the only plausible explanation and it affected both of them in the first few minutes after surfacing. The "deco stop" was so short it may not have been acute nor even had any type 1 symptoms at that time/yet. Peter regained consciousness on the deck, Rob was waiting behind the boat ladder, sank and drowned.

 

[justinthedeeps]

Rob's shearwater profile doesn't support hypoxia at all.

Acute (cerebral/ type 2) DCI is really the only plausible explanation and it affected both of them in the first few minutes after surfacing. The "deco stop" was so short it may not have been acute nor even had any type 1 symptoms at that time/yet. Peter regained consciousness on the deck, Rob was waiting behind the boat ladder, sank and drowned.

I'm talking about the possibility of accidental hypoxic diluent addition after reaching the surface. Unlikely? But possible.

Nothing to do with the dive profile, which (as posted above) does not include data on the surface, or afterwards. Was the unit/computer switched off upon surfacing?

Why didn't the computer record a fourth "dive" upon resubmersion? Or did it?

Mouthpiece out?
No gag strap or BOV?
What was the CMF config?

Clear & obvious lessons here about the consequences of underestimating DCI risk in aggressive repetitive trimix deco diving.

But still giving a think about additional possible factors/fixes. As there are additional risks on CCRs beyond just DCI