Filmmaker Rob Stewart dies off Alligator Reef

[scubadada]

I apologize if this has already been answered. If Rob Stewart started his hypoxic trimix CCR course on January 27, would he have been able to finish it prior to the dives on the Queen of Nassau on January 31, or were these likely training dives with his instructor? I don't believe there has been any discussion of dives that might have been made prior to January 31, as part of his course. I noticed that Horizon Divers' Pisces was chartered for the Queen of Nassau for January 30, 31 and February 1. Is it correct that the group that included Rob Stewart were only to dive it on the 31st?

 

[St John the Diver]

Starting from the top: not banging on, expanding my thoughts on some of the theories posted here.
As @cerich and others have stated, two big dives to 230' and another bounce would suck O2 really fast, trying to keep that 1.3 that you refer to. BTW your calculations for 0.16 on the surface (a marginally hypoxic gas already) is correct IF THEY STOP BREATHING WHILE COMING UP.

No bailout: Rob was on the loop when he surfaced by all accounts as was Peter. If there was a significant issue (significant enough to make both of them pass out within seconds of surfacing) it is likely they would have been on bailout if they had an appropriate gas. I can easily see this conversation playing out:
"Drop down to get the anchor?"
"Sure, how's the gas?"
"Should be fine, it's just a quick bounce."
"Ok Instructor who presents lectures and workshops on rebreather operation "
"Bailout? Yeah just grab the big bottle in case, we don't need all the stages etc"
"Are you sure?"
"It will be fine rebreather diver with 6 months or less experience "

I know and know of many very experienced people that have died from stupid. Nobody is immune and CCR magnifies the consequences.

My reason for leaning toward hypoxia? Of the 3 Hs it's the most likely IMO. Hyperoxia would have at least one of them convulsing and unlikely to affect both in the same way (simultaneous RB failures? On a rEvo? Unlikely. )
Hypercapnia? Sorry Pete but again, it is more likely than hyperoxia but would require them to both kill their scrubbers at the same time and would, while incapacitating them would IMO be unlikely to result in Rob showing OK.

Running out of O2 on an OW dive on a RB is a very uncommon event, but then again nobody seems to be making a habit of doing 3 hypoxic dives in a row on the same unit on the same day.

- ^^^^ This. 100%. Common causal factors. It's a damned short list of possibilities.

It's likely either (A): Depletion of 02 or (B): depletion of scrubber.

Sotis over-relied on the rEvo RMS scrubber monitoring system to push scrubbers. That system has huge flaws. Scrubbers could both have been exhausted... Not very far fetched either.

The perceived leadership gradient here was extreme. One diver was making flawed decisions for two people.

 

[packrat12]

You guys are chasing hypoxia and while I first thought that this might be the case, I now believe that hypercapnia is more likely. How DO THEY BOTH run out of O2? ...

Everyone seems to be associating hypoxia with running out of O2 in this case. You just do not need that scenario. Going from 220 with a SP of 1.3 to the surface with out adjusting the O2 in the loop will have an FO2 of .17. Add in other things and I still think it is possible that both divers got into a hypoxic situation, especially if they inhaled a dil of 10/50 on the surface through the ADV and the lower set point of .5. Without knowing the profile and deco stops, it is possible to get hypoxic without running out of anything. This is a risk associated with having a hypoxic dil connected to the CCR on the surface. Also, were these mCCRs? I know some at AH uses them. All assumptions being made of course.

 

[cerich]

Everyone seems to be associating hypoxia with running out of O2 in this case. You just do not need that scenario. Going from 220 with a SP of 1.3 to the surface with out adjusting the O2 in the loop will have an FO2 of .17. Add in other things and I still think it is possible that both divers got into a hypoxic situation, especially if they inhaled a dil of 10/50 on the surface through the ADV and the lower set point of .5. Without knowing the profile and deco stops, it is possible to get hypoxic without running out of anything. This is a risk associated with having a hypoxic dil connected to the CCR on the surface. Also, were these mCCRs? I know some at AH uses them. All assumptions being made of course.

revo's

 

[oya]

"Drop down to get the anchor?"
"Sure, how's the gas?"
"Should be fine, it's just a quick bounce."
"Ok Instructor who presents lectures and workshops on rebreather operation "
"Bailout? Yeah just grab the big bottle in case, we don't need all the stages etc"
"Are you sure?"
"It will be fine rebreather diver with 6 months or less experience "

This is where I'm putting my money.

 

[packrat12]

revo's

rEVO makes manual mCCRs and I have seen AH employees use them. (from rEVO's page: Price is for a Standard mCCR with 2 rEvodreams and no Shearwater. )

 

[St John the Diver]

Everyone seems to be associating hypoxia with running out of O2 in this case. You just do not need that scenario. Going from 220 with a SP of 1.3 to the surface with out adjusting the O2 in the loop will have an FO2 of .17. Add in other things and I still think it is possible that both divers got into a hypoxic situation, especially if they inhaled a dil of 10/50 on the surface through the ADV and the lower set point of .5. Without knowing the profile and deco stops, it is possible to get hypoxic without running out of anything. This is a risk associated with having a hypoxic dil connected to the CCR on the surface. Also, were these mCCRs? I know some at AH uses them. All assumptions being made of course.

The ADV point is well taken. The rEvo has an ADV that's patently unsafe, as it's a fairly high performance second stage mechanism with a HUGE diaphragm (the counterlung) activating it. The system is so sensitive that many divers have a hard time knowing when it's been activated. There have been multiple attempts to fix the problem but it's just basically a bad design. It is very very possible to breathe from it without knowing it. It's a point that I had not thought of until you mentioned it. A few breaths from it on the surface with that gas and it's bad news.

 

[kierentec]

Not assuming that this is related to this incident at all, but just to throw this into the conversation because there had been a lot of talk of loss of O2 supply. While using hypoxic dil (especially as lean as 10/50) it is very possible to go hypoxic on the surface without any loss of O2 supply when diving a CCR with an ADV (especially if that ADV cannot be shut down).

A task loaded diver working hard on the surface handing gear up to the boat and such can easily begin exhaling out their nose subconsciously. As they inhale, they are breathing directly off the ADV (called breathing "open loop" by some manufacturers and instructors when done on purpose). Depending on where the ADV and cells are in the loop, this hypoxic gas may never hit the cells. The controller (and all displays) would assume a breathable loop. Meanwhile, the task loaded diver is working hard breathing at a .10, and it's lights out after a few minutes of that.

 

[Cowfish Aesthetic]

The rEvo has an ADV that's patently unsafe, as it's a fairly high performance second stage mechanism with a HUGE diaphragm (the counterlung) activating it. The system is so sensitive that many divers have a hard time knowing when it's been activated. There have been multiple attempts to fix the problem but it's just basically a bad design. It is very very possible to breathe from it without knowing it.

If that's the case, why would anyone dive the rEvo w/ hypoxic dil? Is there not a better option?

 

[uwxplorer]

You're not waving "I am OK" if you are panting like a dog from hypercapnia, from what I heard others report.
This being said, I would not trust the rMS with my life, from my personal experience with its potential unreliability (cold water, shallower, shorter dives).
But at 2 hr (tops?) per dive during the first 2 dives, in warmish water, unless they had to raise the wreck to free the anchor, I would venture to say that they had plenty of autonomy with proper scrubbers.
Now, there is no way to know whether that was the case, since the rMS reading are not recorded (just a brief cryptic and mostly useless summary post dive, in the best cases).

A simple multideco calculation, 10/50 diluent, using my 30/80 GF settings gives this for 2 dives with 30 min bottom time (22 min at depth) separated by a 3hr SI:

dive 1: RT = 117 min
dive 2: RT = 128 min (CNS toxicity alert)

After 1 hr of trying to get the anchor off the wreck, they go down for a 15 min BT (7 min at depth)
dive 3: RT = 38 min (CNS toxicity alert)

That's not 5 hrs on the scrubber, which is within specs (here). I would not consider hypercapnia of BOTH divers too plausible.

With a 1 l/min O2 metabolism (high), they would have used up very little of their 400 l of O2 at the bottom (assuming a full tank at the beginning), and coming back from 230 ft would essentially require flushing the counter lungs with O2 (4.5 l non CE for the micro) . 117+128+38+3*4.5 = 297 L

Now, without the computer readings, this is all pure speculative scenario.

Edit: the gas consumption used during ascent was corrected.