Filmmaker Rob Stewart dies off Alligator Reef

[hroark2112]

As far as staying on the loop...I was taught "When in doubt, bail out!" The instructors I have had the good fortune to learn from are beyond reproach IMO, and those words are with me on every dive.

It would be interesting to see the remaining tank pressures and what gasses were available to the divers at the time of the accident. Did they have 50% bailout or 100% deco gas available in the water? Was this a case of "didn't know what he didn't know" or was it something else?

 

[St John the Diver]

considering you're hiding who you are, getting offended that we don't accept your unquestioned authority, experience and all around greatness is silly. Fess up or live with it.

Now.."The heart pumps about 2,000 gallons (7,571 liters) of blood a day through its chambers." 2,000 gallons per day works out to 83 gallons per hour, or nearly 6 quarts per minute. So it takes about one minute for blood to make the round trip to the heart"

the brain box is on a highway, not a byway and gets the oxygenated blood fairly quickly, however, you can keep asserting that hypoxic mix on the surface is only a few seconds..maybe you better define that "few". Be happy to join you in a chamber and test out our respective theory (again for me..but it has been a minute or so)

I would argue those "few" seconds can be the rest of your life in some circumstances

I'm not offended at all. And I've witnessed many hundreds of hypobaric chamber runs as an inside monitor. That's a high altitude chamber. Close up and personal with literally dozens of unconscious trainees who recover when fed better gas thru a mask.

Just sharing what I've seen. Non-functional consciousness in a few seconds, reactive consciousness in a few more. It's a process, not a light switch.

Interestingly enough, at the other end of the excercise (becoming hypoxic): I've stood looking at a semi-concious trainee more times that I can count and had them give me the "Ok" signal while completely unable to help themselves by flicking ONE switch that ends the excercise. So an "OK" means zip as a signal that someone is concious and responsive. Tou need a lot more of a responce than that to ensure someone is really OK. Just as a data point we generally work at an altitude where the PP02 is 0.10... Sound familiar? At rest the time of useful consciousness there is between 3 and 10 minutes depending on the individual. When working all bets are off. But again, loss of conciousness at 0.10 is a process not a light switch. But going lower... Things happen fast.

 

[St John the Diver]

considering you're hiding who you are, getting offended that we don't accept your unquestioned authority, experience and all around greatness is silly. Fess up or live with it.

Now.."The heart pumps about 2,000 gallons (7,571 liters) of blood a day through its chambers." 2,000 gallons per day works out to 83 gallons per hour, or nearly 6 quarts per minute. So it takes about one minute for blood to make the round trip to the heart"

the brain box is on a highway, not a byway and gets the oxygenated blood fairly quickly, however, you can keep asserting that hypoxic mix on the surface is only a few seconds..maybe you better define that "few". Be happy to join you in a chamber and test out our respective theory (again for me..but it has been a minute or so)

I would argue those "few" seconds can be the rest of your life in some circumstances

So if I can attach pics: here are two charts of interest. One is time of useful consciousness (TUC). The other is PP02 at altitudes. 18,000 feet is about 0.10 PP02. Note the TUC there. Lots longer than divers are taught. But note the rapid decrease in TUC with additional small changes in altitude.

A loop drops VERY fast from 0.10 to 0.05 if you're breathing on it. Look at how that affects TUC...

18,000 feet is about 0.10
35,000 feet is about 0.05

Look at the difference in TUC. It's staggering.
That's less than a minute on a 5 liter loop that started at 0.10

This is DIRECTLY applicable to rebreather physiology. Hypoxia is hypoxia.

Scary.

Think you might understand why a diver could give the OK and then disappear a few seconds later?

But I don't know what I'm talking about...

Enjoy.

 

[KevinNM]

I would argue those "few" seconds can be the rest of your life in some circumstances

None of the Columbia astronauts got their visors down and locked when Columbia depressurized. It's a very simple and fast procedure they were highly familiar with. And none of them got it done before they passed out.

 

[Patoux01]

I still don't get how on surfacing from a 70m dive, you would have a hypoxic breathing gas. Or they deco'd on OC, and then for some reason switch to a corrupt loop on the surface (come on, that's nonsense), or they simply can't deco... The deco time would shoot through the roof if that's in your loop. Or they'd go for a loop flush right at the end of deco? And doing that while the recommendation is to stay on O2 for a while after the deco?

To me that scenario is good for a Bollywood movie, but certainly not for real world dives.

 

[RainPilot]

I still don't get how on surfacing from a 70m dive, you would have a hypoxic breathing gas. Or they deco'd on OC, and then for some reason switch to a corrupt loop on the surface (come on, that's nonsense), or they simply can't deco... The deco time would shoot through the roof if that's in your loop. Or they'd go for a loop flush right at the end of deco? And doing that while the recommendation is to stay on O2 for a while after the deco?

To me that scenario is good for a Bollywood movie, but certainly not for real world dives.

The current theory is that they ran out of O2 for the RB. Because of this, they would have had only the dil to increase the loop PPO2 which with a hypoxic dil doesn't work too great. Thus at the deco stop they would have had a steadily reducing PPO2 until eventually they would be breathing a hypoxic mix. This is fine at 20 ft but from there to the surface gets all kinds of fun all kinds of fast.

If they were doing a bounce to get the anchor as has been postulated, its entirely possible that they grabbed a bottom bailout before splashing, not necessarily thinking this through. In that case they would have had a hypoxic bailout also no help.

Just thinking out loud, in aviation we have a phenomenon where it is REALLY hard to abandon a "serviceable" piece of equipment even when its the best thing to do. CCR training is all about staying on the loop, mostly I suspect from the cave diving roots of much of the training where every meter longer on the loop is more OC gas reserve.

In a situation where a diver is at 20 feet with a perfectly functional (though hypoxic) RB and a bailout of e.g. 32% or such, I wonder how much subconscious resistance there would be to bailing out. In the Rec CCR world the mindset is "when in doubt, bailout" i.e. there is NO pressure to stay on the loop at all. Obviously staying on the loop is an important factor when deep in a cave etc etc but something to consider when diving more forgiving gas-situations.

 

[Dan]

...I'm not a CC diver, but have dove with a few CC divers, done a fair amount of research, participated in breaking down a unit before and watched a lot of the DAN videos on the subject, mostly Mr. Simon Mitchell's presentations. One of the things that has stuck with me from his presentations is regarding the extraordinarily high number of deaths with rebreather divers compared to OC. At the end of the day, a fallible human really needs to think about what he's doing and why he's doing it. The technology easily allows divers to push limits and put themselves in places and situations they normally wouldn't find themselves in OC. And taking high risks without thinking about self preservation.

Case and point. Too much too fast and relatively inexpensive repetitive deep Trimix dives which would normally be cost prohibitive on OC allowed Rob to probably push the limits.

A good watch for those who haven't seen this one before.

Speaking of what things can go wrong (failure modes) with CCR & their implications. Here is a page of Mr.Simon Mitchell's presentation (that CuzzA posted earlier) that makes me think using CCR is way over my head & scares the heck out of me:

 

[cerich]

So if I can attach pics: here are two charts of interest. One is time of useful consciousness (TUC). The other is PP02 at altitudes. 18,000 feet is about 0.10 PP02. Note the TUC there. Lots longer than divers are taught. But note the rapid decrease in TUC with additional small changes in altitude.

A loop drops VERY fast from 0.10 to 0.05 if you're breathing on it. Look at how that affects TUC...

18,000 feet is about 0.10
35,000 feet is about 0.05

Look at the difference in TUC. It's staggering.
That's less than a minute on a 5 liter loop that started at 0.10

This is DIRECTLY applicable to rebreather physiology. Hypoxia is hypoxia.

Scary.

Think you might understand why a diver could give the OK and then disappear a few seconds later?

But I don't know what I'm talking about...

Enjoy.

Thanks... but your charts here more seem to back up what I was saying versus what you were saying.

My point was after breathing 10/50 for a deco period at say 20ft, even upon surfacing and breathing from the atmosphere with it's rich 20.9% O2 there is a lag perod, during which it can be expected that the diver will pass out. To think that one or two breaths of surface air and all will be ok is foolish.

Your earlier argument that I pushed back on was that the surface atmosphere air would help somebody fast enough that there wouldn't be a problem, mine was it would not. Now you seem to be arguing that I was wrong with data and statements that argue my point.

 

[St John the Diver]

Thanks... but your charts here more seem to back up what I was saying versus what you were saying.

My point was after breathing 10/50 for a deco period at say 20ft, even upon surfacing and breathing from the atmosphere with it's rich 20.9% O2 there is a lag perod, during which it can be expected that the diver will pass out. To think that one or two breaths of surface air and all will be ok is foolish.

Your earlier argument that I pushed back on was that the surface atmosphere air would help somebody fast enough that there wouldn't be a problem, mine was it would not. Now you seem to be arguing that I was wrong with data and statements that argue my point.

No, you're just arguing for the sake of arguing, for no reason at all other than to argue.

There's no conflict between what we are saying. (1): recovery once you breathe atmospheric air is "rapid" and (2): it might not be rapid enough.

There's no conflict there. It takes one second for an unconscious person to drown.

Bark less. Wag more.

Woof.

 

[cerich]

I wasn't just arguing for the sake of it, I don't want people to get the impression that a gas switch...UW or on the roof off the loop is a "instant" fix to hypoxia (or other gas related issues).

Once things go pear shaped extreme diligence is needed by the team, including surface support.