Filmmaker Rob Stewart dies off Alligator Reef

[Dan]

Scubaboard posts cited in this article on Rob Stewart:

Standing Up for Sharks: The Legacy of Rob Stewart - Planet Experts

Thanks for posting the link. Michael Buckley, the writer of the above article, has very valid questions, which I'm not sure we have discussed here.

"On January 31st, Rob Stewart surfaced after a deep dive with Sotis, coming up from a depth of almost 70 meters — the third deep dive of the day. Here the story becomes murky. According to OutsideOnline.com, Sotis blacked out after surfacing and getting onto the dive-boat, the Pisces, and was given oxygen to revive. In the confusion of the moment, Stewart, still in the water, apparently disappeared from view.

There are a few things wrong with this narrative. Why did instructor Sotis embark on three 70-meter-deep dives in a single day in the first place — when even experienced tech divers would stop at two — with the second dive likely limited to 50 meters? That is reckless — if not downright dangerous. How is it possible that the rebreathing instructor, Peter Sotis — the most experienced with this equipment — blacked out when he surfaced? This would indicate that Rob Stewart probably suffered the same fate. And why would the attention be on instructor Peter Sotis? Surely the attention of the crew should have been on the client, Rob Stewart?"

 

[RainPilot]

All these questions have been discussed. In fact this thread is where I believe he found these issues in the first place.

 

[Ron Lee]

The first post can always be updated. Many things discussed are using assumptions.

 

[TONY CHANEY]

Yes, I'll elaborate. It is your statement, "addition, the increased partial pressure of oxygen forcibly displaces some carbon monoxide from the hemoglobin." As the article stated, hemoglobin has an affinity for CO 200 times more than O2. According to the ideal gas laws all gases exert their pressure equally. So as the ppO2 increases so does the ppCO increase. Once all 4 receptor sites on the hemoglobin are full, remember that the CO loads on about 200 times faster than O2, nothing else can load until the gas is off loaded at the tissue level where it takes on CO2. The hemoglobin then goes from arterial to the veins and back to the lungs, via the right side of the heart, and is exhaled. We could go deeper but this should help explain my point of view.

 

[eeel]

Tony,
I agree with everything you wrote above, but at higher PO2s there is enough dissolved oxygen in the blood to maintain metabolic function even with much of the hemoglobin bound by CO. If the PO2 drops with no hemoglobin to carry the O2 suddenly you become hypoxic and it's over and out.

 

[swamp diver]

Tony,
I agree with everything you wrote above, but at higher PO2s there is enough dissolved oxygen in the blood to maintain metabolic function even with much of the hemoglobin bound by CO. If the PO2 drops with no hemoglobin to carry the O2 suddenly you become hypoxic and it's over and out.

Yes as seen in this figure. At depth the oxygen dissolved in the plasma (yellow area) also increases with depth which does maintain metabolic function. As one surfaces the CO remains bound to the Hb and the extra O2 dissolved in the plasm in lost.
http://www.coheadquarters.com/figco06.htm

This effect was seen in the Maldives CO fatality where divers were able to finish their dives but on surfacing lost consciousness. If I recall one died and a handful were unconscious but were rescued on surface.

 

[RainPilot]

The first post can always be updated. Many things discussed are using assumptions.

As mods we don't willy nilly change peoples posts in terms of content. Since this isn't a courtroom, the definition of "facts" is a bit vague here. It can be argued that the only FACT we have is that Rob went missing, there was a long search and he was found dead.

It can be argued that everything else is conjecture / hearsay / WAG because none of us was there and everything is second hand. Some of those conjectures I personally have high confidence in, others not so much, but for the purposes of this forum that's ok. I (and many others) use these threads to play a game of "what if..." with the intention of spotting correlations to our own diving and seeing if there are safety improvements to be made.

In this thread, I have already made a fundamental change to my RB diving in that I now make a BIG point of closing the DSV once Im on the surface and go off loop for ANY reason (possible buoyancy loss from CL)

Since Im not Mod 3 yet, the hypoxic dil issue is not applicable but its in the mental toolbox now.

Making sure I have enough O2 is also something I am looking at.

All of these are positive contributions to my own diving safety even if none of them end up being applicable to this incident!

This is where folks need to remember that this is not meant to be an online investigation to determine the cause of the accident, but a way for us to take what useful items away from someone else's accident as we can for the good of the community.

 

[boulderjohn]

The idea of updating the key information in the beginning of an A&I thread was discussed by the moderating staff 5-6 years ago. We even tried doing it in one thread, with CaveDiver doing the work. It clearly did not work. It was, first of all, way too much work for a volunteer moderating staff. In a thread like this, whoever is doing it would have to be working on it continually, 24 hours a day. More importantly, though, it can be very hard to know what the facts really are. For example, in this thread we had a witness saying that Peter Sotis passed out on the boat. Then we had a quote from Peter Sotis saying he did not pass out. Then we had another statement that he did pass out. Put yourself in the moderator's shoes updating that one simple "fact."

 

[St John the Diver]

Tony,
I agree with everything you wrote above, but at higher PO2s there is enough dissolved oxygen in the blood to maintain metabolic function even with much of the hemoglobin bound by CO. If the PO2 drops with no hemoglobin to carry the O2 suddenly you become hypoxic and it's over and out.

True in theory but generally irrelevant in the case of a rebreather diver.

Do some simple math:

Rebreather:

1: The divers carry ONE 2 litre cylinder of diluent.

2: That cylinder has 10% oxygen, 50% helium, and 40% nitrogen.

3: that has is "heliair", meaning it's blended very simply: fill the bottle half way with helium and then top off with air.

4: one litre of volume in the cylinder is then "occupied" by air.

5: let's imagine that they filled the cylinder to 200 bar. That's now 200 litres of free air available to the diver that was produced by a compressor.

6: that tiny amount of gas is used (blended with helium) as a diluent, and it's rebreathed again and again and again. And only a fraction of the cylinder volume is actually used on a dive series.

7: the percentage of carbon monoxide in that small amount of gas needed to impact a diver would be so extremely high as to be nearly impossible to obtain.


Contrasting:

Open circuit:

At even, say: 5 ATM (40 metres) a diver is honking thru 4x the surface volume consumed. It's likely he's chugging down the amount of gas a rebreather diver consumed as diluent on a complete dive ON EVERY BREATH and bonding whatever CO is in the gas mix to hemoglobin continuously.

Bottom line is that a CO level that would be lethal to an open circuit diver is an irrelevancy to a rebreather diver.

This is an red herring theory not developed by anyone who has actually thought it thru.

 

[Dan]

.... For example, in this thread we had a witness saying that Peter Sotis passed out on the boat. Then we had a quote from Peter Sotis saying he did not pass out. Then we had another statement that he did pass out. Put yourself in the moderator's shoes updating that one simple "fact."

Yea, I agree, that's not easy tasks. However, one needs to weigh in the source of information.