Filmmaker Rob Stewart dies off Alligator Reef

[fsardone]

Just for clarity and without prejudice:
In 1993 I experimented with hypoxia [...] I went unconscious as surely as if I had a bullet in the brain. The mouthpiece fell out and when I came round some hours later, I suffered an almighty hangover.

John I am glad you are still with us ...
Doing hypoxic breathing experiments solo is not recommended: it is not assured you will automatically revive you might need help from a qualified medic (I am told).
I have experienced hypoxia in a hipobaric chamber to learn about symptoms: initial and recurrence training. There are symptoms at high altitude where you are supplied with a lower ppO2 for longer times. For example at 15000' pressure is about 500 mbars and ppo2 is about 0.105 and you start loosing color perception, coordination, math capability. FAA rules (14 CFR 91.211 - Supplemental oxygen) grant 30 minutes flying without supplemental oxygen between 12500' and 14000' and you can fly a plane without supplemental oxygen without limits below 12500'. Oxygen is required for crew above 14000' and passenger only from 15000'. Obviously you are not exercising on a plane!
About the symptoms: the main problem is ... most of the time you are unaware because of the impaired brain capability to understand the situation. This is why, in case of doubt you gangle up the oxygen regulator trowing the three switches up: Oxygen on (green switch) Oxygen 100% (white switch) and emergency oxygen on (red switch delivers oxygen under positive pressure). This is an engrained response to any perceived symptoms or if in doubt. All the time you have is the time of useful consciousness (TOC). which at 18000' could be several minutes and at 35000' could be a few seconds. But your mental process are affected (according to FAA) above 12500'.

Unfortunately, in a rebreather, oxygen does not stay constant at any level: will drop with every breath you take so, as you found out, is like a bullet in the brain. Your TOC could be as short as taking a single breath. This is because inspiring a breath of hypoxic gas will create a gradient that further desaturate you blood by moving oxygen from blood to the lungs. This impoverishes the blood going through the pulmonary circle depriving it of oxygen and a few heart beats later this reaches the brain and lights off.

Switching to OC (and a respirable gas at that depth) should be an ingrained automatic response. You can always analyze the situation and go back to the loop if you find out it is respirable, but if you pass out you have no options.

Bottom line is: assume the worst, take proper action and solve the emergency after you ensure what you are breathing is a life sustaining mix.

In flying, the mantra is maintain aircraft control, analyse the situation, take proper action. In diving I would say: keep breathing (proper mixture in case of tech diving), analyse the situation, take proper action. IMHO flying the plane and ensure you are breathing a proper mixture has to be automatic, muscle memory, no need to think about it. Just do it. This also mean that the regulator you switch has to be connected to the right gas. I use a BOV and I do connect it to the different bailouts on my way down and on my way up. I am pro BOV because a single gesture will close the loop and give me good gas. Also in case of CO2 hit I do not need to take my gas source out of my mouth.

I believe developing this automatic response is a prerequisite for safe CCR diving and until you have it ingrained you should be nowhere near hypoxic diluents.

Just my 2 cents.
BTW very enlightening thread, sorry for the loss of life.

 

[dumpsterDiver]

I always thought this was cool.

 

[TONY CHANEY]

I did the chamber while going thru fight physiology. You do not see it coming and it is different for everyone. My Lt was totally confused on the on set, but Doc was the last man standing and the crew had to ask him to return to O2 because the class was waiting. The Lt and I were playing paddy cakes and I could not imagine trying to figure out O2pp, depth, buddy, TTS, set point, etc.

Not sure what happened. Could have been a hypoxia hit and could have been a CO2 hit. I don't believe it was a CO hit. (Usually you do not walk away for a high CO hit).

 

[fsardone]

@dumpsterDiver

It is cool seeing but cooler doing it.
I am fortunate because my job requires it but anybody interested can buy a ride (I believe FAA requires pilots flying pressurised a/c to be familiar with hypoxia).
In my view, for a rebreather diver it is worth experiencing it.
I prefer this video because it explains the feeling.
The conclusion is worth noting: even if you realise you are hypoxic you don't care!

 

[Capt Jim Wyatt]

It is cool seeing but cooler doing it.

Cool maybe if it is closely supervised by someone who is certified, educated, qualified or whatever to do it. Otherwise it is a fool's errand.

 

[fsardone]

Cool maybe if it is closely supervised by someone who is certified, educated, qualified or whatever to do it. Otherwise it is a fool's errand.

Jim, not to derail the thread, but I do not believe anybody that has a chamber would let anybody in without a tech outside and a medic under oxygen inside, following a strict protocol in term of altitude and exposure time. In most you are also required to wear a saturimeter (an instrument measuring oxygen saturation by means of a LED and sensor on a finger).

Also doing hypoxic experiments on your own is mortally dangerous and that is why I said I was glad John was still with us a couple of messages above where I also stated you should not be playing with hypoxia unsupervised.

 

[Capt Jim Wyatt]

Also doing hypoxic experiments on your own is mortally dangerous and that is why I said I was glad John was still with us a couple of messages above where I also stated you should not be playing with hypoxia unsupervised.

Thank you.

 

[TONY CHANEY]

Don't try this at home!

 

[venonguy]

Just for clarity and without prejudice:

In 1993 I experimented with hypoxia (while not underwater) because with a prototype rebreather I was anxious to know the symptoms of oncoming hypoxia. I discovered that there were none. I breathed off the loop while lying horizontal on a bed, with the O2 turned off. It was probably extremely quick but the truth is I cannot remember, because I went unconscious as surely as if I had a bullet in the brain. The mouthpiece fell out and when I came round some hours later, I suffered an almighty hangover. If I had been in the water, I would have surely drowned. What I learned from this was that when you surface, close the mouthpiece and get off the loop. Drowning is a real possibility otherwise and if your wing was not inflated, you would drop too.

I am not saying this is what happened to Rob Stewart but it is a possibility if O2 was low or even turned off (as was the case with Dr Max Hahn, a famous decompression expert and early CCR casualty).

John,

your advice to surface and "Get off the loop" is totally contrary to any CCR training. The recommended training advice for the Rebreathers is to stay on the loop until you are securely back on the boat or on dry land. This is best practice both before the dive "pre breathing" and upon surfacing.

 

[The Chairman]

CO is scrubbed pretty quickly from the loop by the same mechanism that cleans CO2. Remember, very little dil is used by a competent rebreather pilot. If it were a problem, then it would have manifested itself on the first two dives. and we know it did not. Sotis' stupor on the boat is consistent with CO2 as was his combativeness. It's my understanding that he had a problem getting up the ladder as well, but he never passed out. Again, there's no compelling reason to believe that Stewart had the same issue as Sotis. He was in much better shape and gave a clear OK signal on the surface. Fatigued, he probably accidentally flooded his loop swimming from the buoy to the boat and could not cope with the suddenly heavy rebreather. That's the simplest theory that fits the facts as I understand them.