Filmmaker Rob Stewart dies off Alligator Reef

[crharnett]

There was a tv episode with Chatterton and Kohler - each had two computers and all four failed. This never happens, right? Two divers lose consciousness at the surface. This never happens, but it did. There is a reason. Hope he is found. Hope we can learn from it.

 

[chillyinCanada]

I've probably missed it within the thread, but why do some posters seem to believe he's floating?

 

[USdiver1]

Does anyone know what kind of buoyancy profile Mr. Stewart would commonly adopt for his CCR dives? i.e. would he be X lbs. negative and dive with a camera that was X lbs. positive to obtain a neutral profile, or would every dive be different depending upon the circumstances?

Also would a bounce dive purportedly to clear an anchor require a CCR diver to adopt non-standard buoyancy control, or at least something out of the ordinary for typical CCR use?

 

[steady1570]

I might have missed it but do you know what ccr they were using?

I didn't meant to give that impression and apologise if I did. I more wanted to point out that in normal operation a hypoxic dil does not in itself cause issues above 20ft as I interpreted the post by Q1988. That's not to trivialise the precautions that must be taken in any way.

-Mark

 

[Ron Lee]

I've probably missed it within the thread, but why do some posters seem to believe he's floating?

It seems like a reasonable possibility.

The other search option is underwater. I do not know if that is being done or how hard it would be considering currents, depth of the ocean bottom and visibility.

 

[Cowfish Aesthetic]

I've probably missed it within the thread, but why do some posters seem to believe he's floating?

Because he was seen at the surface, gave the ok, and was in a dry suit. Presumption is he was likely positively buoyant at that point. But of course there have been plenty of cases where that was not true.

 

[lamont]

Ok, perhaps I should have put "in normal circumstances". Bounce dive or not, you must always know your ppO2. For one diver to come to the surface fast and not notice ppO2 falling below 0.16 is unusual (especially for a diver of the experience level necessary to do that sort of dive - I am not casting aspersions on anyone involved here to be clear), but for two divers to make the same mistake? I would suggest that is very unlikely.

-Mark

If both divers had run out of higher percentage O2 (possibly due to bailing out) and were on hypoxic diluent (either with or without a functioning RB) then there could have been a situation where both of them would have had to try to do a blow-and-go from 20 feet to the surface with hypoxic gas.

In that situation since your lungs only contain hypoxic gas there will be a tissue-gas gradient in the O2 concentration which will pull O2 off the hemoglobin and into the lungs. Even if you fully exhale there's still lung volume with hypoxic gas there. It only takes the heart about 3 beats to push your blood through the lung filter and that will be enough to cause an appreciable drop in O2 saturation in the blood. Loss of consciousness will happen fast. The only way to pull this off would be to do everything your diving training tells you not to do and take one last breath at 20 feet, fully exhale and swim up while hammering on your inflator (remember they taught you to never do that with CESAs in OW?), try to as quickly as possible reach the surface so you can take a breath of 21%, and then roll over on your back so that you don't drown if you still pass out. Of course with a dive going sideways this badly you may not have any inflation gas left (although with trimix for dil they should have had an argon or "air"-gon inflation bottle on the unit so even if they drained there dil that wouldn't imply they drained their inflation gas) and struggling to orally inflate at the surface while going hypoxic would increase the risk of unconsciousness and sinking and drowning.

Note that in this situation they'd know exactly what was going on, but with no high concentration O2 to use, you get stuck with no choice.

People tend to focus on hyperoxia with CCRs a lot, but hypoxia kills you a lot quicker, and if you run out of high concentration O2 on your ascent you can become very screwed, very quickly.

I still think the neuro-DCS due to a bounce dive to pull the hook and shunting a compressed bubble shower sounds more likely, but this plausible. It explains both of them having problems together, the disabling event happening at the surface, and possibly the quickness with which he went down (and potentially the failure to inflate and stay on the surface).

 

[dumpsterDiver]

If the guy sank wearing a dry suit rebreather and bc. And assuming he was unconscious,. Would not the compression of all three gas volumes cause his density to increase rapidly and for him to sink fast. If they were diving on a wreck. I would assume they know with good accuracy where he disappeared from.

So I would assume that with very calm sea state that the underwater search should find him quickly unless possibly a shark found him and moved him.

If the diver passed out at depth we would assume his bouyancy would be neutral, and the body would be more subject to the current.

Am I correct in assuming that the rebreather would become more negative than an open circuit scuba unit?

Were they baiting sharks at the time? It seems to be growing in popularity.

 

[Cowfish Aesthetic]

If both divers had run out of higher percentage O2 (possibly due to bailing out) and were on hypoxic diluent (either with or without a functioning RB) then there could have been a situation where both of them would have had to try to do a blow-and-go from 20 feet to the surface with hypoxic gas.

I know nothing about CCRs, this may be a dumb question, but wouldn't that scenario require them both to have had their own independent failures? Seems unlikely, though not impossible, which is why I (like you) keep coming back to the neuro-DCS theory.

 

[cephalopod2]

I might have missed it but do you know what ccr they were using?

His Instagram says he only ever uses the rEvo. However I have not seen any confirmation he was diving a rEvo the day he went missing.

Instagram photo by Rob Stewart • Oct 29, 2016 at 4:41pm UTC