Filmmaker Rob Stewart dies off Alligator Reef

[doctormike]

Rob gave an OK sign before passing out, sank & drown. Had he just kept the mouthpiece on, did a MOF & breathed through his nose, would that prevent him from passing out or at least from sinking & drowning?

If you are out of O2 and your dil is hypoxic, you need to do two things when you are on the surface: get off the loop and close the DSV. At that point, unless you are seriously bent, you will probably be OK. The earth's atmosphere will soon fix any hypoxia / hyperoxia / hypercapnia issues that you may have developed, but if you don't close the DSV, the loop will flood and you will become negatively buoyant quickly. .

Trying to bump up the PO2 in a hypoxic loop by adding (lean) surface air through your nose Isn't a good plan. Just close the DSV and use your hypoxic dil to fill your wing. It won't support life at the surface, but it will float just fine....

 

[PT4476]

I guess jaw would drop & mouthpiece comes off when a diver pass out on the surface. Is that one of the reasons you have a gag strap?

Have anyone found unconscious diver floating on the surface with mouthpiece on without gag strap?

Since the chance of survival / being found floating on the surface by SAR is much better than on the bottom of the sea, is there a better mouthpiece design that will keep it stay on the mouth when diver becomes unconscious?

As mentioned above that mouthpiece, gag strap or not, was most likely delivering gas to the diver that rendered him unconscious.

 

[Wookie]

That is a particularly heavy mouthpiece, and that rebreather design is such that the counterlungs would collapse when there is no lung pressure on the mouthpiece to keep the counterlungs inflated. Different rebreathers, particularly ones with the counterlungs above the lungs, may stay inflated more easily.

I am not a rebreather diver, but I've learned some by osmosis.

 

[Dan]

I think Capt. Jim's response is, if the amount of O2 in the blood is no more than 10%, that is survivable at 20 feet on a safety stop (PPO2 .14). As soon as you surface, your blood PO2 crashes (to .10 PPO2) and you're going to pass out. Period. Maybe without enough time to close your mouthpiece or breath through your nose. Note. A PPO2 of .14 is not recommended, but survivable. He would be dopey as hell at the end of his safety stop.

Although he passed out then, at least he would still be floating & unconsciously breathing, unless the mouthpiece fell off his mouth, which seemed to be what happened in this case.

 

[Wookie]

Although he passed out then, at least he would still be floating & unconsciously breathing, unless the mouthpiece fell off his mouth, which seemed to be what happened in this case.

That is the ME's assumption. Rob suffered from Hypoxia, passed out on the surface, lost his mouthpiece, counterlungs deflated, Rob sank. The Coast Guard will have a report too. I have been answering your questions, but not speculating, because I believe the CG report may draw a different conclusion, we'll find out soon.

The MEs report is completely logical. Only time will tell.

 

[doctormike]

That is a particularly heavy mouthpiece, and that rebreather design is such that the counterlungs would collapse when there is no lung pressure on the mouthpiece to keep the counterlungs inflated. Different rebreathers, particularly ones with the counterlungs above the lungs, may stay inflated more easily.

I am not a rebreather diver, but I've learned some by osmosis.

Although he passed out then, at least he would still be floating & unconsciously breathing, unless the mouthpiece fell off his mouth, which seemed to be what happened in this case.

The gag strap is really meant to keep the mouthpiece in underwater in case of unconsciousness. As Wookie pointed out, it doesn't always do the same thing on the surface. I dive a JJ with backmounted counterlungs, and you definitely feel the pressure when on the surface and vertical. I'm assuming that a gag strap wouldn't maintain an airtight seal in that scenario (I don't dive one myself, so I might be wrong).

And if the gag did work as Dan was mentioning, it would have killed him pretty quickly by making him breathe hypoxic gas at the surface. Best case scenario with a surfaced unconscious diver and a hypoxic loop is that the mouthpiece falls out but somehow doesn't flood for long enough for the diver to get pulled out of the water.

 

[PT4476]

I dive a revo, I doubt the gag strap would stop the counterlungs from deflating if the diver is unconcious, in a vertical position, on the surface.

 

[Capt Jim Wyatt]

I am wondering how a medical examiner can actually make a finding of hypoxia, or hypoglycemia-- seems to me these attributes are very transient and would not be all that accurate to measure several days after death.

 

[Capt Jim Wyatt]

I meant had he taken off his mask, before giving OK sign & breathed fresh air on the surface through his nose, rather than through his mouth on the mouthpiece while floating. Would that be survivable?

I think so...but I am no physiologist. Seems to me breathing atmospheric air would quickly, but not immediately reverse a hypoxia event.

 

[doctormike]

I am wondering how a medical examiner can actually make a finding of hypoxia, or hypoglycemia-- seems to me these attributes are very transient and would not be all that accurate to measure several days after death.

I'm no pathologist, but I think that there are characteristic types of tissue damage that occur with different injuries and which will persist after death. For example, you might see tissue bubbles in DCS, you might see dilated cerebral vessels or microhemorrhages in hypercapnea. And in hypoxia, there are apparently changes in the neurons.

Tissue hypoxia can be caused by both underperfusion (like with a heart attack or a stroke caused by blood vessel occlusion) or by systemic hypoxia (from suffocation or hypoxic dil). If the pathologist finds no reason to suspect a perfusion problem, but they see evidence of neuronal hypoxic injury, in this setting they might conclude the most likely cause of hypoxia.