Fiona Sharp death in Bonaire

[Dan]

Yes, but that's a different scenario than this one.

I'm not up on the latest from that tragedy, but in that case the gag strap might have prevented the loop from flooding on the surface, causing him to sink after he lost consciousness, presumably from DCS, right? So they might have been able to recover him and resuscitate him if he were floating and unconscious.

No, Rob's lost consciousness was caused by hypoxia, according to Sharkwater Extinction

 

[runsongas]

Unless you are talking about just falling asleep, I haven't heard of that.

Losing consciousness on a rebreather would likely be from hypoxia or hyperoxia (hypercapnea can also cause LOC, but would probably with more of a prodrome). So if nothing changes with the loop contents, not sure why you would spontaneously regain consciousness.

hypercapnia clearing due to lack of movement / lower co2 generation, o2 consumption falling low enough from non-movement for leaky valve or hccr/eccr solenoid to catch up and recover hypoxic loop, recovery from hyperoxia seizure by breathing down the loop. just wondering if there were any incidents where FFM made a difference.

 

[CptTightPants21]

No, Rob's lost consciousness was caused by hypoxia, according to Sharkwater Extinction

Except that the computer log showed the loop never dropped into hypoxic levels. It was a widely held belief that he lost consciousness due to hypoxia until the computer data was released. Now the reason for loss of consciousness is unknown, but leans a little towards a DCS hit.

 

[Ayisha]

...the reason for loss of consciousness is unknown, but leans a little towards a DCS hit.

Yes, Rob Stewart's computer data leans toward DCS (12 minutes omitted deco at a GF of 90/90 + rapid ascent of 75 feet/minute or 23 meters/minute)/hypercapnia/dwelling.

His computer data shows the PPO2 never went below 1.0, so hypoxia is not supported.

 

[doctormike]

hypercapnia clearing due to lack of movement / lower co2 generation, o2 consumption falling low enough from non-movement for leaky valve or hccr/eccr solenoid to catch up and recover hypoxic loop, recovery from hyperoxia seizure by breathing down the loop. just wondering if there were any incidents where FFM made a difference.

Not sure. The one of those that I thought of was hypercapnea from overexertion with a functional scrubber, but I think that would be less likely to cause plain LOC than the other symptoms. The other recovery scenarios seem pretty remote, but there is a bell curve for everything...

I guess my concern about these arguments for gag straps or FFM is that they put more responsibility on these devices than they are really good for, and thus imply that solo CCR diving is fine as long as you have one of them. From the limited data out there, it seems that their main benefit is allowing for a buddy rescue, as in the Gempp paper. Not for these remote scenarios where a solo diver recovers from a significant neurological hit like LOC.

 

[JohnnyC]

Unless you are talking about just falling asleep, I haven't heard of that.

Losing consciousness on a rebreather would likely be from hypoxia or hyperoxia (hypercapnea can also cause LOC, but would probably with more of a prodrome). So if nothing changes with the loop contents, not sure why you would spontaneously regain consciousness.

I have heard of a case where a diver diving an mCCR went hypoxic while heavily working and passed out. Because he went from a working level of consumption to basically none, the unit was still leaking O2 into the loop, and he reached a point where the PO2 was high enough and he regained consciousness. Again, totally and completely hearsay, could be entirely made up.

 

[doctormike]

I have heard of a case where a diver diving an mCCR went hypoxic while heavily working and passed out. Because he went from a working level of consumption to basically none, the unit was still leaking O2 into the loop, and he reached a point where the PO2 was high enough and he regained consciousness. Again, totally and completely hearsay, could be entirely made up.

I would believe it, although you would have to ignore your PO2 for quite a while for it to get that low if the valve was working at all, right? Score one for the FFM/gag strap.

 

[Scuba Lawyer]

In 1980 I was diving off Andros Is. Bahamas on this nice little reef in 20 feet of zero current water happily blowing open circuit bubbles. I was laying down on a white sand bottom watching little fishies dart about in the sunshine when all of the sudden someone shook me. I looked at my pressure guage and it was low. I looked at my watch and 20 minutes had passed in the blink of an eye. Yup, so relaxed I fell asleep. No harm occurred. I guess if my reg had fallen out of my mouth (it didn't), I would have noticed something. Other divers on that trip started calling me Rip Van Snorkel.

 

[JohnnyC]

I would believe it, although you would have to ignore your PO2 for quite a while for it to get that low if the valve was working at all, right? Score one for the FFM/gag strap.

Not necessarily, if you were working hard you would have to add more often than you normally would. And if you had a rather low bottom PO2 for whatever reason. If you had a needle valve and you hadn't opened it enough or it had accidentally closed, the addition rate wouldn't be what was expected. All of which could lead to a hypoxic scenario in not a long amount of time, although there would definitely be a failure on the divers part to allow any of that to happen.

Remember with an mCCR you either set your orifice size (CMF) below your metabolic rate, or with a needle valve, you tune it to your metabolic rate and depth. If your workload suddenly increases, you either have to add more often in the case of a CMF orifice, or you have to open your needle valve to compensate, and/or add more often. If you don't compensate for your increased workload, your usual addition cycle gets out of whack. Get too complacent and PO2 tanks too much.

 

[shoredivr]

It would be great to see the dive profile. How quickly she went to 300' and what was her bottom time at that depth.

Is it possible to make a quick dip to 300' with such gear set up and survive to tell the tale?

The reef at Buddies drops quickly down to 150, then there’s a long flat plane of sand that goes for quite a while. Not sure where the next drop off is, but it’s not a sheer wall where losing a bail out would mean it fell quickly to 300ft.