Virginian diver dead at 190 feet - Roaring River State Park, Missouri

[inquis]

@steinbil, because they quantified the difference, I suspect that particular post was talking about with helium, not without as stated.

Adding O2 (because the setpoint is higher than the ppO2 from the diluent alone) makes the helium a smaller percentage of the new total. Targeting ppO2 of 1.3 vs 1.0 from 15/55 dil (@190 ft), the effective mix becomes 20/52, changing END from 67 fsw to 71 fsw. As you can see, it's not a huge impact in this case.

Others have pointed out the bigger narcotic issue (CO2) which is correlated with the high gas density of nitrox.

 

[Brad_Horn]

My argument on that is that it is not actually the gas being breathed but the increased WOB of the rebreather verses OC - the increased WOB is actually causing a lower CO2 flush from your lungs - CO2 is 10x more narcotic then Nitrogen or Oxygen.

Which raises the question: what was the WOB as tested of the KISS Sidewinder rebreather in the configuration dived?

How much higher was this than the optimum lowest WOB for a rebreather?

 

[steinbil]

Adding O2 (because the setpoint is higher than the ppO2 from the diluent alone) makes the helium a smaller percentage of the new total. Targeting ppO2 of 1.3 vs 1.0 from 15/55 dil (@190 ft), the effective mix becomes 20/52, changing END from 67 fsw to 71 fsw. As you can see, it's not a huge impact in this case.

Yes, with a helium mix that makes sense. I guess that's where the confusion came from, maybe Nitro was thinking about a diluent with helium, that would also be closer to the quoted increase in "depth" from 58m to 60m.

In any case I learned more about CCRs, and I'm even more convinced then before of how narced the deceased diver must have been in this situation. Gas density is no joke.

 

[makar0n]

Cannot resist...

 

[Nitrogenius]

Obviously. I’m just puzzled how a gas consisting of oxygen and nitrogen can be more narcotic on a CCR than on OC, it seems to defy logic…

I think what was written was simply a shortcut for writing out that the mix itself is not more narcotic, but the person is more susceptible to narcosis because of the various factors involved in CCR diving versus OC.

Stuartv: nope is is really two independent topics..
WOB can influence the effects of narcosis but Narcotic depth is totally independent and is tied to the %of Nitrogen at the specific depth while you compare it to which depth the resulting partial pressure of Nitrogen would be the same if you dove air.

So Steinbil:
This is where it stems from. On a CCR you are not diving a fixed mixed but a fixed setpoint of partial pressure of oxygen.
S
Meaning yiu are constantly changing your mix as in percentage oxygen, Nitrogen and if present Helium.

So diving air as diluent is very different from diving air on OC.

As long as the partial pressure of oxygen would be lower than air at the given depth you will have less Nitrogen in your loop than compared to air.
But as soon as you dive deeper and your PO2 would (if it was OC air) exceed your setpoint, then you do even get more %Nitrogen in the loop than OC air..
Hence the END raises further.

 

[Whitrzac]

Stuartv: nope is is really two independent topics..
WOB can influence the effects of narcosis but Narcotic depth is totally independent and is tied to the %of Nitrogen at the specific depth while you compare it to which depth the resulting partial pressure of Nitrogen would be the same if you dove air.

So Steinbil:
This is where it stems from. On a CCR you are not diving a fixed mixed but a fixed setpoint of partial pressure of oxygen.
S
Meaning yiu are constantly changing your mix as in percentage oxygen, Nitrogen and if present Helium.

So diving air as diluent is very different from diving air on OC.

As long as the partial pressure of oxygen would be lower than air at the given depth you will have less Nitrogen in your loop than compared to air.
But as soon as you dive deeper and your PO2 would (if it was OC air) exceed your setpoint, then you do even get more %Nitrogen in the loop than OC air..
Hence the END raises further.

Increased WOB = more CO2 retention = more narcoses. Its not a set value, but any experianced RB diver would take it into consideration.

Oxygen is has been widely proven to have the same narcotic effects as nitrogen. Diving a nitrox mix does not reduce narcosis in any way.

 

[tursiops]

Oxygen is has been widely proven to have the same narcotic effects as nitrogen. Diving a nitrox mix does not reduce narcosis in any way.

^^^THIS^^^

 

[lermontov]

As long as the partial pressure of oxygen would be lower than air at the given depth you will have less Nitrogen in your loop than compared to air.

thats not quite accurate - At the transition point there is a range where the ccr PN2 is higher and then OC PN2 catches up - that transition point (depth) will vary depending on the CCR set point

eg 6 ata air is Po2 1.26 and Pn2 of 4.74 and on ccr set point of 1.2 the ppo2 is 1.2 (lower) and the Pn2 is 4.8 (higher) the range that this is applicable is approx 5m

 

[inquis]

Oxygen is has been widely proven to have the same narcotic effects as nitrogen.

While I still calculate END assuming that is true, I seem to recall @Dr Simon Mitchell hinted that may not be so cut & dry a month or two (?) ago. I saw this yesterday about a recent study:
Is Oxygen Narcosis A Thing?

 

[inquis]

Found what I was remembering. It was more than a hint and occurred back in the summer. Hopefully this links back to his full posting.

There seems to be a general sense on this thread that oxygen has been demonstrated to be as narcotic as nitrogen. This is not true. It is a complicated matter and still debated in the scientific literature.