What went wrong on your dive today/recently? And what did you learn?

[UofMI_Divegeek]

This is implausible. According to MultiDeco, the gas density for air and 32% at 60 ft are both just 3.4 g/l

Along with the fatigue was massive sweating and a mild headache ... the sense of air starvation was extreme.

The gas density difference is extremely small (need more than 2 significant figures to see the difference) which is why the density difference seemed so weird. But, this is what the Israeli's noticed in their combat swimmers. This observation was so profound that they even suggested CO2 tolerance testing for anyone prior to using EANx.
and
we were doing extreme aerobic exercise which was generating lots of metabolic CO2.
and
the same dive on compressed air did not create the problems we encountered on NOAA I, so the only apparent difference in observed symptoms was the breathing gas.

and, yes we analyzed to make sure the O2 was 32%.

 

[scubadada]

Hi @UofMI_Divegeek

Thanks for the detailed reply.

I remain skeptical

 

[VikingDives]

the Israeli's noticed in their combat swimmers. This observation was so profound that they even suggested CO2 tolerance testing for anyone prior to using EANx.

Do you have a link to this study?

 

[UofMI_Divegeek]

It was decades ago, all I remember was that it was in Undersea Biomed Research

BTW: All our xs CO2 issues resolved at depth when we rested. (We embedded our river sticks in the bottom and rested until respiration was normal, then we resumed the dive). This occurred on 2 dives with. both divers experiencing the same issues.

All my library is currently in a 40" shipping container since my apartment is being renovated. When my stuff is restored, I will look for it. Sorry I can't give you a rapid response.

 

[scubadada]

Hi @UofMI_Divegeek

It appears Undersea Biomed Research has not been published since the early 1990s but it is still listed on PubMed. Despite searching on a wide variety of terms, I was not able to find your cited article. If you eventually find it, please let us know.

 

[UofMI_Divegeek]

Hi @UofMI_Divegeek

It appears Undersea Biomed Research has not been published since the early 1990s but it is still listed on PubMed. Despite searching on a wide variety of terms, I was not able to find your cited article. If you eventually find it, please let us know.

Undersea Biomed Research was the official publication of the US based Undersea Medical Society. Sometime in the 1990's, they changed their society name to include hyperbarics (Undersea and Hyperbaric Medical Society ... UHMS). Their journal is now the Journal of Undersea and Hyperbaric Medicine.

 

[VikingDives]

I found this study: https://diving-rov-specialists.com/...-retention-hyperbaric-exercise-4060nitrox.pdf

(Undersea 6 Hyperbaric Medicine, Vol. 22, No. 4, 1995 CO2 retention during hyperbaric exercise while breathing 40/60 nitrox D. KEREM, Y. I. DASKALOVIC, R. ARIEL], and A. SHUPAK Israeli Naval Medical Institute)

Just skimming it, I found this:

"The group mean C0, production rates were 1.15 i 0.22 liter min during the air phase and 1.09 i 0.43 liter min during the nitrox phase. The difference is not significant."

I also found this: https://apps.dtic.mil/sti/pdfs/AD0784151.pdf

(Lanphier EH. (1955). Nitrogen-Oxygen Mixture Physiology, Phases I and 2. Formal Report 7-55, Washington: Navy Experimental Diving Unit)

which indicates that there is greater CO2 retention for diving with Nitrox 45 vs 45% oxygen and 55% helium.

 

[scubadada]

Hi @UofMI_Divegeek

I found the same 1995 article that @VikingDives found CO2 retention during hyperbaric exercise while breathing 40/60 nitrox - PubMed

The hypercapnia appears to have been diver dependent and not gas dependent. The real risk was diving to a PO2 of 1.6 along with the elevated CO2, increasing the risk of oxygen toxicity.

I probably should have known about the name change for the journal as I trained as a chamber operator and was a member of the Undersea & Hyperbaric Medical Society in a previous life. Unfortunately, I never joined the medical faculty at one of the offshore medical schools and ran the hyperbaric chamber on the side. The best laid plans, But, my retirement is more secure now.

 

[UofMI_Divegeek]

Th

Hi @UofMI_Divegeek

I found the same 1995 article that @VikingDives found CO2 retention during hyperbaric exercise while breathing 40/60 nitrox - PubMed

The hypercapnia appears to have been diver dependent and not gas dependent. The real risk was diving to a PO2 of 1.6 along with the elevated CO2, increasing the risk of oxygen toxicity.

I probably should have known about the name change for the journal as I trained as a chamber operator and was a member of the Undersea & Hyperbaric Medical Society in a previous life. Unfortunately, I never joined the medical faculty at one of the offshore medical schools and ran the hyperbaric chamber on the side. The best laid plans, But, my retirement is more secure now.

View attachment 780883That is noi the article I was remembering.

This is not the article I remember.

Bottom line: 2 divers on 2 dives experienced symptoms consistent with high CO2 and the symptoms were not present using compressed air on the same dive.. So the gas was clearly a component.

and
the point of the article was to make divers aware to be alert for CO2 issues, especially under workload., not that it was a certainty

and
using compressed air knocked 3.5 minutes off the dive (we did not have to stop to remove the air-starved feeling) ... which is why we labeled it a fly.

and
I personally talked to Ed about this and similar situations. I got my concerns about CO2 from him.

Finally, I strongly believe that CO2 is an underrated culprit in diving scenarios.

 

[johndiver999]

I think if gas density were this critical (in miniscule amounts), people would be getting in huge problems on relatively high exertion dives on deep air dives all the time. The anecdotal report is not convincing evidence of this effect, especially when many hundreds of thousands of dives don't create the effects observed on these two dives.

Just for a sanity check what is the comparable gas density difference? less than one foot of depth (between air and nitrox at 2 atm)??? Somebody should do the math to bring some perspective.