Should TDI Helitrox replace AN+DP?

[doctormike]

I had the opportunity to discuss Narcosis very briefly with John Chatterton. It was never my impression that he was suggesting constant exposure to Narcosis as a way of developing tolerance. He was critical of standardizing gases due to a totally different reason. To him, making conservative rules that would apply to a vast population was often a substitute for more in depth knowledge. He wanted all his students to understand various components that factor into narcosis and none of those would be necessary if the technical diving population was being trained to switch to Helium at the lowest common denominator. He was of the opinion that WOB (Work of breathing) has a lot to do with how Narced you would be and managing WOB was one of the fundamental aspects of Narcosis management in his view. So there was a skill or technique to diving deep while maintaining brain function and it was not repeated and constant exposure.

I did my OC AN/DP with John, and his point was that hypercapnea (which correlates with increased WOB) was the culprit in a lot of cases written off as "nitrogen narcosis", especially at shallower depths.

Here is his blog post on that topic.

 

[doctormike]

Wrong answer try again.

Do me a favor and go dive Ginnie on air or 32%. Then do the same dive on something like 30/30 or 21/35 and let me know how different the cave looks. I work in Largo and live in St Pete and have a booster and a compressor. I'll even fill your tanks for you for free (if you have an appropriate cert) so we can see how the experiment goes. The first time my wife dove Ginnie with helium creeped her out. It was a totally different cave and she was shocked at how much she hadn't seen. Even for me and her that rarely get narced, the difference was and is eye opening.

I think the joke was that it's a shame to waste our limited supply of helium by throwing it away into the water column as bubbles. Not that helium doesn't work to manage narcosis.

 

[cerich]

I did my OC AN/DP with John, and his point was that hypercapnea (which correlates with increased WOB) was the culprit in a lot of cases written off as "nitrogen narcosis", especially at shallower depths.

Here is his blog post on that topic.

I believe he is correct.

https://pdfs.semanticscholar.org/afde/24eec20198e349ca45daa59411ffa15edf03.pdf

 

[leadduck]

Of course there were many fatalities when they chased deep air records in the 1990s when Gilliam made his successful 450ft record air dive, and the 1980s with Exley's cave dives to 360ft with air. That was far deeper than the range you're discussing here. They wouldn't have called 150ft "deep air". Plus, cave diving on air is more dangerous as one cannot immediately ascend and solve the issue as soon as you feel it. Cave divers must of course be more cautious and so I see nothing wrong with GUE recommending trimix below 30m.
At 150ft with air, narcosis and the difference to trimix is noticable. But are there any recent accidents documented where open water diving to 150ft on air caused a fatality?

 

[rjack321]

But are there any recent accidents documented where open water diving to 150ft on air caused a fatality?

About half the deaths reported in DAN's 2018 annual report for the US and Canada were on air or nitrox (10 of 18) and not even technical dives. There was one case of "overworking" lobstering as shallow as 20ft which eventually led to a fatality. Would that have been prevented with trimix? Probably not. But you can't separate the breathing gas out as "the thing" in most cases as the causes almost always are multifactored.

https://www.diversalertnetwork.org/medical/report/AnnualDivingReport-2018Edition.pdf

Similarly you can't say it was CO2 or N2 as they coexist.

 

[cerich]

Of course there were many fatalities when they chased deep air records in the 1990s when Gilliam made his successful 450ft record air dive, and the 1980s with Exley's cave dives to 360ft with air. That was far deeper than the range you're discussing here. They wouldn't have called 150ft "deep air". Plus, cave diving on air is more dangerous as one cannot immediately ascend and solve the issue as soon as you feel it. Cave divers must of course be more cautious and so I see nothing wrong with GUE recommending trimix below 30m.
At 150ft with air, narcosis and the difference to trimix is noticable. But are there any recent accidents documented where open water diving to 150ft on air caused a fatality?

regs are much better these days with lower WOB and less CO2 retention than back in the day. many regs in the 90's started to show their weakness past 160 or and some were not at all a good idea to have at that depth or deeper. Many mid range balanced regs of then are well out performed by current unbalanced pistons today.

I

 

[CAPTAIN SINBAD]

About half the deaths reported in DAN's 2018 annual report for the US and Canada were on air or nitrox (10 of 18) and not even technical dives. There was one case of "overworking" lobstering as shallow as 20ft which eventually led to a fatality. Would that have been prevented with trimix? Probably not. But you can't separate the breathing gas out as "the thing" in most cases as the causes almost always are multifactored.

https://www.diversalertnetwork.org/medical/report/AnnualDivingReport-2018Edition.pdf

Similarly you can't say it was CO2 or N2 as they coexist.

Since most of the diving happens on air and nitrox most of the fatalities will also be on those gases. We cant take that to mean that the gases were causing those fatalities and use of Helium in those situations would prevent those. The highest number of fatalities (Figure 15.3) happened in less than 30 feet of water.

 

[leadduck]

About half the deaths reported in DAN's 2018 annual report for the US and Canada were on air or nitrox (10 of 18) and not even technical dives. There was one case of "overworking" lobstering as shallow as 20ft which eventually led to a fatality. Would that have been prevented with trimix? Probably not. But you can't separate the breathing gas out as "the thing" in most cases as the causes almost always are multifactored.

https://www.diversalertnetwork.org/medical/report/AnnualDivingReport-2018Edition.pdf

Similarly you can't say it was CO2 or N2 as they coexist.

From these reports (as well as the previous years' and BSACs) I see that most fatalities are related to cardiac problems, low level of fitness, in combination with "being alone in the water" (group fell apart, diver with problem was alone).

Now about deep air, if 150ft "deep" air dives were so dangerous then I expect to see at least a few related fatalities, at least from regions where 150ft on air is considered normal and frequently done such as France and Italy. There should be at least a handful of fatalities over the past 20 years that can be traced back to being incapacitated at 150ft on air. Else, the conclusion would be that there's a difference between "I feel it" and "it kills me".

 

[rjack321]

Since most of the diving happens on air and nitrox most of the fatalities will also be on those gases. We cant take that to mean that the gases were causing those fatalities and use of Helium in those situations would prevent those. The highest number of fatalities (Figure 15.3) happened in less than 30 feet of water.

By the same token you cant blame the trimix dive on helium.
Having a single causal factor to point to and blame (other than certain medical events) just doesn't happen.

 

[doctormike]

There should be at least a handful of fatalities over the past 20 years that can be traced back to being incapacitated at 150ft on air. Else, the conclusion would be that there's a difference between "I feel it" and "it kills me".

Yeah, but that would be a very difficult thing to prove. Nitrogen narcosis isn't an all or nothing thing like a seizure, and the narcosis itself doesn't kill you. What can be potentially lethal is the degradation of your baseline skills, especially on a challenging dive.

So if someone was diving deep on air and got entangled or had an unrecoverable free flow, would you chalk that death up to narcosis? Would it be a contributing factor? Or would either of those things have caused death just the same at 60 feet? You would never really know, right?