Effect of gas density while deep diving

[rjack321]

So you think they are aware of the issue and neglect it? I wonder if anyone has stats on how common this is in regards to diving accidents for technical or even deep recreational dives. I am not sure of this, but could it be that it may not be that much of an issue for the agency's to care about it?

Its a huge issue

But they are in the business to sell training and certifications - not continually redesign their programs and retrain their instructors to follow the best available science. You could always decide PADI's Tec40/50 program isn't for you and go to an instructor/agency that has long understood the risks of CO2 and the value of helium - even before there was peer reviewed and published recommendations with relatively precise density thresholds to consider when planning dives.

 

[Swamp_monster]

Maintaining sufficient O2 saturation has nothing to do with the gas density problem.
Its all about elimination of CO2

So if you are not eliminating co2 would that not affect your 02 sat in your blood which would be detectable?

 

[rjack321]

So if you are not eliminating co2 would that not affect your 02 sat in your blood which would be detectable?

No
Co2 retention does not affect O2 saturation.
There are times when you can suffer from hypoxia (lack of oxygen). That is pretty much exclusively a shallow water or surface problem. At depth where gas density is an issue and Co2 could be retained due to too much exertion or work of breathing being too high, hypoxia is not an issue.

 

[Storker]

Dr. Simon Mitchell explains the challenge of gas density

And the research he quotes indicate that gas density becomes borderline already somewhere between 30m/100' and 40m/130' unless you have some He in your mix.

 

[Storker]

You'll see the original paper was in that context, as well as the study that noted the spike in CO2 issues once you get above 6.0g/L was in rebreather divers. Gas density impacts OC divers for sure, but it's likely much more an issue on CCR

There are papers indicating that it may well be an issue also on OC. I'm too lazy to dig up the link, but it has been discussed here on SB.

 

[jgttrey]

I don't dispute that it is an issue on OC as well - Dr. Mitchell makes it clear that though the data is sparse, the same sort of results are seen on OC - but it would seem to be even more critical on a rebreather.

Clearly the physiological considerations (meaning how the respiratory system itself responds to excessively dense gas) would be the same, OC or CCR. But, CCR divers have additional challenges because the nature of their gear. They are already managing other factors -- possible static lung loading due to counterlung placement, higher baseline equipment-induced WOB, more induced WOB changes as density increases, decrease scrubber efficiency as density increases, increased likelihood of breakthrough when gas velocity increases in response to fast breathing, etc.

I'm not aware of data on it, so this is just me speculating, but I wouldn't be surprised if we ultimately ended up with one set of gas density recommendations for OC and another, partially overlapping, set of recommendations for CCR that are more conservative.

 

[Swamp_monster]

And the research he quotes indicate that gas density becomes borderline already somewhere between 30m/100' and 40m/130' unless you have some He in your mix.

This is where I am blown away where this is not more commonly known because this is quite a common depth for rec divers to hit.

 

[rjack321]

I'm not aware of data on it, so this is just me speculating, but I wouldn't be surprised if we ultimately ended up with one set of gas density recommendations for OC and another, partially overlapping, set of recommendations for CCR that are more conservative.

I'm having a hard time imagining anyone doing a retrospective analysis of OC diver's gas density similar to what Anthony and Mitchell published in 2015.
The pool of dives is immense and the outcomes are not as clear.

 

[rjack321]

This is where I am blown away where this is not more commonly known because this is quite a common depth for rec divers to hit.

Commonly known and commonly ignored too.

Should TDI Helitrox replace AN+DP?
Diving air to 60m
A reminder about deep air/ or not
Diver dies on 60m deep air dive

There are literally hundreds of posts and threads here where divers are claiming to be "just fine" on air at 130ft/40m or even far deeper.

 

[rsingler]

This is where I am blown away where this is not more commonly known because this is quite a common depth for rec divers to hit.

But it's a very small population at risk:
IF you're a non-responder to elevated CO2, and
IF you're at 130', and
IF you're unexpectedly forced to exert yourself with otherwise low-resistance equipment (open circuit), then you are starting to be at risk for gas density issues.

Just not many folks in that camp who aren't already thinking trimix...

Ah, @rjack321 beat me to it.
The info is out there for folks that dive this way...