Effect of gas density while deep diving

[Swamp_monster]

This may be way beyond my skills and knowledge however I am interested in learning more about the principal of gas density at depth leading to suffocation from co2 poisoning. This seems kinda neglected by training agencies like PADI in terms of the physiology side of gas density (at least in recreational diving). I know the basics of the matter "don't work hard at depth" however I am wanting a more in-depth explanation. My understanding of this right now is the density of gas at 1ata is about 1.29 grams per liter. This changes with depth every ata. The thicker the air the harder it is for the body to 'process' and if working too hard the body will be making more co2 and will not be able to replace it with 02 fast enough leading to slow suffocation. If my understanding is completely off please correct me and let me know. So how does this affect deep recreational diving and deep technical diving? I understand there is a lot of personal physiology involved but are there general guidelines for this? If you are familiar with the unfortunate case of David Shaw it is my understanding that is exactly what lead to his death. I know there is a huge difference between a 900 ft dive and a 200 ft dive however at what depth does this become a real issue?

 

[FreeFlyFreak]

If I recall correctly, above approx 7 g/l is where the real issues begin to show themselves. But it's a sliding scale with lots of variables, work rate, OC/CC Work of breathing etc.

I cant find the reference right now, but I'm fairly sure it was something by @simonmitchell (sp?)
Either a video presentation on YouTube or a published paper.

 

[wstorms]

Recently there was blogpost on this: Density Discords: Understanding and Applying Gas Density Research

And the link to the actual study:
https://www.omao.noaa.gov/sites/def...rs and Scientific Diving Proceedings 2016.pdf

Hope that helps.

 

[Swamp_monster]

Recently there was blogpost on this: Density Discords: Understanding and Applying Gas Density Research

And the link to the actual study:
https://www.omao.noaa.gov/sites/default/files/documents/Rebreathers and Scientific Diving Proceedings 2016.pdf

Hope that helps.

If I recall correctly, above approx 7 g/l is where the real issues begin to show themselves. But it's a sliding scale with lots of variables, work rate, OC/CC Work of breathing etc.

I cant find the reference right now, but I'm fairly sure it was something by @simonmitchell (sp?)
Either a video presentation on YouTube or a published paper.

The issue with this is it is not very deep compared to what some people are doing... 7g/l is like 5.4 ata on air. If this is the limit shouldnt it put tech diving out of business?

 

[Lorenzoid]

The issue with this is it is not very deep compared to what some people are doing... 7g/l is like 5.4 ata on air. If this is the limit shouldnt it put tech diving out of business?

That's part of the reason for helium in breathing mixes.

 

[kierentec]

The issue with this is it is not very deep compared to what some people are doing... 7g/l is like 5.4 ata on air. If this is the limit shouldnt it put tech diving out of business?

It should absolutely put deep air diving out of business.

 

[Swamp_monster]

That's part of the reason for helium in breathing mixes.

I guess trimex is lighter which makes sense but even so the limit for that is so shallow compared to what some of these guys are doing. With that limit, it makes it hard to do a 300-400 ft dive correct? (I am not planning this, I am just mind blown that this is the first I am hearing of this)

 

[wstorms]

oh and if you are looking for a basic understanding you are off to a good start. The deeper you go, the ticker the gas, the ticker the gas, the more effort it takes to breath. This causes the body to produce more CO2.

High CO2 is very narcotic, and that (seems to have, I wasnt there) contributed to David Shaw's death (there were a lot of other things in that particular incident pit). CO2 is not really toxic (unlike CO which is really toxic) but dozing off because you are breathing narcotic gas is not a happy end underwater either, so you really want to manage the CO2 load: limit workload at depth, stay in shape, hydrate etc. etc. Another really important way of managing it is to reduce the gas density by adding helium to the breathing mix. More helium means less nitrogen, and the main point of that is to reduce the density of the breathing gas.

Edit: seems people beat me too it

 

[wstorms]

I guess trimex is lighter which makes sense but even so the limit for that is so shallow compared to what some of these guys are doing. With that limit, it makes it hard to do a 300-400 ft dive correct? (I am not planning this, I am just mind blown that this is the first I am hearing of this)

At some point, heliox (He and O2, no N2) becomes the way to go.
Picking a suitable gas for a particular depth is relatively easy, but when you add in real life factors (profile, stops, gas logistics etc.) and the skills involved with dealing with all of that, it becomes complex.

btw, the fact that some guy did do something once and got away with it does not make it a good practice ;-)

 

[rjack321]

I guess trimex is lighter which makes sense but even so the limit for that is so shallow compared to what some of these guys are doing. With that limit, it makes it hard to do a 300-400 ft dive correct? (I am not planning this, I am just mind blown that this is the first I am hearing of this)

You can play around with the values in here Gas density guidelines

But to achieve 5.2g/L density at 13 ATA / 400ft you are looking at using a gas in the ~80% helium range.

While mildly applicable at even the 130ft recreational limits, if you aren't doing 250+ft dives I wouldn't expect you to have ever really been introduced to this issue before.