Breathing air maximum terminal depth

[Kevrumbo]

One thing which usually isn't considered is gas density. After reading @Dr Simon Mitchell 's thread on gas density, I started doing some calculations. It turned out that maximum recommended gas densities are reached at roughly the same depths where an equivalent air depth of 30m is reached. So, it's not just the narcosis, but also the WOB and CO2 ventilation that is affected by depth.

The numbers I got from that exercise cemented my personal choice of staying shallower than ~30m/100' unless I have a bit of helium in my gas. Which I'm not certified for, but that's different topic.

A gas density of 6 grams/liter was found by Dr Mitchell's study to induce a gross increase of CO2 retention with exercising test divers at depth (see video above).

Interestingly, at the recreational maximum recommended depth limit of 39m/130ft, the gas density of Air is around 5.5 g/L

 

[Kevrumbo]

The problem is if you cannot eliminate metabolic CO2 fast enough by ceasing the physical activity causing it (and/or fixing the Scuba/Rebreather malfunction that can be causing it as well), then CO2 retention Hypercapnia can quickly develop causing anxiety and panic, or worse incapacitate into unconsciouness. This can happen at any depth whether breathing Air, Nitrox or Trimix. . .

 

[Diver0001]

I was reading an old Aquacorps magazine the other day and was looking at the Hall Watts 40 Fathom Grotto advertisement for his deep air diver course. Level 7 was to 300ft. I may have taken that course but can't be sure

@RainPilot said everything perfectly above.

Just adding to what Dave said, Brett Gilliam has written quite a bit about his adventures at these depths, and deeper, on air although his stories (embellished or not) make it sound like a comprehensively BAD idea!

Mark Ellyatt is also quite open about having made dives to about these depths on air as well, as have many divers in places like Egypt, where a bounce to this depth can be done with minimal equipment. I don't know if he's written about it but I do recall hearing a thing or two from the horse's mouth, particularly about the auditory hallucinations (a sort of WAH-WAH-WAH sound) that also made doing such dives seem entirely not worth it.

Rainpilot talked about adding HE to the mix at 30m. Most divers I know wouldn't even consider that but beyond 40m many/most probably would, especially if the dive were non trivial and provided proper qualifications etc etc.

R..

 

[BRT]

Pardon me, but just out of morbid curiousity.

What is the maximum depth a diver can make while breathing air underwater before becoming crazy, unconscious and dying? What exactly happens physiologically when a diver descends too deep while breathing air?

I saw this infamous video on youtube of this diver who descended deep before he lost his mind. And all sorts of questions rose up.

Check Ultra Deep Air in Wikipedia. Some people are both good and lucky. Most not.

 

[Dr Simon Mitchell]

Hello,

As clearly illustrated by the discussion above there are multiple risks in breathing air at progressively greater depths, but with one exception (see below) there are few data defining clear thresholds at which the "big three" risks (narcosis, oxygen toxicity, gas density and CO2 retention) become intolerable. Indeed, as has been pointed out, there is strong evidence that there is considerable variability (both between and within individuals) in the expression of these problems.

Arguably, of these risks, the one with a threshold that is now best defined by data is the risk of CO2 retention due to rising gas density. As pointed out by Kev, the relevant data were compiled by Gavin Anthony of QinetiQ from a database of test dives, and we published those data together last year. To summarise, when gas density exceeded 6g/L during modest work (100 - 125 watts) underwater there was a sharp inflection in the risk (to over 40% of dives) of developing dangerously high levels of body CO2. 6g/L corresponds to use of air at about 40m.

Right there we now have a strong evidence-based argument for avoiding use of air deeper than recommended by the recreational training agencies. I would remind you that development of a high CO2 level is also a significant risk factor for oxygen toxicity. So, using deep air has been clearly demonstrated to increase the risk of CO2 retention, which in turn also indisputably increases the risk of another catastrophic complication.

Yes, I know that many vocal divers have used air at great depths. That, of itself, is not a valid justification of the practice in the face of hard evidence that it is dangerous. These people are a self selected population of survivors, and are around to talk about it, but the ones that died doing it are not.

Simon

 

[Kevrumbo]

I saw this infamous video on youtube of this diver who descended deep before he lost his mind. And all sorts of questions rose up.

The infamous Yuri Lipski video of his own demise:
Opinion: Assuming normal BCD function with full inflation, positive lift capacity was probably negated by excessive lead weighting and compounded by loss of wetsuit buoyancy, resulting in an uncontrollable fast descent to a hard rocky reef bottom of over 90m depth. Rule out as precipitating cause of accident: Unable to equalize (?) -Ear Barotrauma with resulting incapacitating Vertigo along with extreme Nitrogen narcosis handicapping arrest of descent and regain of control.

Primary COD: Drowning.
Secondary to: Rule Out Hypercapnia; Oxygen Toxicity; Exhaustion of Air Supply.

 

[Jared0425]

There was a diver that reached around 500 feet on air. If I remember correctly there was some detrimental side effects. That is the deepest I've ever heard for someone on air.

 

[Akimbo]

...
Right there we now have a strong evidence-based argument for avoiding use of air deeper than recommended by the recreational training agencies. I would remind you that development of a high CO2 level is also a significant risk factor for oxygen toxicity. So, using deep air has been clearly demonstrated to increase the risk of CO2 retention, which in turn also indisputably increases the risk of another catastrophic complication....

I'm confused, the risk of Oxygen Toxicity on air is a relatively minor concern. Gas management and Narcosis is are the main factors deeper than 130 and above 285'. Obviously gas density and CO2 retention is a factor in Narcosis, which is a killer by inducing "stupid". I'm in no way encouraging air dives to 285', but isn't 130' is a bit of an overstatement considering the tremendous number of successful dives to up to 165'/50M?

 

[dberry]

Interesting. TDI Deco Procedures states a diver is "qualified to conduct staged dives to 45 msw / 150 fsw." I believe DP always comes before Trimix, so that means air dives. Compared to the 40 m (5 bar) recommended by Dr. Mitchell, 45 m (5.5 bar) would give a gas density 10% higher, or ca. 6.6 g/L.

It makes sense the CO2 retention would depend on the level of exertion, but I don't have a feel for what constitutes "moderate work." Gently finning? or swimming against a current? Or panic-induced stress?

 

[Storker]

I'm confused, the risk of Oxygen Toxicity on air is a relatively minor concern. Gas management and Narcosis is the main factor deeper than 130 and above 285'. Obviously gas density and CO2 retention is a factor in Narcosis, which is a killer by inducing "stupid". I'm in no way encouraging air dives to 285', but isn't 130' is a bit of an overstatement considering the tremendous number of successful dives to up to 165'/50M?

On air, EAN32 or EAN28, gas density reaches 6 g/L around 35-36m (115 to 120 feet). 6 g/L seems to be a limit for proper ventilation of CO2.

Which means that according to those data, it's probably a good idea to use a bit of helium at greater depths than some 30-something meters/100-something feet.