An age-old question: ways to 60m.

[CG43]

Good point. Many people are unaware that CO2 is narcotic as well as toxic. Buhlmann believed that CO2 was more responsible for narcosis than nitrogen.

As far as I know, it was Bühlmann's idea that the oxygen was more narcing than the nitrogen.
That's why Hannes Keller made a dive in 1959 for 4 minutes at a depth of 120 m (394 feet) with a mixture of 5% O2 and 95% nitrogen. This can still be read today e.g. "divemaster 108" April, May, June, 2021.
To verify this I also tried something similar.
I made a mix of 10% O2 and 90% nitrogen and tried it at a depth of 60 m.
My buddy and I hadn't dived at that depth for some time; the water was very cold, very murky, and we were already narced on air. After we switched to 10% O2 and 90% nitrogen, absolutely nothing changed for us; we remained narced the same. After that, I no longer believed this story and did not pursue it further.

By chance, I later found an interview with Hannes Keller in which he said that he actually dove with 5% O2 and 95% helium. He was the only one who mixed gases and therefore knows it with absolute certainty.
He only told the story the wrong way to please Bühlmann because Bühlmann beliefed that oxygen was noticeable more narcotic the nitrogen .
It is amazing how long such stories can persist even though they can be disproven by amateur experiments.

 

[leadduck]

(...)

As for the now bolded above, that should be what everyone strives for, especially the deeper one goes, and to try and maintain the 'hairyer' the situation. But as we know, in some circumstance it takes a lot of mental strength (for want of a better word) / training and experience to do that in all situations that may arise. And even then, both of the bolded above will likely go up to a certain degree, no matter how well 'prepared' you are.

Exactly. And I think that's the biggest risk of deep air: that on some occasion, maybe after 200 uneventful deep air dives, something unexpected happens (reg freeze, getting stuck, dry suit leak, buddy has an issue and needs help, whatever) that causes workload and stress, your SAC rate goes up, and "narcosis" (not literally being unconscious, let's say "mental impairment") kicks in right at the most inconvenient time.

Agreed, the regulator is not the problem.
However, the diver at 50 m who thinks he needs more air only needs less CO2 .
The question is how to get rid of the evil CO2 as effectively as possible.

Second stage , mouth , throat , bronchi and alveoli form a dead space which cannot be avoided .
To leave a small amount of CO2 after exhalation, you have to exhale deeply.
When inhaling, the residual amount of CO2 is diluted with the low-CO2 inhaled air, the more you inhale, the lower the CO2 concentration will be . After that, the amount and concentration of CO2 increases due to the supply from the venous blood until the respiratory threshold is reached and exhalation begins.
In order to keep the average CO2 value as low as possible, the starting value must be as low as possible, and that requires a deep exhalation followed by a deep inhalation , followed usualy bei a rest .

When I see videos of divers, some breathe so effectively and others breathe quickly and rather shallowly.
It should not surprise anyone that the latter is not good at a depth of 50 meters.
I myself dived with divers who had the greatest difficulties at depths between 32m to 52m .
But after some "effectively breathe" trainig we could dive much deeper without significant problems.

There's nothing wrong with breathing more effectively, and training for that, but: if you use that training to dive deeper on air then don't forget that this works only as long as everything goes smoothly. In an emergency with unexpected stress and workload at a depth and gas density that severely limits maximum lung ventilation, paCO2 will inevitably and quickly rise.

 

[old frogman]

Exactly. And I think that's the biggest risk of deep air: that on some occasion, maybe after 200 uneventful deep air dives, something unexpected happens (reg freeze, getting stuck, dry suit leak, buddy has an issue and needs help, whatever) that causes workload and stress, your SAC rate goes up, and "narcosis" (not literally being unconscious, let's say "mental impairment") kicks in right at the most inconvenient time.



There's nothing wrong with breathing more effectively, and training for that, but: if you use that training to dive deeper on air then don't forget that this works only as long as everything goes smoothly. In an emergency with unexpected stress and workload at a depth and gas density that severely limits maximum lung ventilation, paCO2 will inevitably and quickly rise.

It's a matter of establishing the context of the dive. Yes, if you are going to do a 60 metres dive in the North Sea which is cold and murky and then deeply penetrate the hull of a virgin wreck. Agree, Trimix is the safer option. Along with a myriad of other precautions. Conversely, if you are somewhere in the South Pacific, warm water 24C+, 30 metres + visibility in gin clear water, no currents and you are simply cruising down over a reef at 60 metres depth, looking at marine life. For some (not all), deep air is a doable option.

The bottom line is, establish the context, identify the risk, assess the risk, evaluate the risk, if necessary, treat the risk and finally make a decision. If the risk is not acceptable or tolerable cancel the dive.

 

[Kay Dee]

It's a matter of establishing the context of the dive.
For some (not all), deep air is a doable option.

The bottom line is, establish the context, identify the risk, assess the risk, evaluate the risk, if necessary, treat the risk and finally make a decision. If the risk is not acceptable or tolerable cancel the dive.

All of the above, especially this (in all dives)!

Some (not all) people here seem to think that all you need to get outta trouble is to be breathing helium mixes, when in fact it is your skill sets / decision making that (under pressure, if you'll pardon the pun) play a big part.

 

[iliketopetsharks]

All of the above, especially this (in all dives)!

Some (not all) people here seem to think that all you need to get outta trouble is to be breathing helium mixes, when in fact it is your skill sets / decision making that (under pressure, if you'll pardon the pun) play a big part.

No one thinks that.
The lack of skillset and teamwork is another kettle of fish, it's just that even the best and most skilled parajumper is gonna have a hard time if his chute (und backup) fails.

 

[old frogman]

No one thinks that.
The lack of skillset and teamwork is another kettle of fish, it's just that even the best and most skilled parajumper is gonna have a hard time if his chute (und backup) fails.

It's all about risk perception. Most parachute malfunctions are what are called partial malfunctions. The canopy only partially inflates. This was the case with first generation "ram air" canopies (square canopy to some). The malfunction rate, in practice, was about one malfunction in every four jumps. When this happened, you found yourself at the bottom of a large pendulum oscillating in ever increasing circles and at an increasing speed. Some pooped themselves and cut away from the main canopy (which looked like a bag of washing) and deployed the reserve canopy. Others enjoyed the ride and pumped the steering toggles until the collapsed portion of the canopy inflated open and then yelled hooyahh.

Eventually, in following generations of "ram air" canopies a modification called "cross port ventilation" was introduced which solved the problem and took the fun out of jumping the ram air canopy.

The point is, some people are risk averse. No shame in that. Just don't bore those adventurous souls that enjoy a well calculated risk.

 

[leadduck]

It's a matter of establishing the context of the dive. Yes, if you are going to do a 60 metres dive in the North Sea which is cold and murky and then deeply penetrate the hull of a virgin wreck. Agree, Trimix is the safer option. Along with a myriad of other precautions. Conversely, if you are somewhere in the South Pacific, warm water 24C+, 30 metres + visibility in gin clear water, no currents and you are simply cruising down over a reef at 60 metres depth, looking at marine life. For some (not all), deep air is a doable option.

The bottom line is, establish the context, identify the risk, assess the risk, evaluate the risk, if necessary, treat the risk and finally make a decision. If the risk is not acceptable or tolerable cancel the dive.

Theoretically, yes: a risk has multiple factors that you can trade off against each other. The challenge with "assess and evaluate the risk" is, that this is not about your gut feeling and limited personal experience, but about hard data.

Avalanche risk in alpine ski touring is a good example. The physics of snow are complex but well understood, there's a ton of data collected over decades, many professionals working on that risk assessment, resulting in a complex set of rules to make decisions depending on daily specialized local avalanche weather reports, exposition, time of day, slope, and many more. There are thick books about evaluating this risk, decision making flow charts, methods to mitigate certain factors. You take classes about this.

Nevertheless about 100 skiers perish per winter in avalanches in the Alps because they don't understand or don't want to follow the rules. The psychology of "the wreck/mountain is here and now, I can't wait another year, I want to do it now, screw the rules" is always there. They talk about taking an informed decision but what they actually do is just follow their gut feeling and normalize deviance.

 

[Kay Dee]

No one thinks that.
The lack of skillset and teamwork is another kettle of fish, it's just that even the best and most skilled parajumper is gonna have a hard time if his chute (und backup) fails.

No one thinks what?

 

[Kay Dee]

............................................ they don't understand or don't want to follow the rules. The psychology of "the wreck/mountain is here and now, I can't wait another year, I want to do it now, screw the rules" is always there

Whose / what 'f'ing scuba diving 'rules'? Yours? Gue's? XXX? That 'rule' ain't written on my 'license to dive'. So certainly not mine, nor many of the folks I know / knew. Boy oh boy, are some of you people THICK!
Think the below might apply then to you and yours;
"Rules are mostly made to be broken and are too often for the lazy to hide behind." (Gen. Douglas MacArthur) "Learn the rules so you know how to break them properly." (The Dalai Lama)

BTW, I know more folks personally, by far, who have died diving on OC mixed gas / CCR than deep air. By far!

 

[iliketopetsharks]

The point is, some people are risk averse. No shame in that. Just don't bore those adventurous souls that enjoy a well calculated risk.

I have a carbon fiber-hulled submersible to sell you...