An age-old question: ways to 60m.

[scubaozy]

This is an oranges and apples comparison. If you normalize for risk exposure of dives (e.g., PrT — avg depth x square root of time) I assume the split would be different. Tech dives are inherently more dangerous than NDL dives in OW, this is why tech diving requires equipment, procedures, and training to mitigate the risk.

Well tech diving is clearly different than rec diving, I am discussing risk exposure cost of choosing tec vs rec and ccr vs deep air. Normalization of risk exposure can only make sense if you have the data, it is practically impossible to collect dive profile for every single dive. You can only speculate, say average rec dive is 20m and average tec dive is 60m, 3 times deeper, that begs the question, why the fatality is 10 times.

 

[Nick_Radov]

When people denounce deep air diving today more than 25 years ago, I don't think it's because people got more risk averse. It's rather that back then we didn't know better, had a few misconceptions about adaptation to nitrogen narcosis. But we know more about it today, and we have more accident reports and are more aware of statistical effects (people are really bad at dealing with small but severe risks, survivorship bias, embarassing near misses are underreported, ...)

So everybody making a well informed decision about taking a risk or not may decide differently today than 25 years ago in the same situation if they learnt that the risk is higher than they thought back then.

Let's not make excuses for ignorance and laziness. These exact same discussions happened on the old Aquanaut Techdiver email list even further back than 25 years ago. The information on the dangers of deep air, including numerous fatality reports, were readily available to anyone who cared to look. And we had the same type of impoverished Europeans whining about how they couldn't afford helium but still wanted to do deep dives. Some of them later ended up as the subjects of incident reports themselves. Nothing ever changes.

Statistics aren't going to convince anyone. Most of the quantitative data we have is low quality from questionable sources. You can torture the numbers to appear to support any point you want. But the essential physics and physiology are understandable to anyone with a high school education, and haven't significantly changed in decades.

 

[Nick_Radov]

Translation: We are better than the rest of you, but I refuse to explain it further. Spend the money on the Kool-Aid, like we did.

Invent all the snarky translations you like but the reality is this is a nuanced subject on which whole books have been written. There literally isn't space in a ScubaBoard comment to explain everything without over simplifying it in ways that would be prone to misinterpretation.

If you honestly want a good explanation then you're not going to find it here, from me or anyone else. I recommend starting with Bennett and Elliotts' Physiology and Medicine of Diving for the theory, then move on to the GUE Fundamentals / Tech 1 / Tech 2 course materials. These books are (relatively) cheap and address the current topic far better than I can.

 

[Wibble]

I am not sure what point you are trying to make. But from what you are saying, regarding OC versus CCR, to me appears to actually support the stats above which are based on a fatality rate per 100,000. This rate is a staple metric in epidemiology. It is used by professionals to compare the rate of fatality across different discipline, geographic regions, populations, etc.

Supporting the other point about comparing apples with oranges @LFMarm made.

All CCR dives are technical dives (i.e. mixed gases, massive monitoring load, bailout requirements, etc.).
The "vast majority" of OC dives are recreational dives, i.e. limited in scope, kit requirements, lack of decompression stress, etc.

The stats you posted show greater 'incidents' with technical dives simply because they're much more challenging in just about every way: kit, dive profile, decompression obligations, physical and physiological stress, skill requirements, emergency procedures, diagnosis skills, etc., etc.

 

[David Carron]

Statistics aren't going to convince anyone. Most of the quantitative data we have is low quality from questionable sources. You can torture the numbers to appear to support any point you want. But the essential physics and physiology are understandable to anyone with a high school education, and haven't significantly changed in decades.

What statistics would convince you?

Again, I don't think that there's any real debate that deep air is, globally speaking, more dangerous than trimix at the same depth.

The question is "how much more dangerous" and the hundreds, certainly thousands, of air dives in the 40m to 60m range executed without problem every year a stone's throw from where I'm sitting at least suggest that the answer, at least for that depth range, may be "not that much"

 

[leadduck]

I hear what you are saying re not expelling the Co2 fast enough, but I overhear divers around the traps talking of being surprised in finding their regs hard to breath at depth, and that (sub standard equipment for depth, i.e. regs in this example) problem is part of the reason that Co2 is building up in the first place. And note that I said 'part of' not 'the only'.

That's a very plausible observation and not a contradiction. High airway resistance in the lungs *feels* like the reg is hard to breathe. Same like immersion pulmonary oedema (IPO): diver signals out of gas and switches regulators, but the new reg isn't better because the problem is actually caused by water inside the lungs and that just feels like the reg doesn't give enough air.
At least since 1994, norm EN250 requires every sold regulator, even the cheapest model, to deliver a lot more air at 50m than your lungs can take in. So as long as the reg is well maintained and not broken, it's probably not the reg causing the issue although it feels like that.

 

[passeparici]

Let's not make excuses for ignorance and laziness. These exact same discussions happened on the old Aquanaut Techdiver email list even further back than 25 years ago. The information on the dangers of deep air, including numerous fatality reports, were readily available to anyone who cared to look. And we had the same type of impoverished Europeans whining about how they couldn't afford helium but still wanted to do deep dives. Some of them later ended up as the subjects of incident reports themselves. Nothing ever changes.

Statistics aren't going to convince anyone. Most of the quantitative data we have is low quality from questionable sources. You can torture the numbers to appear to support any point you want. But the essential physics and physiology are understandable to anyone with a high school education, and haven't significantly changed in decades.

Yeah Europeans are very bad people

 

[passeparici]

What statistics would convince you?

Again, I don't think that there's any real debate that deep air is, globally speaking, more dangerous than trimix at the same depth.

The question is "how much more dangerous" and the hundreds, certainly thousands, of air dives in the 40m to 60m range executed without problem every year a stone's throw from where I'm sitting at least suggest that the answer, at least for that depth range, may be "not that much"

I quite agree with that. With caution, respect of the depth and training...

Comparing as it is done here with dives 40 years ago or more is not fair. When you speak with divers who used to dive at this time you realise sometime the dives were made without much caution. It was a more "dare devil" time, with divers going down to 80 m on air and don't really thinking about it, so of course there were accidents !

Clearly another point is the way we dive in Europe and how it is made in America : in America there are clear distinction between rec dives on ndl at around 20 to 30 m and tec dives (PADI and the other agencies have made their job). In Europe it is a bit different the distinction is not that clear : we have deco dives, sometime we go below 40-45 m, even on air, but don't always think it is tec dives. But many accidents with dives on air in the 50 m range ? Not really. But as David said it is certainly more cautious to dive with something else than air at those depth

 

[leadduck]

Yeah Europeans are very bad people

The yankees dive so cautiously because their healthcare costs so much. No free chamber rides, can you imagine?

 

[flymolo]

The yankees dive so cautiously because their healthcare costs so much. No free chamber rides, can you imagine?

what healthcare?