Help me to understand what happened

[MattK911]

What 2nd stage was on his backgas and what was on his deco cylinder?

An already task loaded/ uncomfortable/ anxious diver switching to a regulator that doesn’t breathe as easily could have indeed been the cause. I’ve heard quite a few stories about something similar.

My shop owner told me of the most shocking examples. He had a couple students panic during a lights out air share drill due to switching from a balanced 2nd stage (ex. g250) on their longhose to an unbalanced 2nd on their necklace (ex R190). The difference in work of breathing was enough to make them believe that they weren’t able to breathe and they snatched the long hose back. This happened in 2 separate instances. One student got out of the water and adamantly claimed his necklace regulator was broken until they tested it and it was all within manufacturers specifications.

This happened back in the late 90’s/ early 2000’s. After the second occurrence he did not allow students to use unbalanced 2nd stages as necklace regulators for obvious reasons.

 

[Latenight]

Had he ever done more than 10 minutes of stops?

That is quite a big deco obligation for a first timer.
The course can say what it likes, it can take a long time to never for people to be relaxed about this. It is not a rational thing.

No, that was his first two deco dives.

 

[Latenight]

I'm guessing anxiety but...
Has anyone else tried this dubious or questionable regulator - just on a practice dive?

No one, as far as i remember, but himself. First dive prior to "real" deco dive was practice dive max. 20 meters where we were practicing switching from backgas to stage regulator which he did without any problem. Of course, on that dive he didn't have deco obligation.

 

[jale]

Hi
+1 with anxiety but one thing I don't get.
You mean the dive was the first real deco dive and also the first time switching regs?!
I hope it was not as, normally, you get students to pratice switching regs during "fake deco dives" first before you take them to real deco dives with really needed switches.
EDIT: oops questions answered during my typing

 

[Latenight]

What 2nd stage was on his backgas and what was on his deco cylinder?

I am not sure, but something like Apeks AT

 

[Latenight]

Hi
+1 with anxiety but one thing I don't get.
You mean the dive was the first real deco dive and also the first time switching regs?!
I hope it was not as, normally, you get students to pratice switching regs during "fake deco dives" first before you take them to real deco dives with really needed switches.
EDIT: oops questions answered during my typing

No, we did few practice dives before "real" deco dive. At first dive, they were just getting used to diving technical configuration. After that, there were 2 more practice dives practicing skills (S-drills, DSMB, switching regulators...) and after that there was real deco dive. I agree that this was too fast for someone who only dove rec configuration to that day.

 

[jadairiii]

Anxiety. A lot of people are completely comfortable diving and breathing from a regulator but really freak out just taking a regulator out of their mouth and/or switching to a new regulator. That momentary lack of breathing and a regulator that has water in it will send people over the edge quickly. And up until tech, that is not really a skill that is trained hard.

That is why many if not most OOA situations become full fledged panic when the diver that is OOA aspirates just a bit of water. Add to that a regulator that is de-tuned or not as good as the primary just makes matters worse.

I have been witness to this.

 

[Angelo Farina]

My opinion, very old school.
I did hundredths of deco dives.
Down to 60m max.
All in air with doubles, and using back gas for deco. Sometimes also with a pony for added safety in caves, but also the pony with plain air.
Never used Nitrox. Never switched gas for deco. Never a problem.
I was not convinced on those theories about accelerated deco thanks to higher ppO2. Those theories are based on over-simplified models (such as Haldane or Bulhmann) of what happens inside our body.
Albeit these models were tuned so that they fit with large data series of dives without DCS (the same data series used for compiling the US Navy or the PADI deco tables) there is no proof that the same theories work well in the anomalous conditions of accelerated deco breathing highly oxygenated mixtures.
Personally I decided that these techniques involving gas switching are too advanced and too complex for me.
I have no problem doing a deco dive in air: I did always consider a dive planned just beyond NDL limits to be actually safer than a dive planned on the edge of NDL.
The deco dive will be done with more gas, with more redundant equipment and more strict procedures.
From this I scaled up to more serious dives where the limit is usually given by narchosis.And this can be done entirely in air, for example 20 min at 60 m.
Going further requires He mixtures.
Too much for me.
Making a dive to less than 60 m and switching gas just for shortening deco times looks unsafe and not worth the complexity and risk.
Air is good. Air is safe.
So I would warmly suggest to your colleague who suffered of problrms when switching gas, simply to avoid doing it again. There is no need to switch gas for deco when doing a dive in air at 40 or 50 m....

 

[helodriver87]

My opinion, very old school.
I did hundredths of deco dives.
Down to 60m max.
All in air with doubles, and using back gas for deco. Sometimes also with a pony for added safety in caves, but also the pony with plain air.
Never used Nitrox. Never switched gas for deco. Never a problem.
I was not convinced on those theories about accelerated deco thanks to higher ppO2. Those theories are based on over-simplified models (such as Haldane or Bulhmann) of what happens inside our body.
Albeit these models were tuned so that they fit with large data series of dives without DCS (the same data series used for compiling the US Navy or the PADI deco tables) there is no proof that the same theories work well in the anomalous conditions of accelerated deco breathing highly oxygenated mixtures.
Personally I decided that these techniques involving gas switching are too advanced and too complex for me.
I have no problem doing a deco dive in air: I did always consider a dive planned just beyond NDL limits to be actually safer than a dive planned on the edge of NDL.
The deco dive will be done with more gas, with more redundant equipment and more strict procedures.
From this I scaled up to more serious dives where the limit is usually given by narchosis.And this can be done entirely in air, for example 20 min at 60 m.
Going further requires He mixtures.
Too much for me.
Making a dive to less than 60 m and switching gas just for shortening deco times looks unsafe and not worth the complexity and risk.
Air is good. Air is safe.
So I would warmly suggest to your colleague who suffered of problrms when switching gas, simply to avoid doing it again. There is no need to switch gas for deco when doing a dive in air at 40 or 50 m....

The vast majority of modern data would disagree with you, both on backgas choice and the use of accelerated deco. It's fine if that's your personal choice, but deep air with air deco isn't something I'd suggest to anyone these days.

 

[Angelo Farina]

The vast majority of modern data would disagree with you, both on backgas choice and the use of accelerated deco. It's fine if that's your personal choice, but deep air with air deco isn't something I'd suggest to anyone these days.

I told you. I am old school...
And that is not "deep air".
Down to 60m is normal range for air. Deep air is BELOW 60m and down to 90m...