Doc Deep dies during dive.

[Nick_Radov]

Off topic, but we need to stop perpetuating the myth that panic attacks have something to do with someone's experience/mental "toughness"/etc. Especially in diving, physiological response to eleveated CO2 levels is usually the culprit.

Is there a safe way to induce hypercapnia in a controlled training environment? It's a weird feeling. If divers knew what to expect then they wouldn't be surprised and would be less likely to panic.

I have been on the edge of panic myself once due to (I think) CO2 loading from working too hard and over breathing my regulator (and yes, I was using a high-quality, properly maintained regulator with a low-density gas mix). Tech diving courses do cover the risks of CO2 but it's hard to appreciate without experiencing it yourself.

 

[The Chairman]

If divers knew what to expect

Any narcosis would dull or disguise what they would feel at depth. Of course, narcosis combined with CO₂ is an extremely bad combo in its own right.

 

[grantctobin]

Is there a safe way to induce hypercapnia in a controlled training environment? It's a weird feeling. If divers knew what to expect then they wouldn't be surprised and would be less likely to panic.

A certain pSCR class in the US taught (or may still teach the few times a year it is taught) such a thing. How safe it is up for debate, but you could even do it sitting on your couch if you wanted to experience the sensation. I can’t recommend it in good conscience.

 

[Vicko]

You all experienced hypercapnia before. It's the feeling of being winded after a hard run, now get winded and try breathing trough a tube (snorkel works), now cover the end of that tube with duct tape and poke a few small holes in it. It takes a big effort of will not to rip out the snorkel out of your mouth and breath the air unrestricted. If you try it for long enough you will notice that you can't even hold the breath for long enough to remove the tube, easy to see how that would kill you underwater.

 

[Lorenzoid]

My suspicion is that panic, as we know it, is commonly induced by some combination of hypercapnia and the fight-or-flight reflex. If I'm building up CO2 in a controlled environment, I might feel safe enough that I don't panic; I might just pass out rather peacefully.

 

[Vicko]

There is nothing peaceful about hyperventilating to death.

 

[kammel78]

A certain pSCR class in the US taught (or may still teach the few times a year it is taught) such a thing. How safe it is up for debate, but you could even do it sitting on your couch if you wanted to experience the sensation. I can’t recommend it in good conscience.

I've heard from older ccr instructors that it was quite common to force students to sit on a couch and breathe their unit without the scrubber.

 

[kammel78]

Is there a safe way to induce hypercapnia in a controlled training environment? It's a weird feeling. If divers knew what to expect then they wouldn't be surprised and would be less likely to panic.

Or, and this is an admittedly crazy thought...let's train to people to avoid high CO2 scenarios by using proper gas mixes, streamlined gear and trim, efficient propulsion techniques, and encourage some basic fitness levels. Oh, and I would be remiss if I didn't beat my GIVE THE PEOPLE HELIUM horse.

Personally, I have a very low level of tolerance for CO2, so I dive trimix almost exclusively on my ccr when diving caves (especially high flow caves) and I've implemented "smoke breaks" during long dives where I periodically stop, bail out to OC, and rest for a min. There's no hurry and it's good bo practice.

 

[Lorenzoid]

There is nothing peaceful about hyperventilating to death.

No, but pure CO2 is considered by some to be a humane method of stunning animals before slaughter or euthanizing, the thinking being that it induces unconsciousness or something to that effect, without inducing panic. Now, someone securing a bag over your head--that would induce panic and hyperventilation.

 

[Vicko]

No, but pure CO2 is considered by some to be a humane method of stunning animals before slaughter or euthanizing, the thinking being that it induces unconsciousness or something to that effect, without inducing panic. Now, someone securing a bag over your head--that would induce panic and hyperventilation.

That's because diffusion sucks out all the oxygen (there is a 100% gas gradient) from the alveoli and instantly knocks you out, like breathing any other inert gas, be it Co2, Nitrogen or Helium.
Respiration will slowly accumulate the co2 even with a bag over your head, leading to hyperventilation. In this case hypoxia happens because of extremely shallow breathing leading to no exchange of gas.