Free diving, tank sharing fatality - Australia

[Dan]

The depth wouldn't, but adding the gas breathed in, bring the lungs to full would dilute the CO2 in your lungs. I'm out of my are of expertise, which is why I tagged Duke Dive Medicine to straighten me, and anyone else in my position, out.


Cheers

Bob

Ah, yes that makes sense. Sorry I misunderstood your point earlier.​

 

[Bob DBF]

Sorry I misunderstood your point earlier.

No worries, I try to make any point I'm proposing clear, but sometimes I don't do the job I think I'm doing.


Bob

 

[johndiver999]

Itis the low oxygen levels that cause a shallow water blackout not high Co2. And swimming down to 30 feet and exhaling some air is not difficult in the least.

 

[Bob DBF]

Itis the low oxygen levels that cause a shallow water blackout not high Co2. And swimming down to 30 feet and exhaling some air is not difficult in the least.

Got sidetracked on the CO2. Shouldn't breathing off a reg at depth increase O2 level substantially? Especially for a direct ascent to the surface.


Bob

 

[johndiver999]

Of course, breathing off a scuba tank is going to lower Co2 and increase oxygen levels. that is sorta the idea..

 

[Dan]

Itis the low oxygen levels that cause a shallow water blackout not high Co2. And swimming down to 30 feet and exhaling some air is not difficult in the least.

Aren’t we referring to the same situation? When you have 8% CO2, that means we would have 13% O2 as the balance of 79% N2 would remain constant. According to Oxygen and Human Requirements the lowest oxygen level to survive is 15% or 6% CO2.

 

[seeker242]

Aren’t we referring to the same situation? When you have 8% CO2, that means we would have 13% O2 as the balance of 79% N2 would remain constant. According to Oxygen and Human Requirements the lowest oxygen level to survive is 15% or 6% CO2.

SWBO is typically caused by the rapid drop of ppO2, from an already depleted O2 supply. Similar to how you can't breathe a hypoxic mix at the surface, but you can at depth. SWBO= hypoxia. It's typically not spoken of in terms of high CO2 levels because even low CO2 levels increase the chances of blackout, AKA hyperventilation. High CO2 level is a good thing because that's what prompts you to surface before your system turns hypoxic. High CO2 level = less chance of blackout.

 

[Bob DBF]

SWBO is typically caused by the rapid drop of ppO2, from an already depleted O2 supply. Similar to how you can't breathe a hypoxic mix at the surface, but you can at depth.

I can understand that, the question is when a free diver breathes off a reg at depth, will the increase in O2 from that air be enough to stop SWBO if the diver makes a direct ascent to the surface.

I would think the freediver breathing off a reg would be able to make a successful CESA same as a SCUBA diver, however if the article was incorrect and he continued the freedive there would be a different answer.

Bob

 

[Dan]

1. SWBO is typically caused by the rapid drop of ppO2, from an already depleted O2 supply. Similar to how you can't breathe a hypoxic mix at the surface, but you can at depth. SWBO= hypoxia. It's typically not spoken of in terms of high CO2 levels because even low CO2 levels increase the chances of blackout, AKA hyperventilation. High CO2 level is a good thing because that's what prompts you to surface before your system turns hypoxic. High CO2 level = less chance of blackout.

Thanks for the info. This website is also helpful in explaining how SWBO happens: How It Happens — Shallow Water Blackout Prevention

This story is an eye opener of the risk of breath holding: Whitner's Story — Shallow Water Blackout Prevention


Also this:

 

[Dan]

Another good awareness of the danger of breath holding: