Free diving, tank sharing fatality - Australia

[Bob DBF]

The point is that trained freedivers tend to know what they're doing, their main scourge is SWBO, a local freediver says it's probably SWBO --

What puzzles me is the mechanism of SWBO in this case assuming the freediver breathed off the reg and went directly to the surface as the article describes. The freediver has exhaled CO2 and inhaled air (?) at depth, so as he ascends he is breathing off/out CO2 and still has air to provide O2 to his body as it expands. At least that's how I see it.

As I said before, if he used that to extend his time underwater, SWBO could still be the problem.


Bob

 

[Dan]

Quite possible when you freedive often, you build up a muscle memory to breath hold when you are underwater. That’s what I meant by freediver & SCUBA diver don’t mix.

 

[yle]

0.3 bar is at about 9 km altitude above earth surface. Just pulling your leg I know you meant 0.3 bar gauge or 1.3 bar absolute or 3m below sea level. I just can’t believe you can blow a lung by bolting from 3m to surface. Any data to support that?.

Keep in mind 0.3 bar is about 40 psi. That's 40 pounds of force on every square inch. This is typical pressure for a kid's bike tire (or a car tire, but car tires have more structure.)

If you can imagine the strength of a rubber tube in a kid's bike tire, inflated to 40 psi... and then replace that rubber with lung tissue. Would the lung tissue withstand that pressure?

Lung tissue is fragile and water pressure is much greater than people intuitively recognize. Dangerous combination, even from a depth of less than 10 feet.

 

[yle]

Quite possible when you freedive often, you build up a muscle memory to breath hold when you are underwater.

Yes... you hit the nail on the head. Experience, complacency, muscle memory all go together.

 

[Dan]

What puzzles me is the mechanism of SWBO in this case assuming the freediver breathed off the reg and went directly to the surface as the article describes. The freediver has exhaled CO2 and inhaled air (?) at depth, so as he ascends he is breathing off/out CO2 and still has air to provide O2 to his body as it expands. At least that's how I see it.

As I said before, if he used that to extend his time underwater, SWBO could still be the problem.


Bob

I like to know that too.

My guess is the minute the freediver breathe from the reg, his lung would expand back to their normal sizes. The air coming from the reg would immediately mix with the atmospheric gas in his lung. The lung would act like a vacuum bag being filled with the compressed air to the ambient pressure. So no gas would be coming out of his mouth as his lung was shrunk before inhaling the compressed air from the reg.

The gas in his lung would have elevated concentration of CO2 after the O2 is consumed during metabolism and converted to CO2. By inhaling fresh compressed air, the CO2 concentration in his lung would drop to lower level. However his lungs would return to their normal sizes so he has to exhale the mix gas during ascent to avoid the lung over expansion injury.

The SWBO happens when the CO2 concentration in his lung is above the limit that his body can tolerate. That would be my guess.

This article, below, says that you would become unconscious, leading up to death, when the CO2 concentration in the lung reaches 8%.

https://www.fsis.usda.gov/wps/wcm/c...4-9d2615f376e0/Carbon-Dioxide.pdf?MOD=AJPERES

So during the free diving my guess is CO2 level will keep increasing as O2 is consumed during metabolism and you have no where to release and lower it as your lung acting like a vacuum with no source of fresh air to replenish the O2. Someone with fast metabolism in his body would elevate the CO2 too fast to the level beyond the body can handle and passed out.

 

[Dan]

Keep in mind 0.3 bar is about 40 psi. That's 40 pounds of force on every square inch. This is typical pressure for a kid's bike tire (or a car tire, but car tires have more structure.)

If you can imagine the strength of a rubber tube in a kid's bike tire, inflated to 40 psi... and then replace that rubber with lung tissue. Would the lung tissue withstand that pressure?

Lung tissue is fragile and water pressure is much greater than people intuitively recognize. Dangerous combination, even from a depth of less than 10 feet.

1 bar = 14.5 psi. 0.3 bar = 4.35 psi.

 

[Bob DBF]

So no gas would be coming out of his mouth as his lung was shrunk before inhaling the compressed air from the reg.

It would depend on depth whether you could breath out to clear the reg, the article does not specify depth. At one ATM I can, because I forgot to put the reg in my mouth and got over 30' down before I realized I should do something about it, funny story but longer. Deeper than say 100' you would lower the CO2 concentration by 2/3, then going directly to the surface should not increase the CO2 significantly as the work load should be small and exhaling on the way up should also decrease concentration.

Took me, probably a post too long, but may be @Duke Dive Medicine could sort this out for us, if we ask nice. Please.


Bob

 

[Dan]

That would be a good experiment for me to try to hold my breath & descend to a depth where I no longer can exhale the air that I have in the lung during entry. I guess if you have a strong chest muscle and diaphragm to be able to exhale the atmospheric air at 30' depth.

 

[Dan]

Deeper than say 100' you would lower the CO2 concentration by 2/3, then going directly to the surface should not increase the CO2 significantly as the work load should be small and exhaling on the way up should also decrease concentration

I don't think depth would lower the CO2 concentration. It would be lowered by inhaling fresh air and exhaling the spent air, i.e., by flushing & purging the gas in your lung. The CO2 concentration would stay the same or even higher if you hold your breath and sink to the abyss.

I can see that the rate of CO2 generation is less with less work load.

 

[Bob DBF]

I don't think depth would lower the CO2 concentration. It would be lowered by inhaling fresh air and exhaling the spent air, i.e., by flushing & purging the gas in your lung. The CO2 concentration would stay the same or even higher if you hold your breath and sink to the abyss.

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