Compressed air mid-freedive

[5ata]

That is correct. She becomes a scuba diver. The problem was compunded by the fact that there weren't enough tech divers in the water to cover her descent - Pascal Barnebe was the lone diver at the bottom - the next support diver was halfway back up. The so called technical issues that occurred weren't technical - the tank used to inflate the lift bag wasn't filled to full capacity - read "Neglegence" It's a depressing thing to relive for me but needless to say - things were not done according to IAFD standards and procedures - and hence - IAFD no longer exists for this very reason...

 

[Charlie99]

Once she breathed compressed gas, she wouldn't be able to keep holding her breath.

TRUE.

She would have to continue breathing on scuba.

FALSE.

Ascending while exhaling (or just keeping the airway open and letting excess gas bubble out) from that point is no different than a scuba diver making an emergency swimming ascent. Since she hadn't been down long enough to have signficant N2 loading, an ESA would be reasonably safe.

If you google on submarine escape procedures and training you'll find some interesting info about people breathing compressed air at depth, and then making ascents from relatively deep.

 

[Charlie99]

At the surface, a freediver starts their dive with proportional amounts of oxygen and CO2 with traces of nitrogen.

The "traces of nitrogen" are about 78% unless they are prebreathing O2.

Once you breath off a tank, you introduce a fresh supply of air, which also then introduces the small percentage of nitrogen. Since it is compressed at depth, it is at a constant pressure - reascending, of course means the nitrogen will expand - you have become a scuba diver and can no longer freedive for the rest of the day.

There are two issues ---- 1) lung barotrauma from expanding gases and 2) DCS from inert gases such as nitrogen.

Keep the airway open and you won't have lung barotrauma.

DCS risk is based upon time & depth exposure. More specifically, it is based upon time and partial pressures of the gas in your lungs. The pressure of the gas in your lungs is the close to the same whether you are freediving or on scuba -- the ribs and body isn't a very rigid container and the pressure inside is close to that outside. The fraction of N2 stays pretty much the same since the amount of nitrogen absorbed during a freedive is small compared to the mass of N2 in the lungs, so the DCS risk for a freedive profile done as a breathhold, and a freedive profile done while breathing compressed air are very similar.

Freedivers can get bent, particularly when doing repeated deep dives with short periods in between (as in pearl diving). Breathing compressed air at depth, doesn't suddenly change the physics of N2 and DCS. It's just a very small difference, much less than the difference between different free dive profiles.

 

[Marlinspike]

Listen to 5ATA. The reason you come up slow from a dive isnt just to prevent your lungs from bursting. Nitrogen and HELIUM also play a part when you breath off a techdivers gas supply at say...record breaking depth. Getting bent on Helium is also fairly easy to do and harder to treat than nitrogen bends.

As soon as she took a breath from the LONE safety diver close to her, she was on the LONE safety diver's profile. She could probably have been passed up to another diver a bit further up the column of water and to safety sooner, IF THERE HAD BEEN ONE there.

Tragic, and preventable.

~Marlinspike

 

[Charlie99]

As soon as she took a breath from the LONE safety diver close to her, she was on the LONE safety diver's profile.

Please explain. Do you mean that she suddenly, mysteriously acquired the same loading as the safety diver, who may have been in place for a few minutes?

Do you mean that, now she has to make the same ascent as the guy with her gas source on his back? Well. Duh.

Or does "As soon as she took a breath from the lone safety diver close to her, she was on the lone safety diver's profile" have some other meaning?

 

[Marlinspike]

"Lone safety diver" means there was only one diver down there and no other safety divers close to her. He could not get her anywhere close to the next safety diver, given his profile.

GEEZ, its not that hard...read it m o r e s l o w l y i f y o u h a v e t o .

There is a reason why MANY MANY MORE safety divers are required by reputable freediving record sanctioning bodies.

~Marlinspike

 

[5ata]

Marlin Spike is correct

 

[Lightning Fish]

Ascending while exhaling (or just keeping the airway open and letting excess gas bubble out) from that point is no different than a scuba diver making an emergency swimming ascent. Since she hadn't been down long enough to have signficant N2 loading, an ESA would be reasonably safe.

If you google on submarine escape procedures and training you'll find some interesting info about people breathing compressed air at depth, and then making ascents from relatively deep.

Right. I neglected to mention that. In this case (according to post 4) she reached about 500 feet so I didn't think a ESA would be reasonable. At 60 fpm, it would take over 8 minutes to come up. Is it reasonable for a well trained freediver to be able to exhale, or leave their throat open, for 8-9 minutes?

Bill.

 

[Charlie99]

Right. I neglected to mention that. In this case (according to post 4) she reached about 500 feet so I didn't think a ESA would be reasonable. At 60 fpm, it would take over 8 minutes to come up. Is it reasonable for a well trained freediver to be able to exhale, or leave their throat open, for 8-9 minutes?

Bill.

Why 60fpm? Her N2 loadings were no different than if she had only been freediving for the same length of time.

 

[Lightning Fish]

Why 60fpm? Her N2 loadings were no different than if she had only been freediving for the same length of time.

So what you are saying is that she shouldn't have breathed off of scuba but just started ascending? So what is the maximum possible rate of ascent for swimming up? Is swimming up from 500 feet reasonable considering that her intent was to use a balloon?

Bill.