Two questions for diving science nerds only

[Charlie99]

The fact that some survive unscathed by a rocket escape and others die of AGE or suffer barotrauma seems mysterious. It may be related to the manner of breathing during ascent.

Doesn't seem mysterious to me. A panicked diver is likely bolt to the surface while holding his breath by closing the glottis. That's a sure way to cause AGE. Breathing out, or keeping the airway open as you ascend is NOT the natural thing to do.

 

[shakeybrainsurgeon]

Doesn't seem mysterious to me. A panicked diver is likely bolt to the surface while holding his breath by closing the glottis. That's a sure way to cause AGE. Breathing out, or keeping the airway open as you ascend is NOT the natural thing to do.

You are right, but the mystery isn't why people get AGE from a cork-like ascent, but why many do not? Everyone has stories of seeing or hearing of divers (or being a diver!) who shot to the surface and laughed about it later. It may be a simple matter that the AGE people hold their breaths and the unaffected ones don't, that's possible. It's also possible that some people equalize their lungs more readily than others, just as some people equalize their ears better than others. The bronchial tree and laryngeal anatomy vary from person to person and it only takes one small bronchus, one tiny portion of a lung or some unruptured pulmonary bleb to be blocked to cause death, given the pressure gradients involved. In fact, two AGE deaths in 2005 from rapid ascent were due to ruptured pulmonary blebs, suggesting that these poorly ventilated parts of the lung may be susceptible to injury during rapid decompression.
This would imply that people prone to such blebs, or to regional bronchial entrapment, namely smokers with extensive pack year histories and emphysematous changes, are at risk for AGE during rapid ascent. Looking at the statistics, however, smokers don't seem over-represented in the DAN mortality data.

 

[terrasmak]

Lets see 200 feet , someone stupid enought to drop weights , they would probably be bent into a pretzel when they hit the surface if there not dead from it.

 

[shakeybrainsurgeon]

Lets see 200 feet , someone stupid enought to drop weights , they would probably be bent into a pretzel when they hit the surface if there not dead from it.

I'm not being argumentative, since I have no experience here (the deepest I've gone is 80 ft and that was with the floor just another 5 ft below me), but is dropping weights the stupid thing to do in all scenarios? Granted, simply getting into this position may show poor judgement, but can't it happen that someone loses buoyancy control over an abyss (or over a depth they are not prepared to go) due to a) bladder failure b) insufficient gas left to inflate the bc further at that depth c) fatigue, cramping, loss of orientation that inhiibits finning to the surface? Is not pulling at least some weight an option (the lesser of two evils)?

A tec instructor in our LDS related a story: he was part of a team doing a 300 ft wreck dive. At a decompression stop, I don't recall the depth but it was 100 to 150 ft range, one of the team mistakenly switched to his pure oxygen and immediately began to convulse. They were in no position to ascend with him, so they inflated his bc, pulled his weights and sent him to the surface with a "godspeed my friend". When they finished their ascent, they found their friend breathing oxygen on the boat unharmed. A miracle to be sure, and I have no clue if this was the "correct" handling of this disaster, but that was the story. Like many stories, it may be BS, I wasn't there. However, there are no doubt cases of missile launches from the depths without serious injury, and not just "bounces" where people have spent little or no time at depth.

My point is that some people survive maximal ascent rates and others don't and, since the statistics suggest that such ascents make up a large fraction of deaths and injuries (particularly if we exclude heart attacks underwater or on the surface, which aren't really scuba accidents in my opinion), it would be nice to know why. It may be, as has been suggested above, a simple matter of not holding your breath.

 

[Kim]

When they finished their ascent, they found their friend breathing oxygen on the boat unharmed.

Sounds like BS to me. Yes, maybe he survived the Oxtox from breathing the O2 too deep....but what about blowing off the deco obligation from the 300ft dive? Presumably they weren't using gas switches and deco stops for nothing.....

You don't give the details of the dive profile but when the dive already involves a gas switch deco deep stop (in the range you mention)....blowing that and any other subsequent stops would probably leave you with foam for blood.

 

[shakeybrainsurgeon]

I suspect you are right, but I may not have all the details either. For example, I have no knowledge of whether he was treated in a chamber later, nor do I know how long they were at that stop when the event occurred. They must have been close to completing that stop or the outcome couldn't have been good. The story is only that he survived unscathed eventually. Even at shallow depths, underwater seizures supposedly have a near 100% injury/death rate in and of themselves.

DCS is weird though --- when I was in the Caymans last year at a medical meeting, one of the participants told me that her husband ended up in a chamber the day before after a rec reef dive that appeared quite ordinary otherwise. Again, no details of the profile etc, other than he was experienced middle-aged diver doing a standard cattleboat dive and had developed perioral and hand numbness shortly after coming onto the boat. He was apparently fine after treatment.

There was one story of a rocket ascent I trust: a close friend of mine in Florida, a sporadic diver himself, often pilots the boats for his friends and stays on board. One friend went down and five minutes later came flying back up with some alacrity (although he didn't "breach"). His weight belt had dropped off at depth. He suffered no ill effects, grabbed another weight belt, and finished the dive --- but he had little bottom time and how deep he was, I don't know. One can question the wisdom, however, of not aborting the dives that day after an uncontrolled ascent.

 

[TRIG]

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[Kim]

Well, I'm not trained in deco so there are many here who can give you a more definitive answer. It would seem to me though, within my limited knowledge, the books I've read, and the stuff here...on TDS...other places etc.....that a deco stop at the depths you mentioned would only be the first in a series...and one of the shortest. I can't understand how anyone could be "breathing oxygen on the boat unharmed." after missing the rest of their deco.
There might be more to the story than I know, but judging from what's been told it sounds like BS to me. Discussion on a board like this is great....but we don't want to create untrue impressions that could influence people and possibly get them hurt. Having said that though I suppose it's unlikely that any new, untrained diver, is going to do a 300ft dive and then to all intents and purposes an ESA from 100/150ft blowing all their deco stops!!! Just in case though.......I thought I'd mention what the real problems with this might entail......

 

[Charlie99]

A tec instructor in our LDS related a story: he was part of a team doing a 300 ft wreck dive. At a decompression stop, I don't recall the depth but it was 100 to 150 ft range, one of the team mistakenly switched to his pure oxygen and immediately began to convulse. They were in no position to ascend with him, so they inflated his bc, pulled his weights and sent him to the surface with a "godspeed my friend".

My understanding is that it is common during convulsions to close the airway, and a rapid ascent while in convulsion would be much more dangerous than just keeping him face down, and shoving a reg with a different gas into his mouth when possible.

I don't think convulsions kill people. Drowning sure does. Making a rapid ascent from 100'+ with a closed airway sure does.

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Rarely is dropping weights at depth ever the right move. If properly weighted, you will only be negative by the weight of the gas you are carrying (about 6 pounds in a full AL80) and whatever wetsuit compression there is from being at depth. Unless you are grossly overweighted, you should be able to swim up against that weight, and if a diver isn't able to swim for some reason, that weight should be well within the capabilities of another diver's swimming and BC lift.

If you ditch more weight than that of the gas currently in your tank, you won't be able to control your ascent.


Ditching weights is something you do ON THE SURFACE to get additional buoyancy to keep your mouth and nose well above water without having to fin.

Charlie Allen

 

[TeddyDiver]

A couple of years ago in Narvik was incident where a diver at 180' had a malfunction with BC inflator and thereby a runaway ascend to surface. Oxygen on one hour right after and no symptoms of DCS.
30 hours later they started journey back home. The road climbs right up from Narvik to aprox 2000' where he got bends and lost consiousness.
Chamber etc..