Uncontrolled ascent

[UWSojourner]

... the diver needs more experience in the area of gas management, buddy skills, and buoyancy control before attempting a dive to this depth ... regardless of cylinder configuration and gas mix.

Even with those extra skills aren't you subject to various responses due to narcosis? At that depth it must have been bad. Extra skills might not help if your brain isn't functioning correctly.

 

[lamont]

:06:
I should preface this by saying I don't (generally) do deco diving (and was never trained in it) and don't know CMAS procedures.....(so this is more of a question from me for my own understanding)

.....but I was under the impression that if you'd had an uncontrolled ascent from depth and broke all your deco stops, you were at extremely high risk of DCS (even if no immediate symptoms visible), but if I am reading the above correctly it states the CMAS procedure is to go back down to de-gas ??

I thought the usual procedure would be to get to O2 and not go back down (as you'd run the risk of the DCS happpening when you were underwater which makes you difficult to rescue)?
..or am I misreading the above (or incorrect in my assumption)

...from the post, the guy didn't go back down and was immediately put on O2 [but had been given the option of another tank]

The "skipped deco stop" procedures are based on analogy to what divers with shipboard chambers will do routinely, which is to surface immediately skipping all their deco, climb into a chamber and repressurize and complete deco obligations. That's similar to blowing off deco, surfacing, grabbing a tank and heading back down. In-water recompression is riskier though because you're not a chamber and you can drown if something bad happens.

For rec divers the recommendation is not to attempt in-water recompression for a case of DCS or rapid ascents / skipped safety stop, but the deco obligation of a rec diver is minimal and therefore DCS symptoms will probably be minimal and will likely be treatable with 100% O2. The hazards of IWR tend to outweigh the risks of DCS for recreational divers. For tech divers, it seems like opinions differ widely on IWR from being insane to being proper procedure...

 

[WJL]

The research on the subject is inconclusive and unfirtunately many people and agencies seem to cherry pick the data and only quote the studies that support theire views.

I disagree that the research is inconclusive. The overwhelming majority of studies I have read that are based on objective performance testing or physiological changes show no meaningful adaptation to repeated exposure to high pressure nitrogen. It is true that studies which merely report divers' subjective assessment of their adaptation to narcosis report positive findings, but I believe this only confirms the point that in general perceived adaptation is not real.

The reality is that there are a large number of variables that must be controlled before an accurate study of the effectiveness of adaptation and/or accomodation can be studied.

In an earlier post I provided links to several controlled studies, some of which suggest that the body does in fact make physiological adaptations to long term (i.e. many days) or repeated short term exposure (nine times) to pressurized nitrogen, but these studies do not suggest that the adaptations eliminate the narcotic effect, only dampen it to a certain degree. It also seems to me that the conditions under which any actual physiological adaptation has been found are quite different than those experienced by normal scuba divers. Most of us are not going under for days on end or doing nine deep dives a day.

There is both subject and experimenter bias due to the beliefs and training they may have regarding the effects of narcosis as well as a plethora of individual differences in divers that affect their individual abilities to function with varying degrees of exposire to nitrogen at depth.

Experimenter bias is easy to find in many published studies, particularly those which simply ask divers how they feel as opposed to testing their performance or brain chemistry. My impression is that the more rigorous the testing protocol, the more likely the study will find little or no appreciable adaptation.

Impairment certainly occurs but due to differing physiology the effects occur aliong a continuum rather than as an absolutle and unvarying effect on all divers across all settings. The variables in human performance are important as well. A diver who has higher cognitive functioing or dexterity at the surface has more room to accomodate deficits than a diver who already functions in the low average range anyway befor ethey even start the dive.

Not all divers react exactly the same to pressurized nitrogen, just as not all divers react the same way to alcohol or drugs. That does not mean that narcosis can be overcome by willpower or learning. What does occur is that through repeated exposure the diver learns to recognize the onset and effects of narcosis and to develop compensating behaviors that mask the actual impairment of brain function. This is much the same phenomenon as is seen in habitual alcohol abusers. The narcosis is still there and is still hampering brain function. The effect can be compensated for if the brain is allowed to repeat simple familiar tasks - rote learning as opposed to active cognition takes over to a certain degree. As soon as the brain is required to perform a task outside rote functioning, the impairment again becomes apparent.

Experience is also a key issue, as an experienced diver who has things down to the point where they are automoatic and requires little or no concious effort (bouyancy control etc) is also at an advantage at depth compared to a new diver who is going to be overloaded managing the basics in addition to the objectives of the dive even thouigh they may have similar cognitive abilities.

This is correct, but in my opinion should not be considered as much of an advantage. Habitual drunks learn to walk and drive while under the influence. They are not overcoming the effect of alcohol on their brains, they are compensating for it by using parts of the brain that don't require much of what we would call rational thinking. This is what repeated exposure to high pressure nitrogen does (apparently without the permanent damage to the brain, liver and other organs caused by overexposure to alcohol).

If an emergency occurs, often you need to be able to think coherently. Automatic responses may not be sufficient. Even if you just want to remember what happened during your dive, narcosis is an impediment.

In short, a definitive study will have to be very carefully designed and will have to control for several factors other than just exposure to nitrogen.

I think a serious effort has been made to do that in some of the studies I cited.

You kind of allude to that here where you cite the advantage of experience. If you are not unintentionally admitting to the possibility of adaptation, you are at a minimum admitting to the potential for and value of accomodation for the effects of narcosis.

I agree that more exposure to narcosis provides a diver with more familiarity with the syndrome. That may tend to create compensating behaviors (e.g. "I know I'm narced so I have to go slow here"), but it does not mean that the diver is no longer experiencing narcosis.

 

[MXGratefulDiver]

Even with those extra skills aren't you subject to various responses due to narcosis? At that depth it must have been bad. Extra skills might not help if your brain isn't functioning correctly.

Yes and no ... the degree to which one feels and reacts to narcosis varies greatly from diver to diver. And even with the same diver, it can vary from dive to dive. So it's hard to predict how a person will respond on a given dive.

However, practiced skills reduce the margin for error because when you are familiar with how something is done you require less cognitive ability to do it ... your body goes into "autopilot" and you respond more from familiarity with the process than with conscious decision-making.

That's why it's important, once you learn a skill, to practice it. Once learned, you know the procedure. But only practice will make it possible for your body to react while your brain may be impaired, or otherwise engaged ...

... Bob (Grateful Diver)

 

[vjongene]

I preface this by the now obligatory disclaimer that I'm not providing any solutions here. just admiration

Just wanted to say I admire the courage of your divers that have adapted to the available diving to go to 40-60m regularly. Wow, that is serious depth. You guys have to get some shallower fish. I would question using a single cylinder in view of the safety margin that diving should include but I don't have the technical knowledge of diving at such depth.

I'll hold your wallet for you back on the boat, then we go for some great Hefeweizen!

Just to bring some perspective here:

1) The CMAS limit for diving on air is 60 m. This is indeed well over what e.g. PADI would recommend. We do not go to such depths during OW training In fact, all of the dives for our two star certification (Rescue equivalent) are to less than 30 m. It is only afterwards that we gradually work to greater depths, being careful that no dive goes more than 3 m beyond the deepest one performed before. This also allows each diver to test his or her comfort zone. I have found out that I do not like to dive beyond 50 m in the dark, cold water of the lake. Some of my buddies regularly go deeper.

2) For the three star certification, all skills are tested at about 40 m depth, i.e. under significant narcosis. As Grateful Diver pointed out, only repeated training can bring the kind of "autopilot" behavior that will ensure safety at those depths. A three star diver should be able to demonstrate a full range of skills (including rescue skills) in open water at 40 m or more.

3) For much of the year, visibility in the lake becomes acceptable only beyond 35 m or so. Many of our dives are beyond that limit if only because that is the only way to see anything. And there are indeed some spectacular walls and overhangs to be visited.

4) The dive community in this area has not really taken to mixed gas diving, although it is available. It can of course be argued that this is a Bad Thing. The fact is that there are many divers in the lake, and hardly any using He-based mixes.

This all being said, I have no idea of the level of training of the two divers mentioned in my post. I do not know them personally. I suspect that the diver who experienced the uncontrolled ascent was not very comfortable with dry suit diving, and had not developed the constant awareness of air supply that is necessary for doing the kind of diving that he was engaging in. Having done many dives of this kind, with many different buddies, I have never come close to running out of air.

Victor J.

 

[vjongene]

New divers wanting to dive to 50/60 metres should be talking to instructors on how to do it properly - I'm a novice diver so I am not going to suggest to anyone how they should have planned that dive but if a novice like me can see the danger in it and suggest not doing it then why couldn't they?

I am reasonably sure that these guys were not novices. But I do suspect that the one who went ballistic had not yet developed an "instinctual" control of his dry suit. As to planning the dive, I cannot tell. Most of these dives are essentially bounces, with only a few minutes spent at the maximum depth. Maybe they got distracted by the fish...

 

[liberato]

I am reasonably sure that these guys were not novices. But I do suspect that the one who went ballistic had not yet developed an "instinctual" control of his dry suit...

I don't dive with a drysuit but I am curious about what happens in an uncontrolled ascent. I understand the physics involved but can a diver who is not paniced get into an unrecoverable situation? In other words, can everyone get so out of controll speed-wise that inverting and kicking hard while yanking the bottom BC dump valves would not stop it in time?

 

[MXGratefulDiver]

I don't dive with a drysuit but I am curious about what happens in an uncontrolled ascent. I understand the physics involved but can a diver who is not paniced get into an unrecoverable situation? In other words, can everyone get so out of controll speed-wise that inverting and kicking hard while yanking the bottom BC dump valves would not stop it in time?

The simple answer is yes ... you can get into an unrecoverable situation.

Drysuit exhaust valves are more limited than those on a BCD ... particularly wrist dumps, which are typically very small.

If you do not respond quickly, you will begin to accelerate upward and eventually gas expansion will exceed your dump valve's capacity to exhaust it. At that point you have two choices ... open a wrist or neck seal (assuming that's possible), or go fins-up and kick down. The latter will usually, at best, only slow you down. At worst, the air migrating to your feet will cause your boots to expand, and possibly cause your fins to pop off (seen this happen once), at which point you are in a really bad situation, as you will accelerate surfaceward feet first with no way to right yourself. Without fins you are effectively helpless, and better hope there's someone on the surface to help you because you won't have the mobility to force your feet down to the point where you can vent the air out of your suit.

As I stated earlier, I saw this happen to a diver once. Fortunately there were divers already on the surface who saw him come up feet first and were there quickly to help him ... and the fins were recoverable, as they were plastic and eventually floated to the surface. The guy didn't get bent, probably because he hadn't been down very long before shooting up from about 70 fsw ... and I'm happy to say I saw him recently and he's turned into a reasonably competent diver.

BTW - This potential scenario is one reason why I don't agree with the common practice of teaching people to use their drysuit for buoyancy control. The less air you have in your suit, the less chance there is for this to be an issue.

... Bob (Grateful Diver)

 

[JasonH20]

The simple answer is yes ... you can get into an unrecoverable situation.

I've just started to get my OW cert, so forgive me if this is a dumb question. Since I'll be diving in 50 degree water, I opted for the additional training (an extra pool session) and will be doing my OW dives in a dry suit. Reading this post, and having heard a few stories from other divers, it's frankly got me a little anxious about using a dry suit.

So I'm curious, if you were in an uncontrolled feet first ascent, is it impossible to bend over and break the seal around the ankles?

Also, would you ever consider unzipping the dry suit and flooding it in a situation like this? Or would that just add even more problems to bad situation.

Last, how easily can someone get into a situation like this! Is it normally avoidable as long as you don't panic.

Thanks!
Jason

 

[jbd]

I've just started to get my OW cert, so forgive me if this is a dumb question. Since I'll be diving in 50 degree water, I opted for the additional training (an extra pool session) and will be doing my OW dives in a dry suit. Reading this post, and having heard a few stories from other divers, it's frankly got me a little anxious about using a dry suit.

So I'm curious, if you were in an uncontrolled feet first ascent, is it impossible to bend over and break the seal around the ankles?

Also, would you ever consider unzipping the dry suit and flooding it in a situation like this? Or would that just add even more problems to bad situation.

Last, how easily can someone get into a situation like this! Is it normally avoidable as long as you don't panic.

Thanks!
Jason

Best thing to do in a dry suit is to be horizontal. Its much easier to head downward from horizontal than from vertical. Although there is much debate about using the dry suit for buoyancy control or not; I agree with NWGD thoughts on this.

As far as I know there are no ankle seals on drysuits. You can vent from a wrist seal on some suits or the neck seal as NWGD mentioned.

Its easy to get into a runaway situation if you are not properly weighted and thereby use a lot of air for buoyancy control. Before you could ever unzip a drysuit you would most likely be at or very near the surface already.

You must be ahead of the game at all times and fully situationally aware.