Deep Air - Here we go again....

[Kevrumbo]

Well Slamfire . . .I learned it the hard way!

http://www.scubaboard.com/forums/near-misses-lessons-learned/264517-type-i-bends-hit-chuuk.html

 

[DaleC]

Dale, just let me know when you get the boat.

As with all things SCUBA; Don't hold your breath!

Besides, Marc, you don't count. You dive deep air. You previously stated that your max END is 110. :crocodile:

Oh that Mark, I wish he would learn how to dive already

And what's wrong with independant Al 80's anyways? Trimix in one, air in the other and a back mounted spare air with 100%O2 for deco sounds like the perfect recreational deep diving rig to me.



and yes, I'm kidding. I would just use 50/50 for deco.

 

[Slamfire]

And now, the Eanx 50 switch and the Fateful Blunder: I signaled seven minutes deco time. My buddy queried back, "Seven?" I signaled again definitely seven minutes. Buddy looks at me with a puzzled face; and this is where it all started to go wrong for me-- with the fist-to-forehead signal, I yielded and gave back control of the Deco Stops to my Buddy.

You're at 70' in this gas switch. By that time narcosis would've been mitigated or gone altogether. I realize that narcosis probably did play a role when your buddy recalculated the deco schedule at depth and like most dive accidents it is the result of the snowballing of multiple problems. The point is that at 70 an on 50% with little or no narcosis it was still rescueable.

When I'm approaching my personal max of 150 END for cold water I take additional precautions. I never overstay my planned bottom time and I never exceed my planned max depth. So I effectively do a profile where my average bottom depth is less than what I planned. I try to leave complex calculations out of the way at least until I'm above 100', and usually during the slightly longer oxygen-window-stop at the 70' gas switch. Also with my buddies (usually UTD trained) whoever calls for a more conservative deco schedule after we've gone underwater, gets it (of course within the limits of available gas).

Now I'm not saying that what happened to you will never happen to me because I am too good of diver. You have more formal training than I have and probably more experience too. All I'm saying is that there are strategies, procedures and a mindset that will help you better handle deep air dives -- these are usually seen in deep air training. BTW, I think that what you did when you submitted your case for accident analysis is very cool.

So you learned the hard way indeed, but you did not answer my question. Do you think deep air training is useless? Maybe I was imprudent with my quick comments and shooting you the question and placed you uncomfortably in the spot. In my defence, I am drinking some warm brandy while posting so I allege narcosis of about 147' -- it's the booze typing. Of course you don't have to answer, if you don't want to. I won't be offended.

 

[Kevrumbo]

You're at 70' in this gas switch. By that time narcosis would've been mitigated or gone altogether. I realize that narcosis probably did play a role when your buddy recalculated the deco schedule at depth and like most dive accidents it is the result of the snowballing of multiple problems. The point is that at 70 an on 50% with little or no narcosis it was still rescueable.

When I'm approaching my personal max of 150 END for cold water I take additional precautions. I never overstay my planned bottom time and I never exceed my planned max depth. So I effectively do a profile where my average bottom depth is less than what I planned. I try to leave complex calculations out of the way at least until I'm above 100', and usually during the slightly longer oxygen-window-stop at the 70' gas switch. Also with my buddies (usually UTD trained) whoever calls for a more conservative deco schedule after we've gone underwater, gets it (of course within the limits of available gas).

Now I'm not saying that what happened to you will never happen to me because I am too good of diver. You have more formal training than I have and probably more experience too. All I'm saying is that there are strategies, procedures and a mindset that will help you better handle deep air dives -- these are usually seen in deep air training. BTW, I think that what you did when you submitted your case for accident analysis is very cool.

So you learned the hard way indeed, but you did not answer my question. Do you think deep air training is useless? Maybe I was imprudent with my quick comments and shooting you the question and placed you uncomfortably in the spot. In my defence, I am drinking some warm brandy while posting so I allege narcosis of about 147' -- it's the booze typing. Of course you don't have to answer, if you don't want to. I won't be offended.

I would like to see a Deep Air course include some initial sham scenario & contingency training dives breathing regular air inside a Recompression Chamber (i.e. something similar to the orientation dives in the Education Programs of the Catalina Hyperbaric Chamber here in Socal); and then later doing actual checkout dives on deep air, but with the evaluating instructor & safety tech divemasters assisting breathing trimix instead. . .

 

[hg frogman]

To Kevrumbo:
The first event leading to the bends you experienced is the MAJOR change you did in your dive plan while underwater (extending your bottom time from 30 to 50 minutes). How do you link this with Air diving ? Do you think that with Trimix you can do such changes underwater without any issue ? I mean, is that a practice that you would recommend to others ? Or were you so narced at depth that neither you nor you buddy realized that such a change was a BIG change ?
(No offense intended, I am just curious about some aspects of this mishap).

To All: What is "deep air diving" ? Is it only about narcosis ?
From their posts, I guess many would answer "deeper than my END" which often seems to be around 30 meters/100 feet. For me, using some Helium for every open water dive deeper than 30 meters/100 feet is plain (and costly) overkill, but feel free to do it, as long as you don't force me to do the same. In temperate to warm water, for open water dives with visibility at least 10 meters, I think that for the majority of adequately qualified and trained divers there is no specific issue diving Air down to 50 meters/165 feet, provided bottom time isn't too long (more details about this below).

I agree that the range 50 to 60 meters (165 to 200 feet) is more critical, even for open water dives in "mild" conditions - for most divers, narcosis seems to become really impairing somewhere in that range. More than 60 meters/200 feet with Air is playing dangerously with OxTox (with Air, ppO2 1.4 bar is attained around 57 meters, 1.6 bar around 66 meters, in salt water).

Or is it also about bottom time ?
In "deep diving" there is not only depth, but also bottom time. Probably we are not talking about the same dives here, and part of the argument comes from this. For example, I am always amazed to see in a training manual (namely DSAT Tec Rec) examples of dives like 40 minutes at 45 meters/150 feet, because for me, rightly or not, this is a long bottom time for this depth, and a really "serious" dive regarding DCS risk.

In their presentation of the French Comex/MT92 tables that have to be used in France by professional divers using Air, Dr Gardette and JP Imbert (from Comex), using huge databanks of commercial air dives, gave statistics of DCS cases (while using first releases of MT92 tables) according to the "severity" of the dive. This severity, introduced previously by Dr Shields and noted Prt, is defined as the depth (in meters) multiplied by the square root of the bottom time (expressed in hours, eg 20' is 0.33 hour).

For "mild" severity dives (Prt<25, eg 20' at 39 meters/130 feet), DCS occurrence was 0.14/1000 (for 7129 recorded dives).
For "standard" severity (25<Prt<35, eg 30' at 45 meters/150 feet), DCS occurrence was 0.14/100 (for 8384 recorded dives).
For "severe" dives (Prt>35, eg 35' at 50 meters/165 feet), DCS occurrence was 0.82/100 (for 2055 recorded dives).

Note that those DCS cases were mostly bends (with almost no cases of neurological DCS : with MT92 tables these seem due to sawtooth profiles that are not properly taken into account by Comex databanks).

Last thing : MT92 tables stipulate that, if the deco chamber is more than one hour away, total deco time should not be more than 15 minutes. This maximum total deco time is also, very often, the limit set by French dive operations during the pre-dive briefings.

My conclusion is, there are two different kinds of "deep open water dives" :
1) Dives like 20' at 45 meters/150 feet or 15' at 50 meters/165 feet are not really technical and can be done with a single tank of Air and no stage by the majority of adequately qualified and trained divers. This practice is very common in France.
2) Dives like 30' at 55 meters/183 feet or 25' at 60 meters/200 feet are technical dives; one needs to use a twinset, and stage(s) are more than welcome; and if one has to carry this burden, then it's better to use Trimix with a suitable END (eg between 30 and 39 meters/100 and 130 feet).

 

[Blackwood]

Oh that Mark, I wish he would learn how to dive already .

me too

 

[Slamfire]

To All: What is "deep air diving" ? Is it only about narcosis ?

The most vocal detractors of deep air also happen to be alums of the DIR philosophy as taught by GUE and UTD. Often times the verbiage of their detractions has a language tone that sounds very close to industry wide impositions. Something like, "this is the way I do it, this is the best way, this is the way everybody should do it. If you're not doing it this way you're doing it the wrong way and you are running serious risks against your life." So in order to provide a concrete definition of deep air, I proposed that we define it by the max END stated in the training standards of these agencies, ie. 100 ft. Therefore Deep Air = anything below 100ft/33m.

Or is it also about bottom time ?

Earlier on the discussion had devolved to include many subjective factors that can't be measured. Along these we had an accompanying disrespectful debate that included personal insults. I tried to bring back the discussion to civility by simplifying the discussion and trying to limit it to concrete numbers and facts. For the sake of simplicity I proposed that we focused the debate only on depth (END). After all, according to the training standards, max END restrictions are applicable universally irrespective of bottom time, equipment, previous experience, how 'advanced' the course may be, etc.

Introducing another variable to the discussion opens a very large set of combinations and permutations when we still are nowhere near closing the debate based on only one variable. Also, you introduce a very valid second variable, then who's to say we shouldn't introduce another equally valid third variable, such as equipment or experience. When you do that, if you're lucky enough to still have a productive, respectful, and civil debate, you are basically rewriting training standards and your discussion no longer is about just deep air.

 

[hg frogman]

Slamfire:
What you say is fair enough. I just wanted to point out that all "deep air" dives are not the same. That's the heart of the matter, as far as I can see. (But being not JJ, and not even God or the one who wrote the Bible, what I can see or say is quite limited )

 

[LiteHedded]

Slamfire:
What you say is fair enough. I just wanted to point out that all "deep air" dives are not the same. That's the heart of the matter, as far as I can see. (But being not JJ, and not even God or the one who wrote the Bible, what I can see or say is quite limited )

let's be real for a second. everyone in this thread (probably) has been deeper than 100' on nitrox. it depends on the dive.

 

[DCBC]

What is "deep air diving" ? Is it only about narcosis?

I believe that deep air should be considered any dive below the maximum range of normal recreational diving; which has historically been set at 130 FSW. From a practical perspective however, it doesn't matter what "deep air" is defined to be.

END is not appropriate to this discussion as we are not discussing mixed-gas.

What is more important is the individual's need to understand how deep is too deep on air and to plan their air dives within their operational envelope. All divers who plan these dives near their limit, should take deep air training in a similar way as those who wish to penetrate a wreck or a cave, or dive under the ice.