Deep Air Dives In Tech Classes

[lv2dive]

Late getting back to this... @victorzamora is correct. And my takeaway was that I didn't want to continue to follow a program that required non-Trimix dives through Tec50 because I philosophically disagreed with it - I think Jelium should be introduced at 100'

That is not to say to say that I think everyone out there should dive Trimix below 100' - but for me and my team, I think it's important. Does that mean I would never ever dive below 100' without Trimix? Never say never - but at this time, I can't foresee a time I would plan to do so.

When I took PADI's Tec50 class, I had the choice to do the last two experience dives on Trimix or a "best mix" EANx mix. I figured since I would be certified to do theses dives on deep air, better to do them in class with an instructor, rather than on my own.

I was very narc'ed in the low vis, cold (40's F) lake water, and going forward, pretty much decided to follow some other agencies' recommendations regarding Helium for dives deeper than 100'.

So the dives up to that point it was mandatory to do on air?

Not to answer for Kate, but: Yes. Tec50 is not a trimix course, and, as such, the diving is done on air/nitrox.

 

[stretchthepenn]

I don't see any risk in eating pasta, unless they were really bad, so that analogy doesn't suit. If he had said "if you can't afford a redundant setup, why do you dive to 60m?", would that still have hurt your feelings? I certainly hope not. There's no actual need to go that deep, there's plenty of safe dives to be made without more gear or training.

In all honesty, yes, I'd be quite offended if someone asked me that question as it's phrased. I'd not mind, however, if the question were, "If you don't have a redundant setup, why do you dive to 60m?" That question cuts to the heart of the technical matter; the original question digs into my personal life.

If someone wants to do a 300' dive on air and the reason they give is that they cannot afford helium, they should not be doing those dives. There is a cost of entry/progression into the sport, thankfully it can be pretty low but... once you start getting to technical diving there are some things you could skimp on, but your breathing gas is not one of them.

It's like people overdiving scrubbers because they want to save 20$ on adsorbent and then they cost their families a lot more in funeral bills. That's if people like @PfcAJ and @kensuf have managed to go and recover them, using gas and sorb that they have paid for themselves.

Agreed, and wholeheartedly. From a purely instrumental standpoint, it's vital to have the financial resources to support more complex dives. I'm mostly concerned about the manner in which the subject is approached.

 

[BoltSnap]

I see your point, but I mostly disagree. The greater point is that financial resources do matter, but telling someone "you're too poor to ______" is, at its core, elitist.

Certainly, if someone is doing something blatantly unsafe--such as racing motorcycles without any safety gear whatsoever or, as you pointed out, cave diving without training--then it's ethically correct to step in and say "dude...don't do that."

However, what we're discussing here doesn't push those extremes. Let's say that our motorcycle racer has secondhand riding gear, or a previous-generation crash helmet. Modern protective clothing would make our hypothetical motorcyclist much safer, but unless we're discussing elite racing or particularly dangerous stunt riding, then older gear will be entirely adequate, and telling the rider to come back when he's rich enough to afford top-of-the-line equipment is neither necessary nor desirable.

With the analogy of cave diving, there's a big difference between saying, "you really should get cave training before attempting that dive" and saying, "you can't afford cave training, so go away."

I'm sensitive on this subject because, back when I was a relatively new diver and working as a retail-wage-slave, I was a member of a scuba club that held its meetings over dinner, at a spaghetti restaurant that charged us a modest ten bucks or so per head. One member floated the idea of changing the meeting site to another restaurant, one that was much more expensive, and I ventured the opinion that changing venues wasn't the best idea because some of us (such as myself) were on budgets. The member came back with "Well, if you can't afford this, why are you even diving?"

If you can't afford (money or time or effort) proper training and proper equipment for any type of diving activity, you should NOT take any short cuts of any kind and shouldn't do it if you can't afford it.

I was a "poor starving student" in undergraduate school and in graduate school and I would only "do it" when I can afford it. If I can't afford it, I don't get involved. There is nothing elitist about it at all. It is just common sense.

 

[Kevrumbo]

You mentioned prolonged hyperveventilation can lead to CO2 retention.

I was not aware this was possible. I thought hyperventilation always resulted in low CO2.

Can you explain how this may occur?

It's possible in this instance because of physical exertion in a dynamic immersed hyperbaric environment (i.e. the basic physical activity and pressure effects of Scuba Diving).

Look at this simple graphic demonstration of the dynamics of immersion Work-of-Breathing (WOB), exertion physical exercise, and ambient pressure differential, just by trying to talk and tread water at the surface:
Now what if @Dr Simon Mitchell in the video was at 10ATA depth in heavy physical exercise and further handicapped by the increased breathing gas density and regulator WOB of Air? -->An increased spike of metabolic CO2 that he may not be able efficiently expel fast enough resulting in CO2 retention, worst case deteriorating into a spiraling vicious cycle of building inefficient hyperpnea leading to acute Hypercapnia, unconsciousness and death.

Note that the depth/pressure of 40meters/5 ATA happens to be the long established recreational depth limit. With regard to CO2 retention, there finally appears to be scientific validation for this: The Gas Density of Air at the surface is 1.3 grams/liter; but at 5 ATA this value is five times as much or 6.5 g/L. A gas density over 6 g/L has been found to increase susceptibility to CO2 retention along with increased risk of Oxygen Toxicity. Compare this to a depth of 90meters/10ATA, where the gas density of Air is ten times that at the surface, or a dangerously gross 13 g/L . . . !

Finally, there is a fundamental and dangerous flaw not taken into account in the whole PADI Tec 40/45/50 course progression & certification to begin with: The Density of Bottom Gas Nitrox 24% to 21% for a max working ppO2 of 1.2 bar is 6 g/L and higher, with Tec 50 on Air at 7.2 g/L. (Refer again to article: Advanced Knowledge Series: The Gas Density Conundrum | Dive Magazine )

The point is there's no safety margin left at all for the hazards of CO2 retention and narcosis problems that arise with unforeseen heavy physical activity and increased work-of-breathing at these certification depths of 40/45/50 meters on primarily non-Helium, high gas density Oxygen-Nitrogen Blends (essentially Extended Range Deep Air). And to recover at depth from CO2 retention, you need plenty of bottom gas and some minutes time to relax & regain a normal non-exertion respiratory rate -if possible- before safely aborting the dive and nominally ascending to any required deco stops.

 

[Dr Simon Mitchell]

You mentioned prolonged hyperveventilation can lead to CO2 retention.

I was not aware this was possible. I thought hyperventilation always resulted in low CO2.

Can you explain how this may occur?

Hello,

You are correct. By definition (in the absence of CO2 rebreathing as in a failed scrubber) CO2 retention is always a result of hypoventilation. I guess what Kev is referring to are those scenarios in which the diver is trying to hyperventilate (a natural response to high CO2) but is limited in some way (high gas density, equipment resistance, dynamic airway compression) so that they actually end up hypoventilating.

Simon M

 

[PfcAJ]

If you can't afford (money or time or effort) proper training and proper equipment for any type of diving activity, you should NOT take any short cuts of any kind and shouldn't do it if you can't afford it.

I was a "poor starving student" in undergraduate school and in graduate school and I would only "do it" when I can afford it. If I can't afford it, I don't get involved. There is nothing elitist about it at all. It is just common sense.

Agreed. If you can’t afford it, accept that and move on.

You can see how involved the ego is with some of these responses.

 

[Kevrumbo]

Agreed. If you can’t afford it, accept that and move on.

You can see how involved the ego is with some of these responses.

"Ego", "stupidity" or your "Socio-Economic Status" troll has nothing to do with this thread, @PfcAJ. . . Isn't that clear from the reaction to your useless inflammatory post?

It's all about discussing and understanding the limits, hazards and dangers of choosing to utilize Deep Air.

You mentioned prolonged hyperveventilation can lead to CO2 retention.

I was not aware this was possible. I thought hyperventilation always resulted in low CO2.

Can you explain how this may occur?

Hello,

You are correct. By definition (in the absence of CO2 rebreathing as in a failed scrubber) CO2 retention is always a result of hypoventilation. I guess what Kev is referring to are those scenarios in which the diver is trying to hyperventilate (a natural response to high CO2) but is limited in some way (high gas density, equipment resistance, dynamic airway compression) so that they actually end up hypoventilating.

Simon M

Alright then Simon -you have an initial exercise Tachypneic response at depth which leads to compensating Hyperpnea appropriate for metabolic needs of body for the moment. However due to high gas density, WOB equipment resistance, and/or dynamic airway compression & essential atelectasis, this ultimately deteriorates into a spiraling Hypoventilation/CO2 Retention vicious cycle, worst case leading into acute Hypercapnia, unconsciousness and death. Is that a better more correct patho-physiological description?

In terms of respiratory physiology and Carbon Dioxide generation in the immersed hyperbaric environment (your quote @Dr Simon Mitchell from the linked article below):

"Causes of increased CO2 production: Carbon dioxide is produced as a waste product of metabolism and must be eliminated. . . Fundamentally [other than a rebreather scrubber failure], the only cause of increased CO2 production is increased work. Thus, exercise results in production of more CO2 whereas rest should reduce it. . . when CO2 rises, respiration will be stimulated, and when CO2 falls, respiratory drive will be reduced. The only point that requires emphasis in regard to diving is that breathing itself requires work and results in production of CO2. When a diver breathes dense gas, and/or if the underwater breathing apparatus imposes significant degrees of resistance, then the work of breathing can be a significant contributor to CO2 production and in some scenarios may be virtually all that the diver is capable of doing. . . We don’t notice the work of breathing under normal circumstances because we are well adapted to the normal demands. However, it is important in diving because it can be increased by immersion, the use of underwater breathing equipment and by increases in gas density. Though perhaps stating the obvious, the diver’s ability to respond to increases in work of breathing is not unlimited. The corollary is that respiratory muscle exhaustion or failure to respond to increased work demand for any reason will result in inadequate ventilation (“hypoventilation”) and an increase in arterial CO2. . ." (https://www.diversalertnetwork.org/files/Tech_Proceedings_Feb2010.pdf, beginning on p.12.)

My take on this and Lessons Learned from my 90msw Air Dive:
If you cannot ventilate and expel this metabolically generated CO2 efficiently enough, you will degenerate into a hypercapnic vicious cycle condition and/or increasing the risk of an Oxygen Toxicity Event.

 

[Dr Simon Mitchell]

Alright then Simon -you have an initial exercise Tachypneic response at depth which leads to compensating Hyperpnea appropriate for metabolic needs of body for the moment. However due to high gas density, WOB equipment resistance, and/or dynamic airway compression & essential atelectasis, this ultimately deteriorates into a spiraling Hypoventilation/CO2 Retention vicious cycle, worst case leading into acute Hypercapnia, unconsciousness and death. Is that a better more correct patho-physiological description?

Yep, perfect. That certainly can happen, which, as you will see in my response to GJC was what I thought you were trying to say. I thought it was important, in order to avoid confusion, to acknowledge the fundamental correctness of what GJC was trying to say: unless CO2 rebreathing is involved, hypoventilation is always the base cause of CO2 retention.

Simon

 

[Patoux01]

In all honesty, yes, I'd be quite offended if someone asked me that question as it's phrased.

Yeah I'm not much of a words person. However, I have to say that the situation in which each sentence could be said is different.

If I were to see a friend planning his 60m dive on a single tank with no back-up, I would say "Doesn't it seem off to you to do such a dive without redundancy?". If I were to hear him say before hand "I dive on a single tank because I can't afford a second reg", damn right I'll tell him that if he can't afford the gear, he can't afford the dive. Why? Because he already knows inside that he is doing something stupid because he can't afford it.

Like I've said, there's plenty of dives where the gear the person has will be suitable, and typically nearby, so it's really pointless to claim "I can't afford to do it properly so I'm doing it badly".

 

[MaxBottomtime]

At the same time I've done a few hundred deep dives with manifolded doubles and deco bottles. I planned the dives using well known deco software and enjoyed every dive, yet there were still a few who told me that if I couldn't afford to use trimix on those dives I shouldn't make them. For better or worse, tech diving brings out the worst elitist attitudes in some people.