Deep diving advice that goes against conventional thought?

[waterpirate]

Ego and hubris, the downfall of many. I am an underwater killer, just as friends of mine fly into Alaska and elk hunt with no suppport for weeks at a time. It is about mitigating risks. The risks are not the same for everyone, that is just life.

I often compare spearing with photogs. It is extreme task loading and at depth it can cause real problems. I simply ask " How many videoagraphers do you think dive deep air and get the great footage?". The true answer is a very small percentage of the group are familar with and practice deep air, the others take other measures to ensure great performance and mitigate their risks.
Eric

 

[hroark2112]

He's got a point.

If you go to 240', you won't get narced if you don't breathe....even if you stay for a really long time.

Sounds like a great idea. I'm going to call my ex-wife and see if she'll try it & let me know how it works out.

 

[John C. Ratliff]

There is a fallacy that is being passed on in this thread. It comes from a lack of understanding of the lungs and the physiology of breathing. Our Total Lung Capacity (TLC) is our Vital Capacity (VC) plus our Residual Volume (RV) [see the link in the previous sentence].

If we inhale to the maximum, then exhale to the maximum, we will be exhaling our Vital Capacity (VC). There is still a Residual Volume of air in our lungs, or our air sacs would collapse. Normally we breath in what is called the Tidal volume (TV), leaving an Inspiratory Reserve Volume (IRV) and an Expiratory Reserve Volume (ERV). In diving, we normally will inhale deeper, and could inhale to our limit, then exhale. We would then have our Inspiratory Reserve Volume plus our Tidal Volume being used. That leaves the Expiratory Reserve Volume, plus the Residual Volume of our lungs with air. We will not use up the 79% of the air that is nitrogen, so that nitrogen is under pressure no matter whether we are "breathing" fast or slowly. (We will breath, or we would not surface.)

Therefore we will continue to have nitrogen diffusing into the blood stream no matter our breathing rate, as it is simply a pressure diffusion situation. The fallacy is that we can decrease this uptake of nitrogen by decreasing breathing. That probably is more a factor of heart rate than of breathing, as the blood moving through the lungs is where the gas exchange occurs. And this would be mostly independent of the inflation of the lungs.

This is why free divers can get bent, and why the U.S. Navy has to be very careful about its submarine escape practice sessions in a water tank, as the instructors were diving down to about 70 feet all day free diving to supervise the trainees, and some got bent doing that. Here is a recent paper on Decompression Sickness following Breath-hold Diving.

SeaRat

 

[Akimbo]

Obviously this a “don’t try this at home” kind of thing, but it is educational to look at what is going on. On one hand divers are taught that exceeding limits far less than the OP describes should never be done. On the other, people do stuff like this all the time. No wonder new divers are confused.

There is a lot of human variability where decompression sickness and oxygen toxicity are concerned. Same for Nitrogen Narcosis, but many believe including me that repeated short-term exposure increases tolerance. There are also different “acceptable occurrence” values. Zero risk is easy, never go underwater.

Hundreds, and possibly thousands, of US Navy First Class Diver candidates have made simulated dives in a chamber to 285' on air. These dives were in very controlled conditions but, if the mission required it, divers were expected and did make dives in open sea using surface-supplied Mark V deep sea gear… a much more controlled situation than in Scuba.

The Navy Experimental Diving Unit has run across a few people who have not developed DCS symptoms nearly as readily as most of their other human test subjects. There just isn’t enough data to know what percentage of Navy divers they represent, what happens to their tolerance with age and physical condition, or if the lack of apparent symptoms had long-term detrimental effects compared to their peers. That some people are less likely to develop DCS symptoms is undeniable… and unpredictable.

Same with oxygen toxicity. The July 1963 US Navy Diving Manual, Part 2, Page 55 states:

DEPTH EFFECT
(4) Oxygen toxicity limits the safe depth of operation for closed-circuit (pure oxygen) scuba. Extensive operations are hazardous below 30'…

(That’s about 2.0 ATA working, not emergency)

The Navy has adopted more conservative Oxygen exposure limits in the last couple of decades. It isn’t unusual for Navy combat swimmers (SEALs and the UDT before them) to exceed 60' under very stressful conditions without OxTox symptoms, even though it far exceeds the depth considered safe.

What is Safe?
As you can see, the answer is a pretty squishy and highly variable, but then what about diving isn’t besides maybe air embolism? Deeper, longer, and worsening sea conditions all compromise diving safety. Skill, equipment, and experience can offset SOME of that risk. What the OP describes is certainly on the less-safe end of the spectrum, but not impossible or certain death.

Does it Make Sense?
That is a value judgment. Apparently these divers think so… they must really like fish. Every diver must ask themselves what risk is acceptable. It is the responsibility of each diver to understand those risks, how to mitigate them, and gain sufficient experience. It really doesn’t matter if it is learning not to embolize yourself in water shallow enough to stand up in or performing saturation dives at 1000'+ in Sea State 6.

 

[John C. Ratliff]

Akimbo, thanks, and I think I'd rather be at 1000 feet in a saturation dive than on the surface in Sea State 6.

SeaRat

 

[DCBC]

...It isn’t unusual for Navy combat swimmers (SEALs and the UDT before them) to exceed 60' under very stressful conditions without OxTox symptoms, even though it far exceeds the depth considered safe.

Yes, in-fact Table 6A (USN) requires that the Diver breathe 100% O2 for 25 minutes (then a 5m Air break before it's repeated) at a PPO2 of 2.8 ATA (approx 60 FSW).

---------- Post added March 12th, 2014 at 04:12 AM ----------

Hundreds, and possibly thousands, of US Navy First Class Diver candidates have made simulated dives in a chamber to 285' on air.

As you're well aware, Commercial Divers have worked (and continue to work) underwater all over the planet (for millions of hours) at a depth between 150 and 200 FSW breathing Air. They're not just undertaking a dive, but complete work which is required to be completed to specs (they can't be narced out of their mind). These Divers have been trained to do this work and I think that this is something to keep in-mind. People are capable of breathing Air safely in 200 FSW.

Often I hear the advantages of mix and that some divers brand any dive to 150 FSW without it as foolhardy and shake their head. That's just crap. What needs to be realized is that training, experience and the diving conditions are variables in determining what is and is not safe.

I'm not advocating Deep-Air for the beginner, or to anyone without proper training. That said, I've taught mixed-gas for 40 years. It seems that today people feel that MG is a passport to diving deep without sufficient experience, knowledge or fitness. There is much more to a 300'+ dive than what you're breathing.

 

[ajduplessis]

As you're well aware, Commercial Divers have worked (and continue to work) underwater all over the planet (for millions of hours) at a depth between 150 and 200 FSW breathing Air. They're not just undertaking a dive, but complete work which is required to be completed to specs (they can't be narced out of their mind). These Divers have been trained to do this work and I think that this is something to keep in-mind. People are capable of breathing Air safely in 200 FSW.

The difference is that commercial divers do this on a daily basis and have a dedicated crew topside "babysitting" and monitoring every move in a controlled manner. This can't and should not be used as reference to any form of non-commercial deep air diving. In fact, commercial diving activities should not even be mentioned in threads like this. It is not relevant!!!!!!!!!!!!!!!!!!!!

 

[DCBC]

The difference is that commercial divers do this on a daily basis and have a dedicated crew topside "babysitting" and monitoring every move in a controlled manner. This can't and should not be used as reference to any form of non-commercial deep air diving. In fact, commercial diving activities should not even be mentioned in threads like this. It is not relevant!!!!!!!!!!!!!!!!!!!!

The point is that a person that's properly trained can be competent / safe to breath air beyond 150 FSW. The equipment and diving procedures used, do not affect the degree in-which inert gas narcosis affects a human being. Such dives meet the standards of government regulatory bodies, as well as Worker's Compensation Boards.

Some would have us believe that you are being foolish to complete such a dive regardless of your training and experience. This is a narrow-minded and incorrect view.

Can Deep-Air be done safely? Yes it can, but with every aspect of diving it's not without risk. Acceptable risk is something that must be determined by the individual. Under no circumstances should it be dictated by others (that's what laws are for).

A believe a Diver should dive within their personal safe diving envelope. This varies between individuals and is dependent on training, experience and physical condition/health.

 

[Freewillow]

Bad english, bad science, bad everything..............................Not worth saying more on this B.S.

 

[ajduplessis]

The point is that a person that's properly trained can be competent / safe to breath air beyond 150 FSW.

So which agencies provide deep air training beyond 150FSW? PADI? IANTD? UTD? NAUI?