CMAS & BSAC vs others Schools depth limit on Air

[Lorenzoid]

. . .

Long time ago I did read ( don't remember which book but it was a book ) that the 53m was the gate of lala land.

There is no "gate" or threshold for narcosis. My understanding is that it is a continuum: the deeper you are, the more you are subject to narcosis, and as far as anyone knows there is really no threshold depth at which you begin to be subject to it. It's become clear to me that narcosis is difficult if not impossible to measure objectively.

 

[Remy B.]

There is no "gate" or threshold for narcosis. My understanding is that it is a continuum: the deeper you are, the more you are subject to narcosis, and as far as anyone knows there is really no threshold depth at which you begin to be subject to it. It's become clear to me that narcosis is difficult if not impossible to measure objectively.

I agree, but it said that after that 53m you more likely were doomed, or at least the mayority of people was, this was a old book, it also mention that back in the days there was people doing even deeper dives that were able to couple with narcosis, as well that back then a lot of people as well loss their lives and were never found, it is a little different for every body.

But it could have been as well related to other problems, only the death know.

If not mistaken the world record is 350+ feet on air I believe it was 2007 or 2009 don't remember, this guy as well mention of the different tolerance levels of narcosis between individuals.

I will guess that eventually the authorities set a safe mark of 40m, were they know the mayority will have some narcosys, and may have some impediments and gaps in your memory but were able more likely to surface, if that was not the case the limits had been set less than 40m, not saying I'm right but it seems resonable

 

[alewar]

If not mistaken the world record is 350+ feet on air I believe it was 2007 or 2009 don't remember, this guy as well mention of the different tolerance levels of narcosis between individuals.

Sheck Exley went to 465ft in salt water in the 70s on air.

 

[Akimbo]

Here is a list of deep air records with dates:

Deep diving - Wikipedia, the free encyclopedia

 

[Dr. Lecter]

At some point between 200' and 300'+, it becomes a race between CNS toxicity and N2 narcosis as to which one will overtake the individual's physiology first. Because the two seem to be somewhat exclusive--narcotic impairment may be quelling CNS seizure activity that would otherwise hit--the PPO2 that's working at most of those depths would probably kill you a lot faster on deco mixes at much shallower depths. Don't try this at home, kids/Remy.

 

[Lorenzoid]

Is it even based on solid scientifically gathered data whether we can say "a majority" (i.e., more than 50%) get narced at any specific depth? I know there have been narcosis studies (mostly in a chamber, am I correct?) but I have yet to hear anything that would give us divers solid guidance. Seems to me it's a big unknown, beyond the sweeping statement that the deeper the dive, the greater the risk--and to make any more definitive statement about what percentage of divers get narced to what measurable extent and what impact that has on their abilities isn't based on enough hard data.

This discussion prompted me to see what DAN has to say on narcosis, and I found this article that addresses a lot of "deep diving" considerations: How Deep is Too Deep? ? DAN | Divers Alert Network ? Medical Dive Article

I especially like the way they explained this:

"It becomes obvious that there is no safe depth limit that applies to all divers all of the time. A diver’s ability to cope with depth depends on a number of highly variable factors. The depth of the onset of the effects of the exotic cocktail of elevated pressures of nitrogen, carbon dioxide and oxygen, coupled with the sensory deprivation and stress associated with diving, are not always predictable."

 

[Edward3c]

There is no "gate" or threshold for narcosis. My understanding is that it is a continuum: the deeper you are, the more you are subject to narcosis, and as far as anyone knows there is really no threshold depth at which you begin to be subject to it. It's become clear to me that narcosis is difficult if not impossible to measure objectively.

One of the scientists with Coral Cay Conservation did research on the effects of narcosis on survey result reliability. Which started to affect results from 15m.

 

[DivemasterDennis]

I have never felt any reluctance to go to recreational limits on air ( 130 feet or 39 meters) but the ndl limits are very short. I have scores of dive to 100+ on air without ill effects, most of the multi-level variety. Nitrox does no allow greater depth than air, in fact, the "floor" is shallower than for air. For time at depth you need those exotic mixes techies are so fond of. That is not in my pay grade. All of that said, I have been 142 feet on air for a spefic closely supervised training exercise. I know some crazy divers who have been to 2o0 feet or more on air- not an adventure I ever care to share.
DivemasterDennis

 

[Dr. Lecter]

There's nothing crazy about 200' on air, aside from the speed with which your deco obligations accrue. It's not so deep gas density is a big issue, nor is the 1.48 ppO2 huge, and the narcosis is generally quite managable. There are lots of good reasons for inexperienced divers to stay away from diving to that depth, but it being a "crazy adventure" isn't one of them.

 

[JMBL]

There's nothing crazy about 200' on air, aside from the speed with which your deco obligations accrue. It's not so deep gas density is a big issue, nor is the 1.48 ppO2 huge, and the narcosis is generally quite managable. There are lots of good reasons for inexperienced divers to stay away from diving to that depth, but it being a "crazy adventure" isn't one of them.

Totally agree with you, doc. I've logged about 40 dives between 50m/164 ft and 62 m/203 ft on air, none of them done on the crazy or jackass mode. All the posts have been focused on PPO2, being narked, and wob, with good reasons, but I'd like to add something : water and diving conditions.

More that 90% of those dives I've done deep on air where made in the Med, during summer, in clear and rather warm water, and after many dives in the season. Sure, I was narked during those dives, but never incoherent or whatever.

But I would never have dream of diving so deep on air in the Atlantic, which is almost always below 14°C/57°F and often as dark as Hell where I live. On those dives, I much prefer trimix to avoid crazy adventures. I remmember one special dive on air in such conditions : I was pissed narked, not incoherent but on autopilot and couldn't remmember much of what I've seen. That's my point : with tougher conditions, you get narked quicker and stronger.

As far as why deep diving on air still exists in several training agencies, I should advise you to take a trip to old Europe :most of the time the real problem is not the price of trimix, but the fact that trimix is not avaible, except for trimix classes. So, basically, you can learn to use it, but not dive with it... So, as I can get my own personnal mobile filling station, I do certain dives on air.