CMAS & BSAC vs others Schools depth limit on Air

[Lorenzoid]

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.

What do you make of the quote in the DAN article I posted above that suggests that the impairment a diver has to "manage" may not be due to any one factor but rather the combined effects of narcotic gas, CO2, higher PPO2, higher density, and even sensory deprivation and increased stress (presumably from simply being so deep)? There are so many unknowns. I wouldn't stop at saying that "inexperienced divers" should stay away from combining so many unknowns but would say something more like the only divers who should remotely consider diving to those depths should be those with a LOT of experience diving to increasingly greater depths and figuring out how they handle the effects.

 

[Dr. Lecter]

This being Basic Scuba, all I'm going to say further on the subject is that it's not rocket surgery or particularly demanding as far as diving goes, but it is soldily within the realm of technical diving. That should be sufficient to warn off unqualified divers without resorting to spinning tall tales of the horrors of air as a breathing gas much past 130'.

 

[Remy B.]

---------- Post added October 17th, 2014 at 08:44 PM ----------

My mistake, the record was Bret Gilliam with 475' in 1993, don't know from were I got those numbers, it had to be related to something else in diving.

Here was a small letter Gilliam wrote, this is the one I read about a month ago.

Oxygen Toxicity & deep dives on Air

 

[pdhenry]

Nitrox does no allow greater depth than air, in fact, the "floor" is shallower than for air.

Also, breathing Nitrox doesn't have a significant impact on narcosis compared to air. Oxygen seems to have equally narcotic properties under pressure as nitrogen.
You can dive to 130' on EAN30 (pO2 1.5) and still have a significant gain in bottom time..

 

[Lorenzoid]

This being Basic Scuba, all I'm going to say further on the subject is that it's not rocket surgery or particularly demanding as far as diving goes, but it is soldily within the realm of technical diving. That should be sufficient to warn off unqualified divers without resorting to spinning tall tales of the horrors of air as a breathing gas much past 130'.

Well stated.

Now, why are we discussing world-record depths in Basic Scuba forum?

 

[Jim Lapenta]

Cause it's the internet.

 

[Akimbo]

...Now, why are we discussing world-record depths in Basic Scuba forum?

It's not like this is the first time: http://www.scubaboard.com/forums/basic-scuba-discussions/492971-world-record.html

 

[Nasser]

I was trained as a BSAC diver in the late 90's and the Sport Diver qualification had a max. depth of 50m on air. The training was over several weeks and quit extensive but at the time I never actually felt a compelling reason to go to 50m just for the sake of pushing that limit. There was (and still is) plenty to see at the so called recreational sport limit of 40m and IMHO it is a reasonable recommendation.

As a tech diver, I have generally taken the view that any deeper excursions and the training/equipment required for it are merely a means to an end. If there is an interesting geological formation or historical wreck down there then I'll make the dive to see it and will treat it as a tech dive. This frequently involves diving up 55m on air and from my personal experience the effect of narcosis is very minimal and the dives very "do-able" - in the diving environment I usually dive. Deeper than that and I start to feel fuzzy and will use trimix.

The overriding factor here is that if you want to conduct deeper dives and stay down longer (on air or mix) then get the training for it. It's not so much that there is this rule that says beyond 40m on air is a big no-no ... or that it becomes strictly a tech dive, etc...

It has much more to do with understanding what is involved as you venture towards these deeper depths - The effects of the gas you're breathing at depth, crossing over to the "virtual ceiling" that defines a deco dive, and what equipment considerations need to be taken as you move into this realm of diving. It is the mindset involved and being able to understand the various factors and anticipate the consequences of any mishaps that are of so much importance. This way you have a more comprehensive understanding to make your own decision as to what kind of dive you want to make, how deep to go, and the risks involved.

 

[niavlys]

In France the limit for air diving is 60m at this depth the NDL is 0. (the depth limit is fixed by the PpO2 (it must be between 0.16 and 1.6 bar)).

 

[captain]

I regret I have but one data point: me. My own experience seems to jibe with what I recall being taught was PADI's position, which is that their depth limits are based in part on the fact that narcosis becomes a problem for most people somewhere in the range in question.

I feel it gradually increasing with depth, up to the point where at 100 feet or so, I feel like I've drunk a 12 oz. beer. When my buddy surprises me at 100 feet or so with a narc test by holding up fingers, to which I'm supposed to respond by adding or subtracting one depending on how many she holds up, I fail surprisingly often (and don't fail when we do this at the breakfast table). And that scares me. Since I have no known health issues that might predispose me to this, it seems reasonable to believe it happens to many other divers. Narcosis has been discussed in many other threads, so I'll leave it at that. My one data point. I don't care about any agency's official depth limits--I know what MY limits are.

I seem to have seen a study some where that suggested that those who were taught they will suffer an effect at some specific point claimed they were affected, those not so trained did not claim to be affected. Mind over matter.