Exactly how deep is "Deep Air?"

[hg frogman]

Limits for air diving from my personal experience
Diving air down to 45 meters/150 feet in open water dives (no penetration) I am not worried by narcosis. This attitude comes from my inner perceptions (no symptoms of narcosis) and from no significant evil specific to narcosis ever arising at this range of depth in my experience (about 200 air dives deeper than 40 meters/130 feet). Some of my buddies experienced mild symptoms (eg music in their mind) while diving with me at 40 meters, but they behaved all right. Also we did some mistakes when we had less experience - like not stopping at 40 meters/130 feet to perform a narcosis test before getting any deeper.

Between 45 meters/150 feet and 55 meters/183 feet I take air diving very seriously - I never felt impaired but I tell myself that I am most probably significantly slowed down. So I only do open water (no penetration) air dives to these depths, and only with buddies I know well, and with everything in good conditions (sea, viz, temperature, currents, buddies and myself: fit, slept well, not stressed, well hydrated, no alcohol ...). And systematically we stop at 40 meters/130 feet to perform a test of narcosis before going deeper (or not).

I did a handful of air dives between 55 meters/183 feet and 65 meters/215 feet. I didn't feel impaired (that's subjective, objective testing probably would have shown severe slowing down) apart from a over-cautious sort of mild paranoia. I think it's a bit too much on the edge (akin from South Col to the summit of Everest) for the amount of risk I am ready to take. Twice I had dive buddies impaired and I had to assist them to go up. Same criteria than above (but even more adamant) about buddies, conditions and narcosis test. But I try to keep these dives exceptional.

Deeper than 65 meters/215 feet I never went (and I don't want to) with air. I have no idea of the subjective effects of narcosis on me at this depth (it's like drugs, I am not interested in knowing these effects anyway) but OxTox risk scares me enough to not go. I know fellow divers who dive deeper than that with air, but for very very short bounces. I have been amazed to read about those air divers penetrating a submarine at 220 feet : I'd never do that !

Limits for air diving from a law perspective
- In France it's 60 meters/200 feet (if you are adequately certified) with your deco also on air (or on Nitrox if you have this additional certification)
- In Great Britain it's 50 meters/165 feet (or more ?) for BSAC
- For TDI it's 55 meters/183 feet
- For DSAT it's 50 meters/165 feet
- In Egypt it's 40 meters for recreational certs (and 55 meters for tech certs, eg TDI, if I am not wrong)

Limits for air diving from an historic and environmental perspective
- SCUBA diving began around 1943 with Jacques Cousteau in the Mediterranean sea, where the interesting dives (especially for the fixed fauna) are mostly 40 meters/130 feet to 60 meters+/200 feet+ deep. Deco (air) diving has been the norm there for decades. That has set (and still does) the kind of training, and the limits for air diving, in Europe.
- In the Caribbean there is plenty of stuff to see in shallow waters. That, plus the RSTC agencies philosophy (which is not the topic here), has set the limits for air diving shallower (eg 40 meters/130 feet) for the so-called "recreational divers" (a notion that doesn't exist in Europe : all leisure divers, even those diving with Heliox rebreathers, are called "recreational" there).
- In France many divers still dive air down to 60 meters/200 feet (for open water dives) but there is a growing minority of French divers systematically using Trimix for (no penetration) dives deeper than 50 meters/165 feet. They often tend to use less helium than in some other places, though (typically Tx20/25 for a 60 meters/200 feet open ocean dive, with an END = 40 meters/130 feet).
- French cave divers and French divers penetrating wrecks (that's not all wreck divers) have their own set of rules.

Conclusion
I am probably a bit optimistic about narcosis, given I come from a country where diving is not felt and done the same way than, for example, most North Americans do. And also given that my diving experience has limits (mostly temperate and tropical waters with decent viz). On the other hand, many North Americans are likely to be a bit pessimistic about narcosis. And in any country these things evolve in time. So finally I would say, deep air diving begins at 40 or 45 meters (130 or 150 feet) and finishes at 55 or 60 meters (183 or 200 feet) from where in most cases it's better to dive trimix in my opinion (and it may well be a good idea to add some Helium as soon as 45 meters/150 feet if one can afford it). Same than for rock climbing : pioneers climbed with nailed shoes but we don't have to do the same - but in the other hand diving the Doria with only 100 dives under one's belt because one uses trimix is probably tempting the devil, as DCBC rightly says - and air diving, unlike nailed shoes for climbing, isn't so bad finally, it's simple and light, provided one doesn't go behind one's and buddies' limits.

Last comment
In several threads from this board I found that those who are against "deep air diving" are much more normative than their antagonists. Anyway, thanks to the OP for giving us an opportunity for clarifying what we mean by "deep air".

 

[AfterDark]

Trimix is great if you can afford the gear to use. If not like EVERYTHING else in life we must compromise. Diving "deep" on air for some of us is that compromise. I'd rather drive an SUV they are safer but like trimix gear they are beyond my budget. I also made the decision not to use nitrox as it limits my depth on any given dive which to me is just not acceptable.

 

[PfcAJ]

As you would have guessed, I put END>100. Every deep cave diving death (that I know of, anyway) has an END >100, as well as every OW death. I believe that if one wants to partake in these activities (which are inherently more risky than shallow/non overhead diving), than narcosis is something that needs special attention and needs to be avoided. Since the number of cave diving/OW deaths with ENDs less than 100ft (when diving past 100 ft) is near zero, 100' is my cutoff. Just to clear the air (pun, hahah), I dive 32% for just about everything shallower than 100' .

A person's subjective assessment of how they feel is a horrible indicator of whats really going on, and as such, I don't use it. Feeling bad about something is a great warning sign, but just because you feel good doesn't mean it is good. Routine demonstration of a handful of skills will become possible in an impaired state. Its when something novel happens (reg free flow, BC sticks on, etc) that the diver is unable to make quick, accurate, and appropriate decisions.

I know not of this special trimix gear I see people post about. When I do a nitrox deco dive, I carry the same amount of stuff as I would a 150' trimix dive. Naturally, if the dive is deeper/longer, I'll add another deco gas to shorten the deco and give me more options under water. Doubles are a must anyways, to provide enough gas too have a reasonable bottom time, as well as enough reserve. I don't really know what is "trimix specific" about that.

Trimix is obviously more expensive, so if I can't afford it, I'll just save my nickels until I can. In the meantime, I dive shallower stuff. No biggie. There is nothing that I just HAVE to dive, its all a choice and it all can be postponed until everything (including gas, equipment, right buddy, etc) is in place to dive it. Its not going anywhere.

 

[LiteHedded]

Trimix is great if you can afford the gear to use. If not like EVERYTHING else in life we must compromise. Diving "deep" on air for some of us is that compromise. I'd rather drive an SUV safer.

you SHOULD be using the same gear on any deep dive

 

[AfterDark]

you SHOULD be using the same gear on any deep dive

What? I don't understand your point. Where did that came from?
Since it's me you quoted there must be something in my post that you misunderstood, no?

 

[Rhone Man]

It is always hard to draw a bright white line.

• For me, I know that performing mental calculations below about 120' becomes much more challenging, but it is all manageable.
• Below about 150' concentrating on any task becomes hard for me, and I would not want to be in an overhead environment.
• Below 180' I will not go, and any dive to those depths is something I do only after careful consideration and a few "work up" dives.

I went with 150-165' on the poll.

 

[The Chairman]

Deep air is not my personal limit, but I believe that it starts at 100FSW. For most people their bovine index is about .7 or so at that depth. At 150 FSW your bovine index approaches 1.

Too many people look for a dramatic transformation (such as Cool Tech felt) to define the depth they get narced. Paranoia is the SAFEST response to narcosis, but in reality most of us just morph into having the cognitive abilities of a cow (bovine index)... and we are too stupid at that depth to realize it. You're a cow and don't even realize it.

Someone mentioned muscle memory helps, and I have to agree with them. The more your reactions to a given situation are automatic/instinctual AND appropriate the less likely you will be harmed. However, if you have to reason yourself out of a situation though, all bets are off. Your ability to comprehend and react to an unforeseen situation are dramatically reduced even though there was no dramatic transition.

 

[Superlyte27]

You know studies have shown (chamber experiments though I'd have to go find the study I read) that toxing is extremely random and varies greatly from day to day. I don't think one tolerance test would do you much good.

You are right, and that's why they don't do them anymore.

*edit* and it wasn't one test, it was one test per year.

 

[hg frogman]

I know not of this special trimix gear I see people post about. When I do a nitrox deco dive, I carry the same amount of stuff as I would a 150' trimix dive. Naturally, if the dive is deeper/longer, I'll add another deco gas to shorten the deco and give me more options under water. Doubles are a must anyways, to provide enough gas too have a reasonable bottom time, as well as enough reserve. I don't really know what is "trimix specific" about that.

With air, you can do your deco on backgas. Lots of people have done that in the past, and lots still do it. So you don't need to carry any deco stage. With trimix (especially those with a lot of He that are standard gases for some agencies) you need to carry deco stage(s).

(Edited thanks to post from LiteHedded thereafter). This is not true for all trimix though. For instance Tx25/25 isn't very different from air for deco. (End edit).

Diving without any deco stage is more streamlined, I believe we can agree on that.

On the other hand, I agree with you on that, if one dives deeper than 45 meters/150 feet AND has to carry deco stage(s) then he'd better use trimix as backgas (less narcosis, longer deco but you carry the deco stages anyway). At which END is another matter of debate, though.

Netdoc:
What you say makes sense but maybe you are too pessimistic about what you call the "bovine index", especially at 30 meters/100 feet. Several times while having students doing calculations at this depth for the AOW course they were better and faster performers than at the surface (more concentrated I guess, possibly a mild-paranoia-like effect of narcosis but didn't decrease their performance). I never saw more than 30 to 50% of slowing down during these tests, but maybe I don't do them right (?)

 

[Superlyte27]

On the other hand, I agree with you on that, I you dive deeper than 45 meters/150 feet AND have to carry deco stage(s) then you'd better use trimix as your backgas. At which END is another matter, though.

Why?
I dive Air all the time and use 100% Oxygen to deco on. What's the significance of the stage requiring Trimix, is it because you enter Deco?

I swear I'm growing more and more convinced that all this Deep Air contraversy is stemmed from a need for instructors and LDS to make money. But I guess that's another topic.