Reaching Greater Depths

[stuartv]

On an Al80? What would be your minimum tank pressure at that depth?

I don't know those details yet. I'm not even signed up for the Deep Diving specialty yet - and probably won't be for a while, as I just got my OW cert.

As far as max depth, it seems like every responsible diver would want to know at what depth they are likely to get narked to the point of impairment. And, yes, I understand that even for a single individual it can vary depending on other factors beyond just mix and depth.

If you don't know your personal limits, then you don't really know what margin safety margin you are diving with. I like to know my limits - and not so that I can dive (or engage in any other activity, for that matter) to that limit. Rather, so that I can set myself a safety margin and know (as best I can) that I am diving with that much safety margin, instead of just picking an arbitrary limit and hoping that I am well away from my actual limit.

It seems to me that if you know your limit tends to be around 120 feet, then you can dive to 100 feet and be a much safer diver than another who has arbitrarily limited themselves to 100 feet and doesn't know that that is their actual personal limit, because they have never dived deeper than that.

 

[Storker]

As far as max depth, it seems like every responsible diver would want to know at what depth they are likely to get narked to the point of impairment.

But what's "the point of impairment"? Thinking slower, beginning mental tunnel vision? Narked out of your gourd bovine stupid? Lala-land denizen donating air to the pretty fishes? For me, it's the first, so I know my point of impairment already.

If you don't know your personal limits, then you don't really know what margin safety margin you are diving with. I like to know my limits - and not so that I can dive (or engage in any other activity, for that matter) to that limit. Rather, so that I can set myself a safety margin and know (as best I can) that I am diving with that much safety margin, instead of just picking an arbitrary limit and hoping that I am well away from my actual limit.

It seems to me that if you know your limit tends to be around 120 feet, then you can dive to 100 feet and be a much safer diver than another who has arbitrarily limited themselves to 100 feet and doesn't know that that is their actual personal limit, because they have never dived deeper than that.

I think I understand your POV, I just don't agree. When I drive on ice or snow, I don't need to know my car's ultimate limits, i.e. at what speed I'm pretty much guaranteed to end up in a ditch or wrapped around a tree. For me, it's enough to recognize the first signs of slipping tires before I let off on the accelerator.

Similarly, when I dive, I don't need to know at which depth I'm going to be so stupid that I just stare dumbly at my buddy when he's slashing his hand across his throat. I just need to know at what depth my mental processes are affected enough that I'm becoming bandwidth-limited. As I'm getting older, I've become rather risk-averse, and since I don't dive with a guide, DM or instructor to look after me, I need to be in full control of the situation, both for my own sake and for my buddy's sake.

My limit isn't arbitrary, it's the depth where I know from experience that I'm starting to lose mental bandwidth. If you want to descend to the land of bovine stupid to find your limits, I won't stop you. But I think you should bring enough gas to take you out of a situation that may occur, and that you should know how to calculate how much gas "enough gas" is.

 

[stuartv]

But what's "the point of impairment"? Thinking slower, beginning mental tunnel vision? Narked out of your gourd bovine stupid? Lala-land denizen donating air to the pretty fishes? For me, it's the first, so I know my point of impairment already.


I think I understand your POV, I just don't agree. When I drive on ice or snow, I don't need to know my car's ultimate limits, i.e. at what speed I'm pretty much guaranteed to end up in a ditch or wrapped around a tree. For me, it's enough to recognize the first signs of slipping tires before I let off on the accelerator.

Similarly, when I dive, I don't need to know at which depth I'm going to be so stupid that I just stare dumbly at my buddy when he's slashing his hand across his throat. I just need to know at what depth my mental processes are affected enough that I'm becoming bandwidth-limited. As I'm getting older, I've become rather risk-averse, and since I don't dive with a guide, DM or instructor to look after me, I need to be in full control of the situation, both for my own sake and for my buddy's sake.

My limit isn't arbitrary, it's the depth where I know from experience that I'm starting to lose mental bandwidth. If you want to descend to the land of bovine stupid to find your limits, I won't stop you. But I think you should bring enough gas to take you out of a situation that may occur, and that you should know how to calculate how much gas "enough gas" is.

Wow! That seems like a whole of assumptions put on me.

I didn't say I want to know what depth I become so stupid I forget to breathe. Knowing at what depth you start to experience any signs of impairment is knowing your limit (for starting to become impaired). Knowing when the tires on your car are just starting to slip is knowing your limit (of when the tires are starting to slip). Each person has to decide what "the point of impairment" is for them. Personally, I would say that the point of impairment is the point at which the first sign of any type occurs that indicates slower thinking, unexplained euphoria, or whatever symptom happens to occur that is a sign of narcosis.

If you want to dive without any signs of impairment, then knowing the depth at which you start to become impaired IS knowing your limit. Since (I gather) that limit can vary for an individual diver based on other factors, KNOWING that your limit for that is, say, 100 feet, you can make a choice to never descend below 80 feet (just as a made up number for example purposes) to have high confidence that even if those "other factors" are working against you one day, you still (most probably) won't get narked.

And if you never explore your limits to find out at what depth you start to experience the first signs of impairment, then you might find out the hard way that your limit was actually 100 feet all along and the one day when you happened to descend to 100 feet AND the "other factors" happen to be working against you that day is the day that you get narked and do something fatally stupid. All because you never bothered to figure out your personal limitations, you never knew that going to 100 feet really was your personal limit, and thus, you never set yourself a less deep limit to give yourself a margin of safety.

 

[victor]

Pride comes before a fall. Last month you might have been comfortable at 130 ft. That does not mean you will be safe today 100 ft. Fatigue, hydration, etc. all may or may not have an impact.
For ME the important thing is to recognize when narcosis starts to happen, and head up. Not everyone can recognize the onset of their symptoms, it depends how it affects them.

It seems to me that if you know your limit tends to be around 120 feet, then you can dive to 100 feet and be a much safer diver than another who has arbitrarily limited themselves to 100 feet and doesn't know that that is their actual personal limit, because they have never dived deeper than that.

 

[stuartv]

Pride comes before a fall. Last month you might have been comfortable at 130 ft. That does not mean you will be safe today 100 ft. Fatigue, hydration, etc. all may or may not have an impact. I don't see how statement detracts in any way from what I said. It seems to reinforce it, actually.

For ME the important thing is to recognize when narcosis starts to happen, and head up. Not everyone can recognize the onset of their symptoms, it depends how it affects them.

Right. Some people (apparently) simply cannot recognize the onset of narcosis. The first symptom for them is losing the ability to recognize the symptoms. For example, TSandM, based on her post. But, for others, don't you think it helps to recognize the onset of narcosis if you have experienced it before? When you drink alcohol, don't you think prior experience with being buzzed (or drunk) helps you recognize the first signs of getting a buzz? I would say that I am much more sensitive to the first little signs of an alcohol buzz, now that I'm experienced drinker, than I was when I had my very first beer, many years ago.

 

[TSandM]

I would agree with you, Stuart, if there were easily discernible symptoms that accompanied the first signs of cognitive impairment. But as I have written, and others have confirmed, that is not necessarily the case. By the time you feel drunk, you aren't in the first stages of cognitive impairment -- you are, to use the car metaphor, already skidding, and just hoping you won't hit a tree.

I don't feel the least bit different when I am stupid. I'm diving along, looking at the environment, enjoying being there. And then a piece of information shows up -- a navigation point, or in particular something that isn't what it should be -- and instead of seeing it, understanding what it means, and thinking, "Okay, we need to change course or take action as a result of this!", I just look at it and go, "Huh. That's odd . . . " and keep swimming. I feel fine. But I just ignored something important. I'd hate to think how I would deal with a real emergency in that befuddled state.

I don't know how deep I'd have to go to recognize narcosis symptoms. I've been to 130 on air, early in my career. It was in warm, clear water, and I had no duties or responsibilities. I was following an instructor, and I felt fine. Maybe I was fine. I don't know, because I didn't have to cope with anything. But going down there with the instructor didn't teach me anything about my susceptibility to narcosis, because I didn't recognize any impairment. It took years later and being in situations where I routinely had to process information, to get the repeated experiences that have taught me I can't DO that well at depth.

I don't think doing the dive with your instructor is dangerous or reprehensible. I do think you should be cognizant of the gas requirements, because running out of gas is a bad thing. I just don't know how much you will learn from it.

 

[Dr. Lecter]

Considering the forum in which this discussion is taking place, I will refrain from going into too much deep air detail, but suffice to say I'm happy with air for depths up to at least its MOD for those who follow the 1.4 limit. My experiences have been that I'm able to navigate inside wrecks and handle sudden and complex problems like multiple entanglements on a manifold behind my head (no, the entanglement did not occur because of narcosis...the hatch was blocked by an explosion of braided cable) while sufficiently narced to feel a buzzing wet blanket pressing down on my higher brain functions. I have caught myself mentally wandering when it's clear, warm open water and I don't have the tasks and enclosure of a wreck to keep me focused, however. I don't dive caves - if I did, I might reconsider my personal acceptable level of narcotic distraction, much as I've done since switching to CCR.

Having moved to a rebreather I now dive trimix dil with 50-60% helium for pretty much everything, which is mostly driven by wanting much less distraction on CCR than I would tolerate on OC (and partly driven by WOB benefits...though being able to do a three hour dive on $5 worth of helium doesn't hurt). For OC dives where helium was required to bring the bottom pO2 down to what I considered an acceptable level for the dive, I generally planned for an END of roughly 180'-190' because that's where I felt was a good balance for me between narcotic distraction and the demands of the dive/equipment chosen. Everyone else's mileage will likely vary.

 

[stuartv]

I don't feel the least bit different when I am stupid. I'm diving along, looking at the environment, enjoying being there. And then a piece of information shows up -- a navigation point, or in particular something that isn't what it should be -- and instead of seeing it, understanding what it means, and thinking, "Okay, we need to change course or take action as a result of this!", I just look at it and go, "Huh. That's odd . . . " and keep swimming. I feel fine. But I just ignored something important. I'd hate to think how I would deal with a real emergency in that befuddled state.

As I said earlier, I understand that there are some people (like yourself) for whom the first symptom is that they can't recognize other symptoms. Nevertheless, you illustrate my point well. You have already learned what your personal limit is (to the best degree of certainty that one can) and so you use that information to help you plan your dives so that you don't have problems because you exceeded your own personal limitations.

Whether you recognize that you're getting stupid at the time, or whether you realize it after the fact and think "oh, crap! I can't believe I did that!" You have still learned a huge amount about your personal limits. I suspect that many, particularly if they've been limited to 100 feet in depth by a rule or by their instructor's personal limits, are diving to 100 feet on their own now without any such knowledge of how close they are to their own limits.

I don't know what my instructor does with his students on that 3rd, deep, dive. Given the thoughtfulness he's already demonstrated in what he's told me so far, maybe he will have me attempt to perform some mental exercises or something to get an idea of if or how narked I am. I know he would almost certainly be using his rebreather. If his intention is to have me stay down to the NDL and I don't have enough gas, maybe part of the instruction is to share air with me while we're down, to preserve my own air for the ascent. I don't know.

What I do know is that the better I get to know my instructor, the more respect I'm developing for him and the more inclined I am to expect that he has a plan that will work and assure I get out safely. And ensure that I am as ready as I can be to determine my own safe limits and do deep dives without him being with me. Of course, I will still make sure I understand the plan fully and am comfortable with my safety for myself - not just "trust him" and follow him down blindly.

 

[Tony387]

I don't know those details yet. I'm not even signed up for the Deep Diving specialty yet - and probably won't be for a while, as I just got my OW cert.

As far as max depth, it seems like every responsible diver would want to know at what depth they are likely to get narked to the point of impairment. And, yes, I understand that even for a single individual it can vary depending on other factors beyond just mix and depth.

If you don't know your personal limits, then you don't really know what margin safety margin you are diving with. I like to know my limits - and not so that I can dive (or engage in any other activity, for that matter) to that limit. Rather, so that I can set myself a safety margin and know (as best I can) that I am diving with that much safety margin, instead of just picking an arbitrary limit and hoping that I am well away from my actual limit.

It seems to me that if you know your limit tends to be around 120 feet, then you can dive to 100 feet and be a much safer diver than another who has arbitrarily limited themselves to 100 feet and doesn't know that that is their actual personal limit, because they have never dived deeper than that.

As a new diver, developing skills should be your objective, not discovering at what depth the skills you don't possess yet, would be compromised by narcosis.

 

[TSandM]

Just one more comment . . . when I did my AOW and Deep specialties, I was asked to do specific tasks underwater, like doing a math problem. I knew I would be asked to do those things. I did them very quickly and accurately. In my opinion, such exercises tell you essentially nothing about how impaired you are. You need to be shown situations where tunnel vision or lack of attention are the problem, or be given a novel situation to assess and react to. Even then, because you KNOW those things are coming, you are not in the state you would be in if you were simply diving on your own.