First dive at 40 meters - Newbies recreational

[Storker]

Its was quite unnerving when I started with 300bar cylinders and seeing the pressure drop to around 250bar in not time

That, and the fact that the adiabatic heating of the tank has a more profound effect on pressure when you're in compressibility territory.

When I fill my tanks, I generally overfill by some 10%. The day after, when the tank has cooled down, the pressure is usually down to some 270-280 bar. If you don't top up your tanks or overfill more than I'm comfortable with, you're going to have a short fill.

In the winter, I like to leave my tanks in the car overnight before topping them up on the day of the dive. That way, I don't lose some 20-ish bar just from the tank cooling after I've jumped in.

<anecdote>
I know a couple folks who have been participating in the Bjurälven exploration project. They can have topside temps down to 20-30 below, and the first minutes of their dives they may see negative gas consumption numbers. Just from the tanks heating up from 20-30 below to a couple degrees above.
</anecdote>

 

[Edward3c]

That, and the fact that the adiabatic heating of the tank has a more profound effect on pressure when you're in compressibility territory.

When I fill my tanks, I generally overfill by some 10%. The day after, when the tank has cooled down, the pressure is usually down to some 270-280 bar. If you don't top up your tanks or overfill more than I'm comfortable with, you're going to have a short fill.

In the winter, I like to leave my tanks in the car overnight before topping them up on the day of the dive. That way, I don't lose some 20-ish bar just from the tank cooling after I've jumped in.

<anecdote>
I know a couple folks who have been participating in the Bjurälven exploration project. They can have topside temps down to 20-30 below, and the first minutes of their dives they may see negative gas consumption numbers. Just from the tanks heating up from 20-30 below to a couple degrees above.
</anecdote>

For normal diving I don't worry about not having a 300bar fill, as most of my buddies are on 232bar 12Lt. That said I have one who gets two, sometimes three, dives from his single 232; then I make sure mine is pumped to at least 300bar. Then again, with another buddy (trainee instructor) I use a 10Lt 232 as he'll burn through his 15Lt first.

 

[lowwall]

Speaking as a regular diver, not an instructor or tech diver of any sort, a couple of things stood out to me.

10 minutes after water entry, the DM gives the descend sign. SPG at 180/ 190 bars for everyone

I'm not going to go into detailed discussions about gas usage, 12 liters at 210 bar (with a buddy) is clearly enough for a trip to 40m and back safely in good conditions. However, that's assuming you get to that depth with nearly all your gas. I would never leave for 40m just to look around after 10 minutes at 20m.

You always need to be willing to modify your plan to accommodate the realities of the dive. With 180 bar left, this would have become a 30m max dive for me.

...I am surprised when my computer alerts me that I am approaching 40 meters

This is frightening and should have you second guessing the entire dive if not your entire training.

Never rely on computer alerts for vital information, you'll be surprised how often you miss them. You should know your approximate depth at all times, and you should be checking religiously when playing with the limits of depth, NDL time, and gas remaining.

No Nitrogen narcosis

Yes there was. It's physiologically impossible for there not to have been. Nitrogen narcosis for most people doesn't equal euphoria, much more common is a narrowing of perception and a general decrease in mental skills.

40 is the saint barrier. The ultimate psychological goal.

This is just silly. 40 is just a number. Look at in in my local number to see how silly this is: 131.234 feet.

There might be a legitimate reason to go there, but fixating on the number itself is irrational. I am using the term "fixating" deliberately, because of the decision to go there instead of something more shallow after the overly long initial descent.

computers start beeping: 1 minutes to NDL. WTF!

Again, the only WTF here is why you weren't monitoring your NDL time at this depth. You are quite lucky that narcosis didn't interfere with your ability to understand that the alarm meant you needed to look at your watch.

I'm not going to address the ascent, it was more or less reasonable given the conditions you encountered. But IMO, you really need to spend time (in shallower water) practicing estimating and confirming your current depth, NDL and gas remaining. And you need to realize the danger of target fixation. These are rec dives, you need to be willing to modify your plan (or fall back on a secondary plan) if conditions aren't exactly what you foresaw.

 

[Dody]

Sorry t

Speaking as a regular diver, not an instructor or tech diver of any sort, a couple of things stood out to me.

10 minutes after water entry, the DM gives the descend sign. SPG at 180/ 190 bars for everyone

I'm not going to go into detailed discussions about gas usage, 12 liters at 210 bar (with a buddy) is clearly enough for a trip to 40m and back safely in good conditions. However, that's assuming you get to that depth with nearly all your gas. I would never leave for 40m just to look around after 10 minutes at 20m.

You always need to be willing to modify your plan to accommodate the realities of the dive. With 180 bar left, this would have become a 30m max dive for me.

...I am surprised when my computer alerts me that I am approaching 40 meters

This is frightening and should have you second guessing the entire dive if not your entire training.

Never rely on computer alerts for vital information, you'll be surprised how often you miss them. You should know your approximate depth at all times, and you should be checking religiously when playing with the limits of depth, NDL time, and gas remaining.

No Nitrogen narcosis

Yes there was. It's physiologically impossible for there not to have been. Nitrogen narcosis for most people doesn't equal euphoria, much more common is a narrowing of perception and a general decrease in mental skills.

40 is the saint barrier. The ultimate psychological goal.

This is just silly. 40 is just a number. Look at in in my local number to see how silly this is: 131.234 feet.

There might be a legitimate reason to go there, but fixating on the number itself is irrational. I am using the term "fixating" deliberately, because of the decision to go there instead of something more shallow after the overly long initial descent.

computers start beeping: 1 minutes to NDL. WTF!

Again, the only WTF here is why you weren't monitoring your NDL time at this depth. You are quite lucky that narcosis didn't interfere with your ability to understand that the alarm meant you needed to look at your watch.

I'm not going to address the ascent, it was more or less reasonable given the conditions you encountered. But IMO, you really need to spend time (in shallower water) practicing estimating and confirming your current depth, NDL and gas remaining. And you need to realize the danger of target fixation. These are rec dives, you need to be willing to modify your plan (or fall back on a secondary plan) if conditions aren't exactly what you foresaw.

Sorry to say but I think that we disagree on almost ever everything. First, your experience of air consumption is what it is: personal. Don't make a rule out of it for others.
When I wrote that I am surprised that my computer alerts me, it is a figure of speech. I should have said "indicate". I was watching my computer and my SPG. I was surprised that it happened so fast and without other "signs". 40 m felt no different that 20 and it seemed to me that it took less than a minute to get there while we were on a slope. Again, we are talking about sensations, it is not a the precise report of a dive by the second.
For me, diving should also be fun. And going to the limit as per safety and training regulations are concerned is fun. Lots of people don't share the same feeling of fun or challenge but on this point, really, saying that it is silly to desire to go to 40m on a deep training dive that stipulates that you will go to 40, I don't envy your sense of perspective. I don't dive to be the Diving World Champion but I set myself some objectives both technical and fun.
For NDL, as I said, we had 4 minutes when we reached 40m. I checked. The next thing I know, we only have one. Has my computer accelerated or have 2 minutes elapsed without me realizing it? Both can be possible. Was narc involved? Maybe, maybe not. Once again, the the specialized physicians admit that they are not themselves knowledgeable enough to edict theorems. The fact is that 10 seconds afterwards, we were ascending. OK. I could have been more careful. That was my first dive really looking at NDL and I learnt my lesson.

 

[Storker]

Was narc involved? Maybe, maybe not.

Not "maybe". Definitely not "maybe not". Everbody, including those who claim that they are never narked, is narked at 40m. At 40m your brain is slow as molasses, the only individual factor is how cold the molasses is. And whether you've trained yourself to dive narked, in which case you may be able to solve routine issues, but probably will be thoroughly screwed if you have to handle something out of the ordinary.

 

[yle]

For me, diving should also be fun. And going to the limit as per safety and training regulations are concerned is fun. Lots of people don't share the same feeling of fun or challenge....

Oh boy.

The reason that few people share your "feeling of fun" is that many of the people that did feel the same as you are no longer with us. When you gain experience, you will begin to understand that "fun" and "going to the limit" are incompatible goals.

I hope you carefully consider the feedback you've received on this thread.

 

[yle]

I don't dive to be the Diving World Champion

There is no "diving world champion". Scuba diving is not a competition. Understanding this is the best thing you can do for your longevity.

Has my computer accelerated or have 2 minutes elapsed without me realizing it? Both can be possible.

No. Both are not possible. Your computer did not "accelerate", and suggesting that this is a possibility is a huge concern. The two minutes elapsed without you realizing it for one simple reason. See the next response below.

Was narc involved? Maybe, maybe not.

Definitely. See the response above.

That was my first dive really looking at NDL and I learnt my lesson.

It doesn't seem that you have learned any lesson, considering how defensive you are being toward some of the feedback on this thread from people that really want to help you. We are all hoping that you do eventually learn, however, and are able to continue diving safely for years to come.

 

[Storker]

The reason that few people share your "feeling of fun" is that many of the people that did feel the same as you are no longer with us. When you gain experience, you will begin to understand that "fun" and "going to the limit" are incompatible goals.

Maybe it's because I'm an UW photog, but I see no reason at all to go deep. Unless there's something down there that I'd like to see. The shallower I am, the more ambient light there is to balance my strobes. If I could spend a whole dive at 5m, I'd do it. My problem, it usually doesn't clear up before I'm below some 20m. So, most of my dives are in the 20-30m range. Not because I've got this number thing, only because that's where it's nice to be.

 

[KenGordon]

18 m/ min is not no gas planning. This is a freaking emergency.
I meant 50l/ min per person as I divided 150 bars by 2.
This spreadsheet helps.

Being out of gas is not an emergency if you have a plan that can handle it. If you need to ascend at 18m/minute then it will turn into an emergency because you will actually be short on gas or have no idea whether you have maintained 18m/minute.

Honestly you will not manage 18m/minute. It is hard enough doing 10m/minute. You should try doing going from 25 to 10 or 15 as fast as you dare and see how that turns out.

 

[Dody]

Not "maybe". Definitely not "maybe not". Everbody, including those who claim that they are never narked, is narked at 40m. At 40m your brain is slow as molasses, the only individual factor is how cold the molasses is. And whether you've trained yourself to dive narked, in which case you may be able to solve routine issues, but probably will be thoroughly screwed if you have to handle something out of the ordinary.

Once again, this is wrong. If you read all the medical litterature on the subject, there is a relative consensus that everybody is affected at 60/ 70. Not 30 or 40 while some can be affected as shallow as 20 meters.

Oh boy.

The reason that few people share your "feeling of fun" is that many of the people that did feel the same as you are no longer with us. When you gain experience, you will begin to understand that "fun" and "going to the limit" are incompatible goals.

I hope you carefully consider the feedback you've received on this thread.

I have taken most of the comments of this thread into consideration. However, I totally disagree with your latest post. Fun does not mean stupid and brainless. And all my choices and decisions result from thinking not impulse. If you believe that you can’t do a risky activity without enjoying it and without having fun, then we just don’t see life through the same eyes. When I was driving at over 300 km/h on a track, it was very risky but I can tell you that all the pilots had fun. And those who died are not the one who the more fun in the track. Really, I find it ridiculous.