Intro to recreational deep diving

[HateCheese]

After reading your posts, I'd say you are asking the right questions. If the sand is at 120, a 1.3 PO2 is definitely conservative from my perspective. Only think I'd ask is what tank were you using on your dives to 100ft? Look thru your log book to examine dive times and gas useage. Disregard other posters who say 120 cu ft isn't enough because some might get 2 dives off of a 120cu ft tank and others may burn thru it well coming close to their NDL, i.e. gas useage is specific only to you.

Narcosis will occur to some degree at 120. My experience is that it is dive by dive. Since this is 20ft deeper than your previous deepest dive, make sure to not 'dive bomb' to the bottom - use the time in the slower descent of the last 30-40ft to evaluate yourself. Slowing your decent at those depths essentially addresses your question about bouyancy - adjust to control your descent at the rate you are comfortable with.

Other things to think about - Don't add anything else new to this dive. 20ft deeper is enough to think about without anything else thrown into the mix. It won't hurt your piece of mind to add a little time to your safety stop. I remember doing this (and still sometimes do this) when I first started regularily diving past 100ft. Another piece of mind - pad your NDL more than normal, if you normally turn a dive with your regular buddy at 3 min remaining, turn this one at 5 or 6 etc. Lastly, check your gauges often. Expect that you will burn thru your gas faster, think about it beforehand, and it won't be a surprise.

Have fun

 

[scubadiver888]

I hope the smiley face means you don't really mean this . . . Because if somebody kicks off your mask at depth, you're going to HAVE to be able to put it back on!

I'm kind of serious. With a hood and 5mm gloves on, I can get the mask on my head but getting the skirt under the hood and my hair out of the skirt would be a big challenge.

I think if I lost my mask I could get it back on well enough to clear it but it would leak enough that I'd call the dive after that.

The steel tank and wetsuit thing has to do with the very large loss of buoyancy that you have, when you take thick neoprene to depth. You can lose up to 20 lbs of lift from a 7 mil suit at 100 feet -- if you're diving a steel 130, say, and you're near the beginning of the dive, you can be ten pounds negative from gas as well. If you lose all lift from your BC at that point, you are 30 lbs negative that you have to be able to swim up. An aluminum tank will simply ensure that you are carrying more ditchable weight, but in a single tank, you're likely to be carrying ditchable weight, anyway (steel OR aluminum). In steel DOUBLES, you may well not be carrying any extra weight, and then you're on the bottom, thirty or more pounds negative, in a world of hurt.

Not sure if I follow this. I think you are saying *IF* you are overweight with AL80 you can always ditch some weight but if you are overweight with steel doubles you might not have enough lift and no weight to ditch. Right?

It's a good exercise to try over a benign bottom, to dump your BC and see if you can swim your rig upward easily. (You have to do it fairly deep, if you're doing it in a wetsuit, to make the test useful.)

Interesting. I think I'll try this next time I'm diving here. Unfortunately, will not be until May or June.

 

[Sas]

Sounds like you will be doing some diving off the coast of NC. Some great wrecks out there. I think you'll do just fine at 120, especially if you have several dives to the 100 ft range and have had no problems. Chances are you'll have a instructor or DM with you since this will be your first dive to 120. Certainly a good idea. I wouldn't worry too much about narcosis if you haven't felt it at 100 ft. I'm the same way. Of course people will tell you that you are narced and don't know it. But if you have done fine at 100 ft., 120 won't be a drastic change for you.

I noticed a difference in narcosis between 100 and 110ft, for example... Also susceptibility to narcosis varies between people, and in the same person on different days.

I have told people they are narced and they don't know it. That is because it is true. One buddy ran out of air for one thing, which followed some of the strangest behaviour I have seen underwater. Behaviour that disappeared when we started our ascent.

 

[BDSC]

I noticed a difference in narcosis between 100 and 110ft, for example... Also susceptibility to narcosis varies between people, and in the same person on different days.

I have told people they are narced and they don't know it. That is because it is true. One buddy ran out of air for one thing, which followed some of the strangest behaviour I have seen underwater. Behaviour that disappeared when we started our ascent.

Like you said, it varies between people. I feel absolutely no difference between 100 and 120 ft. But that's me. Perhaps when the OP does his dives to 120 ft. he'll get back with us and tell us how he was or was not affected and if he felt any difference with the extra 20 ft. in depth.

 

[Sas]

Like you said, it varies between people. I feel absolutely no difference between 100 and 120 ft. But that's me. Perhaps when the OP does his dives to 120 ft. he'll get back with us and tell us how he was or was not affected and if he felt any difference with the extra 20 ft. in depth.

Yep they might be fine, they might not. That is why I refrained from commenting that they would feel either way. Because you and I have no idea. I think it is best as a new diver to be fairly careful and watchful for signs of narcosis rather than to treat it as something unlikely to occur, in case you tend to be susceptible. Hopefully not! So as it varies so much, I don't particularly think the OP coming back and saying on one dive they didn't feel a difference between 100' and 120' is useful to make any generalisations about narcosis.

 

[BDSC]

Yep they might be fine, they might not. That is why I refrained from commenting that they would feel either way. Because you and I have no idea. I think it is best as a new diver to be fairly careful and watchful for signs of narcosis rather than to treat it as something unlikely to occur, in case you tend to be susceptible. Hopefully not! So as it varies so much, I don't particularly think the OP coming back and saying on one dive they didn't feel a difference between 100' and 120' is useful to make any generalisations about narcosis.

It wouldn't be useful in making generalizations as a whole in talking about narcosis but I would be interested in finding out how he is affected which is what this thread is really all about. While I certainly have no proof that he won't be affected at 120, I have a pretty good idea that the effect will be so minimal he won't notice based on what he has told us so far.

 

[Web Monkey]

But, I'm carrying about 9# of ditchable weight (from the default values with Light = 0 and Integrated = 0). So, worst case, I have to swim 8# off the bottom. By the time I reach 3m, I should be neutral again.

Maintaining more than 8 pounds of thrust, continuously for several minutes is a huge effort and will also send your SAC rate thought the roof.

If you have a BC failure, and need to swim it up from the bottom (if there is a bottom) it's also possible that you'll also be OOA at some point during your ascent due to the increased effort and air consumption.

Although I've never measured it, i'm also not certain that an average diver can actually maintain 8 Lbs (more actually, since you want to move) of thrust over an extended period.

And that assumes a 100% failure of the wing. It is possible to imagine all kinds of failure mechanisms but some are pretty unlikely.

OK: Torn inflator hose (the big flexible one), broken or cracked elbow, elbow pulled out of BC and hole is damaged, failed or missing elbow gasket, torn or punctured bladder, broken inflator (valve assembly), BC seam failure. Lots of others I can't think of right now.

Before you say "these are all really unlikely", I'd like to mention that I had #1 on the list on my #7 OW dive ever, on a wall dive.

Nobody is saying "if you go over 100', you'll die" (well maybe some are). All we're saying is that deeper divers require more thought, more planning, more training and maybe different equipment.

Just as an example, what happens if your buddy gets caught in some discarded mono-filament or steel leader and now you're 10 minutes over the NDL and have a deco stop. You've been working harder and are almost out of gas, and your buddy who didn't have enough to handle his own deco stop certainly doesn't have enough to handle yours.

When you start working closer to the edge, little problems can easily turn into major disasters if you didn't plan for them before hitting the water.

If you're thinking about wandering around near the edge of the no-deco limit, I'd suggest taking a deco class where you'll learn about all the things you need to be aware of and how to plan for and handle them.

Lots of people do 120' dives every day with single tanks and live to tell the tale, however it's only because nothing bad happened. You'll be much safer if you know that you and your buddy can handle almost anything that's likely to happen.

Terry

 

[ItsBruce]

You have asked the right questions. You should ask those questions for every challenging dive. However, if you ask them of anyone but yourself, you are probably not ready to do the dive.

As to narcosis, at 100 feet, you will most likely be narced. However, that does not mean it is a "black" narcosis like some have described or a "falling down drunk" narcosis.

 

[Sas]

It wouldn't be useful in making generalizations as a whole in talking about narcosis but I would be interested in finding out how he is affected which is what this thread is really all about. While I certainly have no proof that he won't be affected at 120, I have a pretty good idea that the effect will be so minimal he won't notice based on what he has told us so far.

Hopefully narcosis won't be an issue for the OP. Yes I agree one shouldn't make generalisations about narcosis at all. I.e. if someone where to say they don't get narcosis at all and therefore the whole concept is overblown. That would be a generalisation that is not useful I believe.

I think the thing with narcosis though, is that many people do not realise they are narced, until something goes very wrong. And they have to try and figure out a solution whilst impaired. Narcosis is a spectrum of symptoms, some serious, some not so.

 

[String]

Im worried by the admission on here that someone cant refit and seal their mask with gloves on! If you cant do that you should NOT be diving with those gloves on. Its a basic and absolutely essential skill.