Deep Diving Specialty Vs Mid Depth Cold and Low Vis

[Remy B.]

I have a question, I just finished me Deep Diving Course, but it actually was not deep, 1st day dive "1" at 27m 3 to 12' visibility for 38min, dive "2" same depth and conditions at 18*C but for 45min, 2nd Day dive 24m less than 2' visibility, with 17*C for 38min all dives with 7mm wetsuit and hood.

I always hear that there is a equivalence between diving at 40m in clear water and 20m in cold and low visibility, but what suppose one to feel different ?? I don't believe this can be taken as a rule of thumb.

I know the course is about learning how to plan your dive and gas, but circumstances at my point of view were not a challenge or it suppose not to be like this ??

 

[knotical]

I’ll assume PADI, although your profile says PDIC. Since you only mention three dives, I would further assume one of the four required dives for the PADI deep specialty was from your AOW course.
PADI requires the four deep dives be between 18 and 40 meters.
They recommend, but do not require, that one of the dives be between 30 and 40 meters.
So, from that aspect, it appears what your instructor did would be within PADI standards, don't know about PDIC.
caveat: I don’t have the latest Instructor Guide, but I don’t think there has been a change to the above.

There is some evidence that from a DCS perspective, colder dives are more challenging.
There is some evidence that from a narcosis perspective, lower visibility can be more psychologically challenging.
I don't know of any rule of thumb about how much adjustment one would make for cold/vis/depth.

As far as a challenge to you - did you experience narcosis? When I conducted the course, that was one of my primary goals.- that the student experienced narcosis while under instructor supervision. Did your instructor have you do any narcosis-testing puzzles? How did you do?

 

[Subcooled]

I have a question, I just finished me Deep Diving Course, but it actually was not deep

It's not the depth, it's the equipment and procedures, darling.
You can dive deep tomorrow now.
Be carefull. It feels different.

I always hear that there is a equivalence between diving at 40m in clear water and 20m in cold and low visibility

I have dived to 40m/120ft in a +32C pool (The Y-4o Deep Joy) and that was nice and recreational, while a dive to six feet in a zero viz river among bicycles and broken glass was... very serious. So yes, it's not just about depth. Depth of course infers some decompression risk and increased gas consumption and lesser safety margins, but loss of visibility causes risks too. If you are afraid of dark and cold then those could actually increase the risk significantly (remember: panic kills). Cold water reduces blood flow in the extremities... but not immediately. This means than nitrogen can get in at first but not out later. Staged decompression should be conservative if you feel cold, but then again don't get serious hypothermia. Getting cold or hungry or not seeing or needing to pee in drysuit may also confuse one - as does nitrogen.

but what suppose one to feel different ??

On air:
You can detect the presence of narcosis as a cetain slowness at 30m/100ft if unexpected things happen.
At 40m/120ft narcosis is quite noticeable. You feel it.
At 48m/157ft your fingers get slightly clumsy and stiff. It is still easily manageable. Logic fails, though. We did tests in a dry chamber. It was sad seeing a mathematician fail in elementary school maths. Perhaps you are superior?

circumstances at my point of view were not a challenge

You will have plenty of chances to push YOUR envelope even so slightly. Just a little bit more. Enjoy it.
A small challenge = manageable when the **** hits the fan.
A big challenge = no worries anymore when the **** hits the fan.

 

[RJP]

I’ll assume PADI...

I think it was an SSI course, based on the instructor the OP mentioned in another thread.

---------- Post added September 7th, 2015 at 04:59 PM ----------

I have a question, I just finished me Deep Diving Course, but it actually was not deep, 1st day dive "1" at 27m 3 to 12' visibility for 38min, dive "2" same depth and conditions at 18*C but for 45min, 2nd Day dive 24m less than 2' visibility, with 17*C for 38min all dives with 7mm wetsuit and hood.

I'm assuming you didn't do these dives in Curacao :shocked2:

I always hear that there is a equivalence between diving at 40m in clear water and 20m in cold and low visibility, but what suppose one to feel different ?? I don't believe this can be taken as a rule of thumb.

Where do you "always hear" this? Certainly cold water and low vis is an extra level of challenge, and can potential for narcosis/confusion, so it's a good idea to reduce depth a bit. But certainly not by HALF. Maybe from 40m to 30m

I know the course is about learning how to plan your dive and gas, but circumstances at my point of view were not a challenge or it suppose not to be like this ??

Yup - that's what you're supposed to learn. It's also valuable for divers who haven't been "deep" before to experience things like increased gas consumption, color loss, buoyancy considerations, and even a little light narcosis. 27m is typically deep enough for all of these things for divers used to 18m or so... though narcosis being diver-dependent. However, there's no real reason for the dives to specifically "present a challenge" per se. I wouldn't take a typical recreational Deep Diver class deeper than ~30m, unless they already had experience diving in that range. (Even then, I'm not sure.)

 

[TMHeimer]

I think these Deep courses vary a lot. Mine was May 26/27 in NS in 33F (+1C) water diving wet. Did go to 120' twice, 130' (40m) once. We did the puzzle test and I didn't sense any narcosis, though I've read some always exists at this depth. My buddy (an instructor) asked what I'd like to do for the 4th dive. I said whatever gets me out of the water quickest..... I could see the boat during my rather frigid ascent from a depth of about 70' (very unusual for NS). Lots of nice shells though.

 

[Rhone Man]

Narcosis is imperfectly understood, but anecdotally there is an awful lot of evidence that cold and dark makes it worse. It may just be that stress makes it worse, and cold and dark exacerbates that.

It is also fair to say that narcosis affects different people to different degrees (also not really understood, but indisputable). Some people can remain largely functional to astonishing depths on air. Other people are going fuzzy before they hit 100 feet / 30 meters. Best to learn which you are in a safe and supervised environment.

 

[eelnoraa]

17C is cold??? That is almost 65F, not cold by stretch, maybe another 10C lower. But 27m (90ft)isn't shallow for recreation dive IMO. Low viz is always challenge. But I don't think there is equivalent for depth. gas planning for a 40m dive is significantly more strict than 27m.

 

[Yoyodyne-88]

No hard rule will cover it. 42ºF and black as night, versus 80ºF and sunny clear water, but both at 130 feet... No comparision. In one case narcosis may manifest as fear, or clumsiness. In the other as bliss and lack of caution.

But in all cases I will suggest that the hazard to consider is that at depth things will happen much much faster than you think they are happening. Especially as you are enjoying "Martini's Law."

Air consumption/depletion, decompression obligation, etc., can bite you in the butt before you know it. Plan your dive, and dive your plan, with a very close constant eye on the gauges/screens.

 

[Bob DBF]

No hard rule will cover it. 42ºF and black as night, versus 80ºF and sunny clear water, but both at 130 feet... No comparision. In one case narcosis may manifest as fear, or clumsiness. In the other as bliss and lack of caution.

And you won't know which it is until it happens.


I can understand not wanting to push the depth while training a student, however I do not understand giving a deep cert for dives you are certified to do with a AOW cert. You may have learned theory and procedures but have yet to experience your personal reaction to a deep dive so have someone along with as much experience as possible when you do, because you may need him.

There is no equilivence between cold and depth or visibility and depth, each presents its own chalanges. Try 2' viz (with light), 49 degrees F (wetsuit) at 120' and get back to me.

As for narcosis, the puzzle is keeping track of gas, depth, and time to surface, even though you have a fuzzy idea of what you are doing. Worse case, you space out all of it. Usually that happens deeper, but if you loose track of depth, you could be deeper.

I'm not trying to be overly melodramatic, may be a little, but diving deep on air is not a trivial matter. With narcosis you may not notice it until you have do something important and are too mentally sluggish to accomplish it quickly enough. Or say, look at your SPG and take forever to read it and finally understand that you should have surfaced 500# ago.


Whenever I have not done a deep dive (>100') for several months, I do a number of work up dives before I hit 130' or more. I need to know that the procedures I have made to work for me over the years still work, and the depth is affecting the way I remember.


Bob
--------------------
I may be old, but I'm not dead yet.

 

[Germie]

Narcoses is strange, I never feeled it when I was a sportsdiver. Or better: I thought I never had it. But when I started trimixdiving I knew I had had it.

There is a big difference in narcoses between 30m and 40m, even if the water is cold or warm or dark. At 30m most people don't feel anything, not in cold water, not in dark waters, not in warm waters and clear waters. But at 40m most divers experience narcoses. Maybe not by calculation 5+6, but by checking the pressure gauge and show how much gas is left, or by the reaction time of signing OK.

I understand that an instructor does not want any problems under water and stays shallower than 30m, but the most important question for you as student is now: are you ready to go to 40m? Do you feel ready? If not, then I would discuss it and ask if a little bit deeper than 30m dive is possible to make you feel more comfortable. The gap from 30m to 40m can be really big.