Deep Diving on Nitrox question

[savsuds]

I have always preferred to stay with a 28 or 29 blend down to 130'. I have never tried 130' on a 32 mix and would therefore be reluctant to do that dive. I however do have well over 70 dives to that depth using air. I sacrifice bottom time at depth, but know how my body will react at depth. That level of comfort makes my dive more relaxing and stress free.

You were wise to voice your desires. Too bad it did not coincide with the dive operator. but, any dive is a good dive.

 

[gfaith]

@NWGratefulDiver. Bob, did you ever see anyone dive sidemount with them? Are DIN valves available? I'll be traveling from now on with SM gear and a DIN-to-yolk converter for those times where I can't get a DIN valve.

I am curious if Aldora allows SM as well. of course, diving your tanks would not apply. A SM diver would have to ascend with everyone else and I am pretty sure they have DIN valves. Maybe Dave will address some of these and the Nitrox 32% in the Devil's Throat.

 

[MXGratefulDiver]

@NWGratefulDiver. Bob, did you ever see anyone dive sidemount with them? Are DIN valves available? I'll be traveling from now on with SM gear and a DIN-to-yolk converter for those times where I can't get a DIN valve.

I was there before I started diving sidemount ... and before sidemount had started making its way out of the caves, actually. But to answer the DIN question, I went with a bunch of GUE-trained folks, and we all brought DIN regs. Nowadays, most places use Thermo Pro or comparable valves with the insert, to accommodate both reg styles.

... Bob (Grateful Diver)

 

[Lorenzoid]

Yes, there was a sidemount diver on our Aldora boat.

 

[Stoo]

Personally, I would have avoided it. 1.6 is great at a resting deco stop, but I would really prefer to avoid swimming around with that pO2. Reduce the O2, and do a little deco if you must, but ox-tox is generally lethal underwater and comes without warning.

 

[uncfnp]

To clarify why I would have done DT on 32 if it was a dive I cared to do.
As with any advanced dive there are multiple factors to consider.

1) My understanding is that it is a long descending swim through that begins around 80 feet and exits anywhere from 125 to 138 (I have seen different numbers given). So the vast majority of the dive, before and after, is well below the 1.6 limit and even the 1.4 PPO2 limit commonly used. So only at the very end of the swimthrough will you be at the higher PPO2 numbers and once you exit there is no barrier to quickly ascending to a "safer" level (78% at 1.6 for 35 minutes) as opposed to the deco dive when PPO2 may be sustained at 1.6 for a prolonged time.

2) This is clear, warm water with no current (drift) or surge to increase the level of exertion.

3) The real risk of unplanned deco, increased if air used, and limited gas availability.

4) Narcosis in a "cave"

5) And my personal history with cutaneous DCS


Edited for my usual typos...

 

[MXGratefulDiver]

Regarding #4 ... there is no detectable difference in narcosis levels between EAN32 and EAN21 ... oxygen is virtually as narcotic as nitrogen. If narcosis is a concern, put some helium in your mix.

... Bob (Grateful Diver)

 

[uncfnp]

Regarding #4 ... there is no detectable difference in narcosis levels between EAN32 and EAN21 ... oxygen is virtually as narcotic as nitrogen. If narcosis is a concern, put some helium in your mix.

... Bob (Grateful Diver)

Agreed. Not a real concern I admit but thought it at least needed to be mentioned since narcosis is often cited at depths beyond 100 and trimix not in the "mix."

 

[k4kafka]

Agreed. Not a real concern I admit but thought it at least needed to be mentioned since narcosis is often cited at depths beyond 100 and trimix not in the "mix."

Forget "Trimix"...this is resort diving in Cozumel, remember.

 

[Kevrumbo]

My favorite dive operation on Cozumel (Aldora) routinely takes divers down into "Devil's Throat" using Nitrox 32. I recently dived this site and hit the first bar of deco on my computer. I would have preferred diving "Devil's Throat" using plain-old fashioned AIR, but in order to the keep everyone on the same profile...we had Nitrox.
Any opinions on this....?

As I recall that site involves 40m at some point. 5*32 is 1.6.

1.6 is a fine ppO2 at a stop, relaxed, on the way up and likely shallower than 40m.

At 40m on a nitrox mix, ie no helium, your gas density will be significant and tending towards reducing the effectiveness of your breathing and especially your ability to get rid of CO2. CO2 tends to exasperate the risk of an O2 hit.

There can be a downcurrent at the exit beyond the ledge & drop-off at 40 meters -a worst case scenario of exertion fighting a downdraft, at a ppO2 of 1.6 or greater past MOD on Nitrox32, and an increasing gas density approaching and exceeding 6 g/L -a critical value in terms of Work of Breathing, CO2 retention, and potential spiraling cycle into Hypercapnia & Ox-Tox risk as you are drawn deeper in depth. (Note: Air or Nitrox32 is approx 1.2 g/L at the surface 1 ATA).

So don't be tempted to look over the ledge into the drop-off. . .