deco mix & travel gas for hypoxic dives; thoughts

[LiteHedded]

I'm not using travel mixes for mildly hypoxic gases like 15/55.

For even deeper dives (12/65 or less that I'm not doing around her cause its too damn cold) I would almost for sure have a 3rd deco gas along which I would use before EAN50 if it was absolutely required. But even 12/65 I'd probably just deal with the surface on the surface breathing air, then pop the reg in and drop. We don't screw around at ~8ft, we hit the trigger and go down down.



On SCR with a ~20% ppO2 drop = something like 8/70.

yea he was on an rb80. they go in on open circuit now.

 

[Kern]

I'm not using travel mixes for mildly hypoxic gases like 15/55.

For even deeper dives (12/65 or less that I'm not doing around her cause its too damn cold) I would almost for sure have a 3rd deco gas along which I would use before EAN50 if it was absolutely required. But even 12/65 I'd probably just deal with the surface on the surface breathing air, then pop the reg in and drop. We don't screw around at ~8ft, we hit the trigger and go down down.

We don't use DPV's & there's usually a bit too much chop & current, so a bit of effort in reaching the down line & then hand over hand on the way down, while flapping in the breeze for me to feel comfortable breathing 12% or 15% at the start of the dive. I also prefer to be below the surface current to make the change from 21/35 to BG. Some of that is probably psychological though, for some reason I always feel more relaxed once i'm under than I do at the surface, even in perfect conditions.

For the few sub 80mt dive I'v done I used 21/35, EAN50 & 100% O₂ for deco. I'v been thinking about changing the EAN50 intermediate mix to something with a bit of He, which is why I was interested in what others do. I'm just as interested in what others are using for deco between 55mt & 75mt. I'm actually more interested in why they're using what they do, than just a list of what they use.

 

[liuk3]

With a scooter, we hit 240 fsw in about 2 minutes. No travel gas needed. Even without a scooter, I've been just dropping like a rock in the ocean and not using a travel gas.

 

[rjack321]

We don't use DPV's & there's usually a bit too much chop & current, so a bit of effort in reaching the down line & then hand over hand on the way down, while flapping in the breeze for me to feel comfortable breathing 12% or 15% at the start of the dive. I also prefer to be below the surface current to make the change from 21/35 to BG. Some of that is probably psychological though, for some reason I always feel more relaxed once i'm under than I do at the surface, even in perfect conditions.

For the few sub 80mt dive I'v done I used 21/35, EAN50 & 100% O₂ for deco. I'v been thinking about changing the EAN50 intermediate mix to something with a bit of He, which is why I was interested in what others do. I'm just as interested in what others are using for deco between 55mt & 75mt. I'm actually more interested in why they're using what they do, than just a list of what they use.

55m (180') = 18/45, 50% and O2
75m (246') = 15/55, 50% and O2 and sometimes 35/25 but mostly just a bottom stage of 15/55. I would not bring 21/35 for a 75m dive.

Basically if there is <13mins or less between the bottom and the first deco gas I'm fine with that. 15+ mins of ascent time I add another (deeper) deco gas (at whatever deep stop ascent rate you desire - no need to get into that here). The rock bottom for 15+mins is just rediculous. Adding a deeper gas for only a 220ft dive (eg 35/25) doesn't really do much as far as deco goes it just reduces the rock bottom YMMV.

>75m I'm not doing, its too damn cold around here. The CCR guys are breathing warmer gas and this is pretty much seem to be the CCR-OC breakpoint. There are only a couple guys around here doing >75m on OC.

I would not do a 3 bottle dive in current without a scooter (regardless of mix). The granny line to pull yourself to the anchor line in any kind of current is silly 1990s stuff. With any kind of water movement at all, scooters become required equipment once you add the 3rd bottle IMHO whether its a deco gas or bottom stage doesn't matter much.

 

[Ste Wart]

Was running through my old plans for some of the deeper stuff; sad to note I haven't had a TMX dive in over a year

The last big dive I had was a 101m, the mixes were as follows:
Back gas: 12/54
Travel: 35
Deco:20/30,35 & 80

Basically. I head down on the the 35 to approx 32m. I figure in a minute '****-around' time on Decoplanner, so I have to switch and re-stow lose hoses then head to the bottom.
Coming I'll hit a stop around 75 still on the back gas, the next stop (a deep stop) on the 20/30 all the way up until I can switch to the 35% and then the 80%
My buddy took 100% as well as an 80% for piece of mind and we had a 50% on stand by for surface support.
A nice slick dive. Yes I guess we could have cut some time using a 50% as the travel gas instead, but the 35% worked fine.

 

[Michael Kazma]

You use 21% at 100m????????????? That is one hell of a PO2!

 

[Rhone Man]

You use 21% at 100m????????????? That is one hell of a PO2!

I am glad someone else made that comment - looked mind blowing to me, but no one else had commented on it... 2.31 ATA? Even at 70m it would be 1.68 ATA.

 

[Ste Wart]

You use 21% at 100m????????????? That is one hell of a PO2!

12%

Where did you get 21% from?

 

[Rhone Man]

12%

Where did you get 21% from?

I think Michael was referring to the OP's post about using 21/35 for dives in the 70-100 meter range (I know I was):

Deco gases; recently I thought I'd look around & see what others are doing for deco gases in the 70mt - 100mt range. I'v been using 21/35 & either 50% or 100% depending on availability & actual depth. I'v been thinking about using 30/30 & 100% for the deeper dives in this range. The IART manual I have access to, requires 32% & 80% for training dives to 90mt. For various reasons, IBCD foremost, I didn't like the sound of that very much. What do you use & why?

 

[rjack321]

I think Michael was referring to the OP's post about using 21/35 for dives in the 70-100 meter range (I know I was):

Its used as a 190ft deco gas.