Which mixes for trimix are better for 330 feet (100 meters)?

[Robert Thompson]

You need three gases!!!! End of story. You should carry three stages with 1.5 times your expected gas requirements just in case. I know you think that its only a few more feet, but the likelyhood of getting hit from 200' to 330' goes way up. Pad your deco and take a long time getting back to the surface within reasonable cns % points. It's much easier to do an extra hour of deco than 6hours of recompression, or more.
Oh and 5 minutes seriously.

 

[coldsmoke]

This thread is concerning a 330ft. trimix dive.......were would a hypoxic back gas figure into a contingency if all deco gas/s were lost?

Loss of all deco gas in a dive of this magnitude falls under multiple failures. What are the chances that you are going to lose or not be able to access the gas in all three deco bottles.

I am trained only to a basic trimix level, but the general rule as I understand it is you plan your dive so that your deeper gas can cover the lost gas of the next shallower bottle. Ex - On a dive where you have 120', 70' and 20' gas switches, the back gas would get you to the 70' bottle, the 120' bottle would get you to the 20' bottle, and the 70' would need to be able to get you to the surface.

There are only so many failures you can realistically plan for and still dive.

Hunter

 

[coldsmoke]

Backgas deco normally either takes a really long time, and is miserable, or else is not feasible at all, when the backgas is trimix.

Why is deco not feasible on trimix?

Hunter

 

[texdiveguy]

Don't get me lying. I obviously haven't been trained in the uses of hypoxic mixes. There would be concerns of breathing hypoxic mixes above a certain depth as well as the logistical night mare of carrying that much back gas. I could probably think up a plan, but you wouldn't catch me diving it at my current level.

.............

 

[Rick Inman]

There are only so many failures you can realistically plan for and still dive.

We plan for all of them, just not at the same time (unless it's during your class ).

On a dive deeper than 200', if you lost all you deco bottles, and you had to deco on backgas mix, and your buddies somehow got enough backgas down to you for you to complete your deco, they could drop off the tanks to you, go to a movie and dinner, and then come back for you later. But on a three man team, you could easily dine on your buddy's deco leftovers and go to the show together. On a dive where we'd need to work all that out, I hope I'm with divers with a bunch of dives (more than 100).

 

[grazie42]

Now that Tomeck has fleshed out his planned dive, my only reply would be that I wouldn´t do that dive (too much deco for too little dive)...

I appreciate that the risk/reward-ratio is different for Tomeck (and I make no value judgement about it) so if I was to "theoretically" plan this dive I´d dive
-12/70 (because of PO2 and narcosis)
-21/35 (because I want a semi-deep gas for failiure planning and also a gradual decrease in He)
-50 (failiure planning/accelerated deco)
-100 (failiure planning/accelerated deco)

The reasons for those mix choices would be obvious to those with the appropriate training though I appreciate that others may feel that other alternatives are better for them...

 

[sunkmail]

Maybe I'm missing something, but it sounds like Tomeck dives to a depth and then enjoys the sights on the way up.

Not everyone dives off boats all the time. (There are several interesting Deep shore dives in my area) The BT is not all that critical, as you have a lot to look at on the way up.

I agree, that if you're going to be looking at a line for a really long time, 5 min isn't really worth it, but take the line away and replace it with a nice wall, it's not so bad.

 

[Tomeck]

Now that Tomeck has fleshed out his planned dive, my only reply would be that I wouldn´t do that dive (too much deco for too little dive)...

I appreciate that the risk/reward-ratio is different for Tomeck (and I make no value judgement about it) so if I was to "theoretically" plan this dive I´d dive
-12/70 (because of PO2 and narcosis)
-21/35 (because I want a semi-deep gas for failiure planning and also a gradual decrease in He)
-50 (failiure planning/accelerated deco)
-100 (failiure planning/accelerated deco)

The reasons for those mix choices would be obvious to those with the appropriate training though I appreciate that others may feel that other alternatives are better for them...

Which depth you change from 12/70 to 21/35?

I used V-Planer with these mixes 12/70, 21/35, 50% and 100%, it shows that the change from 12/70 to 21/35 is too 'abrupt' with the red line, why? I think the difference between 8m ead and 32m ead is too large?

Desc à 100m (10) Trimix 12/70 10m/min Descente.
Niveau 100m 5:00 (15) Trimix 12/70 1.30 ppO2, 15m ead, 23m end
Rem. à 72m (17) Trimix 12/70 -10m/min Remontée.
Palier à 72m 0:12 (18) Trimix 12/70 0.97 ppO2, 9m ead, 14m end
Palier à 69m 1:00 (19) Trimix 12/70 0.94 ppO2, 8m ead, 13m end
Palier à 66m 2:00 (21) Triox 21/35 1.57 ppO2, 32m ead, 39m end
Palier à 63m 1:00 (22) Triox 21/35 1.51 ppO2, 30m ead, 37m end
Palier à 60m 1:00 (23) Triox 21/35 1.45 ppO2, 29m ead, 35m end
Palier à 57m 1:00 (24) Triox 21/35 1.39 ppO2, 27m ead, 33m end
Palier à 54m 1:00 (25) Triox 21/35 1.32 ppO2, 25m ead, 31m end
Palier à 51m 1:00 (26) Triox 21/35 1.26 ppO2, 24m ead, 29m end
Palier à 48m 1:00 (27) Triox 21/35 1.20 ppO2, 22m ead, 27m end
Palier à 45m 1:00 (28) Triox 21/35 1.14 ppO2, 20m ead, 25m end
Palier à 42m 1:00 (29) Triox 21/35 1.07 ppO2, 19m ead, 23m end
Palier à 39m 1:00 (30) Triox 21/35 1.01 ppO2, 17m ead, 21m end
Palier à 36m 1:00 (31) Triox 21/35 0.95 ppO2, 15m ead, 20m end
Palier à 33m 1:00 (32) Triox 21/35 0.89 ppO2, 14m ead, 18m end
Palier à 30m 1:00 (33) Triox 21/35 0.82 ppO2, 12m ead, 16m end
Palier à 27m 3:00 (36) Triox 21/35 0.76 ppO2, 10m ead, 14m end
Palier à 24m 3:00 (39) Triox 21/35 0.70 ppO2, 9m ead, 12m end
Palier à 21m 3:00 (42) Nitrox 50 1.52 ppO2, 9m ead
Palier à 18m 3:00 (45) Nitrox 50 1.37 ppO2, 7m ead
Palier à 15m 4:00 (49) Nitrox 50 1.22 ppO2, 5m ead
Palier à 12m 6:00 (55) Nitrox 50 1.07 ppO2, 4m ead
Palier à 9m 8:00 (63) Nitrox 50 0.92 ppO2, 2m ead
Palier à 6m 10:00 (73) Oxygen 1.55 ppO2, 0m ead
Palier à 3m 18:00 (91) Oxygen 1.25 ppO2, 0m ead
Surface (91) Oxygen -10m/min Remontée.

 

[Blackwood]

Which depth you change from 12/70 to 21/35?

What's your max deep PO₂?

190 for 1.4, 220 for 1.6.

 

[Robert Thompson]

Sorry Tomeck with the questions your asking you shouldn't be doing deco to begin with????? Certainly not to 330'.

Take a class, get some dives in and work your way down to that depth. You can't learn this on scubaboard. I promise I am not trying to put you down. YOU ARE NOT READY!!!!!!!!! Please trust me.