triox vs. trimix?

[big_si]

Originally Posted by Clare Gledhill

It was designed for florida caves which rarely go below 30 metres but pump with massive flow which make working very hard. the additional helium makes it easier to stay alert and cope with the complexities of the dive.

Ah! That makes sense. I guess if working hard the greater ease of breathing might help too?

Cheers Claire! Not something I've heard of before. Interesting!

[Brian of Aquanauts]

Originally Posted by big_si

What sort of situation would it be used in?

Not stirring, just curious on the reason for the deviation.

Any dive with a high task loading in 30m. The mixture used within GUE is 30/30.

For instance if I was running a survey of a wreck in a strong current (eg a river mouth) in 30m of water I would use 30/30 in order to keep a very clear head and enable a very easy breath compared to nitrox which becomes quite thick.

There are other DIR (non GUE) divers that advocate a 25/25 mix in up to 45m. But as you say the savings are minimal compared with 21/35.

[weazelz]

hyperoxic trimix - got it, thanks I do rather like the idea of 25/25

[nickb]

Originally Posted by weazelz

hyperoxic trimix - got it, thanks I do rather like the idea of 25/25

25/25 is great for 45m if you're happy with a 30m(ish) END

But as Brian says, there ain't much in it: 3 or 4 minutes less deco and it's about £7-10 cheaper.

[weazelz]

Originally Posted by Brian of Aquanauts

There are other DIR (non GUE) divers that advocate a 25/25 mix in up to 45m. But as you say the savings are minimal compared with 21/35.

I'll caveat this by saying that I don't yet have a trimix cert (although I have a course booked for later this year), but 21/35 looks pretty different from a lost single deco-gas planning point of view. for 30 mins @45m:

21/35:
Dec to 45m (3) Triox 21/35 15m/min descent.
Level 45m 27:00 (30) Triox 21/35 1.15 ppO2, 21m ead, 26m end
Asc to 27m (31) Triox 21/35 -10m/min ascent.
Stop at 27m 0:12 (32) Triox 21/35 0.77 ppO2, 11m ead, 14m end
Stop at 24m 1:00 (33) Triox 21/35 0.71 ppO2, 9m ead, 12m end
Stop at 21m 2:00 (35) Triox 21/35 0.65 ppO2, 7m ead, 10m end
Stop at 18m 3:00 (38) Triox 21/35 0.59 ppO2, 6m ead, 8m end
Stop at 15m 4:00 (42) Triox 21/35 0.52 ppO2, 4m ead, 6m end
Stop at 12m 5:00 (47) Triox 21/35 0.46 ppO2, 2m ead, 4m end
Stop at 9m 9:00 (56) Triox 21/35 0.40 ppO2, 1m ead, 2m end
Stop at 6m 58:00 (114) Triox 21/35 0.34 ppO2, 0m ead, 0m end
Surface (117) Triox 21/35 -2m/min ascent.
Off gassing starts at 32.9m

5280.8 ltr Triox 21/35
5280.8 ltr TOTAL

25/25:
Dec to 45m (3) Triox 25/25 15m/min descent.
Level 45m 27:00 (30) Triox 25/25 1.37 ppO2, 25m ead, 31m end
Asc to 24m (32) Triox 25/25 -10m/min ascent.
Stop at 24m 0:54 (33) Triox 25/25 0.85 ppO2, 11m ead, 15m end
Stop at 21m 1:00 (34) Triox 25/25 0.77 ppO2, 10m ead, 13m end
Stop at 18m 1:00 (35) Triox 25/25 0.70 ppO2, 8m ead, 11m end
Stop at 15m 3:00 (38) Triox 25/25 0.62 ppO2, 6m ead, 9m end
Stop at 12m 5:00 (43) Triox 25/25 0.55 ppO2, 4m ead, 6m end
Stop at 9m 6:00 (49) Triox 25/25 0.47 ppO2, 2m ead, 4m end
Stop at 6m 39:00 (88) Triox 25/25 0.40 ppO2, 0m ead, 2m end
Surface (91) Triox 25/25 -2m/min ascent.

Off gassing starts at 30.4m

4583.0 ltr Triox 25/25
4583 ltr TOTAL

I do appreciate that this may not be applicable to GUE'ers, but as a side-by-side comparison of the gases without agency considerations it is possibly a bit disingenuous to say that the savings are minimal

[Brian of Aquanauts]

Firstly if I'm diving to that depth I'm using a deco bottle of 50%. I have a team around me and i wouldn't really want a narcotic depth of over 30m.

so at 45m 25/25 gives me an END of 31.25m and 21/35 an END 25.75m this alone would make me pick the higher helium %.

Now lets look at the differences in RT for 30 mins at 45m using Bulhmann with GF Low 30% and GH High 85%.

21/35 total RT - 63 mins
Depth Time O2
45 30 21
21 1 50
18 1 50
15 2 50
12 2 50
9 4 50
6 20 50
0

25/25 total RT - 58 mins
Depth Time O2
45 30 25
21 1 50
15 1 50
12 2 50
9 3 50
6 18 50
0

These figures are straight from decoplanner and I haven't adjusted them to what i would actually do but i think that you can see that the difference in RunTime is minimal, for the cost of a narcotic depth of nearly 6m deeper. Also the ppO2 at depth for 25/25 is 1.375 this is way to close to the absolute maximum I'm comfortable working with at depth and so is a little hot for my liking. I prefer to plan for max 1.2 ppO2 allowing a nice contingency of up to 1.4 if needed.

So all in, i'd choose 21/35, for lower narcosis, lower ppO2, and only a minimal cost in terms of deco time.

Re your lost deco gas... i'd just multiply each stop time by 1.5 and share my buddies gas doing half the time on the gas each and the other half on back gas. remember that we always train in teams, and separation is not an option in a well trained team.

Others would pick a different solution, but I like keeping things simple and the standard gases do that for me.

[big_si]

Does look like it pays off for a lost deco gas plan... I guess that plan won't be used 99.9% of the time though...

[Brian of Aquanauts]

Originally Posted by big_si

Does look like it pays off for a lost deco gas plan... I guess that plan won't be used 99.9% of the time though...

Not quite, would you really plan to stay in the water for nearly double your total runtime for a lost deco gas? When it's far easier to just share a bottle?
For a lost deco gas it is way easier to stay with your team member and use the 50% reserve that he's carrying.

Now I appreciate that most don't team train as hard as we do, and so you may need to find compromise solutions like this where you're running more narcotic mixes at hotter ppO2s.

[big_si]

Originally Posted by Brian of Aquanauts

Not quite, would you really plan to stay in the water for nearly double your total runtime for a lost deco gas? When it's far easier to just share a bottle?
For a lost deco gas it is way easier to stay with your team member and use the 50% reserve that he's carrying.

Now I appreciate that most don't team train as hard as we do, and so you may need to find compromise solutions like this where you're running more narcotic mixes at hotter ppO2s.

Agree completely and that's the method that I'd have trained for with my regular buddies too!

With "random" (not in the true sense of the word but with groups from different schools of training) buddies then I can't necessarily guarantee this so would be planning for a shorter runtime.

In the example (depth and time) Andy used it would be a very tiny percentage chance (perhaps 0.01%, perhaps less??) that I would have to use that plan if diving with my more regular buddies. If with a less regular buddy then perhaps it would be more likely than that.

[weazelz]

Originally Posted by Brian of Aquanauts

Now I appreciate that most don't team train as hard as we do, and so you may need to find compromise solutions like this where you're running more narcotic mixes at hotter ppO2s.

oh purrrlease. you're going to quibble over an END of 31.25m when you dive EANx32 to 30m? & sub-1.4ppO2 is just fine by any tech agency except GUE