Advantages of Trimix?

[evil_xander]

It will cost you approx 0,25-0,30 kn/L, take the % of He in the mix you need and multiply with tank volume x operating pressure...it's not cheap.

Of course, depending on your contacts, you can get it cheaper, but this is the commercial price.

 

[ScubaBB]

Let's say around $20 for a 15l -200bar 21/25

 

[DA Aquamaster]

Not if you use it in the manner I described. The potential danger with helium is that it is a very light substance which ongasses and offgasses very quickly. If you're using it for your dive, you should take that into account for your ascent rate ... it's much easier to bend yourself on helium than on air or nitrox. But for a minute worth of breathing at depth, it won't really change anything except your sensory perception ... in effect, you'll suddenly realize how narc'ed you were before switching to it. Switching back to your own gas, you will also be more aware of how narc'ed you become. Now you will have a better comprehension of how insidious narcosis is, and how narc'ed you've been at those depths without even realizing it.

... Bob (Grateful Diver)

Agreed. It was not uncommon at one point in a trimix class to breathe off a stage with air at depth to feel the sudden onset of the narcosis that you other wise fail to notice with a gradual descent. And similarly, in a extended range class, briefly breathing off a stage of trimix would lift the fog so to speak and make the point that trimix is a pretty good idea.

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Trimix fills, starting from zero psi can be a little spendy and I have spent $125 for a fill in 130 cu ft doubles in the past when getting trimix at a shop in Alexandria VA that did not sell a lot of it.

However, my experience in south Florida is that a 30-40 minute bottom time dive in the 170-210 ft range with gasses in the 21/35 and 18/45 ranges will cost about $20-$30 for the trimix and deco gas actually used. Given the cost of the boat ride, motel, meals, gas to get there, etc, the cost of the gas is minimal, and almost insignificant when you subtract the cost of the air fill and deco gasses you'd have needed anyway to do the same dive on air.

For that additional $10-$15 cost of trimix you get a much lower END creating a much greater level of safety on the dive and allowing you to observe more on the dive and remember much more of the dive.

When doing N FL cave dives in the same depth range, the additional cost is probably also in the $10-$15 dollar per dive range (it's harder for me to calculate as we run a tab for the week and make one large payment at the end of the week for O2 nitrox and trimix), but the SA and safety benefits make that extra cost a bargain. In addition, being slighty cheap, I'll plan deeper cave dives early in the week and then top off one pair of tanks with the ever present 32% nitrox for subsequent 100-110 ft range dives. The He percentage declines while the O2 percent increases with each top, and while it's not what you'd call a standard gas, you do gain some END benefit over the course of a few more dives for basically no added cost on that trip.

 

[deadbilly]

Trimix is a substitute gas that prevents 02 tox below 60m

I'd like to revisit this comment. This isn't actually true, is it? My understanding is that the only thing that reduces O2 toxicity is lower partial pressures of O2. You're not replacing O2 with He, you're replacing N2. Otherwise, you're just adjusting your FO2 for your depth. So the above statement is only true if you say "trimix prevents O2 toxicity when it has the right amount of O2 to prevent O2 toxicity." Just adding He doesn't do anything about potential tox factor.

 

[franny]

I'd like to revisit this comment. This isn't actually true, is it? My understanding is that the only thing that reduces O2 toxicity is lower partial pressures of O2. You're not replacing O2 with He, you're replacing N2. Otherwise, you're just adjusting your FO2 for your depth. So the above statement is only true if you say "trimix prevents O2 toxicity when it has the right amount of O2 to prevent O2 toxicity." Just adding He doesn't do anything about potential tox factor.

Billy,

i don't dive trimix, but my understanding is you have the three gasses, Nitrogen, Helium, Oxygen in a tank. Those three gasses can be put into the tank in whatever proportion you feel like.
Normally the setup is normoxic (21% O2, which allows a depth of 56M at 1.4PP02, XX% N2, and the remainder Helium), but if you are going deeper than 60 M you may look at taking multiple mixes, including hypoxic (< 21% O2, a small amount of N2 and the remainder He) as a bottom gas, and a separate mix for deco, which may have more than 21% O2 (hyperoxic) . Someone feel free to correct me, if my understanding is incorrect.

 

[PfcAJ]

^^ Ya you rite.

 

[down4fun]

I'd like to revisit this comment. This isn't actually true, is it? My understanding is that the only thing that reduces O2 toxicity is lower partial pressures of O2. You're not replacing O2 with He, you're replacing N2. Otherwise, you're just adjusting your FO2 for your depth. So the above statement is only true if you say "trimix prevents O2 toxicity when it has the right amount of O2 to prevent O2 toxicity." Just adding He doesn't do anything about potential tox factor.

yes and no. Helium doesn't prevent ox tox in some chemical fashion, but it is used to reduce the amount of O2 in a mix to a level with a PPO2 less than 1.4 (or 1.6 depending on the diver). So in that sense yes helium is used to prevent ox tox.

For example your doing a dive to 190 feet you will probably use trimix 21/35. Meaning it's 21% O2 and 35% He the rest is N2. In this case the He is used to reduce the N2 and narcosis.

Now lets say you are doing a dive to 250 feet. Now your 21% has a PO2 of 1.8, too high, and a risk for ox tox. So to reduce the PO2 you add more helium and dive something like 18/45. The deeper you go the more you dilute your O2 with He. Other common mixes include 15/55 and 10/50.

 

[Tortuga68]

Allegedly... but that is a looooonnnggg conversation.

Point being that the prupose of nitrox isn't to reduce narcosis, as the person I was quoting said. But, you already knew that

 

[down4fun]

Point being that the prupose of nitrox isn't to reduce narcosis, as the person I was quoting said. But, you already knew that

My bad. It's to reduce the nitrogen loading and extend bottom times in the recreational levels. An area i don't spend much time at these days

 

[lsorenson]

It's to reduce the nitrogen loading and extend bottom times in the recreational levels. An area i don't spend much time at these days

So please let me ask this... Since I have a dive that keeps me at 100' (98'-103') I am quite curious about this as I have not given it any though until now (thanks ScubaBB)... I am usually around 34% but even at 36% I can only stay a max of 35 minutes according to PADI or Navy tables. (thats off the top of my head)

If I am reading what yall are saying correctly then I should be able to increase my bottom time going with a 21/35... If this is true, how significant of an increase in time could I see diving at 100'...?

Thanks, lee