When to go to Trimix?

[Jax]

Assuming one is trained in Advanced Nitrox and Decompression Procedures and Trimix (recreational or not) --

At what depth would you routinely prefer to use Trimix? and

At what range is either / or Trimix / Air / Nitrox?

I have read that some people dive air routinely to 200fsw, I have also seen that some people won't go below 100 fsw on air.

So, what is your personal range that you would use one or the other, and at what point would you absolutely not go deeper unless on Trimix?

Oh, yeah, and Why, Please?

 

[MaxBottomtime]

I don't really have a depth range, but a bottom time range. If I'm planning to spend less than ten minutes or so around 200 feet I would prefer to use air. I can't justify the expense of adding helium unless I make a dive with lots of bottom time and deco.

 

[PfcAJ]

I start thinkin about trimix around 100ft. Often shallower (maybe 80') on more complicated dives, but 100' is generally the cutoff. I try not to go below 0ft on air 32% is my preference unless its very shallow.

While narcosis affects everyone to some degree at all depths, past around 100' is where it really starts to affect performance to a degree that, imo, matters. In almost every case of someone dying while diving deeper than 100', their END was deeper than 100'. I also believe that there is a decompression benefit to helium, but thats up for debate.

 

[MXGratefulDiver]

Depends on where I'm diving.

In typical Puget Sound conditions, I'll do any recreational depth (<130 fsw) without helium. If I'm going into an overhead, I'll put some helium in the mix at depths below 100 fsw most of the time. On my recent trip to Florida I hit 114 (briefly) in Bozell on EAN28 without any obvious narcosis effects ... but that was in clear, warm water ...

... Bob (Grateful Diver)

 

[SandyRobinson]

I can tell I am getting narced in the 115 to 120 range. Anything over 130, I'll dive trimix. If I were to make a short/non deco dive from 115 to 130, I would use nitrox. If I made a deco dive to 115 to 130 such as the Bibb in Key largo, I'll use trimix. If I am down that long, I want to make sure I can think clearly.

 

[vinegarbiscuit]

Jax, thank you for starting this thread. I'm currently taking deco training, so this is a subject that interests me. I can tell you that few techies use trimix here on Oahu, because helium is expensive: at least three times more than the going rate back home in NYC (which is currently ~$1.25 cu/ft, I believe). Consequently, all of the folks I've encountered over the past couple of years while living here doing deeper dives (150-200 feet range) use air for backgas.

NB: I think one exception to this rule of costly gas are scientific divers, such as those attached to NOAA. I think they have access to cheaper gases like oxygen and helium than the rest of us.

 

[Rainer]

0-60': Usually air.
60-110': 32%
>110': Trimix

 

[Kevrumbo]

Jax, thank you for starting this thread. I'm currently taking deco training, so this is a subject that interests me. I can tell you that few techies use trimix here on Oahu, because helium is expensive: at least three times more than the going rate back home in NYC (which is currently ~$1.25 cu/ft, I believe). Consequently, all of the folks I've encountered over the past couple of years while living here doing deeper dives (150-200 feet range) use air for backgas.

For this year on a special charter trip to Truk Lagoon, helium will cost $4.50/cu ft (16cents/litre), and Oxygen $1.70 cu ft (6cents/litre); in those warm tropical waters (28 deg C), I usually go with Eanx30 for the majority of the wrecks in the 21m to 39m range, and air bottom mix for external surveys/tours of the wrecks 45m & deeper. If I'm penetrating inside however, I'll use 20/20 trimix for depths of 45m down to a MOD of 60m (a 20/20 trimix blend in a set of double AL80's will cost roughly $170 in Truk). . .

 

[rjack321]

0-110': 32%
>110': Trimix

I pump my own 32% its not worth keeping air around when O2 is $0.08/cf or so. If I am going 120+ I want to: a) remember it b) notice and deal with small problems before they escalate and/or ruin the dive.

On average its ~48-54F here and vis is 8-20ft. If I was someplace tropical I might push the END a bit more although I am not nickel rocket. Any dive >110ft for me is going to be an overhead dive whether there's rock, steel or just water above. And IMO ENDs >130ft are a significant contributor to morbidity and mortality in any overhead diving. One of our local deep air guys just had a huge cascade of problems on air, solo at ~213fsw. He has been in the hospital and rehab for >2 weeks and barely survived.

 

[fdog]

I switch to helium at roughly 100'. Sometimes shallower, if it's dark and/or cold.

...but He is relatively inexpensive, and I'm the guy that blends it. The ease of access definitely leads to more liberal use.



All the best, James