Travel mix

[Doppler]

Things have been quiet around here lately, so.... Let's talk about decompression gases... specifically that third bottle... no, not the oxygen or 50 mix but the... well that's my question: Which do you use and why?

 

[SLJ]

Typically I like to use my deepest deco gas. It keeps the PO2 down and it will usually be the least used gas as far as volume goes so is good for travel also. It's usually not so hypoxic that I can use it almost anywhere except at depth.
Shane

 

[Scuba_Vixen]

It's hard to justify the the extra complexity, weight, and task loading of that 3rd bottle unless it yields some significant reduction in hang time, or offers some added safety margin. Also when you have to carry all your gas, your BT's (and hence depths)are somewhat limitted by the amount of deco mix you can carry, so your stops below 70' don't generally add up to a lot of time (so you don't save that much deco time overall by getting on a higher O2 below 70'). For what I dive here, I use 15/55 most of the time, which generally doesn't seem to justify the hassles of that 3rd tank. On the occasions where I've visited the dark side of the moon, I go with 12/65 back gas and 18/45 (switch at 220, going down and up) as the intermediate 3rd tank. I've also become a 50/50 heliox convert for the 70' bottle and stay on the O2 for that long lazy surface swim back to the beach.

So to answer the pole, when I use a 3rd tank, it's 18/45. You don't need much going down, or comming up, so you have it in reserve if you need it unexpectedly.


Darlene