Maverick wrote:This is a question i hope to get good response from and not get my head bitten off. I am not UTD but very curious why themixes are chossen the way they are. is there a special chart you use, or a way of blending. the reason i ask is because i am getting into mixing my own trimix at home
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I have heard the past few days people talk of utd mixes, well all i can find is that they are close to cave mixes. How can a group of divers call this their mixes and why would they only be allowed to used these designated mixes on a dive. They have been around for a long time, what's makes them UTD mixes. is it that it is easy to blend usiing 32% or that is what th agency recognizes as safe for depth. I mean I realize its the lake and there is bad vis and it causes narcs but 15/55 for a lake dive seem very rrich to me. but i haven't dove the lake much so maybe it is need to keep a clear head. anyone have anything to clear this up, maybe achart of how UTD/DIR/GUE cued these as theirs?
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Hey BJ-
First, I was being sarcastic with my comment regarding using 15/55 for a dive on the Hauler or the Dawn. Matt and I did a dive last summer looking for the Valiant. I was on 25/25 and was really narc'd at 100ffw. We were using the scooters, and as you know, unlike the Sound, the lake has very little reference points on the bottom. So I was whizzing along with no real reference. It became kind of a running joke afterward that my lake mix is now at least 21/35.
As far as your question on standard mixes goes....
The mixes are VERY easy to blend using 32%. That's the primary reason.
Secondly, UTD, GUE, etc don't use the "best mix" philosophy, due to in large part exploration. Each mix serves a range:
32% - to 100'
25/25 - 80 - 130'
21/35 - 130' - 170'
18/45 - 170' - 220'
etc etc etc (Matt posted a link to the standard gases)
When a diver is exploring, and doesn't know the exact depth they'll be encountering, having a range they're able to work within provides them with more flexibility than a "best mix". If you think you're going to be exploring in the 130 to 150' range, and go with 21/35, and the site is deeper than you had planned, you still have the ability to adapt the dive, as 21/35 is good to 170' while keeping the END to 100'. If you were using "best mix", you wouldn't be able to drop to that deeper depth.
That's the logic behind it. Hope that helps.