Northwest Dive Club

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 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?

I won't try to answer most of that, but I'm pretty sure the 15/55 comment was sarcasm. That's a deep hypoxic mix.

i don't claim to know anything either, but i did bookmark this page a while ago. does it help answer some questions?

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 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?

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.

Thanks Brian, I can see how that would be good for exploring.

Brian’s explanation of Bottom gas mixtures is spot on.

Another reason theses mixes were choosen was their usefulness at the local Florida “watering holes”
30/30 for instance is a great “Ginnie Springs” mix as the max depth in that cave is about 120 ft, but 30% He for 100 ft in most of our waters (there are exceptions) is a bit high, so it is not very useful here (plus it is a pain to mix).

A few of the hallmarks of DIR/UTD are

Unified Team:

Teams are always on the same mixes, so dive planning is easy and can be adjusted very simply if need

Conservative gas parameters:

Which equates to a max END of 100 ft and a Max PO2 of 1.4 for bottom mixes (recently made even more conservative at 1.2) and 1.6 PO2 for decompression gases. Both agencies take the stance that O2 is Narcotic and therefore use the most conservative END formula {END = (1- He) *ATA} . They also believe Helium to be much easier on the body than nitrogen, so the more Helium the better.

Most Standard mixes are easy to mix because you simply top the % of desired He with banked 32%

Familiarity with decompression profiles (easier to remember and adjust deco tables if you are familiar with them)

Each bottom mix coves a depth range (very useful for exploration)

These are approximate ranges. As you approach the maximum of the range most divers will move to the next mix for more conservative range. For example I usually use 18/45 for dives in the 160 -200 ft range

15/55 220 -250 ft

18/45 170 -210 ft

21/35 140 -160 ft

25/25 100 -130 ft

30/30 100 ft (for PO2 issue)

32% 100 ft (for END Issue)

Cylinder Marking

Standard mixing allows ONLY certain mixes to be put in certain bottles as these bottles are permanently marked with MOD (deco and stages). This is useful when you have multiple bottles that look identical moving around within a group.

Decompression mixes:

One reason deco mixes are chosen to provide an average 1.2 PO2 over a range of stops (usually 5, but some times more, not for there ease of mixing.

100 % 20 ft (easy of mixing, most efficient decompression)

50% 70ft (still gives a relatively useful PO2 for deco at 30 ft)

35/25 120 ft (allows us to get some of the deco out of the way deeper. If you have this bottle it is most likely because you have to make certain you are carrying enough reserve gas, so why not carry a gas that is useful for decompression. 25% helium is added for END issues)

21/35 190 ft (not the ideal gas, but since it is already a standard gas why make a new one, when this one requires only a small adjustment (more stops over the deco depth range)

I find these mixes are awesome for our waters. We have several wrecks in the 220- 250 ft range (perfect for 15/55), several in the 160- 210 range (perfect for 18/45), several in the 130-150 range (Perfect for 21/35), several in the 100 -120 range (perfect for 25/25), and most of out local watering holes (Cove 2, Redondo, 3 Tree, etc. 32% works perfectly. You get little advantage over 32% by using 33-40% for the 1 or 2 dives a day here)

Scott

thanks Scott, very informative. anyone have anything else to add?

Thanks Brian & Scott. This is one of most informative threads we've had in a VERY long time. We're very fortunate to have resources like you two here.

Sounder what's that brown stuff on your nose. no really good stuff :occasion5: