To_Narced:
Hey Guys,
Just wondering if anyone could explain to me what he diffrence between normoxic and hypoxic is. My buddys are tech divers and I often hear them use these terms but I jave never grasped there full meaning. Thanks to anyone who could help.
They may have been just trying to impress you. Or else they were referring to the classes they took for their trimix C-cards.
In real life all these mixes are referred to verbally simply by their first 2 numbers which represent their oxygen and helium fractions, respectively:
30/30
25/35
20/40
18/50
15/60
12/65
10/70
5/95
etc
They are all identified in the same manner, as TMX xx/xx. Therefore they are all technically called trimix. When speaking about them, divers often mention the numbers first and then say "trimix" afterwards, such as "30/30 trimix." But when ordering them, you alway designate as: "TMX 30/30."
The 5/95 blend is actually called Heli-ox as well, since it contains only oxygen and helium and not air nor any of the gasses found in air, such as nitrogen or argon etc. Although it is not a "tri-mix" in the strictest sense of the term (O2 plus He plus air) it is still designated like a trimix for identification purposes, when you would order it. This is a commercial diving mix that most amateur tech divers will never use.
The hypoxic mixes are anything with an O2 fraction less than 21. These are normally mixes designed for diving deeper than the MOD of air (using 1.4 ATAs for the ppO2), at which point you must thin out the oxygen in order to dive to a shipwreck or reef deeper. The course designation for the certification to dive these mixes is called "hypoxic trimix" but the mixes are simply referred to as TRIMIX. Nobody really uses the term "hypoxic" after they get their advanced trimix C-card. Unless they are trying to impress you.
Anything with a 21 fraction for O2 is normoxic. But it would still be called trimix to indicate that it contains O2, He, and air. The course designation for the beginning trimix class is called "normoxic trimix" but nobody calles the mixes that. Occasionally you will hear a diver say that he/she is certified for "normoxic" trimix. That simply means they have completed the beginner trimix class but are not finished with their advanced trimix training yet.
The hyperoxic mixes are anything with an O2 fraction more than 21. These are normally decompression mixes, although then can also be dived as primary mixes in the shallower ranges from 70ft to somewhat deeper. They are also called Heli-trox by some, a bad conglomeration of "helium" and "nitrox." But again, they are simply referred to as TRIMIX in the general parlance of technical deco scuba, and ordered as TMX xx/xx.
You will hear trimix mentioned all the time around tech deco divers, but more frequently you will just hear them mention the first two numbers of the fraction designation when they are talking about trimix. You will also hear nitrox mentioned, referring to EAN32, or EAN36, or EAN50 to distinguish these mixes as NOT having helium in them. And when divers mention oxygen they are referring to 100% O2. I do not think anyone dives with EAN80 anymore, except possibly in some training classes with older instructors who still believe that pure O2 is a voodoo gas.
Heli-Air? That is what you get when you start with a tank partially filled with Helium, and then you add air to it. It is still designated TMX xx/xx it is just mixed without adding oxygen to the tank first. These mixes tend to be high in nitrogen, and therefore frowned upon. It is not a trimix in the strictest sense of the word, because you did not blend 3 gasses to get it (oxygen, helium, and air), you only blended 2 (helium and air). However the TMX xx/xx designation still represents the 2 major fractions for O2 and He.
If you get your basic nitrox cert, then your advanced nitrox cert, then take a deco class, then basic trimix, and finally advanced trimix, then that will train you for all mixes and all depths. It won't train you to go into a cave or shipwreck, but it will train you for anything else at almost any reasonable depth.
