Trimix is a mixture of three gases, specifically oxygen, nitrogen, and helium. As divers are aware, nitrogen (and oxygen, too) can produce narcotic effects when breathed under pressure which can lead to slowed reaction times, impaired judgment, feelings of euphoria, feelings of anxiety, etc. This phenomenon is known as nitrogen narcosis. However, helium does not produce narcotic effects so divers can replace some of the oxygen and nitrogen in their breathing gas with helium to reduce the symptoms of narcosis.
Technical divers have been using trimix for more than twenty years for extended range diving (diving below the recreational depth limit of 130 feet). Now trimix is becoming more and more popular with recreational divers in order to reduce narcosis between the depths of 80 and 130 feet. In particular, underwater photographers and videographers, wreck divers, cave divers, salvage divers, research divers, etc. who must perform somewhat complicated tasks while underwater have discovered the benefits of breathing trimix.
Trimix blends are referred to according to the particular ratio of oxygen and helium they contain. For example, 15/45 would indicate a mix containing 15% oxygen and 45% helium (and the remaining 40% would be nitrogen). When considering which mix to use for an upcoming dive, the oxygen content is determined by the planned depth just as with nitrox. The helium content is determined by both the planned depth and the desired narcosis level. The balance will then be nitrogen.
If you're already a nitrox diver then you'll already know a lot of what you'll need for trimix. In fact, using trimix within recreational limits for no-decompression required dives is almost as easy as nitrox. However, using trimix for extended range dives requiring staged decompression is quite a bit more involved. We'll start out with lectures explaining the characteristics of helium as a breathing gas and pool sessions to hone such skills as lift bag deployment and stage bottle manipulation. After practicing within recreational limits just to be sure everything is going smoothly, we'll begin gradually increasing our maximum depth and introducing required decompression stops. Trimix certification requires a considerable commitment, but in order to dive below the recreational limit it is the right tool for the job.
| Program: | Qualifies divers to use trimix... |
|---|---|
| Recreational Trimix | on no-decompression required dives within recreational limits |
| Advanced Recreational Trimix | on dives as deep as 150 ft requiring no more than 15 minutes of decompression using EAN50 |
| Normoxic Trimix | on dives as deep as 200 ft using EAN or oxygen for decompression |
| Trimix | on dives as deep as 330 ft using EAN and/or oxygen for decompression |