If you want to dive deep, Helium is the safest way to dive. No matter if you are diving open circuit, sidemount or rebreather once you go beyond certain depths (50 mtrs – 166 feet) the safest way is to dive with a mixed gas of Helium combined with Oxygen.
Trimix means a mix of three components (“tri” and “mix”), and usually when people talk about trimix, they mean the mix of oxygen, nitrogen and helium. Trimix is used in very deep dives instead of air to reduce the partial pressure of oxygen (to avoid oxygen toxicity) and nitrogen (to avoid nitrogen narcosis). Heliox is a mix of helium and oxygen (“heli” and “ox”).
These days its called Normoxic Trimix (min 16% Oxygen) and Hypoxic (anything below 16% Oxygen) Trimix. Normoxic Trimix is a mix with which you can go 60 meters and Hypoxic is the mix you will use to depths of 100 meters – 333 feet.
TRIMIX DIVING COURSES
The percentages of gas components vary depending on the dive. The deeper one go, the less there will be oxygen and nitrogen, and the more there will be helium.
Trimix mixes are labeled for example as “Trimix 10 50″ or “Trimix 10/50″, where 10 represents the percentage of oxygen in the mix, and 50 is the percentage of helium.
Why one should dive deep dives with trimix? The answer is simple:
By decreasing the percentage of oxygen in the mix, one can dive deeper without a danger of oxygen toxicity.
Nitrogen narcosis can be avoided by replacing nitrogen with helium. Helium is not as narcotic as nitrogen.
It is wrong to think that the high price of helium mix is an excuse to dive deep with air. If you can’t afford it, then you don’t dive deep. Nitrogen narcosis can be very dangerous, and oxygen toxicity even worse. Remember still that trimix diving without adequate training is not correct way to dive!