Thailand – Australia – United Kingdom

TDI Advanced Gas Blender Course

Using helium and oxygen to make technical diving gasses

Koh Tao, Thailand

PREPARATION is key when planning a trip to unfamiliar waters where you want to ensure the success of your dive trip and the safety of everyone on it. This is the case with Big Blue Tech who have been preparing to the HMS Repulse Trimix course off the coast of Singapore in a few days.

Teaching a trimix course also involves the careful gas blending and planning to ensure accuracy and safety of the final mix. Recently training has been conducted to ensure the staff of big blue are at least Advanced Gas Blenders and in some instances Mixed Gas Blending Instructors.

For today the staff have been carefully mixing a blend of 18/30 (18 percent oxygen and 30 percent helium) for some trimix warm up dives on a wreck the following day.

The process taken was quite straight forward. We filled the empty twin sets with helium to a certain pressure and then filled the rest of the twin sets with nitrox to create the desired mix. This proved to be a great opportunity to use our booster pump as the pressure in the large helium tank dropped below the amount needed in the twin set. Normally our booster pump is used to increase pressure of oxygen for rebreather divers but today we used it for helium.

Typically rolling the tanks after filling helps with the accuracy of the read and the mix however being a twinset they’re left to cool down before analyzing and topping up whatever is necessary.

The purpose behind all this blending and planning is to go deeper then you can with conventional air and to be able to feel no narcosis. With a mix of 18/30 you would be at 60m but feel like you were at 36m. If you increase the amount of helium you get an effect of essentially being shallower since you’re exposed to less nitrogen.


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