Optimal Trimix Blend
meters feet
What is the best trimix blend?
Calculating the optimal trimix blend consists of finding the mix that contains the correct fraction of oxygen and helium, to ensure the Oxygen partial pressure (ppO2) isn't exceeded, and the Equivalent Narcotic Depth (END) is respected.
Formulas
To calculate the Oxygen fraction, you can use the following formulas:
FO2 = 10×ppO2/(Depth+10) (in meters)
FO2 = 33×ppO2/(Depth+33) (in feet)
To find the helium fraction, knowing the END (Equivalent Narcotic Depth), you can use the following formula if you consider oxygen to be a narcotic:
FHe = 1 - (END+10)/(Depth+10) (in meters)
FHe = 1 - (END+33)/(Depth+33) (in feet)
And the following formulas if you consider oxygen not to be narcotic:
FHe = 1 - FO2-0.79×(END+10)/(Depth+10) (in meters)
FHe = 1 - FO2-0.79×(END+33)/(Depth+33) (in feet)