# The Gas Blender’s Cheat Sheet

By Shaun Notley, July 2020

Disclaimer: This is not intended to replace Gas Blender training, it is designed as a tool for qualified gas blenders. Blending gases can be extremely dangerous, please seek proper training before any gas blending activities. For more information click here.

### Dalton’s Triangle:

PP = Partial Pressure, example PPO2 for Deco Gases 1.6. PP = G x D

G = Gas, always as a fraction. Example, O2 in EANx32 would be 0.32. G = PP ÷ D

D = Depth, always in atm. Example 27m = 3.7 atm. D = PP ÷ G

### Approximate Free Gas Calculation:

Knowing the water volume of the cylinder and fill pressure approximate free gas is calculated.

A cylinder with a water volume of 11.1 Liters filled to 207 Bar would have approximately 2298 Liters of free gas ( 11.1 x 207 ).

### Equivalent Narcotic Depth Calculation (END):

The END for an 18/45 Trimix at 60m would be worked out as follows. 60m = 7 atm. In this example we choose not to consider oxygen narcotic, so the fraction of narcotic gas in 18/45 mix would be 0.55. The END is 3.85 atm or 28.5m.

### Continuous Flow Top Up Calculations:

Used for calculating the correct EANx top up mix for partially filled cylinders wanting to deviate from the current mix.

If we had a partially full cylinder with 50 Bar of EANx32 and wanted to fill it to 200 Bar with a resulting mix of EANx36, the top up gas needs to be EANx37. The equation would look like this:

### Partial Pressure Blending EANx Calculation:

For use with 100% Oxygen, with or without a booster, using air as a top up gas with an empty cylinder.

An empty cylinder that we want to fill with EANx36 to 200 Bar would look like this:

### Trimix Blending Calculations:

Follow steps 1 and 2 if using EANx as a top up gas. If using air, step 3 converts the EANx top up mix in step 2 to an Oxygen fill pressure.

Having a target mix of 21/20 filled to 200 Bar, we would need to add 40 Bar of He and use EANx26 to top up to 200 Bar. Alternatively, we could add 10 Bar of Oxygen, 40 Bar of Helium and top up to 200 Bar with air. The calculations would look like this:

### Transfilling / Decanting Pressure Drop Calculations:

Useful for determining if there is enough banked gas to just decant or if a gas booster pump will be needed. The calculations are split in two. One is for an empty recipient cylinder. The second is for a recipient cylinder with residual gas in. If the BP2 is greater than the RP2 then no gas booster pump is required.

As an example, imagine we have a Helium storage cylinder with a water volume of 50 L. It contains 72 Bar of Helium. We have a set of empty twin cylinders with a combined water volume of 22 L and need to put 40 Bar of Helium inside.

Because the bank ending pressure (BP2) is greater than the required pressure of 40 Bar in our twin cylinders, we will not be needing a gas booster pump and can just decant.