Gas Blender
Tell it what is in the cylinder and what you want. It answers in fill-panel order — helium, then oxygen, then top with air — or tells you honestly when the only route is the drain valve.
| Step | Add | To |
|---|---|---|
| — | ||
Analyse the finished mix before it goes near a diver. Label the cylinder, and have the diver who breathes it analyse it again.
The maths, explained
Partial-pressure blending is Dalton’s law at the fill panel: every gas you add contributes its own pressure, and the final fractions are just those pressures divided by the fill pressure. The planner works backwards from what the cylinder already holds.
The order matters. Helium first — it is the most expensive to correct. Oxygen second. Top with air last — and note that air’s own 21% oxygen is part of the algebra, which is why the oxygen step is smaller than intuition suggests. And the order itself is house convention, not physics — some fill stations run oxygen first and land on the identical mix. Follow the blender on duty.
If the target needs less of a gas than the cylinder already contains, no addition can fix it — the tool computes the pressure to drain to before you start.
These are ideal-gas figures. Real fills run warm and real gases compress imperfectly, so fill slowly, let the cylinder cool, and expect to trim. Then the only step that actually matters: analyse the finished mix, label the cylinder, and have the diver analyse it again.
This Is Exactly What We Teach On the Gas Blender courses
This calculator is the homework; the fill panel is the exam. The blender courses cover oxygen handling and cleaning, decanting, analysis and the records that make a fill trustworthy.
Checked, not trusted: the formulas on this page are pinned by 130 automated reference checks that run on every change — cross-validated against Subsurface’s published planner tests, the independent DecoTengu implementation, printed MOD tables and the team’s own Splash apps.
For training and planning purposes only. Analyse every mix before you breathe it and always dive within your certification.