Gas Blending Calculator
Calculate exactly how much oxygen and helium to add for any nitrox or trimix fill using partial pressure blending - the same method used at professional fill stations worldwide.
Blend Parameters
Nitrox EAN32 blend
Blending Plan
What is gas blending?
Gas blending is the process of creating a specific breathing gas mixture - nitrox, trimix, or heliox - for a scuba tank. There are two main methods: partial pressure blending and continuous flow blending. Partial pressure blending (used by this calculator) is the most precise and widely used method at technical dive centres. It works by adding individual gases to a tank in a specific sequence, relying on Dalton's Law of Partial Pressures.
The blending process
Partial pressure blending follows a strict sequence to ensure safety and accuracy:
- Drain the tank to the residual pressure shown in the calculator. This removes the old gas mix and creates space for the new blend.
- Add oxygen first, to the calculated pressure. Only oxygen-clean equipment should be used for this step. Fill slowly - pure oxygen should not exceed 50 bar/min fill rate.
- Add helium (trimix only) to the calculated pressure. Helium is added after oxygen.
- Top off with air to the final target pressure. This also serves to mix the gases thoroughly.
- Allow to cool, then analyse the final oxygen percentage with a calibrated oxygen analyser. Never dive a mix that has not been analysed.
Safety
Gas blending carries significant risks and should only be performed by trained and certified gas blenders. Key safety considerations include:
- Oxygen-clean equipment: Any equipment that contacts high-pressure oxygen must be scrupulously clean and rated for oxygen service. Hydrocarbon contamination in the presence of high-pressure oxygen can cause fires or explosions.
- Maximum fill rates: Pure oxygen should be added slowly (no more than 50 bar/min) to prevent heat build-up in the tank.
- Always analyse: Before labelling, sealing, and diving any blend, the final oxygen percentage must be measured with a calibrated analyser. The calculator gives a theoretical result - analysing confirms the actual mix.
- Label immediately: Mark the tank with the analysed mix (O2%, He%, MOD) and your initials before it leaves the fill station.