Question 1

What is partial pressure Nitrox blending?

Accepted Answer

Partial pressure blending fills a cylinder with pure oxygen first, then tops it up with air to the final pressure. The oxygen partial pressure is calculated so that, once the air is added, the resulting mix has your target oxygen percentage. It requires O₂-clean equipment and O₂-compatible air because pure oxygen is introduced.

Question 2

What is continuous Nitrox blending?

Accepted Answer

Continuous blending (or pre-mixing) mixes oxygen and air continuously before the gas enters the cylinder. It is common at dive resorts and liveaboards because, for mixes up to 40% oxygen, it does not require O₂-cleaned cylinders. The output is expressed as a ratio of oxygen to air in the mix.

Question 3

How do I verify the blend after filling?

Accepted Answer

Always analyze the final mix with a calibrated O₂ analyzer before diving. Calibrate against air (20.9%) or pure oxygen, flow the gas for at least 30 seconds until the reading stabilizes, and compare against the target. If the reading differs by more than 1%, do not use the cylinder until it is corrected.

Question 4

What does the 40% rule mean?

Accepted Answer

The 40% rule is a widely adopted standard: equipment exposed to 40% oxygen or less does not require special O₂ cleaning, while mixes above 40% require O₂-cleaned cylinders and O₂-compatible air. Our calculator covers the recreational range (EAN22 to EAN40) where the 40% rule applies.

Question 5

What is the MOD of my blended mix?

Accepted Answer

Maximum Operating Depth depends on the oxygen fraction. At the standard 1.4 bar limit, EAN32 has an MOD of about 34 m and EAN36 about 29 m. The richer the oxygen, the shallower the MOD. Our calculator shows the MOD at both 1.4 and 1.6 bar so you can label your tank correctly.

Nitrox Blending Calculator (EAN Mixing)

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