Analyze Nitrox Mix: How to Verify Oxygen Content for Safe Diving

Enriched Air Nitrox (EANx) is one of the most popular specialties in scuba diving, offering qualified divers benefits like longer no-decompression limits and shorter surface intervals. 

But these advantages come with a critical, non-negotiable safety requirement: you must know the exact oxygen percentage in your cylinder before every dive.

This simple procedure is the final and most important safety checkpoint, standing between a safe, enjoyable dive and two potentially lethal risks:

• Hypoxia: Occurs if the mix has too little oxygen, which can cause confusion, loss of consciousness, and collapse, even at the surface or in shallow water.

• Oxygen Toxicity (Hyperoxia): Occurs if the mix has too much oxygen, which can trigger sudden convulsions without warning, leading to loss of the regulator and drowning underwater.

This guide will explain the procedure, the risks, and the tools required to analyze your Nitrox mix correctly, every time.

Understanding Nitrox Mix and Oxygen Percentage

"Nitrox," or Enriched Air Nitrox (EANx), simply refers to any breathing gas mixture composed of nitrogen and oxygen with an oxygen concentration higher than 21% (the amount in standard air).

The reason this percentage is so critical is that it directly dictates how deep you can dive based on your Maximum Operating Depth (MOD). Diving too deep on a given mix exposes your body to a dangerously high partial pressure of oxygen (Pₒ₂), which can cause acute oxygen toxicity.

Below is a quick reference chart showing how oxygen content affects your MOD (calculated for a 1.4 bar Pₒ₂ limit).

Oxygen Percentage vs. Maximum Operating Depth (1.4 Pₒ₂)

Why You Must Analyze Every Nitrox Cylinder

During Nitrox production, the true oxygen percentage can only be confirmed through proper analysis. Labels and previous records are useful references, but they can never replace direct testing.

Analyzing your O₂ percentage is essential to:

1. Verify the Gas: After blending, analyze the cylinder to confirm that the oxygen percentage matches the intended target mix.

2. Program the Analyzer Correctly: Ensure the oxygen analyzer is properly calibrated before testing. An incorrect calibration can lead to false readings and unsafe assumptions about the final gas composition.

3. Establish the True MOD from the Measured Mix: Always calculate your Maximum Operating Depth using the oxygen percentage you actually measured yourself. 

Even tanks filled consecutively from the same system can differ slightly. For this reason, every enriched air cylinder should be analyzed before diving.

How to Analyze Nitrox

Accurate Nitrox verification depends entirely on a properly functioning oxygen analyzer. 

Oxygen analyzers, such as the NRC PIC O₂ Analyzer, are created to monitor oxygen concentration with high accuracy and consistency throughout the blending process.

This precision instrument measures the exact oxygen percentage inside a cylinder and remains the only reliable way to confirm the final gas mix after blending. 

Step-by-Step: How to Use a Nitrox Analyzer

This 5-step Nitrox testing procedure is simple and should be a non-negotiable part of your pre-dive ritual.

1. Calibrate the Analyzer

Turn on the analyzer and hold the calibration button located on the front of the display for a few seconds until the calibration mode appears. 

2. Prepare the Cylinder Valve

Before placing the analyzer on the valve, gently open the cylinder just enough to create a small airflow. This clears moisture and debris from the valve outlet. If the valve threads are wet, dry them before proceeding to protect the sensor.

3. Attach the Analyzer

Position the analyzer’s T-piece or hose extraction connector securely in front of the valve. Make sure gas can flow freely out of the open side of the T-piece. If using the hose extraction set, fit the connector over the valve until it sits firmly in place.

4. Analyze the Oxygen Percentage

Slowly open the valve to allow a gentle flow of gas. The oxygen reading will begin to rise on the display. Wait a few seconds until the value stabilizes. Once stable, this number represents the actual oxygen percentage inside the cylinder.

5. Record and Label

Once you have a stable reading, shut the cylinder valve. On a designated tank label or waterproof tape, write down:

• The measured O₂ percentage (for example, 32.5 percent)

• Your calculated MOD for that mix

Your initials to confirm you completed the analysis 

6. Store the Analyzer Properly

After use, ensure the analyzer is dry before storage. Always keep it in a clean, dry place to protect the sensor and maintain long-term accuracy.

Precision Starts at the Analyzer

Every safe Nitrox mix begins with knowing the exact oxygen content inside the cylinder. When the final blend is properly analyzed, you create the foundation for accurate labeling, correct MOD calculation, and controlled dive planning. 

That level of accuracy only comes from equipment built for consistent, dependable performance. Oxygen analyzers, such as the NRC PIC O₂ Analyzer, are engineered to deliver fast, stable readings and reliable calibration in real-world blending environments. 

Get your NRC PIC O₂ Analyzer and set the standard for precise, dependable Nitrox verification.

Frequently Asked Questions

Do I really need to analyze every tank, even if I get them all from the same shop?

Yes, every cylinder must be individually analyzed. Even when all tanks are filled at the same location, small variations in topping pressure, residual gas, humidity, or simple handling errors can change the final oxygen percentage. Only a fresh analysis confirms the true mix inside each cylinder.

What should I do if my analysis reading is different from the tank label?

You must always trust the calibrated analyzer over the label. If the difference is small, update the label with the exact measured percentage, your initials, and the corrected MOD. If the difference is large, this indicates a blending or labeling error. The cylinder should be clearly marked, removed from service, and reported to the blender or facility immediately.

How often do I need to calibrate my O₂ analyzer?

An oxygen analyzer must be calibrated before every analysis session. If the unit is powered off, stored, or moved between environments, it should be recalibrated before reuse.