Definition and composition
Nitrox, also called enriched air or Enriched Air, is a breathing gas with more oxygen (O₂) than air. Dry air contains approximately 21% oxygen, 78% nitrogen and 1% other gases. Enriched Air Nitrox contains more oxygen than air; the permitted range depends on training, equipment and use.
The most common Nitrox mixes used in training and diving are:
- EAN32: approximately 32% oxygen; the remainder is predominantly nitrogen
- EAN36: approximately 36% oxygen; suitable profiles may allow longer no-decompression limits
EAN stands for Enriched Air Nitrox; the number indicates the oxygen percentage.
How does Nitrox differ from air?
The higher oxygen percentage is Nitrox's defining feature. This has two main effects when diving:
- Less nitrogen: With less nitrogen in the gas, a diver takes up less nitrogen. This can allow longer no-decompression limits at the same depth.
- Increased oxygen exposure: More oxygen in the mix increases oxygen partial pressure (pO₂) at depth, affecting the risk of oxygen toxicity: an important safety limit.
Benefits of diving with Nitrox
Used appropriately, Nitrox offers several benefits:
- Longer no-decompression limits: Less nitrogen can allow more time at depth on suitable dive profiles.
- Benefits for repetitive dives: Lower nitrogen uptake can be useful when planning multiple dives.
- Consider overall nitrogen loading: The effect on nitrogen loading depends on the entire dive profile. Nitrox does not prevent decompression sickness.
- Use on suitable profiles: Nitrox can be an attractive option for shallow to moderate-depth dives.
Important limits – Nitrox is not a deep-diving gas
The essential point: Nitrox does not let you dive deeper. There are depth limits that must not be exceeded.
The reason is oxygen toxicity. With an unchanged mix, oxygen partial pressure (pO₂) rises with ambient pressure, approximately linearly with depth. Elevated oxygen partial pressure can cause oxygen toxicity, with serious consequences such as seizures underwater.
Each Nitrox mix therefore has strict depth limits based on its maximum operating depth (MOD). Find out more in our article on Oxygen limits and MOD.
Gas analysis and labelling
Before using Nitrox, it is essentialto analyse the gas mix. The actual oxygen percentage can differ from the stated value. Gas analysis uses specialised equipment and is an important part of dive planning.
Nitrox cylinders are labelled according to their gas mix, often with a green label or a specific marking. Correct labelling is important for safety and accurate dive planning.
Training and safety
Using Nitrox safely requires appropriate theoretical and practical training. In a PADI Nitrox course or ProNRC Nitrox course you will learn:
- How to analyse and label Nitrox cylinders correctly
- How to calculate and respect maximum operating depth (MOD)
- Correct dive computer settings
- Practical Nitrox dive planning
- Emergency procedures and safety considerations
Conclusion
Nitrox can offer real benefits when diving, but only when it is properly understood and used. With appropriate training and strict adherence to safety procedures, it can be a valuable part of your diving skill set.
For more technical detail, read our articles Oxygen limits and MOD and Planning Nitrox dives.