Enriched-air nitrox is a breathing gas with a higher oxygen percentage than ordinary air. Recreational nitrox commonly contains around 32% or 36% oxygen, although blends vary. Nitrox can reduce nitrogen exposure for a given dive profile, but it does not automatically make a dive safer or permit a deeper dive. Its oxygen content introduces limits that must be understood and planned for.
What are the potential benefits?
Because nitrox contains less nitrogen than air at the same pressure, a properly planned nitrox dive may allow a longer no-decompression limit at a given depth, compared with air under the applicable planning model. This can be useful for repetitive recreational dives. The actual benefit depends on the blend, depth, dive profile, and planning system; it should never be treated as extra time that must be used.
Oxygen exposure and maximum operating depth
Oxygen becomes hazardous when its partial pressure is too high. For this reason, every nitrox blend has a maximum operating depth (MOD) based on the oxygen percentage and the partial-pressure limit used for the dive plan. A blend with more oxygen generally has a shallower MOD. For example, PADI explains that common EANx32 has a maximum depth of about 34 metres/112 feet under its stated planning limit; that example is not a substitute for calculating the MOD for the actual cylinder, training, and dive plan.
Do not assume a cylinder is safe because its label says “nitrox,” and never estimate oxygen content by appearance. Analyse the gas with a suitable analyser, confirm the label and recorded blend, and use the result in the plan. Follow your agency’s training and the equipment manufacturer’s instructions.
Essential nitrox safety steps
- Get the appropriate training. Learn oxygen exposure limits, MOD, gas analysis, labelling, and how to plan dives using your agency’s procedures.
- Analyse every cylinder you will use. Verify the oxygen fraction yourself and confirm that the cylinder marking matches the analysis.
- Plan the MOD before entering the water. Stay within the planned depth and oxygen-exposure limits; do not rely on memory or a generic chart.
- Use compatible, properly serviced equipment. Follow the cylinder, regulator, and gas-service requirements that apply to the blend and jurisdiction.
- Monitor both nitrogen and oxygen exposure. Nitrox changes the calculations; it does not eliminate decompression illness or oxygen-toxicity risk.
Does nitrox prevent decompression sickness?
No breathing gas or table can guarantee that decompression sickness will not occur. Nitrox may change inert-gas loading for a given profile, but divers must still follow the training and planning method for the gas they are breathing, ascend in a controlled manner, and respect no-decompression and oxygen limits.
Who should use nitrox?
Nitrox is suitable for divers who have completed recognized enriched-air training and can follow the gas-analysis and planning procedures. It is not simply a gas upgrade for any dive. If you are unsure how to determine the blend, MOD, or exposure limits, ask a qualified instructor before diving.
Further reading
See PADI’s overview of enriched-air nitrox and review your current training materials. Use the exact blend and limits for your dive; never copy a maximum depth from an example into a different plan.