Nitrox in Scuba Diving: What It Is and Why It’s Used
Nitrox in Scuba Diving: What It Is and Why It’s Used
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author: Eddie Yung
Nitrox, also known as Enriched Air Nitrox (EANx), is a breathing gas mixture that contains a higher percentage of oxygen and a lower percentage of nitrogen than regular air (which is 21% oxygen and 79% nitrogen). The most commonly used Nitrox mixes have oxygen levels ranging from 32% to 40%.
Why Use Nitrox?
Why Use Nitrox?
Extended Bottom Time
Because Nitrox has less nitrogen, divers absorb less of it during a dive. This reduces the risk of reaching nitrogen limits set by dive tables or computers, allowing for longer no-decompression limits (NDLs) compared to diving with regular air. This is particularly beneficial for repetitive dives.
Shorter Surface Intervals
With less nitrogen absorbed, the body requires less time to off-gas nitrogen during surface intervals, allowing divers to get back in the water sooner.
Reduced Risk of Decompression Sickness (DCS)
Lower nitrogen absorption decreases the likelihood of decompression sickness, making Nitrox a safer option for many divers, especially those doing multiple dives over consecutive days.
Decreased Fatigue
Many divers report feeling less tired after diving with Nitrox. While this is anecdotal, it’s believed to be linked to reduced nitrogen absorption.
Considerations and Limitations
Considerations and Limitations
Oxygen Toxicity
The higher oxygen content in Nitrox increases the risk of oxygen toxicity, particularly at greater depths. Divers must monitor their depth closely and stay within the maximum operating depth (MOD) for the Nitrox mix being used.
Special Training Required
Using Nitrox requires specialized training to understand how to calculate oxygen exposure, manage MOD, and use an oxygen analyzer to verify the gas mix in your tank.
Cost and Availability
Nitrox is often more expensive than regular air and may not be available at all dive destinations.
Who Benefits Most from Nitrox?
Who Benefits Most from Nitrox?
Nitrox is especially advantageous for:
Divers doing multiple dives per day, such as on liveaboards.
Photographers or marine biologists who spend extended periods underwater at moderate depths.
Recreational divers who want to maximize bottom time within safe limits.
The most beneficial depths for diving with Nitrox are typically in the 15 to 30-meter (50 to 100 feet) range. Here's why:
1. Extending No-Decompression Limits (NDLs)
1. Extending No-Decompression Limits (NDLs)
Nitrox is most advantageous at moderate depths where nitrogen absorption is a concern but where oxygen toxicity risks can still be managed.
At these depths, the reduced nitrogen content in Nitrox significantly increases your no-decompression limits compared to air, allowing for longer bottom times.
2. Avoiding Oxygen Toxicity
2. Avoiding Oxygen Toxicity
The higher oxygen percentage in Nitrox limits the depth at which it can be safely used due to the risk of oxygen toxicity. For example:
With Nitrox 32 (32% oxygen), the maximum operating depth (MOD) is around 33 meters (110 feet) at a partial pressure of oxygen (PPO₂) of 1.4.
With Nitrox 36 (36% oxygen), the MOD is even shallower, at around 28 meters (92 feet) at the same PPO₂.
3. Optimal Usage Scenarios
3. Optimal Usage Scenarios
Shallower Dives (<15 meters / <50 feet): While Nitrox can still be used here, the benefits are minimal because nitrogen loading is less of a concern at shallow depths.
Deep Dives (>30 meters / >100 feet): Air or trimix is often a better choice, as Nitrox's higher oxygen content becomes unsafe at these depths due to oxygen toxicity risks.
Real-World Application
Real-World Application
Recreational Divers: For dives in the 15-30 meter range, Nitrox can almost double your bottom time compared to air, especially useful for activities like wreck or reef exploration.
Repetitive Divers: Liveaboard trips or multi-dive days are where Nitrox shines, as it reduces nitrogen absorption and shortens surface intervals, allowing divers to maximize their dive time.
Conclusion
Conclusion
The sweet spot for diving with Nitrox is at moderate depths, generally between 15 and 30 meters (50-100 feet), where it provides significant benefits in bottom time and safety while staying within oxygen exposure limits. Always check the specific MOD for your Nitrox mix and plan your dives accordingly!
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