Nitrox for New Divers: What Enriched Air Actually Changes
If you've spent any time on a dive boat, you've seen the green-and-yellow tanks and the divers fussing with a little analyzer before the first dive. That's nitrox. Here's what it is, what it's good for, and what it isn't.
What nitrox is
Regular air is about 21% oxygen and 79% nitrogen. Nitrox, also called enriched air or EANx, is any mix with more oxygen than that. The two you'll see most on dive boats are:
- EANx32: 32% oxygen
- EANx36: 36% oxygen
The big benefit: more bottom time
More oxygen means less nitrogen in every breath, so your body absorbs nitrogen more slowly. On dives in roughly the 50 to 100 foot range, that usually means longer no-decompression limits and shorter surface intervals than on air. On a multi-dive vacation day, that adds up.
The trade-off: a depth limit
Oxygen becomes toxic at high enough pressure, so every nitrox mix has a maximum operating depth (MOD). At the common recreational limit of 1.4 bar of oxygen pressure, EANx32 tops out around 111 feet (34 meters) and EANx36 around 95 feet (29 meters). Nitrox is a gas for longer, moderate-depth dives, not deeper ones. Your training will teach you how to work out the MOD for any mix and set your computer accordingly.
Why you analyze your own tank
The fill station's label isn't enough. Before you dive a nitrox tank, you measure the oxygen percentage yourself with an analyzer, write it on the tank tag, and set your dive computer to match. If the reading is off from what you planned, you replan the dive. It takes two minutes and it's non-negotiable.
Myths worth dropping
- "Nitrox is for deep diving." It's the opposite. The extra oxygen lowers your safe maximum depth.
- "Nitrox stops narcosis." Studies haven't shown it does. See Nitrogen narcosis, explained.
- "Nitrox means no more decompression risk." It lowers your nitrogen load. It doesn't make you immune. Follow your computer and make your safety stops.
How to get certified
Most dive shops require proof of nitrox certification before they'll fill or rent you a nitrox tank. The PADI Enriched Air Diver course is one of the most popular specialties, and much of it can be done as knowledge development before your trip. If you're planning a dive vacation and want help deciding whether nitrox is worth it for the diving you'll do, that's exactly the kind of question Iron Reef dive consulting helps with.
And if you already love it, there's a shirt for that: I Love Nitrox in the Morning.
This article is general information, not dive training. Get certified before diving nitrox, and follow your training, your dive computer and your dive plan.