In the realm of recreational diving, enriched air nitrox (EANx) denotes any gas mixture containing more than the typical 21 percent oxygen found in regular air. Common examples include 32 percent and 36 percent oxygen, often referred to as nitrox 32 (or 36) or EAN32 (or 36). To distinguish them from air cylinders, tanks filled with EAN are marked with a yellow and green tank band near the top, just below the crown. The oxygen mix percentage is indicated on a label or tag, which is vital because it impacts depth limits and no-stop dive time.
**How EAN Nitrox Works:**
Enriched air contains more oxygen than air, which lowers the nitrogen percentage. Consequently, you inhale less nitrogen during your dive compared to using regular air.
During your Open Water Diver course, you learned that as you dive, water pressure causes nitrogen from the air you breathe to dissolve in your bloodstream and tissues. The deeper the dive (higher pressure) and the longer you remain at depth (bottom time), the more nitrogen dissolves. Surfacing with excessive dissolved nitrogen in your tissues can lead to decompression sickness (DCS). Staying within no-stop limits restricts the theoretical amount of dissolved nitrogen, enabling you to ascend directly to the surface (with a safety stop). However, exceeding this limit, as tec and commercial divers do, necessitates mandatory decompression stops during ascent to minimize DCS risk. For instance, based on the Recreational Dive Planner, a diver on air at 100 feet reaches no-decompression after 20 minutes. At 60 feet, the maximum time would be 55 minutes. Nitrox, however, alters these numbers.
As you're inhaling less nitrogen, less dissolves into your body, extending the no-decompression limit. This can be calculated using an equivalent air depth (EAD), which indicates the shallower depth at which nitrogen would dissolve at the same rate if you were using air. For example, at 105 feet with EANx32, the EAD is 90 feet, which means you're absorbing nitrogen as if you were 15 feet shallower. Consequently, your standard no-decompression limit of 15 minutes extends to 25 minutes—a remarkable 66 percent increase in bottom time.
**Advantages of Diving with Nitrox:**
Nitrox is most beneficial in the 50- to 100-foot depth range. No-stop times for dives shallower than 50 feet are often so lengthy that you'll deplete your tank before exhausting your dive time. Utilizing EANx36 at 60 feet, your no-stop limit extends to 80-90 minutes or more (depending on your computer) for your initial dive, meaning you'll be limited by your gas supply rather than your decompression limit.
You were trained to dive well within established limits, and by expanding those limits, you can enjoy longer dives while remaining conservative. Many divers appreciate nitrox diving within or even beyond air limits without approaching the actual no-stop maximum. While this doesn't guarantee 100 percent safety, staying comfortably within limits significantly reduces practical DCS risk for most divers.
**Nitrox Formulas and Definitions:**
- **Normoxic Nitrox:** Regular air or purified air with 21 percent oxygen - **EAN, EANx, Enriched Air, Enriched Air Nitrox:** Any mixture containing more than 21 percent oxygen - **EAD (Equivalent Air Depth):** The depth at which nitrogen would dissolve at the same rate as when breathing nitrox at a specific depth, compared to using air. - **PPO2 (or PO2):** Oxygen partial pressure, calculated as pressure in atmospheres multiplied by O2 percentage = PPO2 - **MOD (Maximum Operating Depth):** Maximum depth = *(1.4 ÷ mix%) - 1) X 33 - **Best Mix:** 1.4 ÷ ((Depth + 33) ÷ 33) = best mix
**SDI COMPUTER NITROX:**
Nitrox is a breathing gas with numerous benefits for both novice and experienced divers. This course covers the use of nitrox mixtures ranging from 22 to 40 percent oxygen.
**Who Should Consider This Course:**
- Certified divers seeking to expand their knowledge and skill set - Certified divers looking to extend their no-decompression time limits
**Course Prerequisites:**
- Minimum age: 18 (or 10 with parental consent) - SDI Open Water Scuba Diver, SDI Junior Open Water Scuba Diver, or equivalent certification, or current enrollment in one of these courses
**What You Can Expect to Learn:**
- The physiology of using different breathing gas mixtures and equipment considerations for nitrox use - Safe utilization of nitrox mixtures up to 40 percent in conjunction with a dive computer - Advantages and disadvantages of nitrox mixtures, along with how to analyze a nitrox blend
- 100 percent comprehension of questions and answers at the end of each chapter in the SDI Computer Nitrox Diving Course - Analysis of at least two nitrox cylinders - Logging of at least one nitrox cylinder - Programming a nitrox computer for a mixture between 22-40 percent oxygen
