Scuba Diving International (SDI) Computer Nitrox Practice Exam

Which gas mixture is primarily used in Nitrox diving for enhancing safety?

1. Helium and oxygen

2. Oxygen and nitrogen

3. Carbon dioxide and nitrogen

4. Nitrogen and argon

The correct answer is: Oxygen and nitrogen

The primary gas mixture used in Nitrox diving is a blend of oxygen and nitrogen. Nitrox, typically referred to as "Enriched Air Nitrox" (EANx), is composed of a higher percentage of oxygen compared to regular air, which contains approximately 21% oxygen. The increased oxygen concentration in Nitrox mixtures (usually between 22% and 40%) allows divers to benefit from reduced nitrogen intake during their dives. This reduction helps to lower the risk of decompression sickness, commonly known as "the bends," because divers absorb less nitrogen into their bodies. Using this specific combination significantly enhances safety by extending the no-decompression limits and allowing for longer bottom times at certain depths. Additionally, the higher oxygen levels can improve diver comfort and reduce fatigue under water. Other gas mixtures listed do not serve the same safety-enhancing purpose for recreational diving. The inclusion of helium in diving mixtures primarily addresses depth-related challenges, and carbon dioxide is generally a waste product that does not contribute to safe diving practices. Nitrogen mixed with argon is also not suitable for enhancing safety in modern recreational diving scenarios.