Scuba Diving International (SDI) Computer Nitrox Practice Exam

What does the term oxygen toxicity mean?

1. Amino acids affecting diving performance

2. Condition from increased PO2 due to depth or duration

3. A decrease in nitrogen absorption

4. An increase in underwater vision quality

The correct answer is: Condition from increased PO2 due to depth or duration

The term oxygen toxicity refers to a condition that arises from an increased partial pressure of oxygen (PO2) in the body, which can occur due to increased depth or prolonged exposure to higher levels of oxygen. When divers breathe gas mixtures with elevated oxygen levels, particularly those used in technical diving or nitrox mixtures, the risk of experiencing oxygen toxicity rises. As a diver descends deeper underwater, the pressure increases, which in turn raises the partial pressure of any gases being breathed, including oxygen. At certain depths or after extended exposure, this heightened partial pressure can lead to symptoms such as visual disturbances, seizures, or even loss of consciousness, as the central nervous system reacts adversely to excessive oxygen levels. This condition is particularly pertinent for divers using nitrox—a blend of oxygen and nitrogen—where the oxygen content is intentionally higher than that found in regular air. Understanding the risks associated with oxygen toxicity is critical for safe diving practices, especially when planning dives that may involve deeper depths or longer durations at elevated oxygen fractions.