Scuba Diving International (SDI) Computer Nitrox Practice Exam

What is the maximum partial pressure of oxygen (PO2) we use in Nitrox diving?

1. 1.2

2. 1.4

3. 1.6

4. 1.8

The correct answer is: 1.6

In Nitrox diving, the maximum partial pressure of oxygen (PO2) that is typically considered safe is 1.4 ATA (atmospheres absolute). This limit is established to balance the benefits of enhanced oxygen levels against the risks associated with oxygen toxicity, which can increase with higher partial pressures of oxygen. At a PO2 of 1.4 ATA, divers can maximize the advantages of using Nitrox, such as reduced nitrogen absorption and extended no-decompression limits, while minimizing the risk of experiencing central nervous system (CNS) toxicity. This is particularly important for dives that involve deeper depths or increased time underwater. The reasons for not exceeding 1.4 ATA are linked to physiological safety thresholds. Exceeding this level can increase the risk of toxicity, which may lead to symptoms ranging from visual disturbances to convulsions. Therefore, while divers sometimes work with higher partial pressures, such as 1.6 ATA or even 1.8 ATA, these levels are generally reserved for specific circumstances and require additional training and precautions. Thus, recognizing 1.4 ATA as the standard maximum limit for recreational Nitrox diving is essential for maintaining safety during underwater excursions.