Which of the following gases requires careful monitoring due to its impact on diving safety?

Oxygen requires careful monitoring during diving because it is involved in the phenomenon known as oxygen toxicity, which can occur at elevated partial pressures commonly encountered when using enriched air nitrox. As divers descend and increase their depth, the pressure increases, and consequently, the partial pressure of the oxygen in a gas mixture also increases.

When the partial pressure of oxygen exceeds 1.4 ATA (atmospheres absolute), there is a greater risk of experiencing central nervous system toxicity, which could lead to seizures and other serious health risks while underwater. This is why divers using nitrox mixtures must carefully monitor their depth and the corresponding partial pressure of oxygen in their gas mix.

Furthermore, oxygen levels need to be controlled to prevent high oxygen concentrations, which can also affect the reliability of diving safety protocols and lead to dangerous situations. Keeping within safe limits ensures the diver can avoid these risks, making the careful monitoring of oxygen not just necessary but critical for safe diving practices.