How does the percentage of oxygen in a Nitrox mixture affect the MOD?

In a Nitrox mixture, the percentage of oxygen directly influences the Maximum Operating Depth (MOD), which is the deepest depth at which a diver can safely breathe the gas without experiencing toxic effects from oxygen. As the percentage of oxygen in the mixture increases, the MOD decreases because of the increased risk of oxygen toxicity at greater pressures.

The rationale behind this is grounded in the partial pressure of oxygen (PPO2). At higher depths, the pressure increases, which in turn increases the PPO2 of the gas mixture. For example, with a Nitrox mix containing a higher percentage of oxygen, the PPO2 reaches the threshold for toxicity at shallower depths. Therefore, having a higher percentage of oxygen leads to a lower maximum operating depth to ensure safety.

This critical relationship necessitates careful planning and adherence to the MOD to avoid harmful physiological effects. In practice, divers must be well aware of their gas mixture's oxygen content and how it governs their diving limits.