When using Nitrox, what does it mean to exceed the MOD?

Exceeding the Maximum Operating Depth (MOD) when using Nitrox signifies that a diver is going deeper than the depth limit recommended for their specific gas mixture. Each Nitrox blend has a calculated depth where it is safe to use, determined by the partial pressure of oxygen in that mixture. When a diver surpasses this depth, the percentage of oxygen they are breathing increases to a level that becomes potentially toxic, leading to oxygen toxicity, which can have serious health consequences, including seizures or loss of consciousness underwater.

This understanding is crucial for careful planning and execution of dives using Nitrox. Divers must always be aware of their specific gas mixture's MOD to avoid the risks associated with exceeding safe depths.