Why are divers advised against switching between air and nitrox during a dive?

Switching between air and nitrox during a dive creates significant complexities in planning and execution, particularly regarding the calculation of Maximum Operating Depth (MOD) and no-decompression limits (NDLs). Each gas mixture has its own specific MOD, which is the deepest depth at which a diver can safely breathe that gas without exceeding safe partial pressure levels of oxygen.

When a diver switches from one gas to another, the calculations related to these limits become more complicated. For instance, if one dives with nitrox and then switches to air, the diver must be aware of how each gas composition affects nitrogen uptake and elimination. The differing properties of each gas can make it difficult to track how much nitrogen the body has absorbed, complicating dive planning, ascent rates, and safety stops required to avoid decompression sickness. This can lead to an increased risk of ascent-related injuries due to improper management of nitrogen loading.

In summary, the key concern with switching between air and nitrox is maintaining clarity in calculations essential for diver safety, making it crucial for divers to stick to one gas type throughout a single dive.