Can you switch from NITROX to air in the middle of a dive?

• A. Yes, Air Decompression Table for the actual depth
• B. No, you must stay on Nitrox table
• C. Use Residual Nitrogen Timetable
• D. Change to standard air table at the surface

Answer: (A)

Switching breathing gas mid-dive means you must follow the decompression schedule for the gas you are now on, at the depth you are at when the switch occurs. Air has a higher nitrogen fraction than many nitrox mixes, so the amount of nitrogen your tissues are carrying changes, and the safe ascent plan is based on air at that actual depth. Using the air decompression table for the current depth ensures your nitrogen loading from the nitrox portion and the switch are both accounted for, guiding you to the correct stops or no-decompression plan.

Continuing with nitrox tables would under-calculate the nitrogen you’re accumulating on air, which isn’t safe. Waiting until surface to switch to an air table ignores the in-water gas change. Relying only on a residual nitrogen timetable wouldn’t provide the full depth-specific decompression guidance required once you’re on air.