Earlier quoted context omitted.
Sorry if this is a stupid question but how far down could you dive?
It depends on the tables and physiology, because you need to safely oxygenate all the body's tissues with regular breathing at depth. He could probably dive [edit: said Nitrox, I'd learned non-air Nitrox increases maximum depth but it increases time-at-depth] Trimix until about 100m, deeper might need a different mix.
- Oxygen 0-20 ft
- Nitrox in-between depending on % oxygen
- Air 0-200 ft
- Trimix 0-250 ft
- Hypoxic Trimix up to 500 ft, minimum depending on % oxygen