MOD — Maximum Operating Depth

The Maximum Operating Depth (MOD) is the deepest point you can go before your breathing gas becomes toxic. It defines the limit where partial pressures reach dangerous levels. You use this calculation whenever you switch from air to enriched air Nitrox. For example, a diver using EAN32 must not exceed 34 m because oxygen toxicity risks increase significantly beyond that depth. If you ignore these limits, you risk seizures.

Always check your computer settings before every descent. I once saw a student in Koh Tao set their Nitrox profile for EAN36 while actually breathing EAN32. This mistake changes your MOD from 34 m to 37 m. That 3 m difference is dangerous. Always verify your gas percentage against your dive computer settings so that you stay within safe limits.