mod/dive plan ?

What can you do if you're diving using a blend of EAN and all of a sudden you notice your buddy or another diver descending unconscious below your MOD and contingency depth. Should you select a blend when planing the dive to deal with such a situation ?

Remember both depth and time matter. You could go over 1.6 ata in an emergency. NOAA gives you 45 minutes at 1.6 Ata. I did a class years ago where we were at close to 3 ata in a chamber and no one toxed. That is not to say you want to routinely do this but the risk for a short exposure less than 2 ata may be low enough to save a life.

My actions would depend on whom the unconscious diver is. But no, I don't plan my MOD around that (though I tend to choose lower PPO2 limits for other reasons).

That's what I was wondering if you could do a rescue and not become a victim if done quickly and not to deep.

That is really very personal decision. Would you take on a 0.1% chance of dieing to save someone who will certainly die? What about 1% or 10% what is your limit? The PPO2 limits are set very conservatively since the goal is to have many thousands of dives occur with no bad outcomes. That said the limits have drifted down over the years. NOAA allowed 1.6 ATA PPO2, and that has dropped down to 1.4 or 1.2 PPO2 depending on the organization. There is no instant death for exposures to 2 or even 2.5 ATA, but it is a slippery slope. Pretty clearly one could justify a higher PPO2 for a short exposure in an emergency than what would be recommended to the diving population for thousands routine dives. There is no right answer.

Then perhaps one way to plan a dive with nitrox would be to use it when you know the bottom depth will not be below 1.6 ata. This could be a problem when diveing dive sites with known downwelling that could potentially take you quite deep.