Just to make sure everyone understands what the "nearest suitable airport" means - it's also time to get to a suitable airport and not just the distance.
For example - overhead an airport at FL 350 that will handle the aircraft, but a better, more suitable airport is 70 nm away. The descent time from FL 350 for both airports is approx the same, so the airport 70 nm away is in fact the more suitable.
It's the crew on the day who make that assessment.