Last weekend I overheard two ladies in the parking lot talking about how they couldn't believe Drop Tower was aloud to reopen after people lost body parts on the ride.
The parks also have a system that will let them know when there is lightning and they have certian distacne markers that they will judge by. If it is within a certian distance even if you don't see it they will shut down rides. I know this is true for Kings Island and not to sure but probably true for CP.