Catch timeouts

I'm resetting set_time_limit() with each iteration of a rather long loop. Right now when the script reaches its time limit I sometimes end up getting just a blank page. Even though I call flush() within each iteration and do lots of error checking along the way, it seems to not be enough. I could have sworn I once saw a function that would check whether the script was being cancelled because a timeout had occured, thereby allowing you to make a more graceful exit from the script. But now I can't seem to locate anything like that in the manual. If someone could point me to the right function, or suggest an alternative method for catching those timeouts, I would be grateful. TIA! -- CC