It is well known the arc flash hazard is very dependent on the arc duration. Having a very long duration due to a protective device not tripping in the instantaneous region can lead to "interesting" results. Many of us have seen this: Arc Flash Boundary calculations with unbelievable distance. Years ago, a friend had one that was pushing half a mile - before they began using the 2 second cutoff.

Here is the question: What is the largest Arc Flash Boundary you have seen or calculated?
Less than 100 ft.
100 to 250 ft.
250 to 500 ft.
500 to 1000 ft.
Greater than 1000 ft. (how large?)

I don't remember the exact distance (it was measured in miles), but the AF boundary was larger than the town in which the paper mill was located. Effectively the problem involved the poor handling of >15kV open air equipment by the typical software methods employed before 2008. Because of these results, our company implemented several engineering standards, including a '2 second cut off rule'

I looked up my old report from 2004 the longest distance, using SKM, was 962,211 inches or some 8000 ft.