tammy tillinghast here is your "unexplained reason"
One of the comments by Tammy Tillinghast said that "One of the only parts I didn't understand was Kevin Corrigan's unexplained, fire-setting character"
What I got from that was, that the industrial company was contaminating the surrounding nieghborhood and cause oil (i think thats what it was) to come up through the grass. He was setting fire to it to show how the industrial world is screwing up their surroundings. At least thats what I got from it. I guess you could take it how you want it.
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"We're going to the mall" Michael, -Dawn of the Dead 2004