You could be a mile away and never be affected by a chemical spill if the prevailing winds and elevation favors you. You could be 500 miles away downstream though and be poisoned without even knowing why. Hell, you could be halfway around the world and eat/drink meat,crops/well water from ground zero and die.
I wouldn't move within 100 miles of a toxic spill knowingly.
One day I'll tell the story of the Burnt Fly Bog in New Jersey. Spooky.
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