This could have been sabotage by anti-domestic energy liberals who sabotage trucks and equipment in the United States and Canada regularly.
It is extremely common.
The initial fire between Nantes and Lac-Mégantic that was put out before the train rolled away and caused a far worse fire might have been sabotage. But the reasons this became such a huge disaster really looks like incompetence.
Time line:
http://www.edmontonjournal.com/news/M%C3%A9gantic+fire+timeline/8626739/story.html