On a warm summer night in July 2013, patrons on a bar terrace in Lac-Megantic, Quebec looked up to see a 10,000-ton freight train screaming around a curve with no lights, no driver, and no horn. What followed killed 47 people and became the deadliest non-passenger rail accident in Canadian history.

This episode is a master class in the Swiss cheese model of disaster, showing how aggressive cost-cutting dismantled every safety net until all the holes lined up. We trace the full mechanical and human chain that turned volatile crude oil into a tsunami of fire.

• How a cheap epoxy engine repair from eight months earlier started the fire that doomed the train
• Why volatile Bakken crude in thin-walled DOT-111 tank cars amounted to liquid dynamite on deteriorating tracks
• The fatal air-brake physics: shutting off the engine  ...