Catastrophe strikes as one of America's most vital freeway intersections erupts in flames and completely collapses in San Francisco; experts use the latest science to investigate how an overturned tanker truck spawned a devastating inferno.

Tragedy strikes in Cincinnati as a sudden bridge collapse leaves one of America's busiest highways at a complete standstill; using scientific methods, expert engineers investigate and reveal how a routine demolition unfolded so disastrously wrong.