Plot: In this hour, we examine a massive oil tanker explosion that killed nine; a subway tunnel cave-in that swallowed part of Hollywood Boulevard; a freighter plane crash that destroyed an 11-story apartment building; an historic molasses flash flood; and a freeway ramp collapse that buried construction workers in rubble and concrete. Investigators from NTSB, Cal/OSHA, and Boeing, structural and geo-technical engineers, and historians explain how so much could have gone wrong, costing so many lives