Four years ago, in August 2012, a corroded pipe at the Chevron refinery in Richmond, California ruptured, resulting in a catastrophic fire and a toxic vapor plume that engulfed, not only the refinery, but also spread over the northeastern San Francisco Bay area. Nineteen Chevron employees were caught up in the vapor cloud and one was trapped by a fireball. Remarkably, all survived. In the next several days, some 15,000 people in communities surrounding the refinery sought medical attention for symptoms related to smoke exposure. According to the U.S. Chemical Safety Board, among the reported…