A high reliability organization (HRO) is an organization that has succeeded in avoiding catastrophes in an environment where normal accidents can be expected due to risk factors and complexity. A high reliability organization (HRO) is an organization that has succeeded in avoiding catastrophes in an environment where normal accidents can be expected due to risk factors and complexity. Important case studies in HRO research include both studies of disasters (e.g., Three Mile Island nuclear incident, the Challenger Disaster and Columbia Disaster, the Bhopal chemical leak, the Tenerife air crash, the Mann Gulch forest fire, the Black Hawk friendly fire incident in Iraq) and HROs like the air traffic control system, naval aircraft carriers, and nuclear power operations. HRO theory flowed out of Normal Accident Theory, which led a group of researchers at the University of California, Berkeley (Todd LaPorte, Gene Rochlin, and Karlene Roberts) to study how organizations working with complex and hazardous systems operated error free. They researched three organizations: United States nuclear aircraft carriers (in partnership with Rear Admiral (ret.) Tom Mercer on the USS Carl Vinson), the Federal Aviation Administration's Air Traffic Control system (and commercial aviation more generally), and nuclear power operations (Pacific Gas and Electric's Diablo Canyon reactor). The result of this initial work was the defining characteristics of HROs hold in common: