History reveals an ever-increasing caboodle of protective measures for assuring an acceptable level of safety for both new product designs and for the remediation of man-made and natural hazards. Some seventy years ago, safety professionals began to functionally categorize these safety tools and rank the categories according to their perceived effectiveness. At first, the resulting hierarchies were designated Safety Hierarchies; later updated versions are now referred to as Hierarchies of Controls. To characterize Hierarchies, sixty-six references were surveyed that were published after 1952. Each of these design recipes begin with the admonition “Eliminate the hazards.” All of the hierarchies were created using consensus or speculation, not research. We establish that the Safety Hierarchies and the Hierarchies of Controls are merely rules of thumb, not theorems. Generally, different hierarchies give rise to different designs. The principal strength of both Hierarchies is their replacement of the myth of colloquial safety as “freedom from harm” with a realistic technical definition of safety as an “acceptable level of risk” that is systematically achievable however tortuous.

safety hierarchy, hierarchy of controls, hierarchies, risk assessment, risk reduction, system safety