To understand system safety, one must know the fundamentals that go into defining the discipline. A system can be defined as a group of interconnected elements united to form a single entity. Systems may include something as simple as a toaster or as complex as a chemical refinery. Perhaps the most important thing about systems is that they can sometimes be and often are further defined into subsystems, assemblies, subassemblies, and components. If the subsystems contain interdependent entities, they then also can be defined as systems. For example, a car brake can be defined as either a stand-alone system or a subsystem of an automobile.
‘‘Safety’’ can be defined as making something free from the likelihood of harm. Roland and Moriarty state that safety in a system is ‘‘a quality of a system that allows the system to function under predetermined conditions with an acceptable minimum of accidental loss.’’