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Freedom from all forms of harm. Nothing is safe. Generals term denoting an acceptable level of risk of, relative freedom from, and low probability of harm. The associated risks that have been identified have been accepted provided that all identified controls are implemented and enforced.

Safety or Safe. Freedom from those conditions that can cause death, injury, occupational illness, or damage to or loss of equipment or property, or damage to the environment.

Note that absolute safety is not possible because complete freedom from all hazardous conditions is not possible. Therefore, safety is a relative term that implies a level of risk that is both perceived and accepted. Thus the emphasis in SSPs as reflected in the definitions above is in managing risk. Chapter 3(FAA SS HB) describes the risk management process. “System” is also a relative term. A subsystem can be viewed as a system with more narrow predetermined boundaries than the system. System safety is not an absolute quantity either. System safety is an optimized level of risk that is constrained by cost, time, and operational effectiveness (performance). System safety requires that risk be evaluated and the level of risk accepted or rejected by an authority. Finally, system safety is a discipline employed from the initial design steps through system disposal (also known as “cradle to grave or “womb to tomb”).

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