Relative Safety: Absolute vs. Acceptable
The term "safe system" may be a reference to either absolute safety or to acceptable safety. As soon as a system is determined to be safety-critical, absolute safety may become an impossible target.
Regardless of whether an explicit value is set on human life, acceptable or relative levels of safety generally imply that there is some way of judging how much harm either justifies more effort or demands a different approach. The principle of As Low As Reasonably Practicable (ALARP) embodies the concept that acceptability can be influenced by the cost of improving safety.
Not all safety standards specify an acceptable level of safety, focussing more on how to ensure and assure that an acceptable level of safety has been achieved.
Acceptable levels of safety can be based on factors including: legal requirements, the regulatory environment, the current level of safety, customer requirements, and corporate safety targets.
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The Ford Pinto fires were a case where different views of the acceptable safety came to light.