Critical Safe Failure
spurious failure of a safety system, due to safe failure(s) of its component(s), triggering the safety action
and leading to a spurious safety action
Note 1 to entry: The concept of critical safe failure is illustrated in Figure B.1.
Note 2 to entry: This is a systemic failure in relationship with a given safety action performed by the safety
system. This concept is irrelevant for an individual item on the shelves.
Note 3 to entry: The same failure of a component belonging to a safety system may be safe or spurious (critical
safe) depending of the system state from which it occurs (e.g. the safe failure of a sensor belonging to 2oo3 is only
safe when it occurs in 1st position. It is critical when it occurs in 2nd position).
Source: ISO/TR 12489:2013(E) Reliability modelling and calculation of safety systems. Global Standards