|Definition:|| criterion (or requirement) applied to a system such that it must be capable of performing its task in the presence of any single failure
- Any single detectable failure within the safety systems concurrent with all identifiable, but non detectable failures.
- All failures caused by the single failure.
- All failures and spurious system actions that cause, or are caused by, the design basis event requiring the safety function.
Note 1 to entry: The single failure could occur prior to, or at any time during, the design basis event for which the safety system is required to function.
Note 2 to entry: This entry was numbered 393-18-27 in IEC 60050-393:2003.