Safe Failures or Spurious Trip Failures
Safe failures (spurious trip failures) are failures that have the potential to trigger the safety function when it is not needed. A single safe failure is generally not sufficient to actually trip unexpectedly a redundant safety system (e.g. 2 safe failures are needed for a 2-out-of-3 voting system).
Source: API STD 689, Collection and Exchange of Reliability and Maintenance Data for Equipment, First Edition, July 2007. Global Standards