The purpose of this standard is to interpret and provide guidance in the application of the single-failure criterion, discuss failures, and present an acceptable method of single-failure analysis. It is not the function of this standard to identify where the single-failure criterion is to be applied or to force compliance on any system; however, in those cases where the single-failure criterion has been invoked, this standard establishes the requirements for its application. This standard shall be used to establish conformance with the requirements of IEEE Std. 603-1981 and the single-failure criterion as stated in that standard. NOTE--The single-failure criterion is also applied to designated safety functions in other standards, e.g., IEEE Std 308-1992, ANSI/ANS 51.1-1983, and ANSI/ANS 52.1-1983. Application of the single-failure criterion to the aggregate of all plant structures, systems, and components is specified in 3.2.1 of ANSI/ANS 51.1-1983, ANSI/ANS 52.1-1983, and IAEA Safety Series No. 50-P-1 (1990).