Common-cause failures as major issue in safety of control systems

In order to gain an improvement of safety or availability measures of the safety-relevant control system through employment of redundancy a redundant system has to comply with the requirement on independence of redundant parts. If the requirements on the independence of redundant parts are unfulfilled, then a common-cause failure can directly cause a hazardous state on a system level through its effects on multiple redundant parts. Identification of sources and quantification of the common-cause failure parameters has been proved to be a formidable task. The latter problem, including other major safety-affecting factors lays in the focus of this paper. Our proposed technical safety analysis concept is extended, so now it partially covers elusive problems related to the common-cause failures.