COMMON CAUSE ANALYSIS (CCA)

Independence between functions, subsystems or items may be required to satisfy the safety requirements.  It is therefore necessary to ensure that such independence exists, or that the risk associated with dependence is deemed acceptable.

Common Cause Analysis (CCA) provides the means to verify this independence, or to identify specific dependencies.

Common Cause Analysis supports the selection of the system architecture through determination that appropriate independence can be achieved.

The system Fault Tree Analysis (FTA) should be supplemented by the Common Cause Analysis to generate the top failure effects of the subsystem FTA.

Similarly, the CCA at the subsystem level should supplement the output of the subsystem FTA to yield the top failure effects at the item level for use in the item FTA.

The item CCA should also supplement the item FTA to further establish the design requirements, development assurance levels, and hardware reliability requirements.

CCA, which is frequently confused with Common Mode Analysis, consists of:

• Zonal Safety Analysis (ZSA),
• Particular Risks Analysis (PRA), and
• Common Mode Analysis (CMA).  By the way, would you like to know how to perform a large portion of Common Mode Analysis easily?  It is just one of many things that you will learn at our system safety courses!