Common Cause Failure

A common cause failure (CCF) - also refered to as Common Mode Failure - is a failure where:

• The function of multiple CI is disrupted or destroyed by the same cause or hazard affecting the CI at the same location or area in the same time frame (e.g., a hurricane blocking roads and affecting telecommunication and power lines; a collapsed bridge which blocks inland shipping, road transport and caused disruption of gas, power and telecommunication lines)
• Item failures result from a single shared cause and coupling factor (or mechanism)

Definitions

National Definitions

Australia

Common mode failure is the coincident failure of two or more independent components as the result of a single cause; of particular concern in an instrument system incorporating redundancy where an event causes coincident failure of two or more of the normally independent channels.

International Definitions

IAEA

Common cause failure is the failure of two or more structures, systems or components due to a single event or cause.

Common mode failure is the failure of two or more structures, systems or components in the same manner or mode due to a single event or cause.

See also

• Geographical dependency - incorrect term often used for Common cause failure