The terminology on common cause failure has changed over the years. In the beginning only common mode failures were considered. Later, the definition of common cause failure was introduced referring to a slightly wider group of failures superseding common mode failures. However, at that time the idea that common cause failure was synonymous with common mode failure was widespread. The issue regarding the difference between common cause and mode was clarified in 1985, when the term dependent failures was introduced to supersede and encompass common cause, common mode failures and “cascade failures”. Cascade includes all dependent failures that are not common cause failures. Common mode failures are a subset of common cause failures, whilst dependent failures encompass both common cause and cascade failures.
“A common-mode failure (CMF) is the result of an event(s) which because of dependencies, causes a coincidence of failure states of components in two or more separate channels of a redundancy system, leading to the defined system failing to perform its intended function”.
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