Annex F: Estimation of CCF

Le misure da adottare per ridurre il rischio di guasti contemporanei

Last edit: 12/07/2023

CCF (Common Cause Failure) is defined as Failure which is the result of one or more events and which causes simultaneous failures of two or more separate channels in a multi channel system, leading to the failure of a safety related control function.

 There are several influencing factors:

  •     The technology used
  •     The architecture
  •     The type of application
  •     The environment in which the machine operates

The CCF rate represents the frequency at which these faults occur on a channel and this is calculated as β•λd.



The Standard EN 13849 establishes that the beta-factor (β) must be below 2%. It provides a series of measures to be taken to reduce β. Table F.1 lists the measures and their scores, based on engineering judgement, which represent the contribution each measure makes in the reduction of common cause failures. The aim is to achieve a minimum score of 65/100 in order to have β≤2%.