Double jeopardy is the occurrence of two independent deviations or two initiating events at the same time. In determining if the causes are independent, careful consideration should be given to common mode failures and process dependencies. Failure of a safety device in response to a control system failure or human error would not be considered double jeopardy. For example, a PSV failing to open on demand in response to high pressure is not double jeopardy.
Care needs to be taken when excluding events because of ‘double jeopardy’. If the HAZOP-Team decides that a particular cause is credible, this shall be evaluated regardless of whether this is ‘double jeopardy’ or not.