Fault tree analysis incorporating dependent events

A direct method of incorporating initiator events with varying potential damage intensities into fault trees is described. This method is applicable to modeling external events and provides inclusion of the complete intensity ranges of the events considered. The resultant cumulative intensity dependent model requires availability data conditional on the event being described. An example considering earthquakes shows the method to be of general use and consistent with present quantification techniques. The shape of the frequency versus intensity function is seen to have a strong influence on the event's unavailability contribution