-147.148 System Hazard Analysis Event Trees vs Fault trees Relief valve 1. Relief valve 2 Pressure decreases Pressure Pressure decreases Fails Explosing Relief valve 1 Relief valve 2 A too high Operator does not Valve Computer does no Valve perator failure open valve I know to open valve 2 Pressure Comput monitor oes not issue indicator indicator /\light fails too latec Leveson − 147,148 System Hazard Analysis Event Trees vs. Fault Trees Relief valve 1 Relief valve 2 Opens Pressure decreases Fails Opens Fails too high Pressure Pressure decreases Explosion open valve 1 Computer does not failure Valve Valve 1 Open does not issue light fails indicator indicator position fails on on command to open valve 1 Computer Computer output too late Pressure monitor failure Operator does not know to open valve 2 inattentive Valve Operator failure does not open Relief valve 2 Explosion Relief valve 1 does not open Pressure too high