Pressure safety valves are installed on every pressure vessel(as defined by API).All relief line are connected to flare header .Before the relief lines are, then, connected to flare header. Before the relief load is burnt at flare, it should pass through the caustic scrubber in order to remove the phosgene in the vapor. Shutdown valves are also installed for insolation in emergency cases. These shutdown valves will isolate the downstream equipment from the effected upstream equipment.