PEOPLES GAS LIGHT & COKE CO

Incident Narrative

AT APPROXIMATELY 9:40 PM ON SATURDAY NOVEMBER 21, 2015 AN EMERGENCY VENT VALVE ON THE EMERGENCY SHUTDOWN SYSTEM FOR THE STORAGE FACILITY AT THE MANLOVE STORAGE FIELD SPURIOUSLY OPENED AND EMITTED GAS FOR 10 MINUTES UNTIL OPERATING PERSONNEL CLOSED BLOCK VALVES TERMINATING THE RELEASE. THIS VALVE IS DESIGNED TO OPEN WHEN THE EMERGENCY SHUTDOWN SYSTEM ACTIVATES. IN THIS CASE THE VALVE SHOULD NOT HAVE OPENED. CALCULATIONS ON THE SIZE OF THE RELEASE WERE COMPLETED AND THE ESTIMATED RELEASE WAS 11.756 MILLION FT3. SINCE THIS EXCEEDS THE REPORTING CRITERIA OF 3 MILLION FT3 LISTED IN 49 CFR191.3 A ONE HOUR CALL WAS MADE TO THE NRC AND A FOLLOW UP CALL WAS MADE TO THE ICC. THE CALL TO THE NRC WAS DELAYED BECAUSE THE INITIAL ASSESSMENT MADE BY MANLOVE PERSONNEL WAS THAT THIS EVENT DID NOT MEET THE DEFINITION CONTAINED IN 49CFR191.3. PERSONNEL AT MANLOVE ORIGINALLY BELIEVED THAT THE DEFINITION LIMITED REPORTABLE RELEASES TO LEAKS IN THE SYSTEM. SINCE THIS VALVE IS AN IDENTIFIED RELEASE PATH, THEY INITIALLY DETERMINED IT WAS NOT REPORTABLE. HOWEVER FURTHER REVIEW OF THE EVENT AND THE REGULATIONS DETERMINED THAT THIS EVENT DID MEET THE DEFINITION CONTAINED IN 49 CFR 191 OF A RELEASE. THE ICC WAS ON SITE ON 11/24/15 AND 11/25/15 FOR THE INVESTIGATION INTO THE INCIDENT. THE INVESTIGATION CONCLUDED THAT THE SEALS/GASKETS HAD BROKEN DOWN IN THE VERSA VALVE. THE SUSPECTED CAUSE OF THIS BREAKDOWN WAS DUE TO NUMEROUS FREEZE AND THAW CYCLES. SUPPLEMENTAL: CHANGED THE TIME THAT THE NRC RECIEVED THE REPORT TO REFLECT THE CENTRAL TIME ZONE. CHANGED THE CLASS LOCATION OF THE INCIDENT TO CLASS 1 SINCE THERE IS LESS THAN 10 OR FEWER BUILDINGS INTENDED FOR HUMAN OCCUPANCY WITHIN THE CLASS LOCATION.