COLUMBIA GULF TRANSMISSION, LLC

Incident Narrative

ON MARCH 14, 2020, AN ALARM WAS ACKNOWLEDGED BY THE US NATURAL GAS CONTROL, EAST TEAM, SUBJECT TO AN EMERGENCY SHUTDOWN (ESD) AT DELHI COMPRESSOR STATION (CS) UNIT 811 FAULT SIGNAL. COLUMBIA GULF TRANSMISSION, LLC (COLUMBIA) OPERATES AND MAINTAINS DELHI CS WHICH IS CLASSIFIED AS A TRANSMISSION CS, IS LOCATED IN RICHLAND PARISH, LOUISIANA AND NEAR THE CITY OF DELHI. AFTER RECEIVING THE NOTIFICATION FROM COLUMBIA MONITORING CENTER, CS PERSONNEL RESPONDED TO THIS ESD EVENT AT DELHI CS AND ADDRESSED THE UNINTENDED RELEASE OF NATURAL GAS (MATERIAL) THAT WAS VENTING INTO ATMOSPHERE FROM THE BLOW DOWN DISCHARGE STACKS. THE CS PERSONNEL INSPECTED AND SECURED THE AREA TO ENSURE THAT IT WAS SAFE TO OPERATE DISCHARGE VALVES BEFORE MANUALLY CLOSING THEM. PRELIMINARY INVESTIGATION IDENTIFIED THE PROBABLE CAUSE THAT LED TO THIS UNINTENDED RELEASE AT UNIT 811 WAS DUE TO A FAULT SIGNAL ISSUED BY THE PROGRAMMABLE LOGIC CONTROLLER (PLC) AT THE INPUT/OUTPUT (I/O) BLOCK. THE ISSUED COMMAND INITIATED THE ACTIVATION OF THE BLOW DOWN VALVE TO OPEN (AS IT WAS DESIGNED TO) HOWEVER, THE SEQUENCING HAD FAILED TO CLOSE THESE VALVES TO STOP THE FLOW AND REMAINED OPEN FOR APPROXIMATELY 38 MINUTES. THE FAULTY PLC I/O CARD AS INDICATED AT THE UNIT CONTROL PANEL WAS REPLACED. ALL ALARMS WERE CLEARED AT THE PLC CONTROL PANEL, REQUIRED FUNCTIONAL TESTS WERE CONDUCTED WITH NO NEW ERRORS GENERATED (TO ENSURE NORMAL OPERATION OF THE UNIT), THEN THE UNIT WAS RETURNED BACK TO SERVICE. ROUTINE SAFETY CHECKS WERE CONDUCTED WHERE THE UNIT WAS MONITORED FOR A WHILE, VERIFIED THAT ALL SYSTEMS ARE RUNNING IN NORMAL MODE WITH NO NEW ERRORS WERE GENERATED THEREAFTER. A CALCULATED VOLUME OF UNINTENDED RELEASED MATERIAL WAS 7,313 MCF INTO ATMOSPHERE WHERE THE RELEASED MATERIAL DID NEITHER IGNITE NOR CAUSE ANY DAMAGE TO ANY OF THE CS DEVICES.