COLUMBIA GULF TRANSMISSION, LLC

Incident Narrative

ON JANUARY 17, 2024, AT APPROXIMATELY 06:20 HRS. CST, TC ENERGY WAS NOTIFIED BY THE PUBLIC OF A POTENTIAL GAS RELEASE AT THE CORINTH COMPRESSOR STATION. TC ENERGY OPERATIONS PERSONNEL ARRIVED AT THE CORINTH COMPRESSOR STATION, LOCATED IN ALCORN COUNTY, MISSISSIPPI, AND DISCOVERED NATURAL GAS BEING RELEASED TO ATMOSPHERE. THE UNINTENTIONAL GAS RELEASE WAS CONFIRMED BY TC ENERGY OPERATIONS AT APPROXIMATELY 07:16 HRS. CST. IT WAS LATER CONFIRMED THAT THE BLOWDOWN VALVE'S (5SH-2D BD) STRATIX SWITCH, WHICH COMMUNICATES THE VALVE STATUS TO THE PROGRAMMABLE LOGIC CONTROLLER (PLC), HAD MALFUNCTIONED. THIS LOSS OF COMMUNICATION CAUSED THE BLOWDOWN VALVE TO LOSE ITS HOLD CLOSED COMMAND FROM THE PLC. THE VALVE TRAVELED OPEN DUE TO THE LOSS OF SIGNAL WHEN THE SWITCH FAILED. THE MALFUNCTIONING SWITCH ALSO CAUSED NO ALARM TO BE CONVEYED TO THE EMERGENCY SHUTDOWN DEVICE (ESD) PLC AND THEREFORE, IS THE REASON GAS CONTROLLER DID NOT RECEIVE A ""CALL OUT"" ALARM FROM THE SCADA SYSTEM. TC ENERGY OPERATIONS MANUALLY CLOSED THE BLOWDOWN VALVE AT 08:05 HRS. CST. THE STRATIX SWITCH WAS REPLACED AND THE ESD SYSTEM WAS PLACED BACK INTO NORMAL SERVICE AT APPROXIMATELY 12:30 HRS. CST. THE CORINTH COMPRESSOR STATION WAS NOT SHUT DOWN DUE TO THIS INCIDENT.