DTE GAS COMPANY

Incident Narrative

(ON JULY 18TH, 2024, A SUPPLEMENTAL-FINAL WAS RESUBMITTED PER THE FOLLOWING REQUEST FROM DARREN LEMMERMAN, PHMSA INVESTIGATOR, ACCIDENT INVESTIGATION DIVISION ON JUNE 25, 2024: OUR INFORMATION RESOURCES MANAGER HAS IDENTIFIED AN ISSUE WITH HOW THE 30-DAY REPORT CALCULATED THE RELEASED GAS VOLUME AND THE COST OF THE GAS/MCF. THE FIX HAS BEEN IMPLEMENTED AND WE HAVE BEEN TOLD THAT IF THE REPORT IS RESUBMITTED AS A SUPPLEMENTAL FINAL THAT THE ERROR WILL BE CORRECTED. IF YOU COULD HELP OUT, IT WOULD BE MUCH APPRECIATED.) A RELIEF VALVE WENT OFF AT LEELANAU GATE STATION AT APPROXIMATELY 8:35 PM ON NOVEMBER 4, 2021 (AT THIS TIME DTE GAS WAS NOT AWARE OF THE RELEASE). DTE GAS RECEIVED A CALL OF ODOR IN THE AIR/GAS BLOWING AT 1:00 AM AND DTE DISTRIBUTION ARRIVED AT 1:20 AM. DTE GAS TRANSMISSION OPERATIONS WERE CALLED AT 1:30 AM. THE TRANSMISSION TECH ARRIVED AT 03:30 AM ON NOVEMBER 5 AND BLOCKED IN THE RELIEF, AS THERE IS NO NEED TO PROTECT A LOWER MAOP DOWNSTREAM. ONLY 1 QUALIFIED PERSON WAS AVAILABLE. HE HAD TO GET A CONFIRMATION (FROM THE OTHER TECH) TO SHUT IT IN. THE GAS CONTINUED TO BE RELEASED INTO THE AIR UNTIL APPROXIMATELY 3:30 AM ON NOVEMBER 5, RESULTING IN ODOR IN THE AIR. THIS RELEASED 5.8 MMCF OF GAS INTO THE ATMOSPHERE, MAKING IT REPORTABLE TO BOTH THE STATE OF MICHIGAN, PHMSA, AND EGLE. GAS CONTROL WAS GIVEN THE RELEASE TO BRING THE PETOSKEY/TRAVERSE CITY SYSTEM PRESSURE BACK UP (HAD BEEN ON A PRESSURE REDUCTION TO BELOW 500 PSIG SINCE JUNE, TO NORMAL LINE PRESSURE, GENERALLY JUST ABOVE 500 PSIG ) AND STARTED BRINGING PRESSURE UP TO AROUND 8:00 PM ON NOVEMBER 4, 2021. AS PART OF THE TRAVERSE CITY ALPENA REINFORCEMENT PROGRAM (TCARP), WE WERE INSTALLING A BRAND NEW STATION/TOTALLY REBUILT AN EXISTING STATION; DE-PRESSURIZED TO INSTALL THE NEW FRANKFORT LOOP PIPELINE. THERE ARE NO ALARMS ON THIS RELIEF (NO HIGH-PRESSURE ALARM BELOW RELIEF POINT) WHICH IS NOT UNUSUAL. THE RELIEF WAS PRESET TO PROTECT THE FRANKFORT PL DOWNSTREAM OF LEELANAU GATE IN THE CITY OF INTERLOCHEN. IT APPEARS LIKE IT DID PROTECT THE SYSTEM (THE RELIEF WENT OFF) AT APPROXIMATELY 507-513 PSIG. THERE WAS NO RETURN TO SERVICE PROCEDURE FOR THE PETOSKEY SYSTEM TO STIPULATE THE NEED FOR A RELIEF OR THE NEED TO BLOCK IN THE RELIEF. THE 8"" DOWNSTREAM PIPELINE STILL HAD AN 812 PSIG MAOP AND HAD NOT YET BEEN DERATED TO 486 PSIG MAOP. THEREFORE, THE RELIEF VALVE SHOULD NOT HAVE BEEN PUT INTO SERVICE PRIOR TO THE DURATION. THE ROOT CAUSE WAS DETERMINED TO BE INADEQUATE PROCEDURAL ADHERENCE TO THE RETURN TO SERVICE PRESSURE CONTROL PROCEDURE (PCP) FOR THE LEELANAU GATE STATION THAT TOOK PLACE ON SEPTEMBER 20, 2021. THE INTENT OF THE PCP WAS TO RUN THE STATION ON BYPASS BUT OPERATIONS MISINTERPRETED ENGINEERING'S PLANNED FLOW PATH IN THE PCP AND OPENED A LEG OF THE STATION PIPING FOR PURGING WHICH ALLOWED THIS NEW RELIEF VALVE TO BE EXPOSED TO THIS HIGHER PRESSURE ONCE THE SYSTEM WAS REPRESSURIZED.