CENTERPOINT ENERGY RESOURCES CORP., DBA CENTERPOINT ENERGY MINNESOTA GAS

Incident Narrative

SUPPLEMENTAL UPDATE 12/08/2017 - THE NTSB PRELIMINARY REPORT ADOPTED ON AUGUST 21, 2017 PUBLICLY DESCRIBES THE EVENT AS FOLLOWS: ON AUGUST 2, 2017, AT 10:22 A.M., A BUILDING AT THE MINNEHAHA ACADEMY (NORTH CAMPUS) IN MINNEAPOLIS, MINNESOTA, WAS DESTROYED BY A NATURAL GAS EXPLOSION. [REFERENCE TO FIGURE REMOVED] AS A RESULT OF THE EXPLOSION, TWO INDIVIDUALS WERE KILLED AND NINE WERE INJURED. AT THE TIME OF THE EXPLOSION, TWO WORKERS WERE INSTALLING NEW PIPING TO SUPPORT THE RELOCATION OF GAS METERS FROM THE BASEMENT OF THE BUILDING TO THE OUTSIDE. TWO NEW METERS MOUNTED ON A WALL WERE READY FOR THE NEW PIPING TO BE CONNECTED. WHILE WORKERS WERE REMOVING THE EXISTING PIPING, A FULL-FLOW NATURAL GAS LINE AT PRESSURE WAS OPENED. THE WORKERS WERE UNABLE TO MITIGATE THE RELEASE OF THE GAS, SO THEY EVACUATED THE AREA. HTTPS://WWW.NTSB.GOV/INVESTIGATIONS/ACCIDENTREPORTS/PAGES/DCA17MP007-PRELIM-REPORT.ASPX FINAL UPDATE AS OF 1/21/2020 ON DECEMBER 4, 2019, THE NTSB RELEASED THE PUBLIC DOCKET FOR ITS INVESTIGATION INTO THE INCIDENT. AS DESCRIBED IN THE DOCUMENTS INCLUDED IN THE PUBLIC DOCKET, THE NTSB FOUND THAT THE RELEASE OF NATURAL GAS AT MINNEHAHA ACADEMY OCCURRED WHEN MASTER MECHANICAL DISASSEMBLED EXISTING PIPING IN THE ACADEMY'S BOILER ROOM. THE MASTER MECHANICAL PERSONNEL BELIEVED A 3-INCH WALWORTH PLUG VALVE UPSTREAM OF THE DISASSEMBLED EXISTING PIPING WAS IN THE CLOSED POSITION ON THE DAY OF THE EXPLOSION, WHEN IN FACT IT WAS OPEN. THE NTSB ALSO PERFORMED A POST-INCIDENT ANALYSIS OF EVIDENCE TAKEN FROM THE SCENE OF THE EXPLOSION AND FOUND THAT INDICATORS ON THE 3-INCH WALWORTH PLUG VALVE CONFIRMED THAT THE VALVE'S ORIENTATION WAS IN THE OPEN POSITION. THE NTSB ALSO NOTED THAT ""CONFIRMATION OF WHETHER THE VALVE IS OPEN OR CLOSED IS THE RESPONSIBILITY OF THE CREW WORKING ON THE PIPING. THIS CONFIRMATION WOULD ENTAIL REMOVAL OF THE HANDLE AND NOTING THE POSITION OF THE PLUG ASSEMBLY."" THE MASTER MECHANICAL PERSONNEL DID NOT PERFORM EITHER OF THESE FUNCTIONS TO CONFIRM THE ORIENTATION OF THE VALVE ON THE DAY OF THE EXPLOSION. AS NOTED IN PARD D 2A OF THIS REPORT, THE EXPLOSION CAUSED AN ESTIMATED $48 MILLION IN ""PROPERTY DAMAGE"" (AS DEFINED IN PHMSA F7100.1) TO THE SCHOOL. THIS FIGURE IS BASED ON ESTIMATES FROM THE SCHOOL AND THE SCHOOL'S PROPERTY INSURER. IN ITS DECEMBER 6, 2019 ACCIDENT BRIEF, THE NTSB STATED THAT ""THE PROBABLE CAUSE OF THE NATURAL GAS EXPLOSION AT THE MINNEHAHA ACADEMY WAS THE DISASSEMBLING OF PIPING UPSTREAM OF A GAS SERVICE METER IN THE BUILDING BY A PIPEFITTING CREW [MASTER MECHANICAL], RESULTING IN THE RELEASE OF NATURAL GAS, WHICH SUBSEQUENTLY IGNITED. CONTRIBUTING TO THE ACCIDENT WAS THE LACK OF DETAILED DOCUMENTATION THAT CLEARLY ESTABLISHED THE SCOPE OF WORK TO BE PERFORMED.