SOUTHWEST GAS CORP

Incident Narrative

AT 17:35 ON OCTOBER 31, 2022, SOUTHWEST GAS RECEIVED A CALL ABOUT AN ODOR/HISSING ON A DIRT LOT NEAR THE INTERSECTION OF LA CIENEGA STREET AND PYLE AVENUE IN LAS VEGAS, NEVADA. CREWS ARRIVED ONSITE AT 18:23 AND BEGAN INVESTIGATION. AT 19:52, SOUTHWEST GAS IDENTIFIED A LEAK ON ITS FACILITIES AND MADE THE AREA SECURE. THE LEAK WAS ISOLATED AND GAS SUPPLY WAS SHUT OFF TO THE AFFECTED PIPE SEGMENT BY 21:24 ON OCTOBER 31, 2022. THIS SEGMENT OF THE MAIN WILL NOT BE RETURNED TO SERVICE. SOUTHWEST GAS EVACUATED A TOTAL OF SIX PERSONS FROM THREE NEARBY HOMES. AFTER GAS WAS SHUT OFF, CREWS BEGAN AERATING THE SURROUNDING SOIL TO REMOVE RESIDUAL GAS IN THE GROUND. ALTHOUGH RESIDUAL GAS READS WERE DROPPING, SOUTHWEST GAS REMAINED ONSITE CONTINUOUSLY MONITORING THE RESIDUAL READS AND AERATING THE SOILS. ON NOVEMBER 30, 2022 SOUTHWEST GAS DETERMINED THAT THE ACCUMULATED EMERGENCY RESPONSE COSTS EXCEEDED $129,300. THE INCIDENT COSTS WERE MOSTLY ATTRIBUTED TO EMPLOYEE LABOR UTILIZED TO CONTINUOUSLY AERATE AND REMEDIATE THE RESIDUAL GAS IN THE SOIL. SOUTHWEST DISCONTINUED ITS EMERGENCY RESPONSE AND DECOMMISSIONED THE INCIDENT COMMAND STRUCTURE ON DECEMBER 8, 2022 AFTER THE RESIDUAL GAS READS WERE REMEDIATED TO SAFE NON-HAZARDOUS CONDITIONS. LABORATORY ANALYSIS COMPLETED IN JANUARY 2023 CONCLUDED: FRACTOGRAPHIC AND ANALYTICAL EXAMINATION INDICATED THAT THE THROUGHWALL AXIAL FRACTURE RESPONSIBLE FOR THE LEAK PATH OCCURRED DUE TO INTERNAL THERMAL-OXIDATIVE DEGRADATION. THE FRACTURE PROGRESSED THROUGH THE WALL OF THE PIPE FROM THE INSIDE DIAMETER TO THE OUTSIDE DIAMETER BY WAY OF HOOP STRESS AND BRITTLE FRACTURE DUE TO DEGRADATION AND LOW SLOW CRACK GROWTH RESISTANCE OF THE PIPE MATERIAL. THIS SUPPLEMENTAL REPORT UPDATES THE CAUSE OF THE LEAK IN PART G BASED ON THE LABORATORY ANALYSIS TO BE A CRACK CAUSED BY DEGRADATION. IT ALSO UPDATES PART J AND THE COSTS ASSOCIATED WITH THE INCIDENT IN PART D.