SOUTHWEST GAS CORP

Incident Narrative

WHILE CONDUCTING AN ANNUAL PVC LEAK SURVEY PURSUANT TO SOUTHWEST GAS' DIMP PLAN ON JUNE 24, 2020, SOUTHWEST GAS' LEAK SURVEY CONTRACTOR CONTACTED SOUTHWEST GAS AT 09:04 PDT AND REPORTED GAS READS OF 1 LEL NEAR THE LAUNDRY ROOM RISER AND ZERO READS INSIDE THE LAUNDRY ROOM LOCATED AT 4337 SILVER DOLLAR AVENUE IN LAS VEGAS, NV. SOUTHWEST GAS CREWS ARRIVED AT 09:35 PDT AND OBTAINED GAS READS OF 4 LEL BY THE RISER TO THE LAUNDRY FACILITY, TURNED OFF THE METER, CONFIRMED ZERO GAS READS INSIDE THE UNOCCUPIED BUILDING, AND CONDUCTED FURTHER LEAK INVESTIGATION. AT 10:13 PDT, IGNITION OF FUGITIVE NATURAL GAS OCCURRED WITHIN THE DETACHED, UNOCCUPIED LAUNDRY FACILITY STRUCTURE RESULTING IN A FIRE AND PROPERTY DAMAGE. POST IGNITION LEAK SURVEY RESULTS DISCOVERED INCREASING GAS READINGS AND LEAK SPREAD RESULTING IN AN EVACUATION OF 14 PEOPLE FROM SOME UNITS OF THE ADJACENT, SEPARATE APARTMENT BUILDING. A LEAK ON A PVC SERVICE LINE COUPLING CONNECTION FITTING WAS REVEALED DURING A LEAK TEST OF THE PVC SERVICE DURING A POST INCIDENT INVESTIGATION. ADDITIONALLY, A LEAK TEST PERFORMED ON THE CUSTOMER'S HOUSELINE FAILED DURING THE POST INCIDENT INVESTIGATION. PART A4: BASED ON COMMUNICATIONS THAT THE PUBLIC UTILITIES COMMISSION OF NEVADA'S REGULATORY OPERATIONS STAFF HAD WITH THE PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION'S ACCIDENT INVESTIGATION DIVISION, ""LOCAL TIME AND DATE OF THE INCIDENT"" REFLECTS THE TIME SOUTHWEST GAS WAS NOTIFIED OF A LEAK ON THE PIPELINE. AT THAT TIME, NO INCIDENT REPORTING CRITERIA WAS MET. PART A6: SOUTHWEST GAS NOTIFIED THE NATIONAL RESPONSE CENTER (NRC) TELEPHONICALLY OF THE INCIDENT ON JUNE 24, 2020 AT 14:33 PDT. THE NRC ISSUED REPORT NUMBER 1280311 FOR THE INCIDENT. SOUTHWEST GAS PROVIDED A 48-HOUR UPDATE TELEPHONICALLY TO THE NRC ON JUNE 25, 2020 AT 15:28 PDT. THE NRC ISSUED REPORT NUMBER 1280402 FOR THE UPDATED REPORT. SUPPLEMENTAL RESPONSE: CHANGED PART G TO UPDATE THE APPARENT CAUSE FROM PART G5 TO G8. THE CAUSE OF THE LEAK REMAINS UNDER INVESTIGATION. CURRENT EVIDENCE SUGGESTS THE CAUSE MAY BE G3, G4, OR G5. THE SAMPLE HAS BEEN SENT TO A THIRD-PARTY MATERIALS TESTING LABORATORY FOR ANALYSIS AND THE RESULTS OF THE ANALYSIS WILL BE PROVIDED IN A SUPPLEMENTAL RESPONSE. THE LEAK WAS ORIGINALLY BELIEVED TO BE DUE TO A SOLVENT CEMENT JOINT, BUT A CRACK WAS FOUND WHEN ASSESSED IN SOUTHWEST GAS'S MATERIALS TESTING LABORATORY. THE CRACK APPEARS TO BE A CIRCUMFERENTIAL CRACK IN THE PIPE NEAR THE LOCATION OF THE PIPE TO COUPLING JOINT. SUPPLEMENTAL RESPONSE 2: FOLLOWING THE INCIDENT, THE SERVICE LINE WAS DISCONNECTED AT THE MAIN. ON MARCH 30, 2021, THE SERVICE TO THE CUSTOMER WAS REPLACED. PART C, 3 AND 4 - CHANGED THE PIPE SIZE AND WALL THICKNESS TO 0.5-INCH AND 0.109-INCH RESPECTIVELY BASED ON 3RD PARTY LABORATORY ANALYSIS. CHANGED PART G FROM G8 - OTHER INCIDENT CAUSE TO G4 - OTHER OUTSIDE FORCE DAMAGE, WITH A SUB-CAUSE AS OTHER OUTSIDE FORCE DAMAGE. AN INDEPENDENT LABORATORY'S MATERIAL INVESTIGATION CONCLUDED THAT THE ROOT CAUSE OF THE FAILURE WAS SUSTAINED EXTERNAL BENDING LOADS LEADING TO SLOW CRACK GROWTH AND CREEP RUPTURE. THE FIELD INVESTIGATION DETERMINED THAT THE PROBABLE CAUSE OF THE BENDING LOADS WAS A CUSTOMER HOUSELINE WATER LEAK WHICH ERODED THE SUPPORT FROM UNDER THE SERVICE LINE'S TRANSITION FITTING.