MONTANA - DAKOTA UTILITIES CO

Incident Narrative

AT 00:39 ON NOVEMBER 18, 2019, EMERGENCY RESPONDERS CONTACTED MONTANA-DAKOTA UTILITIES CALL CENTER TO REPORT A HOUSE FIRE WITH POSSIBLE EXPLOSION. A LOCAL SERVICE TECHNICIAN WAS DISPATCHED IMMEDIATELY UPON NOTIFICATION. UPON ARRIVAL THE SERVICE TECH MADE THE AREA SAFE AND STARTED TO ASSESS THE SCENE. IT WAS CONFIRMED THAT AN EXPLOSION HAD OCCURRED AT A PRIVATE RESIDENCE AND TWO OCCUPANTS WERE TAKEN TO THE HOSPITAL. VERBAL COMMUNICATION FROM THE BILLINGS FIRE DEPARTMENT INDICATED TWO OCCUPANTS WERE TAKEN TO THE BILLINGS HOSPITAL AND THEN FLOWN TO A HOSPITAL IN DENVER. A LEAK INVESTIGATION OUTSIDE THE RESIDENCE WAS COMPLETED, GAS WAS INDICATED AT THE RISER OF THE RESIDENCE WITH HIGHEST CONCENTRATION OF GAS AT THE INTERSECTION OF TWO 1982 VINTAGE 1 1/4"" PLASTIC MAINS ACROSS THE ALLEY. THE MAINS FEEDING THE TEE WERE ISOLATED, SECURING THE LEAK AT 05:50 ON NOVEMBER 18, 2019. THE MAIN WAS EXCAVATED AND A CRACK WAS DISCOVERED AT THE INTERFACE OF THE PIPE AT A SOCKET TEE CONNECTING THE MAINS. FACTORS THAT CAUSED THE GAS TO BE CONTROLLED AT 5:50 WERE THE TIME REQUIRED TO COMPLETE A LEAK INVESTIGATION TO ENSURE THE SAFETY OF THE SURROUNDING STRUCTURES, PINPOINT THE SUSPECTED SOURCE OF THE GAS, GET EMERGENCY LOCATES COMPLETED, EXCAVATE THE LOCATION OF THE HIGHEST CONCENTRATION OF GAS TO ENSURE THE LOCATION OF LEAK, AND EXCAVATE TWO LOCATIONS FOR SHUT OFF OF THE GAS DUE TO THE AREA BEING SERVED FROM TWO LOCATIONS. UPON EXCAVATION, THE PIPE AT THE TEE LOCATION, HAD A DEFLECTION FROM THE MAIN LINE WHICH WOULD BE INCONSISTENT WITH THE STANDARD INSTALLATION OF THE PIPE. THIS DEFLECTION MAY HAVE BEEN CAUSED FROM IMPROPER SUPPORT DURING THIRD PARTY EXCAVATION OR IMPROPER BACKFILL METHODS POST THIRD PARTY EXCAVATION THAT OCCURRED SOMETIME AFTER MONTANA-DAKOTA'S INITIAL INSTALLATION OF THE PIPE. FURTHER INDICATION THAT OUTSIDE FORCES CAUSED THE CRACK INCLUDE BACKFILL MATERIAL SURROUNDING THE PIPE AND TEE THAT APPEARED TO BE FOREIGN FROM NATIVE MATERIALS THAT WOULD HAVE BEEN USED AT TIME OF INITIAL INSTALLATION. 4/8/2021 - THE PE PIPE MATERIAL WAS REVISED TO CORRECT FROM PE 2406 TO PE 2306. 4/19/2021 - THE NUMBERS FOR GAS RELEASED (PG. 1 ITEMS 7) AND GAS CONSUMED (PG. 2 ITEM 21C) ARE NOT KNOWN. PHMSA FORM F 7100.1 REQUIRES A NUMERICAL ENTRY EVEN THOUGH AN ESTIMATED VALUE IS UNABLE TO BE DETERMINED. 5/3/2021 - ADDED THE PIPE MANUFACTURER AND UPDATED NRC REPORT NUMBERS. VOLUME OF GAS UNINTENTIONALLY RELEASED CALCULATED USING AND ESTIMATED OPENING OF 0.05 SQUARE INCHES AND A PRESSURE OF 55 PSIG. FOR PURPOSES OF PROVIDING AND ILLUSTRATIVE CALCULATION OF GAS LOSS, AN ESTIMATED TIME OF 3 MONTHS WAS UTILIZED.