UNION ELECTRIC COMPANY D/B/A AS AMERENUE — Gas distribution — incident on 2005-10-10

Gas distribution incident in BOONVILLE, COOPER County, MO. Reported cause: 23. Reported consequences: 0 fatalities, 0 injuries, $600,000 reported property damage. Operator-reported incident data submitted to PHMSA, generally within 30 days. Records may be supplemented or corrected and do not represent final agency causal findings.

Report number: 20060027.

Operator ID: 20050.

Reported incident date: 10/10/2005.

Cause detail: INCORRECT OPERATION

Cause detail: PRE-INCIDENT INFORMATION: A CAST IRON REPLACEMENT PROJECT WAS UNDERWAY WHICH INVOLVED REPLACING VARIOUS SIZES OF LOW PRESSURE (INCHES OF WATER COLUMN) CAST IRON MAINS AND STEEL SERVICES, AND CONVERTING ALL OF THESE NEW FACILITIES AND SOME EXISTING LOW PRESSURE POLYETHYLENE MAINS AND SERVICES TO AN OPERATING PRESSURE OF 10 PSIG. THE AMERENUE CONTRACTOR COMPLETED THE FIRST PHASE OF THE PROJECT BY REPLACING THE EXISTING CAST IRON MAINS AND STEEL SERVICES. THE SECOND PHASE OF THE PROJECT INVOLVED CONVERTING A LOW PRESSURE AREA WHICH HAD EXISTING POLYETHYLENE MAINS AND SERVICES TO 10 PSIG. THE EXISTING POLYETHYLENE MAINS AND SERVICES HAD AN ESTABLISHED MAOP OF 60 PSIG. THIS REQUIRED SEPARATING A SECTION OF THE EXISTING POLYETHYLENE MAINS FROM THE LOW PRESSURE SYSTEM, ADDING REGULATORS TO EACH METER IN THE SECTION, AND CONNECTING THE SECTION TO AN ADJACENT 10 PSIG GAS SOURCE. THE SECTION TO BE CONVERTED WAS SIZED TO ALLOW FOR THE COMPLETION OF WORK BY THE AMERENUE CONTRACTOR WITHIN A SINGLE DAY TO MINIMIZE GAS SERVICE INTERRUPTION. INCIDENT INFORMATION: THE CONTRACTOR BEGAN THE MORNING BY PERFORMING WORK TO ISOLATE THE SYSTEM TO BE CONVERTED TO 10 PSIG FROM THE LOW PRESSURE SYSTEM. DURING THIS TIME ADDITIONAL CONTRACTOR CREW MEMBERS WENT TO EACH OF THE THIRTEEN METER LOCATIONS DESIGNATED BY AMERENUE AS PART OF CONVERSION TO SHUT OFF SERVICE AND TO REMOVE THE METER FROM THE INLET PIPING. AN AMERENUE INSPECTOR WAS WITNESSING THIS ACTIVITY AND CHECKED EACH SERVICE OFF OF A LIST ONCE THE WORK WAS COMPLETED. THE CONTRACTOR COMPLETED THE WORK TO ISOLATE THE SYSTEM AT APPROXIMATELY 11:00 AM. THE AMERENUE SUPERVISOR, AMERENUE INSPECTOR, AND THE CONTRACTOR FOREMAN MET AGAIN AT APPROXIMATELY 11:30AM TO REVIEW THE WORK COMPLETED TO THIS POINT AND TO REVIEW THE PLANS TO MAKE SURE EVERYTHING WAS READY FOR THE INTRODUCTION OF 10 PSIG INTO THE SYSTEM. THEY REVIEWED THE CONSTRUCTION PRINTS AND DISCUSSED THE MAIN SEPARATION LOCATIONS, TIE-IN LOCATIONS, AND THE THIRTEEN SERVICE LOCATIONS THAT WERE SEPARATED. ALL WERE IN AGREEMENT THAT THEY WERE READY TO PROCEED WITH THE NEXT STEP OF INTRODUCING 10 PSIG INTO THE SYSTEM. AT APPROXIMATELY 11:35 AM, A VALVE WAS OPENED TO INTRODUCE THE 10 PSIG INTO THE SYSTEM. AT APPROXIMATELY 11:53 AM, THE AMERENUE SUPERVISOR OVERHEARD THE AMERENUE DISPATCHER CALLING AN AMERENUE SERVICEMAN TO RESPOND TO A GAS PRESSURE PROBLEM AT A RESTAURANT AT 415 ASHLEY ROAD IN BOONVILLE. THE AMERENUE SUPERVISOR RECOGNIZED THE RESTAURANT WAS LOCATED ON THE LOW PRESSURE SYSTEM JUST NORTH OF THE AREA THAT WAS BEING CONVERTED TO 10 PSIG. HE SUSPECTED THERE MUST BE A PROBLEM RESULTING FROM THE SYSTEM CONVERSION SO HE CALLED THE AMERENUE INSPECTOR AND INSTRUCTED HIM TO CLOSE THE VALVE THAT WAS PREVIOUSLY OPENED. THE INSPECTOR HAD LEFT THE JOB SITE TO OBTAIN ADDITIONAL MATERIALS SO HE CONTACTED THE CONTRACTOR BY CELL PHONE AND INSTRUCTED TO IMMEDIATELY CLOSE THE VALVE. THE AMERENUE SUPERVISOR RETURNED TO THE JOB SITE AND INSTRUCTED THE CONTRACTOR TO OPEN METER SERVICE VALVES IN THE AREA AND CUT A CAP OFF OF AN EXPOSED POLYETHYLENE MAIN TO RELIEVE THE 10 PSIG OF PRESSURE FROM THE SYSTEM. THE AMERENUE SUPERVISOR CONTACTED THE AMERENUE SUPERINTENDENT, ENGINEERING AND OPERATIONS AND NOTIFIED HIM OF THE SITUATION AT APPROXIMATELY 12:10 PM. THE SUPERINTENDENT INSTRUCTED AMERENUE SUPERVISOR TO SEND AMERENUE GAS PERSONNEL TO THE LOW PRESSURE REGULATOR STATIONS TO BLEED THE PRESSURE OFF OF THE LOW PRESSURE SYSTEM THAT WAS AFFECTED. IT WAS DETERMINED THAT THE LOW PRESSURE SYSTEM WAS PRESSURIZED TO 10 PSIG SO THE SUPERINTENDENT INSTRUCTED THE SUPERVISOR TO SHUT DOWN AND ISOLATE THE ENTIRE LOW PRESSURE SYSTEM. THE SUPERINTENDENT ARRIVED AT BOONVILLE AT APPROXIMATELY 12:50PM. AT THAT TIME THE AFFECTED LOW PRESSURE SYSTEM WAS DEPRESSURIZING AND WAS AT A PRESSURE OF 0-1 PSIG. AT APPROXIMATELY 1:30 PM AMERENUE GAS PERSONNEL BEGAN SHUTTING OFF THE METERS THAT SERVED THE LOW PRESSURE SYSTEM THAT WAS ISOLATED. ADDITIONAL A MERENUE GAS PERSONNEL FROM OTHER LOCATIONS WERE CALLED TO ASSIST. THERE WERE APPROXIMATELY 750 CUSTOMERS AFFECTED BY ISOLATING THE LOW PRESSURE SYSTEM. AMERENUE INVESTIGATED AND DISCUSSED THE SITUATION TO DETERMINE THE CAUSE OF THE OVER PRESSURIZATION. IT WAS IDENTIFIED THAT A 4� MAIN CONNECTING THE LOW PRESSURE SYSTEM AND THE SYSTEM TO BE CONVERTED TO 10 PSIG WAS OVERLOOKED AND WAS NOT SEPARATED PRIOR TO INTRODUCING THE 10 PSIG. THIS ALLOWED THE 10 PSIG TO FLOW INTO THE LOW PRESSURE SYSTEM, WHICH IS SUPPLIED BY REGULATOR STATIONS THAT ARE IN A MONITOR CONFIGURATION, CAUSING THE SYSTEM OVER PRESSURIZATION.

PHMSA trend classification: significant incident, not serious, not fire-first.

PHMSA standardized cause: INCORRECT OPERATION — OTHER INCORRECT OPERATION.

PHMSA indexed costs: $600,000 reported total cost, $362,283.618 in 1984 dollars, $892,193.053 in current-year dollars.

PHMSA trend flags, standardized causes, and indexed costs are analytical fields added to operator-reported incident data. They do not represent final agency causal findings.