CENTERPOINT ENERGY RESOURCES CORP.

Incident Narrative

THE INITIAL POST-INCIDENT INVESTIGATION REVEALED EROSION OF SOIL AND CAVE IN OF SURFACE PAVEMENT AROUND A SEWER MANHOLE DISCOVERED ON MAY 6, 2016, WHICH CAUSED DAMAGE TO THE CONNECTION OF A SERVICE LINE PROVIDING SERVICE TO 2437 FAIRFIELD AVE. THIS SERVICE LINE CONNECTION WAS REPAIRED WITH THE INSTALLATION OF A NEW SERVICE LINE AND TAP ON MAY 6, 2016. THIS NEW SERVICE LINE AND CONNECTION DID NOT LEAK AFTER MAY 6. THERE WAS NO CRACK IN THE CAST IRON MAIN AT THE TIME THAT THE MAY 6 SERVICE LINE REPLACEMENT WAS COMPLETED; THE INSPECTION AT THAT TIME DID NOT REVEAL A LOSS OF SUPPORT UNDER THE CAST IRON MAIN. SERVICE TO 2437 FAIRFIELD WAS LEFT OFF AT THE TIME OF THIS REPAIR DUE TO CUSTOMER NOT BEING HOME. ON MAY 23, 2016 A CENTERPOINT ENERGY EMPLOYEE RETURNED TO RESTORE SERVICE TO THIS RESIDENCE AT THE CUSTOMER'S REQUEST. DURING THIS RESTORATION A BAR HOLE INSPECTION WAS MADE IN WHICH THERE WAS NO EVIDENCE OF A LEAK. ON MAY 26, 2016 A CENTERPOINT ENERGY CONTRACT SERVICES INSPECTOR WENT BACK TO SITE OF THE SERVICE LINE REPAIR AND PERFORMED A VISUAL INSPECTION, AND AT THAT TIME THERE WAS NO INDICATION OF A LEAK. ON JULY 31, 2016 AT APP. 16:18, CENTERPOINT ENERGY WAS NOTIFIED AND RESPONDED TO TWO EMERGENCY CALLS REPORTED AT 2437 FAIRFIELD AVE. AN EMERGENCY LEAK INVESTIGATION ORDER AND AN EMERGENCY FIRE INVESTIGATION ORDER WERE CREATED. TECHNICIAN ARRIVED AT APP. 16:53 TO BEGIN AN INVESTIGATION. DURING THE INVESTIGATION OF JULY 31, GAS WAS DETECTED NEAR THE STRUCTURE, AFTER WHICH TELEPHONIC REPORTS WERE MADE TO NRC AND STATE REGULATORY OFFICIALS. DURING ONGOING INVESTIGATION OF THE INCIDENT, A FRACTURE WAS FOUND AUGUST 2, 2016, ON THE CAST IRON MAIN AT A LOCATION OF AN ADJACENT STEEL SERVICE LINE TAP, WHICH WAS 2.8' AWAY FROM THE NEWLY INSTALLED POLY SERVICE LINE TAP. METALLURGICAL INSPECTION OF JANUARY 18, 2017, SHOWED THAT THE PIPE WALL THICKNESS/STRENGTH WAS WELL PRESERVED WITHOUT ANY GRAPHITIC CORROSION BEYOND SHALLOW SURFACE CORROSION. THE METALLURGICAL ANALYSIS AND SUBSEQUENT GEOTECHNICAL INVESTIGATION INDICATED THAT THE PIPE FRACTURED DUE TO A RECENT OVERLOAD EVENT OCCURRING AFTER A LOSS OF SUPPORT, MOST LIKELY CAUSED BY LOSS OF SOIL BY WATER INFILTRATION AND EROSION THROUGH THE VOIDS, CRACKS AND OPENINGS AROUND THE VARIOUS SEWER LINE CONNECTIONS IN THE SEWER MANHOLE AND ON THE MANHOLE WALL ITSELF. THE FRACTURE OCCURRED SUBSEQUENT TO THE MAY 26, 2016 INSPECTION AND BEFORE THE JULY 31, 2016 INCIDENT. THE GEOTECHNICAL INVESTIGATION REVEALED THAT THE CAST-IRON MAIN LINE UNDERWENT DEFLECTIONS DUE TO THE OCCURRENCE OF THE LOSS OF SOIL SUPPORT FROM THE SOIL CAVING, RESULTING IN AN UNDETECTED INCREASE IN STRESSES IN THE MAIN PIPE AT THE LOCATION OF THE CONNECTION OF THE STEEL SERVICE LINE WHERE THE CRACK OCCURRED. THE ODOR OF NATURAL GAS WAS DETECTED BY PERSONS PRESENT AT THE SUBJECT PROPERTY ON JULY 29, JULY 30 AND THE MORNING OF JULY 31 WITHOUT ANYONE CONTACTING CENTERPOINT BEFORE THE FIRE OCCURRED.