MICHIGAN CONSOLIDATED GAS CO (MICHCON)

Incident Narrative

ON OCTOBER 17, 2011, BEGINNING AT APPROXIMATELY 8:45 AM, MICHCON TECHNICIANS EXECUTED A PRESSURE REDUCTION PROCEDURE TO FACILITATE THE CONNECTION OF A NEWLY-CONSTRUCTED REGULATING STATION AT COLLINDALE AVENUE ALONG MICHCON'S 22-INCH SOUTH GRAND RAPIDS 238 PSIG PIPELINE. THE PURPOSE OF THE PROCEDURE WAS TO DISPOSE OF A BUILD-UP OF NATURAL GAS (DETERMINED LATER TO HAVE ACTUALLY BEEN A MIXTURE OR AIR AND GAS) IN THE 22-INCH PIPELINE BY TRANSFERRING IT AT 10 PSIG INTO MICHCON'S GRAND RAPIDS/WALKER DISTRIBUTION SYSTEM RATHER THAN RELEASING IT TO THE ATMOSPHERE AND FLARING (BURNING) THE GAS. THE PROCEDURE WAS EXECUTED PRECISELY AS WRITTEN AND APPROVED BY MICHCON ENGINEERING. AT APPROXIMATELY 10:15 AM, WHILE THE PRESSURE REDUCTION PROCEDURE WAS STILL IN PROGRESS, MICHCON BEGAN TO RECEIVE ""NO-GAS"" REPORTS FROM CUSTOMERS SERVED BY THE SURROUNDING 10 PSIG DISTRIBUTION SYSTEM. AT APPROXIMATELY 11:00 AM, MICHCON PERSONNEL REALIZED THERE HAD BEEN AN AIR AND GAS MIXTURE IN THE 22-INCH PIPELINE, RATHER THAN GAS. PRESSURE REDUCTION OPERATIONS WERE HALTED IMMEDIATELY. MICHCON ENGINEERING AND OPERATIONS PERSONNEL IMMEDIATELY CONVENED TO DETERMINE THE EXTENT OF THE AFFECTED AREA AND THE SOURCE OF THE AIR/GAS MIXTURE. MICHCON DETERMINED THAT APPROXIMATELY 5500 CUSTOMERS OVER AN AREA OF ABOUT 10 SQUARE MILES COULD ULTIMATELY BE AFFECTED. HOWEVER, BETWEEN THE INITIAL OUTAGE REPORTS AT 10:15 AM AND THE EARLY AFTERNOON OF OCTOBER 17, THERE WERE ONLY ABOUT 100 ""NO-GAS"" REPORTS. THIS NUMBER GREW TO APPROXIMATELY 350 OUTAGE REPORTS BY 8 PM AS CUSTOMERS RETURNED HOME AT THE END OF THE DAY. AT 8 PM MICHCON MANAGEMENT DECLARED THIS A ""SIGNIFICANT EVENT"" AND A TELEPHONIC REPORT WAS MADE TO THE NATIONAL RESPONSE CENTER. CREWS WERE MOBILIZED FROM MICHCON REGIONS ACROSS THE STATE OF MICHIGAN TO MAKE A DOOR-TO-DOOR INVESTIGATION OF EVERY CUSTOMER PREMISES IN THE AFFECTED AREA TO ENSURE THAT GAS SERVICE WAS BEING RESTORED AND THAT ALL APPLIANCES WERE OPERATING PROPERLY. MICHCON ENGINEERS DEVELOPED A PLAN TO SYSTEMATICALLY PURGE THE AIR/GAS MIXTURE FROM THE 10 PSIG DISTRIBUTION SYSTEM, AND INDIVIDUAL SERVICE LINES WERE PURGED OF THE AIR/GAS MIXTURE WHEREVER IT WAS FOUND. BY FRIDAY, OCTOBER 21, 2011, EVERY CUSTOMER HAD EITHER BEEN CONTACTED OR THEIR PREMISES WERE ENTERED WITH THE ASSISTANCE OF LAW ENFORCEMENT AND LOCKSMITHS TO CONFIRM THAT GAS SERVICE HAD BEEN RESTORED. THERE WERE NO FIRES, EXPLOSIONS, OR INJURIES REPORTED AS A RESULT OF THIS EVENT. MICHCON HAS DETERMINED THE FORMATION OF THE AIR/GAS MIXTURE INSIDE THE 2.5-MILE SECTION OF THE 22-INCH 238 PSIG PIPELINE BEGAN ALMOST IMMEDIATELY AFTER THE SEGMENT WAS TAKEN OUT OF SERVICE DURING AUGUST 2011. THE 22-INCH PIPELINE HAD BEEN SHUT IN BETWEEN MICHCON'S SOUTH GRAND RAPIDS GATE STATION TO THE WEST AND THE NEW COLLINDALE REGULATING STATION ON THE EAST END OF THE 22-INCH PIPELINE SEGMENT. THE 2.5-MILE SECTION OF PIPELINE HAD BEEN EVACUATED AND PURGED OF GAS, THEN CAPPED OFF AT THE COLLINDALE REGULATING STATION SITE WHILE CONSTRUCTION OF THE STATION WAS COMPLETED. A 22-INCH BLOCK VALVE AT THE SOUTH GRAND RAPIDS GATE STATION THAT WAS USED TO ISOLATE THE WEST END OF THE 2.5-MILE SECTION OF 22-INCH PIPELINE ALLOWED GAS TO SLOWLY BLEED PAST THE VALVE SEAT, MIXING WITH THE AIR LEFT IN THE PURGED SECTION OF 22-INCH PIPELINE DURING THE PERIOD BETWEEN AUGUST AND OCTOBER 2011. THE MICHCON ENGINEER WHO DEVELOPED THE WRITTEN PROCEDURE FOR OCTOBER 17 RECOGNIZED THAT THE GAS BLEEDING THROUGH THE 22-INCH BLOCK VALVE WAS CREATING A PRESSURE BUILD-UP, BUT FAILED TO RECOGNIZE THIS WOULD CREATE AN AIR/GAS MIXTURE THAT WOULD BE UNFIT FOR DISTRIBUTION TO CUSTOMERS. MICHCON HAS DETERMINED APPROXIMATELY 136,000 CUBIC FEET OF AN AIR/GAS MIXTURE HAD ACCUMULATED IN THE 2.5-MILE SECTION OF 22-INCH PIPELINE. A SIGNIFICANT PORTION OF THIS MIXTURE WAS INTRODUCED INTO THE SURROUNDING 10 PSIG DISTRIBUTION SYSTEM DURING THE PROCEDURE EXECUTED ON OCTOBER 17, 2011, RESULTING IN THE CUSTOMER OUTAGES.