{"operation":"document","citation":"PLD18MR003","title":"Overpressurization of Natural Gas Distribution System, Explosions, and Fires","source_type":"incident","agency":"National Transportation Safety Board","status":"current","official":true,"published_on":"2019-09-24","effective_on":"2018-09-13","summary":"Accident. in Merrimack Valley, MA, USA. on 2018-09-13. Columbia Gas of Massachusetts. Leak/explosion/fire","machine_formats":{"json":"https://regulus.evalyn.ai/document/ntsb-case-pld18mr003.json","markdown":"https://regulus.evalyn.ai/document/ntsb-case-pld18mr003.md"},"app_url":"https://regulus.evalyn.ai/document/ntsb-case-pld18mr003","source_url":"https://www.ntsb.gov/investigations/Pages/PLD18MR003.aspx","body":"NTSB investigation PLD18MR003.\n\nEvent Type: Accident\n\nEvent Date: 2018-09-13\n\nEvent City: Merrimack Valley\n\nEvent State Or Region: MA\n\nEvent Country: USA\n\nPipeline Operator: Columbia Gas of Massachusetts\n\nPipeline Type: Distribution\n\nAccident Type: Leak/explosion/fire\n\nCompletion Status: Completed\n\nReport Number: PAR1902\n\nReport Date: 2019-09-24\n\nProbable cause: The National Transportation Safety Board determines that the probable cause of the overpressurization of the natural gas distribution system and the resulting fires and explosions was Columbia Gas of Massachusetts’ weak engineering management that did not adequately plan, review, sequence, and oversee the construction project that led to the abandonment of a cast iron main without first relocating regulator sensing lines to the new polyethylene main. Contributing to the accident was a low-pressure natural gas distribution system designed and operated without adequate overpressure protection.\n\nTier1Name: System maintenance\n\nTier2Name: Pressure/flow control malf/failure\n\nTier1Name: Emergency response\n\nTier2Name: Fire (post-release)\n\nTier1Name: System shutdown\n\nTier2Name: Emergency shutoff\n\nTier1Name: System operating, changing flow/pressure\n\nTier2Name: Servicing event\n\nTier1Name: System maintenance\n\nTier2Name: Product leak/release\n\nTier1Name: Initiating product flow\n\nTier2Name: System disabled\n\nTier1Name: System maintenance\n\nTier2Name: Servicing event\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Management\n\nFinding Tier3Name: Policy/procedure\n\nFinding Modifier Name: Pipeline operator\n\nFinding Report Text: Organizational - Management - Policy/procedure - Pipeline operator\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Support/oversight/monitoring\n\nFinding Tier3Name: Documentation/record keeping\n\nFinding Modifier Name: Pipeline operator\n\nFinding Report Text: Organizational - Support/oversight/monitoring - Documentation/record keeping - Pipeline operator\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Management\n\nFinding Tier3Name: Resources\n\nFinding Modifier Name: Pipeline operator\n\nFinding Report Text: Organizational - Management - Resources - Pipeline operator\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Support/oversight/monitoring\n\nFinding Tier3Name: Safety programs\n\nFinding Modifier Name: Pipeline operator\n\nFinding Report Text: Organizational - Support/oversight/monitoring - Safety programs - Pipeline operator\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Support/oversight/monitoring\n\nFinding Tier3Name: Oversight\n\nFinding Modifier Name: Pipeline operator\n\nFinding Report Text: Organizational - Support/oversight/monitoring - Oversight - Pipeline operator\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Management\n\nFinding Tier3Name: Communication (organizational)\n\nFinding Modifier Name: State/Local agency\n\nFinding Report Text: Organizational - Management - Communication (organizational) - State/Local agency\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Support/oversight/monitoring\n\nFinding Tier3Name: Enforcement\n\nFinding Modifier Name: State/Local agency\n\nFinding Report Text: Organizational - Support/oversight/monitoring - Enforcement - State/Local agency\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Development\n\nFinding Tier3Name: Design\n\nFinding Modifier Name: Not specified\n\nFinding Report Text: Organizational - Development - Design - Not specified\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline operation/capability\n\nFinding Tier3Name: Pipeline temp/pressure/flow parameter(s)\n\nFinding Modifier Name: Incorrect service/maintenance\n\nFinding Report Text: Pipeline - Pipeline operation/capability - Pipeline temp/pressure/flow parameter(s) - Incorrect service/maintenance\n\nFinding Tier1Name: Personnel\n\nFinding Tier2Name: Experience/knowledge\n\nFinding Tier3Name: Experience/qualifications\n\nFinding Modifier Name: Pipeline maintenance personnel\n\nFinding Report Text: Personnel - Experience/knowledge - Experience/qualifications - Pipeline maintenance personnel\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline handling/service\n\nFinding Tier3Name: Servicing\n\nFinding Modifier Name: Related records\n\nFinding Report Text: Pipeline - Pipeline handling/service - Servicing - Related records\n\nFinding Tier1Name: Personnel\n\nFinding Tier2Name: Experience/knowledge\n\nFinding Tier3Name: Experience/qualifications\n\nFinding Modifier Name: Pipeline maintenance personnel\n\nFinding Report Text: Personnel - Experience/knowledge - Experience/qualifications - Pipeline maintenance personnel\n\nOfficial NTSB investigation data. NTSB findings determine probable cause and make safety recommendations; they do not adjudicate civil liability or regulatory violations.\n\nWhat Happened\nOn September 13, 2018, about 4:00 p.m. local time, a series of structure fires andexplosions occurred after high-pressure natural gas was released into a low-pressure natural gas\n\ndistribution system in the northeast region of the Merrimack Valley in the Commonwealth of\n\nMassachusetts. The natural gas distribution system was owned and operated by Columbia Gas of\n\nMassachusetts (CMA), a subsidiary of NiSource, Inc. CMA delivers natural gas to about\n\n325,000 customers in Massachusetts. The fires and explosions damaged 131 structures, including at least 5 homes that were destroyed in the city of Lawrence and the towns of Andover and North Andover. Most of the damage occurred from fires ignited by natural gas-fueled\nappliances; several of the homes were destroyed by natural gas-fueled explosions. Fire\n\ndepartments from the three municipalities were dispatched to the fires and explosions. First\n\nresponders initiated the Massachusetts fire-mobilization plan and received mutual aid from\n\nneighboring districts in Massachusetts, New Hampshire, and Maine. Emergency management\n\nofficials had National Grid United States (NG) (the electric utility) shut down electrical power in\n\nthe area, the state police closed local roads, and freight and passenger railroad operations in the\n\narea were suspended. CMA shut down the low-pressure natural gas distribution system, affecting\n\n10,894 customers, including some outside the affected area who had their service shut off as a\n\nprecaution.\n\nWhat We Found\nWe determined that the probable cause of the overpressurization of the natural gas distribution system and the resulting fires and explosions was Columbia Gas of Massachusetts’ weak engineering management that did not adequately plan, review, sequence, and oversee the construction project that led to the abandonment of a cast iron main without first relocating regulator sensing lines to the new polyethylene main. Contributing to the accident was a low-pressure natural gas distribution system designed and operated without adequate overpressure protection.\n\nWhat We Recommended\nWe made recommendations to the Pipeline and Hazardous Materials Safety Administration, To the States of Alabama, Alaska, Arizona, Arkansas, California, Colorado,\nConnecticut, Florida, Georgia, Idaho, Illinois, Iowa, Kentucky, Louisiana, Maine, Maryland, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Mexico, New York, North Carolina, Ohio, Pennsylvania, South Carolina, South Dakota, Texas, Utah, Virginia, Wisconsin, and Wyoming, To the Commonwealth of Massachusetts Executive Office of Public Safety and\nSecurity and To NiSource, Inc.\n\nPAR-19-02\n<<<PAGE 1>>>\n\nOverpressurization of Natural Gas Distribution System,\nExplosions, and Fires in\nMerrimack Valley, Massachusetts\nSeptember 13, 2018\nAccident Report\nNTSB/PAR-19/02\nPB2019-101365\nNational\nTransportation\nSafety Board\n\n<<<PAGE 2>>>\n\nNTSB/PAR-19/02\nPB2019-101365\nNotation 59529\nAdopted September 24, 2019\nPipeline Accident Report\nOverpressurization of Natural Gas Distribution System,\nExplosions, and Fires in\nMerrimack Valley, Massachusetts\nSeptember 13, 2018\nNational\nTransportation\nSafety Board\n490 L’Enfant Plaza, S.W.\nWashington, D.C. 20594\n\n<<<PAGE 3>>>\n\nNational Transportation Safety Board. 2019. Overpressurization of Natural Gas Distribution System,\nExplosions, and Fires in Merrimack Valley, Massachusetts, September 13, 2018. Pipeline Accident\nReport NTSB/PAR-19/02. Washington, DC.\nAbstract: On September 13, 2018, about 4:00 p.m. local time, a series of structure fires and explosions\noccurred after high-pressure natural gas was released into a low-pressure natural gas distribution system in\nthe northeast region of the Merrimack Valley in the Commonwealth of Massachusetts. The natural gas\ndistribution system was owned and operated by Columbia Gas of Massachusetts, a subsidiary of NiSource,\nInc. Columbia Gas of Massachusetts delivers natural gas to about 325,000 customers in Massachusetts. One\nperson was killed and 22 individuals, including three firefighters, were transported to local hospitals due to\ninjuries; seven other firefighters incurred minor injuries. The fires and explosions damaged 131 structures,\nincluding at least 5 homes that were destroyed in the city of Lawrence and the towns of Andover and\nNorth Andover. Most of the damage occurred from fires ignited by natural gas-fueled appliances; several\nof the homes were destroyed by natural gas-fueled explosions. Fire departments from the three\nmunicipalities were dispatched to the fires and explosions. First responders initiated the Massachusetts fire-\nmobilization plan and received mutual aid from neighboring districts in Massachusetts, New Hampshire,\nand Maine. Emergency management officials had the electric utility shut down electrical power in the area,\nthe state police closed local roads, and freight and passenger railroad operations in the area were suspended.\nColumbia Gas of Massachusetts shut down the low-pressure natural gas distribution system, affecting\n10,894 customers, including some outside the area who had their service shut off as a precaution. The\nNational Transportation Safety Board made new recommendations to the Pipeline and Hazardous Materials\nSafety Administration; the 34 states with an industrial exemption for natural gas infrastructure projects; the\nCommonwealth of Massachusetts Executive Office of Public Safety and Security; and NiSource, Inc.\nThe National Transportation Safety Board (NTSB) is an independent federal agency dedicated to promoting aviation,\nrailroad, highway, marine, and pipeline safety. Established in 1967, the agency is mandated by Congress through the\nIndependent Safety Board Act of 1974 to investigate transportation accidents, determine the probable causes of the\naccidents, issue safety recommendations, study transportation safety issues, and evaluate the safety effectiveness of\ngovernment agencies involved in transportation. The NTSB makes public its actions and decisions through accident\nreports, safety studies, special investigation reports, safety recommendations, and statistical reviews.\nThe NTSB does not assign fault or blame for an accident or incident; rather, as specified by NTSB regulation,\n“accident/incident investigations are fact-finding proceedings with no formal issues and no adverse parties … and are\nnot conducted for the purpose of determining the rights or liabilities of any person.” 49 C.F.R. § 831.4. Assignment\nof fault or legal liability is not relevant to the NTSB’s statutory mission to improve transportation safety by\ninvestigating accidents and incidents and issuing safety recommendations. In addition, statutory language prohibits\nthe admission into evidence or use of any part of an NTSB report related to an accident in a civil action for damages\nresulting from a matter mentioned in the report. 49 U.S.C. § 1154(b).\nFor more detailed background information on this report, visit the NTSB investigation website and search for NTSB\naccident ID PLD18MR003. Recent publications are available in their entirety on the Internet at the NTSB website.\nOther information about available publications also may be obtained from the website or by contacting:\nNational Transportation Safety Board Records Management Division, CIO-40, 490 L’Enfant Plaza, SW,\nWashington, DC 20594, (800) 877-6799 or (202) 314-6551.\nNTSB publications may be purchased from the National Technical Information Service. To purchase this publication,\norder product number PB2019-101308 from:\nNational Technical Information Service, 5301 Shawnee Rd., Alexandria, VA 22312, (800) 553-6847 or (703)\n605-6000, NTIS website.\nNOTE: This report was reissued on November 7, 2019, with corrections to page 60 to remove NiSource employee information.\n\n<<<PAGE 4>>>\n\nNOTE: This report was reissued on November 20, 2019, with corrections to pages 30 and 31 to add a citation to Table 4.\nNOTE: This report was reissued on April 30, 2021, with corrections to pages 29-31, 43-44, and 50.\n\n<<<PAGE 5>>>\n\nContents\nFigures ........................................................................................................................................... iii\nTables ............................................................................................................................................ iv\nAcronyms and Abbreviations .......................................................................................................v\nExecutive Summary .................................................................................................................... vii\n1. Factual Information .................................................................................................................1\n1.1 Accident Synopsis ....................................................................................................................1\n1.2 Background ..............................................................................................................................3\n1.2.1 NiSource ........................................................................................................................3\n1.2.2 Feeney Brothers .............................................................................................................4\n1.2.3 Natural Gas Distribution Systems ..................................................................................4\n1.3 Events Preceding the Overpressure ..........................................................................................7\n1.4 Emergency Response ...............................................................................................................9\n1.4.1 Local and State Response ..............................................................................................9\n1.4.2 Columbia Gas Response ..............................................................................................11\n1.4.3 Community Impact ......................................................................................................13\n1.5 Natural Gas Main Replacement Project .................................................................................13\n1.5.1 Scope ............................................................................................................................13\n1.5.2 Project Reviews ...........................................................................................................15\n1.5.3 Sensing Line Documentation .......................................................................................16\n1.6 Engineering Project Management ..........................................................................................18\n1.6.1 Staffing and Scope of Responsibilities ........................................................................18\n1.6.2 Measurement and Regulation Department ...................................................................20\n1.7 Overpressure Protection .........................................................................................................22\n1.7.1 Overpressurization Protection Requirements ..............................................................22\n1.7.2 Previous Overpressurization Accidents Investigated by the NTSB ............................23\n1.7.3 Previous NiSource Overpressurization Incidents ........................................................25\n1.8 Pipeline Safety Management Systems ...................................................................................26\n1.9 Professional Engineer Review and Approval .........................................................................28\n1.10 Government Oversight ...........................................................................................................31\n1.10.1 Federal Oversight .........................................................................................................31\n1.10.2 Massachusetts Oversight ..............................................................................................31\n2 Postaccident Actions ..............................................................................................................33\n2.1 NTSB Safety Recommendation to Commonwealth of Massachusetts ..................................33\n2.2 NTSB Urgent Recommendations to NiSource .......................................................................34\n2.3 NiSource Emergency Preparedness and Response Actions ...................................................36\n2.4 Industry Actions .....................................................................................................................38\n\n<<<PAGE 6>>>\n\nNTSB Pipeline Accident Report\n3 Analysis ...................................................................................................................................39\n3.1 Exclusions ..............................................................................................................................39\n3.2 Overpressurization Protection for Low-Pressure Natural Gas Systems .................................39\n3.3 CMA Engineering Processes ..................................................................................................40\n3.3.1 Records and Documentation ........................................................................................41\n3.3.2 Constructability Review...............................................................................................42\n3.3.3 Engineering Risk Assessment ......................................................................................43\n3.4 Professional Engineer Review and Approval .........................................................................43\n3.5 Emergency Response .............................................................................................................44\n3.5.1 Public Safety Answering Points...................................................................................44\n3.5.2 Emergency Responder Communications .....................................................................44\n3.5.3 NiSource Emergency Coordination with Municipal Responders ................................45\n4 Conclusions .............................................................................................................................48\n4.1 Findings ..................................................................................................................................48\n4.2 Probable Cause .......................................................................................................................49\n5 Recommendations ..................................................................................................................50\n5.1 New Recommendations ..........................................................................................................50\n5.2 Previously Issued Recommendations .....................................................................................51\nAppendix .......................................................................................................................................52\nAppendix A. The Investigation ......................................................................................................53\nAppendix B. NiSource Safety Management System Plan .............................................................54\nAppendix C. Enforcement Actions ................................................................................................55\nAppendix D. Constructability Safety Review ................................................................................57\nAppendix E. NiSource Operational Notice ON 15-05...................................................................59\nReferences .....................................................................................................................................62\nii\n\n<<<PAGE 7>>>\n\nNTSB Pipeline Accident Report\nFigures\nFigure 1. Map of the damaged structures in the area impacted by the overpressurization. ........... 2\nFigure 2. Remnants of house where the fatality and two severe injuries occurred. ....................... 3\nFigure 3. Typical configuration of the Merrimack Valley low-pressure natural gas distribution\nsystem. ............................................................................................................................................ 5\nFigure 4. Typical configuration of high-pressure natural gas distribution system installed\npostaccident..................................................................................................................................... 7\nFigure 5. Salem Street tie-in for the South Union Street project ................................................... 8\nFigure 6. Location of September 13, 2018, tie-in and the Winthrop Avenue regulator station. .... 9\nFigure 7. Areas along South Union Street with tie-ins impacted by the project.......................... 14\nFigure 8. The Winthrop Avenue regulator station. ...................................................................... 15\nFigure 9. Pipeline SMS maturity model. ...................................................................................... 27\nFigure 10. NiSource Safety Management System Plan Part A. ................................................... 54\nFigure 11. NiSource Safety Management System Plan Part B. ................................................... 54\niii\n\n<<<PAGE 8>>>\n\nNTSB Pipeline Accident Report\nTables\nTable 1. Local fire response. ........................................................................................................ 10\nTable 2. Required CMA project workflow documentation. ......................................................... 15\nTable 3. Sources of sensing line information and select regulator station documentation. ......... 17\nTable 4. P.E. industrial exemption for infrastructure project practices. ....................................... 30\nTable 5. Massachusetts DPU enforcement actions for the 5 years previous to the accident. ...... 55\niv\n\n<<<PAGE 9>>>\n\nNTSB Pipeline Accident Report\nAcronyms and Abbreviations\nAGA American Gas Association\nANSI American National Standards Institutes\nAPI American Petroleum Institute\nASME American Society of Mechanical Engineers\nCFR Code of Federal Regulations\nCMA Columbia Gas of Massachusetts\nCoMIRS Commonwealth of Massachusetts Interoperable Radio System\nDPU Massachusetts Department of Public Utilities\nEOC emergency operations center\nERP emergency response plans\nFMEA failure modes and effects analysis\nFOL field operations leader\nGIS geographic information system\nIC incident commander\nLFE leader of field engineering\nM&R Measurement and Regulation\nMAOP maximum allowable operating pressure\nMEMA Massachusetts Emergency Management Agency\nMOC management of change\nNG National Grid United States\nNCEES National Council of Examiners for Engineering and Surveying\nNSPE National Society of Professional Engineers\nNTSB National Transportation Safety Board\nv\n\n<<<PAGE 10>>>\n\nNTSB Pipeline Accident Report\nON Operational Notice\nOQ operator qualification\nP.E. professional engineer\nPHMSA Pipeline and Hazardous Materials Safety Administration\nPSAP Public Safety Answering Points\npsi pounds per square inch\npsig pounds per square inch, gauge\nPSMS Pipeline Safety Management Systems\nRP Recommended Practice\nRSPA Research and Special Programs Administration\nSCADA Supervisory Control and Data Acquisition system\nSCIP Statewide Communications Interoperability Plan\nSMS safety management systems\nw.c. water column\nWMS work management system\nvi\n\n<<<PAGE 11>>>\n\nNTSB Pipeline Accident Report\nExecutive Summary\nOn September 13, 2018, about 4:00 p.m. local time, a series of structure fires and\nexplosions occurred after high-pressure natural gas was released into a low-pressure natural gas\ndistribution system in the northeast region of the Merrimack Valley in the Commonwealth of\nMassachusetts. The natural gas distribution system was owned and operated by Columbia Gas of\nMassachusetts, a subsidiary of NiSource, Inc. Columbia Gas of Massachusetts delivers natural gas\nto about 325,000 customers in Massachusetts. One person was killed and 22 individuals, including\nthree firefighters, were transported to local hospitals due to injuries; seven other firefighters\nincurred minor injuries. The fires and explosions damaged 131 structures, including at least\n5 homes that were destroyed in the city of Lawrence and the towns of Andover and North Andover.\nMost of the damage occurred from fires ignited by natural gas-fueled appliances; several of the\nhomes were destroyed by natural gas-fueled explosions. Fire departments from the three\nmunicipalities were dispatched to the fires and explosions. First responders initiated the\nMassachusetts fire-mobilization plan and received mutual aid from neighboring districts in\nMassachusetts, New Hampshire, and Maine. Emergency management officials had National Grid\nUnited States (the electric utility) shut down electrical power in the area, the state police closed\nlocal roads, and freight and passenger railroad operations in the area were suspended. Columbia\nGas of Massachusetts shut down the low-pressure natural gas distribution system, affecting\n10,894 customers, including some outside the area who had their service shut off as a precaution.\nThe accident investigation focused on the following safety issues:\n• Adequacy of natural gas regulations\n• Project documentation\n• Constructability review\n• Project management\n• Risk assessment\n• Safety management systems\n• Licensed professional engineer approval of natural gas projects\n• Emergency response\nThe National Transportation Safety Board determines that the probable cause of the\noverpressurization of the natural gas distribution system and the resulting fires and explosions was\nColumbia Gas of Massachusetts’ weak engineering management that did not adequately plan,\nreview, sequence, and oversee the construction project that led to the abandonment of a cast iron\nmain without first relocating regulator sensing lines to the new polyethylene main. Contributing\nto the accident was a low-pressure natural gas distribution system designed and operated without\nadequate overpressure protection.\nvii\n\n<<<PAGE 12>>>\n\nNTSB Pipeline Accident Report\n1. Factual Information\n1.1 Accident Synopsis\nOn September 13, 2018, about 4:00 p.m. local time, a series of structure fires and\nexplosions occurred after high-pressure natural gas was released into a low-pressure natural gas\ndistribution system in the northeast region of the Merrimack Valley in the Commonwealth of\nMassachusetts. The natural gas distribution system was owned and operated by Columbia Gas of\nMassachusetts (CMA), a subsidiary of NiSource, Inc. CMA delivers natural gas to about\n325,000 customers in Massachusetts. The fires and explosions damaged 131 structures, including\nat least 5 homes that were destroyed in the city of Lawrence and the towns of Andover and North\nAndover. (See figure 1.) Most of the damage occurred from fires ignited by natural gas-fueled\nappliances; several of the homes were destroyed by natural gas-fueled explosions. Fire\ndepartments from the three municipalities were dispatched to the fires and explosions. First\nresponders initiated the Massachusetts fire-mobilization plan and received mutual aid from\nneighboring districts in Massachusetts, New Hampshire, and Maine. Emergency management\nofficials had National Grid United States (NG) (the electric utility) shut down electrical power in\nthe area, the state police closed local roads, and freight and passenger railroad operations in the\narea were suspended. CMA shut down the low-pressure natural gas distribution system, affecting\n10,894 customers, including some outside the affected area who had their service shut off as a\nprecaution.\n1\n\n<<<PAGE 13>>>\n\nNTSB Pipeline Accident Report\nFigure 1. Map of the damaged structures in the area impacted by the overpressurization.\nAn 18-year-old male was killed when a home exploded, and the chimney fell onto the\nvehicle where he was sitting. (See figure 2.) Another person in the vehicle at the time of the\n2\n\n<<<PAGE 14>>>\n\nNTSB Pipeline Accident Report\nexplosion was seriously injured, as was someone on the second floor of the house. In total,\n22 people, including 3 firefighters, were transported to hospitals for treatment of their injuries.\nInjuries included respiratory injuries related to smoke inhalation from fires and musculoskeletal\ninjuries from evacuating. Some people were transported to hospitals to maintain ongoing medical\ntreatment that could not be continued in their homes because of the shutdown of natural gas and\nelectricity and the evacuation of residents.\nFigure 2. Remnants of house where the fatality and two severe injuries occurred.\n1.2 Background\n1.2.1 NiSource\nNiSource, Inc. is an Indiana-based energy holding company whose subsidiaries are\nregulated natural gas and electric utility companies serving about 3.9 million customers in seven\nstates.1 Its natural gas distribution operations comprise about 60,000 miles of pipeline and include\n732 low-pressure natural gas distribution systems. NiSource’s Massachusetts subsidiary, CMA,\n1 NiSource is the successor to a corporation organized in 1987 under the name of Northern Indiana Public Service\nCompany Industries, Inc., which changed its name to NiSource in 1999.\n3\n\n<<<PAGE 15>>>\n\nNTSB Pipeline Accident Report\ndelivers natural gas to over 325,000 natural gas customers in southeastern Massachusetts, the\ngreater Springfield area, and the Merrimack Valley.2\n1.2.2 Feeney Brothers\nCMA contracted with Feeney Brothers, a pipeline services firm, to work on a CMA project\nto replace an existing cast iron main with a polyethylene main.\n3 About 7:00 a.m. on the day of the\naccident, a CMA construction coordinator, along with four employees of Feeney Brothers, arrived\nat Salem and South Union Streets in Lawrence, Massachusetts, to continue work on this project.\nThe work they performed that day led to the overpressurization of the natural gas distribution\nsystem. All crewmembers were trained and qualified in accordance with the Pipeline Operator\nQualification Rule, commonly known as OQ.4 Following the accident, the contractor\ncrewmembers, along with the CMA construction coordinator, were alcohol and drug tested in\naccordance with Title 49 Code of Federal Regulations (CFR) Part 199. The test results were\nnegative for alcohol or other drugs.\n1.2.3 Natural Gas Distribution Systems\nNatural gas distribution systems deliver natural gas to customers for heating, cooking,\nlighting, and other uses. A basic distribution system has three elements: (1) natural gas mains that\ntransport natural gas underground, (2) service lines that deliver natural gas from the mains to\ncustomers, and (3) meters that measure the quantity of natural gas used by each customer.\nCustomer piping takes natural gas from the meter to customer’s appliances where it is used. To\nminimize service interruptions, normal maintenance and natural gas distribution system upgrades\nare typically performed with the system operating.\nBoth low-pressure and high-pressure natural gas distribution systems are used to supply\nnatural gas to customers. In a low-pressure natural gas distribution system, the natural gas in the\nmains is essentially the same pressure as the pressure provided to the customer’s piping and used\nby the appliances. Natural gas is typically supplied to the mains from a high-pressure source\nthrough a regulator station that reduces the pressure to that required by the customers. The\nlow-pressure natural gas distribution system in the Merrimack Valley was installed in the early\n1900s with cast iron mains. The system used 14 regulator stations to supply natural gas to the\nmains and control pressure.5 The regulator stations each contained two regulators in series⸻a\nworker regulator and a monitor regulator⸻each with a sensing line that feeds back the pressure in\nthe main to the regulator, forming a redundant closed-loop control system. The worker regulator\nis the primary regulator that maintains the natural gas pressure, and the monitor regulator provides\na redundant backup to the worker regulator. Each of the regulator stations reduced the natural gas\n2 Although CMA had internal guidance documents specifically for its employees, NiSource also had guidance\ndocuments that employees in all its subsidiaries were required to follow. In this report, guidance documents are\nidentified accordingly.\n3 Feeney Brothers, a utility services firm headquartered in Dorchester, Massachusetts, was established in 1988\nand employs over 700 employees and operates throughout Massachusetts, Connecticut, and New York.\n4 Title 49 Code of Federal Regulations (CFR) Part 192, Subpart N.\n5 Regulator stations house the worker and monitor regulators that are used to maintain natural gas pressure.\n4\n\n<<<PAGE 16>>>\n\nNTSB Pipeline Accident Report\npressure from about 75 pounds per square inch gauge (psig) to 12 inches of water column (w.c.),\nabout 0.5 psig, for distribution through the mains and delivery to customers.6\nSince the regulator stations are the primary means of pressure control in the low-pressure\nsystems, an overpressure condition in a natural gas distribution system could affect all customers\nserved by the system. This is an inherent weakness of a low-pressure natural gas distribution\nsystem.\nFigure 3 shows a typical arrangement for the low-pressure natural gas distribution system\nused in the Merrimack Valley before the accident.\nFigure 3. Typical configuration of the Merrimack Valley low-pressure natural gas distribution\nsystem.\n6 In the pipeline industry, it is customary to measure anything less than 1 psig in inches of water column. A\nmeasurement of 1 inch w.c. equals 0.0361 psig.\n5\n\n<<<PAGE 17>>>\n\nNTSB Pipeline Accident Report\nIn a high-pressure natural gas distribution system, the natural gas pressure in the main is\nsubstantially higher than that required by the customer. A pressure regulator is installed at each\nmeter to reduce the pressure. These regulators incorporate an overpressure protection device to\nprevent overpressurization of the customer’s piping and appliances should the regulator fail.\nAdditionally, excess flow valves are installed in the service line.7 Because each customer’s service\nin a high-pressure natural gas distribution system is protected by an excess flow valve and a\npressure regulator, it is highly unlikely that an overpressure condition in the main would impact\nmultiple customers. Figure 4 shows a typical high-pressure natural gas distribution system. This is\nthe type of natural gas distribution system that was installed postaccident in the Merrimack Valley.\n7 An excess flow valve is a mechanical safety device installed on a gas service line to a residence or small\ncommercial gas customer. In the event of damage to the gas service line between the street and the meter, the excess\nflow valve will minimize the flow of gas through the service line. Current federal regulations require a gas distribution\ncompany to install such a device on new or replacement service lines for single-family residences and certain\nmultifamily and commercial buildings where the service line pressure is above 10 psig. See 49 CFR 192.383 for\nspecific requirements.\n6\n\n<<<PAGE 18>>>\n\nNTSB Pipeline Accident Report\nFigure 4. Typical configuration of high-pressure natural gas distribution system installed\npostaccident.\n1.3 Events Preceding the Overpressure\nAbout 7:00 a.m. on the day of the accident, a CMA construction coordinator, along with\nfour employees of Feeney Brothers, arrived at Salem and South Union Streets in Lawrence,\nMassachusetts, to continue work on a CMA project to replace an existing cast iron main with a\npolyethylene main.\nThe crew completed the installation according to the CMA work plan, placed the new\ntie-ins into service, and isolated the existing cast iron main shortly before 4:00 p.m., by closing\n7\n\n<<<PAGE 19>>>\n\nNTSB Pipeline Accident Report\nvalves on a 2-inch plastic bypass pipe between the cast iron and polyethylene mains.\n8 The crew\nthen cut the bypass pipe to abandon the cast iron main. (See figure 5.) In postaccident interviews,\ncrewmembers said that within minutes of closing the valves and cutting the bypass, they observed\nthe pressure gauge on the polyethylene main exceed the expected readings.9 Furthermore, a fitting\non the polyethylene natural gas main blew off into the hand of one of the workers. The\ncrewmembers said that they responded quickly to plug the blowing natural gas, and they heard\nemergency vehicles in the neighborhood and observed smoke plumes in multiple directions within\nminutes.\n2-inch\nbypass with\nvalve at each\nend\nPressure\ngauges\n6-inch main fed by\nnewly energized 8-inch\nplastic main connected\nto Winthrop Avenue\nregulator station\nFigure 5. Salem Street tie-in for the South Union Street project (looking west). Photograph\ncourtesy of Feeney Brothers.\nAt the Winthrop Avenue regulator station, about 0.5 mile south of the work area, the\nabandoned cast iron main was still connected to the regulator sensing lines providing input to the\ntwo pressure regulators used to control the system pressure.\n10 (See figure 6.) Once the contractor\n8 A tie-in involves connecting new piping to existing piping. In this case, the main ran north and south while the\nbranches ran east and west. When the main was replaced, the east and west branches needed to be tied into the new\nmain.\n9 Supporting documentation referenced in this report can be found in the public docket for this accident, accessible\nfrom the NTSB Accident Dockets web page by searching PLD18MR003.\n10 Sensing lines are also called control lines or static lines.\n8\n\n<<<PAGE 20>>>\n\nNTSB Pipeline Accident Report\ncrew isolated the cast iron main, the natural gas pressure began to drop in the cast iron main and\nin the regulator sensing lines. As the pressure dropped, the pressure regulators responded by\nopening further, increasing pressure in the natural gas distribution system. Since the Winthrop\nAvenue regulators no longer sensed system pressure, they fully opened, allowing high-pressure\nnatural gas to be released into the low-pressure natural gas distribution system.\nFigure 6. Location of September 13, 2018, tie-in and the Winthrop Avenue regulator station.\n1.4 Emergency Response\n1.4.1 Local and State Response\nThe overpressurization of the low-pressure natural gas distribution system in the\nMerrimack Valley impacted over 10,000 natural gas customers in three municipalities⸻Lawrence,\nNorth Andover, and Andover. The emergency call centers in these municipalities, known as public\nsafety answering points (PSAP) began receiving 9-1-1 calls immediately following the\noverpressurization from residents and businesses reporting fires and explosions and requesting\nassistance.\nShortly after 4:00 p.m., the fire departments in Lawrence, North Andover, and Andover\nwere inundated with emergency calls reporting structure fires and explosions. Within the first\n30 minutes, all three fire departments had exhausted their list of mutual aid. The incident\ncommanders (IC) fro","truncated":true,"body_characters":195962}