{"operation":"document","citation":"DCA16FP003","title":"Building Explosion and Fire","source_type":"incident","agency":"National Transportation Safety Board","status":"current","official":true,"published_on":"2019-04-29","effective_on":"2016-08-10","summary":"Accident. in Silver Spring, MD, USA. on 2016-08-10. Washington Gas Light Company. Leak/explosion/fire","machine_formats":{"json":"https://regulus.evalyn.ai/document/ntsb-case-dca16fp003.json","markdown":"https://regulus.evalyn.ai/document/ntsb-case-dca16fp003.md"},"app_url":"https://regulus.evalyn.ai/document/ntsb-case-dca16fp003","source_url":"https://www.ntsb.gov/investigations/Pages/DCA16FP003.aspx","body":"NTSB investigation DCA16FP003.\n\nEvent Type: Accident\n\nEvent Date: 2016-08-10\n\nEvent City: Silver Spring\n\nEvent State Or Region: MD\n\nEvent Country: USA\n\nPipeline Operator: Washington Gas Light Company\n\nPipeline Type: Distribution\n\nAccident Type: Leak/explosion/fire\n\nCompletion Status: Completed\n\nReport Number: PAR1901\n\nReport Date: 2019-04-29\n\nProbable cause: The National Transportation Safety Board determines that the probable cause of the explosion in building 8701 of the Flower Branch apartment complex was the failure of an indoor mercury service regulator with an unconnected vent line that allowed natural gas into the meter room where it accumulated and ignited from an unknown ignition source. Contributing to the accident was the location of the mercury service regulators where leak detection by odor was not readily available.\n\nTier1Name: System operating\n\nTier2Name: Explosion\n\nTier1Name: Post-release\n\nTier2Name: Fire/explosion (post-release)\n\nTier1Name: Emergency response\n\nTier2Name: Emergency shutoff\n\nTier1Name: System operating\n\nTier2Name: Product leak/release\n\nTier1Name: System operating\n\nTier2Name: System/equipment malf/failure\n\nTier1Name: Emergency response\n\nTier2Name: Inspection 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: Support/oversight/monitoring\n\nFinding Tier3Name: Enforcement\n\nFinding Modifier Name: Federal agency\n\nFinding Report Text: Organizational - Support/oversight/monitoring - Enforcement - Federal agency\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Support/oversight/monitoring\n\nFinding Tier3Name: Documentation/record keeping\n\nFinding Modifier Name: Not specified\n\nFinding Report Text: Organizational - Support/oversight/monitoring - Documentation/record keeping - Not specified\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: Support/oversight/monitoring\n\nFinding Tier3Name: Documentation/record keeping\n\nFinding Modifier Name: State/Local agency\n\nFinding Report Text: Organizational - Support/oversight/monitoring - Documentation/record keeping - State/Local agency\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Development\n\nFinding Tier3Name: Design\n\nFinding Modifier Name: Inspection organization\n\nFinding Report Text: Organizational - Development - Design - Inspection organization\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipline systems/equipment\n\nFinding Tier3Name: Regulator\n\nFinding Modifier Name: Failure\n\nFinding Report Text: Pipeline - Pipline systems/equipment - Regulator - Failure\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipline systems/equipment\n\nFinding Tier3Name: Venting\n\nFinding Modifier Name: Malfunction\n\nFinding Report Text: Pipeline - Pipline systems/equipment - Venting - Malfunction\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline structure\n\nFinding Tier3Name: Pipe\n\nFinding Modifier Name: Design\n\nFinding Report Text: Pipeline - Pipeline structure - Pipe - Design\n\nFinding Tier1Name: Environment/Infrastructure\n\nFinding Tier2Name: Operating environment/control system\n\nFinding Tier3Name: Sensor/detector coverage/availability\n\nFinding Modifier Name: Awareness of condition\n\nFinding Report Text: Environment/Infrastructure - Operating environment/control system - Sensor/detector coverage/availability - Awareness of condition\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline handling/service\n\nFinding Tier3Name: Operating information\n\nFinding Modifier Name: Not inspected\n\nFinding Report Text: Pipeline - Pipeline handling/service - Operating information - Not inspected\n\nFinding Tier1Name: Personnel\n\nFinding Tier2Name: Action/decision\n\nFinding Tier3Name: Information processing/decision making\n\nFinding Modifier Name: Pipeline maintenance personnel\n\nFinding Report Text: Personnel - Action/decision - Information processing/decision making - Pipeline maintenance personnel\n\nFinding Tier1Name: Personnel\n\nFinding Tier2Name: Action/decision\n\nFinding Tier3Name: Information processing/decision making\n\nFinding Modifier Name: Emergency services personnel\n\nFinding Report Text: Personnel - Action/decision - Information processing/decision making - Emergency services personnel\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipline systems/equipment\n\nFinding Tier3Name: Regulator\n\nFinding Modifier Name: Design\n\nFinding Report Text: Pipeline - Pipline systems/equipment - Regulator - Design\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipline systems/equipment\n\nFinding Tier3Name: Regulator\n\nFinding Modifier Name: Malfunction\n\nFinding Report Text: Pipeline - Pipline systems/equipment - Regulator - Malfunction\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 August 10, 2016, at 11:51 p.m., eastern daylight time, a 14-unit apartment building, located at 8701 Arliss Street, in the unincorporated community of Silver Spring, in Montgomery County, Maryland, partially collapsed due to a natural gas-fueled explosion and fire.\nThe explosion and fire also heavily damaged an adjacent apartment building, 8703 Arliss Street, which shared a common wall with building 8701.\nAs a result of this accident, 7 residents died, 65 residents were transported to the hospital, and 3 firefighters were treated and released from the hospital. The damage from the accident exceeded $1 million.\n\nWhat We Found\nThe probable cause of the explosion in building 8701 of the Flower Branch apartment complex was the failure of an indoor mercury service regulator with an unconnected vent line that allowed natural gas into the meter room where it accumulated and ignited from an unknown ignition source. Contributing to the accident was the location of the mercury service regulators where leak detection by odor was not readily available.\n\nWhat We Recommended\nAs a result of this investigation, we made the following new safety recommendations.\n\nTo the Pipeline and Hazardous Materials Safety Administration:\n\nRequire that all new service regulators be installed outside occupied structures. (P-19-001)\n\nRequire existing interior service regulators be relocated outside occupied structures whenever the gas service line, meter, or regulator is replaced. In addition, multifamily structures should be prioritized over single-family dwellings. (P-19-002)\n\nTo the Public Service Commission of Maryland, the Commonwealth of Virginia State\nCorporation Commission Division of Public Utility Regulation, and the Public Service\nCommission of the District of Columbia:\n\nFollowing Washington Gas’s successful completion of Safety Recommendation P-19-009, audit and verify the performance of Washington Gas’s mercury service regulator replacement program, including its recordkeeping. (P-19-003)\nOversee the replacement process for the mercury service regulators that Washington Gas has in service. (P-19-004)\n\nTo the International Academies of Emergency Dispatch: Revise Protocol-60 Gas Leak/Gas Odor (Natural and Liquified Petroleum Gases) to direct dispatchers to notify the gas company when any odor call is received. (P-19-005)\n\nTo the International Code Council: In coordination with the Gas Technology Institute and the National Fire Protection Association, incorporate provisions in the International Fuel Gas Code that requires methane detection systems for all types of residential occupancies with gas\nservice. At a minimum, the provisions should cover the installation, maintenance, placement of the detectors, and testing requirements. (P-19-006)\n\nTo the National Fire Protection Association: In coordination with the Gas Technology Institute and the International Code Council, revise the National Fuel Gas Code, National Fire Protection\n\nAssociation 54 to require methane detection systems for all types of residential occupancies with gas service. At a minimum, the provisions should cover the installation, maintenance, placement of the detectors, and testing requirements.\n(P-19-007)\n\nTo the Gas Technology Institute: In coordination with the National Fire Protection Association and the International Code Council, work to develop standards for methane detection systems for all\ntypes of residential occupancies in both the International Fuel Gas Code and the National Fuel Gas Code, National Fire Protection Association 54. At a minimum, the provisions should cover the installation, maintenance, placement of the detectors, and testing requirements. (P-19-008)\n\nTo Washington Gas Light Company:\n\nThroughout the Washington Gas network, implement an audit program to verify the data on the service forms used to determine the location and condition of mercury service regulators to ensure the accuracy of this safety-critical data. (P-19-009)\nRevise your procedures and field forms to require technicians to verify the integrity of vent lines following the testing of indoor service regulators throughout the Washington Gas network. (P-19-010)\nEstablish a time frame with specific dates and milestones for the replacement of mercury service regulators throughout the Washington Gas network that recognizes the need to expedite this program and that prioritizes multifamily dwellings where mercury service regulators are located inside the property. (P-19-011)\nInstall all new service regulators outside occupied structures. (P-19-012)\nRelocate existing interior service regulators outside occupied structures whenever the gas service line, meter, or regulator is replaced. In addition, multifamily structures should be prioritized over single-family dwellings. (P-19-013)\n\nPAR-19-01\n<<<PAGE 1>>>\n\nBuilding Explosion and Fire\nSilver Spring, Maryland\nAugust 10, 2016\nAccident Report\nNTSB/PAR-19/01\nPB2019-100722\nNational\nTransportation\nSafety Board\n\n<<<PAGE 2>>>\n\nNTSB/PAR-19/01\nPB2019-100722\nNotation 58957\nAdopted April 24, 2019\nPipeline Accident Report\nBuilding Explosion and Fire\nSilver Spring, Maryland\nAugust 10, 2016\nNational\nTransportation\nSafety Board\n490 L’Enfant Plaza, S.W.\nWashington, D.C. 20594\n\n<<<PAGE 3>>>\n\nNational Transportation Safety Board. 2019. Building Explosion and Fire, Silver Spring, Maryland,\nAugust 10, 2016. NTSB/PAR-19/01. Washington, DC.\nAbstract: On August 10, 2016, at 11:51 p.m. eastern daylight time, a 14-unit apartment building,\nlocated at 8701 Arliss Street, in Silver Spring, Montgomery County, Maryland, partially collapsed\ndue to a natural gas-fueled explosion and fire. The explosion and fire also heavily damaged an\nadjacent apartment building which shared a common wall with building 8701. As a result of this\naccident, 7 residents died, 65 residents were transported to the hospital, and 3 firefighters were\ntreated and released from the hospital. The investigation focused on the following safety issues: the\nlocation and inspection of service regulators within a structure; the inspection of the gas meter\nassembly; the notification of the natural gas odor to Washington Gas Light Company; and the\ndetection of natural gas through odorants and methane. As a result of this investigation, the\nNational Transportation Safety Board (NTSB) makes new safety recommendations to the Pipeline\nand Hazardous Materials Safety Administration; the Public Service Commission of Maryland, the\nCommonwealth of Virginia State Corporation Commission Division of Public Utility Regulation,\nand the Public Service Commission of the District of Columbia; the International Academies of\nEmergency Dispatch; the International Code Council; the National Fire Protection Association; the\nGas Technology Institute; and Washington Gas Light Company.\nThe National Transportation Safety Board (NTSB) is an independent federal agency dedicated to promoting\naviation, railroad, highway, marine, and pipeline safety. Established in 1967, the agency is mandated by Congress\nthrough the Independent Safety Board Act of 1974 to investigate transportation accidents, determine the probable\ncauses of the accidents, issue safety recommendations, study transportation safety issues, and evaluate the safety\neffectiveness of government agencies involved in transportation. The NTSB makes public its actions and decisions\nthrough accident reports, safety studies, special investigation reports, safety recommendations, and statistical\nreviews.\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\nare not conducted for the purpose of determining the rights or liabilities of any person.” 49 C.F.R. § 831.4.\nAssignment of fault or legal liability is not relevant to the NTSB’s statutory mission to improve transportation safety\nby investigating accidents and incidents and issuing safety recommendations. In addition, statutory language\nprohibits the admission into evidence or use of any part of an NTSB report related to an accident in a civil action for\ndamages resulting from a matter mentioned in the report. 49 U.S.C. § 1154(b).\nFor more detailed background information on this report, visit http://www.ntsb.gov/investigations/dms.html and\nsearch for NTSB accident ID DCA16FP003. Recent publications are available in their entirety on the Internet at\nhttp://www.ntsb.gov. Other information about available publications also may be obtained from the website or by\ncontacting:\nNational Transportation Safety Board\nRecords Management Division, CIO-40\n490 L’Enfant Plaza, SW\nWashington, DC 20594\n(800) 877-6799 or (202) 314-6551\nNTSB publications may be purchased from the National Technical Information Service. To purchase this\npublication, order product number PB2019-100722 from:\nNational Technical Information Service\n5301 Shawnee Rd.\nAlexandria, VA 22312\n(800) 553-6847 or (703) 605-6000\nhttp://www.ntis.gov/\n\n<<<PAGE 4>>>\n\nNTSB Pipeline Accident Report\nContents\nFigures ........................................................................................................................................... iii\nTables ............................................................................................................................................ iv\nAbbreviations and Acronyms .......................................................................................................v\nExecutive Summary .................................................................................................................... vii\n1. Factual Information and Analysis ..........................................................................................1\n1.1 The Accident ............................................................................................................................1\n1.2 Accident Site and Property Description ...................................................................................2\n1.2.1 Gas Meter/Utility Room ................................................................................................5\n1.3 The Investigation ......................................................................................................................5\n1.3.1 Gas Odor Leak Calls ......................................................................................................5\n1.3.2 Previous Gas Odor Calls ................................................................................................6\n1.3.3 Emergency Response .....................................................................................................6\n1.3.4 Postaccident Gas Leak Surveys and Odorant Testing ...................................................7\n1.3.5 Fire and Arson Investigations ........................................................................................8\n1.3.6 Explosion Damage and Evidence ..................................................................................8\n1.3.7 Gas Service to the Flower Branch Apartment Complex ................................................9\n2 Safety Issues ............................................................................................................................10\n2.1 Introduction ............................................................................................................................10\n2.2 Gas Meter Assembly Inspection .............................................................................................10\n2.3 Service Regulators ..................................................................................................................12\n2.3.1 Service Regulator Overview ........................................................................................12\n2.3.2 NTSB Materials Laboratory Examination of the Mercury Service Regulators ...........17\n2.3.3 Upper Regulator Union Assembly ...............................................................................19\n2.3.4 Lower Regulator Union Assembly ..............................................................................21\n2.3.5 Vent Line Inspection Practices ....................................................................................22\n2.3.6 Examination and Exclusion of Gas Appliances in the Meter Room ...........................22\n2.3.7 Mercury Service Regulator Testing .............................................................................24\n2.3.8 Natural Gas Accumulation in the Meter Room of Building 8701 ...............................26\n2.3.9 Mercury Service Regulator Replacement ....................................................................28\n2.3.10 Location of Natural Gas Service Regulators ...............................................................29\n2.4 Natural Gas Odor Notification ...............................................................................................30\n2.4.1 Kay Management .........................................................................................................30\n2.4.2 Washington Gas ...........................................................................................................31\n2.4.3 Montgomery County Fire and Rescue Services ...........................................................31\n2.5 Odorant and Methane Detection of Natural Gas ....................................................................32\n2.5.1 Odorant Detection ........................................................................................................32\n2.5.2 Methane Detection .......................................................................................................34\ni\n\n<<<PAGE 5>>>\n\nNTSB Pipeline Accident Report\n3 Postaccident Actions ..............................................................................................................39\n4 Conclusions .............................................................................................................................40\n4.1 Findings ..................................................................................................................................40\n4.2 Probable Cause .......................................................................................................................41\n5 Recommendations ..................................................................................................................42\n6 Appendix .................................................................................................................................47\n6.1 Appendix A: The Investigation ..............................................................................................47\n6.2 Appendix B: Sample of 20 NTSB Investigations of Residential and Commercial Building\nPipeline Accidents Between 1971 and 2018 ..................................................................................47\nReferences .....................................................................................................................................52\nii\n\n<<<PAGE 6>>>\n\nNTSB Pipeline Accident Report\nFigures\nFigure 1. The accident location, 8701 Arliss Street, before the August 10, 2016, explosion. ....... 1\nFigure 2. Buildings 8701 and 8703 Arliss Street, Silver Spring, Maryland, after the explosion\nand fire. ........................................................................................................................................... 2\nFigure 3. Layout of the Flower Branch apartment complex. ......................................................... 3\nFigure 4. A plan for the basement/terrace floor for 8701 Arliss Street and the shared-wall\nportion of 8703 Arliss Street. .......................................................................................................... 4\nFigure 5. Portions of mercury service regulators and gas meters in building 8701\nshowing heat/fire/explosion damage and the unconnected lower regulator vent line. ................. 11\nFigure 6. Building 8701 after debris removal and ATF reconstruction. ...................................... 12\nFigure 7. Exemplar configuration of a mercury service regulator assembly in a similar\nFlower Branch apartment building. .............................................................................................. 14\nFigure 8. Exemplar mercury service regulator taken from a nearby Flower Branch\napartment building. ....................................................................................................................... 15\nFigure 9. Cross sectional image of a mercury service regulator. ................................................. 16\nFigure 10. Mercury service regulators, service line, jurisdictional pipeline, and vent line after\nthe accident. .................................................................................................................................. 18\nFigure 11. Photograph of the lower regulator union assembly parts. .......................................... 19\nFigure 12. A photograph of the exposed external threaded nipple from the upper regulator\nunion assembly.............................................................................................................................. 20\nFigure 13. Photograph of the disassembled union assembly for the accident lower gas regulator\nafter cleaning. ................................................................................................................................ 21\nFigure 14. Hot water heater at the accident scene after the explosion. ........................................ 23\nFigure 15. The main burner assembly, including the separated pipe and the gas control\nvalve assembly. ............................................................................................................................. 24\nFigure 16. Three-dimensional visualization of the meter room. .................................................. 27\niii\n\n<<<PAGE 7>>>\n\nNTSB Pipeline Accident Report\nTables\nTable 1. Valve seat obstruction failure test data. ......................................................................... 25\nTable 2. Diaphragm tear failure test data for a torn upper regulator. ........................................... 25\nTable 3. Loss of mercury failure test data. ................................................................................... 26\niv\n\n<<<PAGE 8>>>\n\nNTSB Pipeline Accident Report\nAbbreviations and Acronyms\nANSI American National Standards Institute\nASME American Society of Mechanical Engineers\nATF US Bureau of Alcohol, Tobacco, Firearms and Explosives\nBSI British Standards Institution\nCFD computational fluid dynamics\nCFH cubic feet per hour\nCFR Code of Federal Regulations\nCOMAR Code of Maryland Regulations\nDOT US Department of Transportation\nECC Montgomery County Emergency Communication Center\nEPA US Environmental Protection Agency\nGAO US Government Accountability Office\nGTI Gas Technology Institute\nIAED International Academies of Emergency Dispatch\nICC International Code Council\nIFGC International Fuel Gas Code\nLEL lower explosive limit\nLP liquified petroleum\nMAOP maximum allowable operating pressure\nMCFRS Montgomery County Fire and Rescue Service\nMCPD Montgomery County Police Department\nNCSL National Conference of State Legislatures\nNFPA National Fire Protection Association\nv\n\n<<<PAGE 9>>>\n\nNTSB Pipeline Accident Report\nNFPA 54 National Fuel Gas Code\nNPS nominal pipe size\nNTSB National Transportation Safety Board\nOTD Operations Technology Development\nPHMSA Pipeline and Hazardous Materials Safety Administration\nPSC Public Service Commission of Maryland\npsig pounds per square inch, gauge\nRMD residential methane detectors\nRSPA Research and Special Programs Administration\nSCFH standard cubic feet per hour\nUEL upper explosive limit\nUL Underwriter’s Laboratories\nWC water column\nWG Washington Gas Light Company\nWSSC Washington Suburban Sanitary Commission\nvi\n\n<<<PAGE 10>>>\n\nNTSB Pipeline Accident Report\nExecutive Summary\nOn August 10, 2016, at 11:51 p.m., eastern daylight time, a 14-unit apartment building,\nlocated at 8701 Arliss Street, in the unincorporated community of Silver Spring, in Montgomery\nCounty, Maryland, partially collapsed due to a natural gas-fueled explosion and fire.\nThe explosion and fire also heavily damaged an adjacent apartment building, 8703 Arliss\nStreet, which shared a common wall with building 8701.\nAs a result of this accident, 7 residents died, 65 residents were transported to the hospital,\nand 3 firefighters were treated and released from the hospital. The damage from the accident\nexceeded $1 million.\nThe following are safety issues in this accident:\n• the location and inspection of service regulators within a structure\n• the inspection of the gas meter assembly\n• the notification of the natural gas odor to Washington Gas Light Company\n• the detection of natural gas through odorants and methane\nThe National Transportation Safety Board determines that the probable cause of the\nexplosion in building 8701 of the Flower Branch apartment complex was the failure of an indoor\nmercury service regulator with an unconnected vent line that allowed natural gas into the meter\nroom where it accumulated and ignited from an unknown ignition source. Contributing to the\naccident was the location of the mercury service regulators where leak detection by odor was not\nreadily available.\nvii\n\n<<<PAGE 11>>>\n\nNTSB Pipeline Accident Report\n1. Factual Information and Analysis\n1.1 The Accident\nOn August 10, 2016, at 11:51 p.m., eastern daylight time, a 14-unit apartment building,\nlocated at 8701 Arliss Street, in the unincorporated community of Silver Spring, in Montgomery\nCounty, Maryland, partially collapsed due to a natural gas-fueled explosion and fire.1 (See\nfigure 1.)\nFigure 1. The accident location, 8701 Arliss Street, before the August 10, 2016, explosion.\n(Photograph from Google Earth, dated November 2015.)\nThe explosion and fire also heavily damaged an adjacent apartment building, 8703 Arliss\nStreet, which shared a common wall with building 8701. (See figure 2.)\n1 All times mentioned in this report are eastern daylight time, unless otherwise specified.\n1\n\n<<<PAGE 12>>>\n\nNTSB Pipeline Accident Report\nFigure 2. Buildings 8701 (right-center) and 8703 (left) Arliss Street, Silver Spring, Maryland, after\nthe explosion and fire. (Photograph provided by the Public Service Commission of Maryland.)\nAs a result of this accident, 7 residents died, 65 residents were transported to the hospital,\nand 3 firefighters were treated and released from the hospital.2 The damage from the accident\nexceeded $1 million.\n1.2 Accident Site and Property Description\nBuildings 8701 and 8703 Arliss Street were part of the Flower Branch Apartments, a\n26-building complex that was constructed in 1955. (See figure 3.) The apartment complex was\nmanaged by Kay Management, a real estate management and development company.\n2 Some of the injuries reported included respiratory problems from smoke inhalation and injuries from falling or\nburns.\n2\n\n<<<PAGE 13>>>\n\nNTSB Pipeline Accident Report\nFigure 3. Layout of the Flower Branch apartment complex. Building 8701 is identified by a red\nstar. (Graphic provided by Kay Management.)\nBuilding 8701 Arliss Street was a four-level structure with a basement and three floors.\nFour apartments were located on each of the upper three levels. The basement/terrace level\nconsisted of one apartment, a meter room, a storage room, and a property management and rental\noffice. (See figure 4.)\n3\n\n<<<PAGE 14>>>\n\nNTSB Pipeline Accident Report\nFigure 4. A plan for the basement/terrace floor for 8701 Arliss Street and the shared-wall portion\nof 8703 Arliss Street. (Graphic provided by Kay Management.)\nAccording to Washington Gas Light Company’s (WG) construction and service records\nfor 8701 Arliss Street, between the years of 1955 and 1969 the natural gas main along Piney Branch\nRoad that supplied this address was a medium-pressure main constructed of 6-inch inside diameter\nwrapped steel. The service line from the main that supplied 8701 Arliss Street was 2-inch nominal\npipe size (NPS) wrapped steel, connected to a 1-inch NPS inlet pipe and a 1-inch outlet pipe after\nthe service regulators.\n3 The main had a maximum allowable operating pressure (MAOP) of\n25 pounds per square inch, gauge (psig) and the operating pressure at the time of the explosion\nwas between 20 and 22 psig.4 This line had been servicing the address for over 60 years until the\nexplosion on August 10, which severed a portion of the service line. The service line construction\nwas completed on May 31, 1955, and the installation of the natural gas meters and regulators was\ncompleted on June 15, 1955. The gas main and service line were buried about 3 feet below the\nsurface. The 2-inch service line ran along the front of the apartment buildings, including 8701\nArliss Street. On September 25, 1969, the service line was relocated about 80 feet and disconnected\n3 NPS is nominal pipe size as defined the American Society of Mechanical Engineers (ASME) B36-10M-2018\nstandards for wrought steel pipe (ASME 2018).\n4 MAOP refers to how much pressure the walls of the pipeline may safely hold in normal operations.\n4\n\n<<<PAGE 15>>>\n\nNTSB Pipeline Accident Report\nfrom the 6-inch medium-pressure wrapped steel main on Piney Branch Road. The service line was\nthen connected to a 4-inch medium-pressure wrapped steel main that ran along Arliss Street.\n1.2.1 Gas Meter/Utility Room\nThe gas meters were located in the meter room in the basement of 8701 Arliss Street on\nthe north facing wall. The gas meter assembly included 15 meters that served 13 apartments, and\nmaintenance and management offices.\n5 The electric meter panel and a commercial-grade gas water\nheater were positioned about 6 feet away from the gas meter assembly. The room was also used\nfor equipment and supply storage. At the time of the accident, it contained supplies and equipment\nneeded for maintenance.\n6\nThe meter room had restricted access and only two windows: one enclosed with glass and\nthe other covered with a piece of wood with two small holes for ventilation. The room was secured\nby a knob lock, a vertical deadbolt lock, and was armed with an alarm system.7 Only Kay\nManagement staff and Montgomery County Fire and Rescue Service (MCFRS) responders were\nauthorized access to the meter room. In February 2016, the lock to the meter room was changed;\nhowever, Kay Management had not placed a copy of the new key in the MCFRS Knox Box,\nlocated on the premises.8\n1.3 The Investigation\n1.3.1 Gas Odor Leak Calls\nPrior to the accident, several residents of buildings 8701 and 8703 reported to investigators\nthat they smelled gas in the weeks and months leading up to the explosion. One resident reported\nthat he smelled natural gas after returning from work around 11:30 p.m. on August 10. While he\nwas taking out the trash, around 11:50 p.m., he smelled a gas odor in the stairwell and walked\ndown to the basement to locate the source. He told National Transportation Safety Board (NTSB)\ninvestigators that he found the odor became stronger as he walked into the basement and he could\nhear a hissing noise from behind the locked doors of the meter room. He said that he planned to\ncall 9-1-1 to report the gas odor after he finished taking out the trash. However, before he could\nreport the leak, as he walked back from the community trash containers about 120 feet away, the\nexplosion occurred.9\n5 The management office was an apartment converted for business purposes.\n6 Kay Management provided an inventory list for the meter room in 8701 Arliss Street.\n7 According to the US Bureau of Alcohol, Tobacco, Firearms and Explosions (ATF) Origin and Cause report, the\nknob lock was locked, and the vertical dead bolt was not locked, prior to the explosion. For more information, see\n“ATF Report” in NTSB Docket DCA16FP003.\n8 A Knox Box system is an access box for fire departments to use in the event of an emergency to enter structures\nor areas that are deemed difficult. This is required under National Fire Protection Association (NFPA) 1, which is a\ncomprehensive fire code that the State of Maryland has adopted by reference in its Fire Prevention Code.\n9 For more information, see “Interview transcript with Resident A” in NTSB Docket DCA16FP003.\n5\n\n<<<PAGE 16>>>\n\nNTSB Pipeline Accident Report\n1.3.2 Previous Gas Odor Calls\nBetween September 2015 and June 2016, Kay Management received six gas odor calls\nfrom residents of 8701 Arliss Street.\n10 Members of its maintenance staff said that when they\ninvestigated, they either did not detect gas through their gas-detection equipment or would report\nthat the painting of apartments was causing the smell. MCFRS fire personnel responded to an odor\ncall at building 8701 on July 25, 2016. According to interviews with Flower Branch residents and\nemployees from Kay Management, residents in the building typically called either the management\ncompany or 9-1-1 to report gas odors. WG has no record of responding to or receiving any\nnotifications of gas odor calls from 8701 Arliss Street in the 5 years prior to the accident.\nThe same resident who detected the natural gas odor on the night of the explosion had\ncalled 9-1-1 on July 25, 2016, to report a strong smell of natural gas both outside and inside of\nbuilding 8701. The resident told the 9-1-1 operator that the strongest smell of natural gas was\ndetected on the first level of the apartment building. The 9-1-1 operator told the resident not to\nturn on anything that could create an ignition source, and to evacuate himself and others out of the\nbuilding. Neither the resident nor the 9-1-1 operator contacted the gas company.\nOn July 25, 2016, MCFRS fire personnel arrived at building 8701 around 10:20 p.m. They\napproached the building using a calibrated four-gas multimeter.11 Residents directed the fire\npersonnel to the main hallway of the first floor, where no combustible gas readings or natural gas\nodors were detected. Although one responder reported smelling “something,” it did not register on\nhis detection equipment. The fire personnel proceeded through the apartment building, checking\ninside occupied apartments and underneath doors of unoccupied apartments. The fire personnel\nmoved to the basement to test the storage and meter rooms but were unable to gain access to the\nmeter room because the locks had recently been changed and the new key was unavailable. The\nfire personnel wedged the top of the doors open but detected no gas. MCFRS departed at\n10:33 p.m. because they did not detect any gas readings throughout the building.12 The Kay\nManagement property manager was not notified of the odor leak call and only learned of it after a\nconversation with a resident days later.\n13 There are no records of additional conversation between\nKay Management and MCFRS regarding the July 25 odor complaint.\n1.3.3 Emergency Response\nOn August 10, 2016, at 11:52 p.m., the MCFRS Emergency Communication Center\nreceived a 9-1-1 call reporting the explosion and fire. Buildings 8701 and 8703 Arliss Street were\nevacuated by two Montgomery County Police Officers who were within 1,000 feet from them\n10 For more information, see “Operations – Kay Management (All Work Orders 08-01-15 thru 08-25-16)” in\nNTSB Docket DCA16FP003.\n11 Four-gas multimeters are devices that measure the atmosphere for the following four parameters: oxygen\nconcentration (in percentage O2), flammability (in percentage of lower explosive limit [LEL]), carbon monoxide\nconcentration (in parts per million), and hydrogen sulfide concentration (in parts per million).\n12 For more information, see “Reg. Oversight – MCFRS Statements on July 25, 2016, incident” and “Interview\nof Montgomery County Fire and Rescue Lieutenant” in NTSB Docket DCA16FP003.\n13 For more information, see “Interview of Manager of Flower Branch Apartments-Errata” in NTSB Docket\nDCA16FP003.\n6\n\n<<<PAGE 17>>>\n\nNTSB Pipeline Accident Report\nwhen the explosion occurred. MCFRS dispatched units to the accident scene at 11:54 p.m., and\nthe first unit arrived at 11:58 p.m. to begin rescue and fire suppression efforts.14 Residents of\nnearby apartment buildings within the complex voluntarily evacuated themselves.\nThe MCFRS Emergency Communication Center called WG at 12:08 a.m. on August 11,\n2016. Within an hour of the initial notification, WG personnel arrived on scene and shut off the\n4-inch diameter main supplying gas to the five apartment buildings along Arliss Street, and the\nMCFRS responders extinguished the fire shortly thereafter.\nThe NTSB concludes that the postexplosion responses by both MCFRS and WG were\nprompt and adequate.\n1.3.4 Postaccident Gas Leak Surveys and Odorant Testing\nNTSB investigators arrived on scene the morning of August 11, 2016. WG pressure tested\nthe main, which held pressure, indicating there was no leak.15 Soil bar hole tests were conducted\nwithin 3 hours of the accident in areas adjacent to the main and the 2-inch service lines in the front\nand back of buildings 8701 and 8703 detected no gas readings.16 Building 8701’s gas regulator\nvent line, which is a pipe that directs the natural gas away from the building and into the\natmosphere in case of an over-pressure scenario, was also tested and showed no obstruction in the\nvent line.\nOverseen by the Public Service Commission of Maryland (PSC), WG performed\npostaccident odorant testing at two different regulator stations in Silver Spring, Maryland, and\nodorant levels were found compliant with Pipeline and Hazardous Materials Safety Administration\n(PHMSA) regulations that require natural gas to be odorized and detected at 1/5th (or 20 percent)\nof the lower explosive limit (LEL).\n17 This safety feature is required for all distribution lines. The\nState of Maryland has a more stringent requirement for odorant levels, which must be detectable\nat 1/10th (10 percent) of the LEL.18 The testing indicated that the levels also complied with the\nCode of Maryland Regulations (COMAR) requirement. At the Flower Branch complex, the natural\ngas service lines were also tested for odorant levels and met the regulatory limits.19\n14 For more information, see “Survival Factors” in NTSB Docket DCA16FP003 for detailed event chronology\nand emergency response activities.\n15 The operating pressure of the gas line that feeds into apartment","truncated":true,"body_characters":145728}