{"operation":"document","citation":"PLD24LR006","title":"Exelon Corporation (Baltimore Gas and Electric Company) Natural Gas–Fueled Home Explosion","source_type":"incident","agency":"National Transportation Safety Board","status":"current","official":true,"published_on":"2026-07-16","effective_on":"2024-08-11","summary":"Accident. in Bel Air, MD, USA. on 2024-08-11. Baltimore Gas & Electric. Leak/explosion/fire","machine_formats":{"json":"https://regulus.evalyn.ai/document/ntsb-case-pld24lr006.json","markdown":"https://regulus.evalyn.ai/document/ntsb-case-pld24lr006.md"},"app_url":"https://regulus.evalyn.ai/document/ntsb-case-pld24lr006","source_url":"https://www.ntsb.gov/investigations/Pages/PLD24LR006.aspx","body":"NTSB investigation PLD24LR006.\n\nEvent Type: Accident\n\nEvent Date: 2024-08-11\n\nEvent City: Bel Air\n\nEvent State Or Region: MD\n\nEvent Country: USA\n\nPipeline Operator: Baltimore Gas & Electric\n\nPipeline Type: Distribution\n\nAccident Type: Leak/explosion/fire\n\nCompletion Status: Completed\n\nReport Number: PIR2604\n\nReport Date: 2026-06-25\n\nProbable cause: The National Transportation Safety Board determines that the probable cause of the August 11, 2024, home explosion in Bel Air, Maryland, was the Exelon Corporation subsidiary Baltimore Gas and Electric Company’s ineffective response to reports of a suspected natural gas leak, which allowed for a suspected leak, caused by electrical arcing of electrical service lines, collocated in a common trench with a plastic gas service-line pipe and its tracer wire, to be left unrepaired for over 10 hours, resulting in gas leaking from the service-line pipe, migrating to the accident home, and igniting.\n\nTier1Name: Emergency response\n\nTier2Name: Evacuation\n\nTier1Name: System operating\n\nTier2Name: Fire/explosion (post-release)\n\nTier1Name: System operating\n\nTier2Name: Product leak/release\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipeline structure\n\nFinding Tier3Name: Pipe\n\nFinding Modifier Name: Damaged/degraded\n\nFinding Report Text: Pipeline - Pipeline structure - Pipe - Damaged/degraded\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 Sunday, August 11, 2024, about 6:48 a.m., a home explosion and fire occurred at 2300 Arthurs Woods Drive in Bel Air, Maryland, resulting in a destroyed home, two fatalities, and three injuries. The explosion also damaged several residences and displaced families. At the time of the explosion, it was daylight and clear; the temperature was 67°F with no precipitation.\n\nWhat We Found\nThe National Transportation Safety Board determines that the probable cause of the August 11, 2024, home explosion in Bel Air, Maryland, was the Exelon Corporation subsidiary Baltimore Gas and Electric Company’s ineffective response to reports of a suspected natural gas leak, which allowed for a suspected leak, caused by electrical arcing of electrical service lines, collocated in a common trench with a plastic gas service-line pipe and its tracer wire, to be left unrepaired for over 10 hours, resulting in gas leaking from the service-line pipe, migrating to the accident home, and igniting.\n\nLessons Learned\nThe Bel Air accident demonstrates the importance of an effective and coordinated response to reports of suspected natural gas leaks, particularly for companies whose operations include natural gas and electric utilities. Utilities collocated in a common trench, or otherwise located in close proximity, pose a hazard if operators do not ensure that adequate separation is maintained. Operators with multiple subsidiaries and utilities, like Exelon, must identify areas where two or more departments or utilities overlap and then prescribe specific procedures to govern how such departments need to work together to ensure public safety.\n\nThis accident showed that natural gas distribution pipeline operators must be able to receive all reports of suspected gas leaks. Operators must ensure that their public-facing phone systems are set up to appropriately receive customer calls and that any call handlers on duty are adequately trained and fit to answer emergency calls. Through our pipeline investigations, we have learned that pipeline safety management systems can help pipeline distribution operators manage risks related to human errors and interdepartmental-safety concerns.\n\nWe found here, and in many previous investigations, that, in the absence of adequate safety procedures and systems, natural gas alarms can be vital safeguards, alerting people to the presence of natural gas leaks. More information about natural gas alarms is available on the NTSB website.\n\nPIR-26-04\n<<<PAGE 1>>>\n\nPipeline Investigation Report\nPIR-26-04\nIssued: June 25, 2026 Pipeline Investigation Report: PIR-26-04\nExelon Corporation (Baltimore Gas and\nElectric Company) Natural Gas–Fueled\nHome Explosion\nLocation Bel Air, Maryland\nDate August 11, 2024\nAccident type Leak/explosion/fire\nPipeline Distribution pipeline\n0.50-inch plastic service line carrying natural gas\nFatalities 2\nInjuries 3\n1 Factual Information\n1.1 The Accident\nOn Sunday, August 11, 2024, about 6:48 a.m., a home explosion and fire\noccurred at 2300 Arthurs Woods Drive (accident home) in Bel Air, Maryland, resulting in\na destroyed home, two fatalities, and three injuries.\n1 The explosion also damaged\nseveral residences and displaced families. (See figure 1.) At the time of the explosion, it\nwas daylight and clear; the temperature was 67°F with no precipitation.\n1 (a) Visit ntsb.gov to find additional information in the public docket for this National Transportation\nSafety Board (NTSB) accident investigation (case number PLD24LR006). (b) All times in this report are local.\n1\n\n<<<PAGE 2>>>\n\nPipeline Investigation Report\nPIR-26-04\nFigure 1. Aerial view of the accident location. (Courtesy of the Harford County Sheriff’s Office.)\nThe accident home, built in 2007, was a multi-story, single-family structure with\nstucco exterior and a paving-stone driveway on a 0.28-acre lot. Exelon Corporation\n(Exelon) owned and operated natural gas pipeline utilities and electrical utilities near the\nhome. Exelon completed some of these functions through their wholly owned subsidiary\nBaltimore Gas and Electric Company (BGE); this report uses the corporation name\n“Exelon” throughout and “BGE” as needed for references to that subsidiary.\n2 Exelon\ndistributed natural gas to the accident home with a 1.25-inch plastic gas main and a 0.5-\ninch plastic gas service line.3 Around the time of the explosion, the gas main and gas\nservice lines near the accident home were operating about 89 pounds per square inch,\n2 See section 1.3 for more on Exelon and BGE.\n3 (a) A gas main is a natural gas distribution pipeline, typically located belowground, that serves as a\ncommon source of supply for more than one service line. (b) A service line is typically belowground and\ntransports natural gas (or other commodities, such as electricity) to a customer.\n2\n\n<<<PAGE 3>>>\n\nPipeline Investigation Report\nPIR-26-04\ngauge, below the maximum allowable operating pressure of 99 pounds per square inch,\ngauge.4\nExelon distributed electricity to the accident home with a secondary main and a\nset of three electrical service lines.\n5 The accident gas service-line pipe and the accident\nelectrical service lines were located in a common trench near the accident home\ndriveway.\n6 Electric-department procedures at the Exelon subsidiary BGE stated that for\nnew construction, common trenching would not be permitted where a 12-inch\nseparation IN ANY DIRECTION [emphasis in the original] could not be maintained\nbetween the gas service-line pipe and the electrical service-line cables. The National\nElectric Safety Code, an organization that established electrical standards,\nrecommended a 12-inch separation between utilities to prevent damage from arcing,\nleaks, or maintenance operations.\nAbout 11 hours before the explosion, on Saturday, August 10, 2024, about\n7:36 p.m., the accident homeowner’s real estate agent reported a power outage at the\naccident home through an Exelon app.7 About 7:51 p.m., an Exelon dispatcher for\nelectric service sent an Exelon electric technician to investigate the power outage.\nMeanwhile, about 0.2 miles south of the accident home, a passerby was walking in the\nneighborhood and smelled natural gas odorant.\n8 About 8:27 p.m., the passerby\nreported the suspected natural gas leak to Exelon’s call center. Because the passerby\nwas not physically located at a building with an associated address, she provided the\nintersection closest to her, and then Exelon’s system identified the home at 2314 Arthurs\nWoods Drive (nearby home), the home closest to the intersection, as the address of the\nreport. The call-center agent added to the call an Exelon dispatcher for gas service, as\nExelon’s procedures required, and, about 8:41 p.m., the gas dispatcher sent a gas\ntechnician to investigate the suspected natural gas leak at the nearby home. The\n4 Unlike pounds per square inch, a basic pressure measurement, pounds per square inch, gauge,\nwhich pipeline systems often use, measures pressure relative to atmospheric pressure (the pressure of the\nsurrounding air).\n5 A secondary main in an electrical distribution system carries electricity from a transformer (a device\nthat changes the voltage of electricity) to multiple service lines.\n6 A common trench is one that carries multiple types of utility lines (such as gas and electric), instead of\ncarrying only one type of line. (See figure 3.)\n7 The BGE mobile app allowed customers or their representatives to report outages.\n8 Because natural gas is odorless, strong smelling chemical additives called odorants are mixed with\nnatural gas to help reduce the risk that leaks will go unidentified. The most common odorant added to\nnatural gas has a “rotten egg” or sulfurous odor.\n3\n\n<<<PAGE 4>>>\n\nPipeline Investigation Report\nPIR-26-04\nNational Transportation Safety Board (NTSB) did not find evidence that the accident\nhomeowner contacted Exelon to report a suspected natural gas leak or that the accident\nhome had a natural gas alarm installed. Figure 2 shows the accident neighborhood,\nindicating the accident home and the nearby home. It also shows the accident leak\nlocation, which section 1.2.1 discusses.\nFigure 2. The accident neighborhood.\nAbout 8:34 p.m., an Exelon electric technician, dispatched to an area near the\naccident home to investigate the power outage, determined that there had been an\nelectrical fault in the area and referred the repair to an Exelon electric contractor.\n9 About\n8:39 p.m., the electric technician reported to an Exelon electric dispatcher the smell of\nnatural gas odorant at the accident-home address. After diagnosing the electrical fault\nand reporting the suspected natural gas leak, the electric technician closed the job ticket\nand left. The electric technician told the NTSB that he was not aware that the electrical\nservice line to the accident home was in a common trench with a gas service line (electric\ntechnicians did not have access to this information).\n9 An electrical fault is an unintended low-resistance electrical pathway, also known as a short circuit.\n4\n\n<<<PAGE 5>>>\n\nPipeline Investigation Report\nPIR-26-04\nAbout 8:59 p.m., an electric dispatcher, relaying the electric technician’s message,\nreported to an Exelon gas dispatcher the smell of natural gas odorant at the accident-\nhome address. The gas dispatcher, the same one who had responded to the passerby’s\nearlier report, told the electric dispatcher that a gas technician was on the way to the\narea, giving the address of the nearby home. The gas dispatcher did not send a gas\ntechnician to investigate the suspected natural gas leak at the accident home. The gas\ndispatcher told the NTSB that the electric dispatcher had provided the same intersection\nthat the passerby had provided about a half hour earlier (the intersection closest to the\nnearby home) as the location where the electric technician had smelled natural gas\nodorant. However, the NTSB’s review of Exelon’s electric-dispatcher call logs showed\nthat the electric dispatcher had provided the accident home address, which was\n0.2 miles away, as the location of the report; the gas dispatcher had not recorded the\ncorrect address of the electric dispatcher’s report of the suspected natural gas leak.\nAbout 9:08 p.m., an Exelon gas technician, dispatched to the nearby home to\ninvestigate the suspected natural gas leak, started checking the nearby home and\nseveral homes north of it for indications of natural gas.10 About 9:45 p.m., the gas\ntechnician reported finding no indications of natural gas at the nearby home and left the\naccident neighborhood.\n11 When the NTSB asked the gas technician whether gas\ndispatch had told him about another report of a suspected natural gas leak in the area,\nhe said that they had not. Consequently, the night before the explosion, while the gas\ntechnician looked for indications of natural gas at several homes in the accident\nneighborhood, he did not look for indications of natural gas at the accident home.\nThe next morning, on Sunday, August 11, 2024, about 6:08 a.m., a county water\nservice technician (county worker) who was marking utilities at the accident home\nsmelled natural gas odorant and heard sounds of gas hissing. (He was marking utilities\nbecause an Exelon electric contractor was scheduled to perform work at the accident\nhome later that day and needed to know where the buried utilities were located.)12 He\nphoned Exelon’s call center to report the suspected natural gas leak. The county worker\ntold the NTSB that Exelon’s call system prompted him on the nature of his call but that\nafter he had advanced through the prompts, the system went blank, as if the call had not\n10 An indication of natural gas is an observable sign, such as a reading from a detection instrument, that\nnatural gas may be present.\n11 The NTSB determined that the gas technician’s investigation of the suspected leak was consistent\nwith Exelon’s leak investigation procedures.\n12 State One Call systems provide customers, contractors, and excavators with a single phone number\nto call, 8-1-1, before excavation or construction, which allows utility companies to mark the location of their\nunderground lines.\n5\n\n<<<PAGE 6>>>\n\nPipeline Investigation Report\nPIR-26-04\nreached a call-center agent. The county worker dialed Exelon’s call center several more\ntimes, each time getting the same blank result. After the explosion, the NTSB’s review of\nExelon call-center logs and its interviews with Exelon employees showed that Exelon’s\ncall system had routed the county worker’s calls to one of five on-call agents, an agent\nwho was on duty but not responsive (accident call-center agent). About 6:16 a.m., as he\nwas leaving the scene, the county worker notified his supervisor of the suspected leak at\nthe accident home and of his inability to contact Exelon.\nAt the time of the accident, Exelon’s call system automatically answered incoming\ncalls before randomly routing them to an available agent, not requiring the agent to\ninitiate action to answer (or “pick up”) the call. The accident call-center agent told the\nNTSB that he had been drinking alcohol before his shift, which was an\nunscheduled-overtime shift, and had fallen asleep at his desk. Exelon did not submit the\naccident call-center agent for postaccident drug and alcohol testing. Therefore, the\nNTSB could not quantify the extent of the call-center agent’s drug or alcohol impairment\nor determine whether it was a factor in the accident.\nAbout 6:22 a.m., the county worker’s supervisor reached an Exelon call-center\nagent and reported the suspected natural gas leak at the accident home. Because the\nsupervisor’s report cited sounds of gas hissing, criteria which Exelon called a “strong”\nreport, in addition to dispatching a gas technician to the accident home, Exelon also\ncontacted the Harford County Fire Department. While the Harford County Fire\nDepartment was on the way to the scene, about 6:48 a.m., the accident home exploded\nand caught fire. An Exelon gas technician arrived on the scene about 7:12 a.m., after the\nexplosion occurred.13\nThe explosion fatally injured the accident homeowner and one of Exelon’s electric\ncontractors (two Exelon contractors had arrived on the scene to work on the power\noutage after the county worker had left). The explosion also injured three other people\n(including the second electric contractor). Table 1 shows a timeline of the accident\nevents.\n13 This was not the same gas technician that investigated the leak at the nearby home a day earlier.\n6\n\n<<<PAGE 7>>>\n\nPipeline Investigation Report\nPIR-26-04\nTable 1. Timeline of accident events.\nDate and approximate time Event\nThe accident homeowner’s real estate agent reported to Exelon (through\nSaturday, August 10, 2024, 7:36 p.m.\nan Exelon app) a power outage at the accident home.\n7:51 p.m. Exelon dispatched an electric technician to the area near the accident\nhome to investigate the power outage.\nA passerby in the accident neighborhood reported to Exelon (through its\ncall center) the smell of natural gas odorant. The passerby provided the\nintersection closest to her as the location where she had smelled natural\n8:27 p.m.\ngas odorant, and then Exelon’s system identified the home at 2314 Arthurs\nWoods Drive (a nearby home), the home closest to the intersection, a home\nabout 0.2 miles south of the accident home, as the location of the report.\nThe electric technician diagnosed an electrical fault near the accident\nhome and referred the repair to an electric contractor. The electric\n8:34 p.m–8:39 p.m.\ntechnician also smelled natural gas odorant at the accident home. After\nreporting the smell to an electric dispatcher, he closed the job and left the\nscene.\n8:41 p.m. Exelon dispatched a gas technician to the nearby home to investigate the\nsuspected natural gas leak.\nAn electric dispatcher notified a gas dispatcher of the suspected natural\ngas leak at the accident home. The gas dispatcher told the electric\ndispatcher that a gas technician was on the way to the area (to the nearby\n8:59 p.m.\nhome) but did not redirect the gas technician from the nearby home to the\naccident home or send a different gas technician to investigate the\nsuspected leak at the accident home.\nThe gas technican investigated the suspected natural gas leak at the\nnearby home, reported to gas dispatch that he did not find a leak there, and\n9:08 p.m.\nleft the scene. He did not investigate the leak at the accident home\n(0.2 miles away) because he was not aware of the suspected leak at that\nlocation.\nA county worker that was working at the accident home smelled natural\ngas odorant and heard sounds of gas hissing. He tried to report what he\nSunday, August 11, 2024, 6:08 a.m.\nsuspected was a natural gas leak to Exelon (through its call center) but did\nnot reach a responsive call-center agent, even after multiple attempts.\nAs he was leaving the scene, the county worker notifed his supervisor of\nthe strong smell of natural gas odorant at the accident home and the\n6:16 a.m.\nsounds of gas hissing. He told his supervisor that he had been unable to\nreach Exelon through its call center.\nThe county worker’s supervisor reported to Exelon (through its call center)\n6:22 a.m.\nthe smell of natural gas odorant and the sounds of gas hissing at the\naccident home.\n6:48 a.m. The accident home exploded.\nA gas technician (not the same gas technician who investigated the\n7:12 a.m.\nsuspected natural gas leak at the nearby home) arrived at the accident\nhome and began Exelon’s emergency response to the explosion.\n7\n\n<<<PAGE 8>>>\n\nPipeline Investigation Report\nPIR-26-04\n1.2 Examinations and Testing\n1.2.1 On-Scene Examinations and Testing\nAfter the explosion, Exelon conducted pressure testing and, under the NTSB’s\ndirection, bar-hole testing to determine the extent of any natural gas migration.\n14 On\nAugust 11, 2024, about 2:23 p.m., the afternoon of the explosion, Exelon conducted\npressure testing at the accident location to determine whether a leak was present on the\ntested section of the gas service-line pipe. During these tests, the gas service line to the\naccident home failed to hold pressure, indicating a leak. Exelon excavated the area of\nthe leak and found a hole in the accident home gas service-line pipe. (See section 1.2.2\nfor more on the gas service-line pipe leak.)\nOn August 12, 2024, through August 14, 2024, Exelon conducted bar-hole\ntesting at the accident location to measure whether natural gas was present in the tested\nsoil. This bar-hole testing showed elevated natural gas readings at the gas leak location\n(under the accident home driveway) that extended toward the perimeter of the accident\nhome.\nExcavation of the natural gas utilities also found that the accident gas service-line\npipe was in a common trench with multiple other utilities near the accident home\ndriveway. In addition to the gas service-line pipe, the common trench also included a gas\nservice-line tracer wire, remains of the accident electrical service lines, a communication\ncable, and a wire from an electric-dog fence.15 Between the natural gas main and the\naccident home, the separation between the gas and electrical service lines varied,\nranging from 3 inches to 15 inches. Because the accident electrical service lines were\ninvolved in an electrical fault and large portions of them had melted, the NTSB could not\ndetermine the separation distance between the accident gas service-line pipe and the\naccident electrical service lines at the time of the accident. Figure 3 shows the excavated\naccident common trench (the gas service-line tracer wire had likely been installed\nparallel to the gas service-line pipe, and the excavation disturbed it).\n14 (a) Bar-hole testing describes a gas measurement technique in which a technician makes a\nsmall-diameter hole in the ground with a steel bar, inserts a probe into the hole, and obtains a gas\nmeasurement. (b) Gas migration occurs when gas escapes from underground piping and travels through\nsoil, rocks, or wells to the surface or to nearby buildings.\n15 A tracer wire is a conductive wire installed alongside a nonmetallic pipe to help identify the pipe’s\nlocation.\n8\n\n<<<PAGE 9>>>\n\nPipeline Investigation Report\nPIR-26-04\nFigure 3. The accident trench.\n1.2.2 Laboratory Examinations and Testing\nThe NTSB examined a portion of the accident service-line pipe that was\napproximately 87 inches long between the capped end and the coupling end, with a\n0.5-inch outer diameter.\n16 The examination found that approximately 17 inches\nupstream of the coupling, the gas service-line pipe exhibited a bulging feature (a\n“blister”) that was about 1 inch long and oval shaped.\n17 The blister resulted in a breach of\nthe pipe wall, which allowed the pipe to leak natural gas. (See figure 4.) The accident gas\nservice-line pipe tracer wire, which was in the common trench next to the gas service-line\npipe, was thermally damaged and had separated into two pieces. The tracer wire was\ncopper and insulated, which made it a good thermal conductor. The soil and debris in\nthe accident trench contained large masses of vitrified soil that included aluminum slag,\nevidence of the electrical fault (high temperatures create vitrified soil and aluminum\n16 A coupling joins two pipes together.\n17 The upstream end of the gas service-line pipe was the connection between the pipe and the\ncoupling, and the downstream end was the connection to the accident home.\n9\n\n<<<PAGE 10>>>\n\nPipeline Investigation Report\nPIR-26-04\nslag). The accident electrical service lines (secondary power cables) were thermally\ndamaged and had missing sections, which had melted as a result of the electrical fault.\nFigure 4. The “blister” on the accident service-line pipe.\n1.3 Exelon Corporation\nAt the time of the accident, Exelon was one of the nation’s largest utility\ncompanies, serving almost 11 million customers through six utilities, including BGE. On\nMarch 12, 2012, Exelon acquired BGE through a merger with Constellation Energy\nGroup, Inc. BGE served more than 1.3 million electric customers and 700,000 gas\ncustomers in Maryland. The BGE President and CEO led five departments, which\ncomprised customer operations (including the customer-call center), electric, gas,\nsupport services, and technical services. BGE electric dispatch was in the electric\ndepartment, and its gas dispatch was in the gas department.\n1.4 Postaccident Actions\nThe Exelon subsidiary BGE has taken the following actions in response to this\naccident:\n• Transitioned to a call-center system that requires agents working overnight\nand weekend shifts to manually answer (or “pick up”) incoming calls.\n10\n\n<<<PAGE 11>>>\n\nPipeline Investigation Report\nPIR-26-04\n• Updated its procedures to require monitoring of natural gas leak calls\nevery hour of the day and every day of the week (“24/7” monitoring). In\naddition, supervisors and quality assurance team members review the calls\nin near-real time. Before the explosion, BGE did not regularly review\nnatural gas leak calls in near-real time.\n• Enhanced call-handler training. Increased dispatcher and call-agent\ntraining from a biannual requirement to a quarterly requirement. In\naddition, BGE reinforced its requirement for call handlers to use job aids\n(process guides) during suspected natural gas leak calls and established\nweekly training on active listening, as part of its training on three-part\ncommunication (give the message, repeat the message, and confirm the\nmessage).\n• Developed a fitness-for-duty questionnaire for call handlers. Established\nquestions supervisors must ask subordinate call handlers (dispatchers and\ncall agents) to determine whether the agents are ready (physically and\nmentally) to answer emergency calls.\n• Updated its procedures for electric technicians responding to electrical\nfaults. Upon arriving on the scene, the electric technician calls an electric\ndispatcher, who determines whether the electrical utility is in a common\ntrench with a gas utility. If a gas utility is in the common trench, the electric\ntechnician must remain on the scene until a gas technician arrives. The gas\ntechnician will then evaluate whether a natural gas leak is present. Before\nthis update, electric technicians at the scene of an electrical fault did not\nhave to determine whether the electrical service lines were in a common\ntrench with gas service lines or, upon determining that the electrical\nservices lines were in a common trench, call for a gas technician and wait\nfor the gas technician to arrive and confirm that there was no natural gas\nleak.\n• Created a program to install a device, a resin conduit called a “split,” in all\ncommon trenches that are opportunistically exposed (uncovered through\ndigging) during construction activities. The split creates a thermal barrier\nbetween the gas and electrical service lines.\n11\n\n<<<PAGE 12>>>\n\nPipeline Investigation Report\nPIR-26-04\n• Developed a pilot program to provide customers with natural gas alarms.\nThe pilot is scheduled to begin in 2026, pending jurisdictional approval.\n18\n2 Analysis\nThe explosion and fire occurred after natural gas leaked from a gas service-line\npipe, migrated to the accident home, and ignited.\n19 The service-line pipe breached\nbecause the plastic pipe and its tracer wire were in a trench with electrical service lines\nthat had faulted, which elevated temperatures near the service-line pipe and\nsubsequently caused the pipe to melt and leak gas. Starting about 10 hours before the\nleak, three people, including an Exelon employee, reported to Exelon that they\nsuspected a natural gas leak in the vicinity of the accident home. Exelon did not repair\nthe reported leak before it became hazardous. The NTSB did not identify issues with gas\npressures in the area of the leak or the effectiveness of local emergency response\nagencies.\n2.1 Inadequate Separation of Utilities in a Common Trench\nThe accident gas service-line pipe and the accident electrical service lines were\nlocated in a common trench. Although the NTSB could not determine how closely the\ngas service-line pipe and the electrical service lines were located at the leak site because\nof the damage the electrical fault caused, an excavation of the accident trench showed\nthat the two utilities were located from 3 inches to 15 inches apart at various points. This\nindicates that, after the explosion, there were some areas where the utilities had less than\n12 inches of separation, the minimum Exelon required between gas and electric utilities\nin common trenches.20\nThe National Electric Safety Code recommended a 12-inch separation between\nutilities to prevent damage from arcing, leaks, or maintenance operations. The NTSB\nfound evidence of arcing and a leak in this accident, including the melted electrical\n18 (a) At the time of this report, BGE had not started the natural gas alarm program. (b) Exelon declined\nto provide information about its other natural gas utilities (Delmarva and PECO). Therefore, the NTSB could\nnot determine whether the postaccident actions Exelon took at BGE would also be appropriate for its\nDelmarva and PECO subsidiaries.\n19 The NTSB did not determine the source of the ignition.\n20 The NTSB’s South Riding, Virginia, investigation of a home explosion that resulted in one fatality and\nthree injuries (one serious) determined that the probable cause of the explosion was inadequate separation\nbetween gas and electric utilities. See Natural Gas Explosion and Fire in South Riding, Virginia, July 7, 1998.\nNTSB/PAR-01/01. Washington, DC: NTSB.\n12\n\n<<<PAGE 13>>>\n\nPipeline Investigation Report\nPIR-26-04\nservice lines and the “blister,” a 1-inch puncture, on the gas service-line pipe. The gas\nservice-line tracer wire, which was thermally conductive and located near the gas\nservice-line pipe, likely transferred and localized the heat from the electrical fault to the\npipe, causing the blister on the gas service-line pipe.\nAfter the explosion, pressure testing at the accident location identified a leak on\nthe accident home gas service-line pipe (where the NTSB lab examination also identified\nthe leak). In addition, postaccident bar-hole testing showed that the ground around the\naccident home’s perimeter was saturated with natural gas. Therefore, the accident\nelectrical service lines faulted and created a heat source, and the gas service-line pipe\ntracer wire transferred this heat to the accident gas service-line pipe, damaging it. As a\nresult, natural gas leaked from the damaged pipe, migrated to the accident home, and\nignited. After the explosion, BGE began installing “split” devices in exposed common\ntrenches to create a thermal barrier between collocated utilities.\n2.2 Ineffective Response to Reports of a Suspected Natural Gas Leak\nThe NTSB identified deficiencies in Exelon’s response to the suspected natural\ngas leak in several departments (electric, gas, and customer operations) within the\norganization. The practices and procedures in place at the time of the accident did not\nensure adequate collaboration between these different departments. As a result, Exelon\nfailed to mitigate the risk that the accident leak posed, even after three people reported\nit. Although the first report of the leak (the passerby’s report) did not provide the exact\naddress where the leak was located, the second and third reports (the electric technician\nand county worker reports) did. Exelon had this critical information about the leak at\nleast 10 hours before the explosion occurred. Thus, Exelon’s ineffective response to the\nreports of the accident leak was likely a key factor in the accident.\nThe electric technician’s report of the accident leak exposed shortfalls in electric\ndepartment practices and procedures. The electric technician told the NTSB that he was\nnot aware that the accident electrical service lines were in a common trench with gas\nservice lines, indicating that BGE had not established clear practices and procedures\nregarding utilities collocated in a common trench. In addition, although the electric\ntechnician had called to report a suspected natural gas leak, he did not stay on the scene\nuntil an Exelon gas technician arrived (at the time of the accident, the electric\ndepartment’s procedures did not require him to stay). After the explosion, BGE began\nrequiring electric technicians who respond to an electrical fault to contact electric\ndispatch to determine whether the service lines are in a common trench and to, when a\njob involves an electrical fault in a common trench, stay on the scene until a gas\ntechnician arrives.\n13\n\n<<<PAGE 14>>>\n\nPipeline Investigation Report\nPIR-26-04\nThe electric technician’s report of the accident leak also exposed shortfalls in gas\ndepartment practices and procedures. After the electric technician reported the\nsuspected natural gas leak at the accident home to an electric dispatcher, the electric\ndispatcher reported the leak to a gas dispatcher. However, the gas dispatcher did not\nsend a gas technician to investigate the suspected leak at the accident home. The gas\ndispatcher told the NTSB that the electric dispatcher had provided the same\nleak-location address that the passerby had provided (the gas dispatcher was also on the\ncall with the passerby, the first person to report the suspected leak), the address of a\nnearby home. However, Exelon’s call logs indicate that the electric dispatcher provided\nthe accident home address when talking to the gas dispatcher. Thus, the gas dispatcher\nand the electric dispatcher did not effectively communicate about the suspected leak’s\nlocation. As a result, a gas technician looked for the leak at the nearby home and did not\nfind it; moreover, he did not look for the leak at the accident home. After the explosion,\nBGE increased the frequency of its call-handler training, reinforced its requirement for\ncall handlers to use job aids (process guides) during suspected natural gas leak calls,\nand routinely emphasized the importance of active listening.\nThe county worker’s report of the accident leak exposed shortfalls in the customer\noperations department practices and procedures. The county worker called Exelon to\nreport the suspected gas leak at the accident home. Exelon’s phone system\nautomatically answered (“picked up”) the call and routed it to a call-center agent who\nwas technically available but who did not respond to the call. The accident call-center\nagent told the NTSB that he had been drinking alcohol before his unscheduled shift and\nthat he had fallen asleep at his desk. Because Exelon did not submit the accident\ncall-center agent for drug and alcohol testing, the NTSB could not determine whether\ndrug or alcohol impairment was a factor in the accident.\n21\nThe county worker called Exelon several times but did not reach a responsive\nagent. This prevented him from notifying Exelon of the suspected natural gas leak in the\ncritical moments before the explosion occurred. About 25 minutes before the accident,\nwhen it was likely too late to prevent the explosion, the county worker’s supervisor\nreached a responsive call-center agent and reported the suspected natural gas leak at\nthe accident home. After the explosion, the BGE call center updated its phone system to\nrequire that call-center agents manually answer (or “pick up”) incoming customer calls\nduring overnight and weekend shifts (the previous system automatically answered\n21 BGE reported to the NTSB that although it had not made any changes to its drug and alcohol testing\nprocesses as a result of the accident and did not plan to make any changes, it continuously reviews\ncompany processes for improvement.\n14\n\n<<<PAGE 15>>>\n\nPipeline Investigation Report\nPIR-26-04\nincoming customer calls at these times) and developed a fitness-for-duty questionnaire\nfor call handlers.\nIn this accident, Exelon responded effectively to the first report of the suspected\nnatural gas leak (the passerby report), given the information that it had. However, Exelon\ndid not respond effectively to the second and third reports of the suspect leak (the\nExelon electric technician and the county worker reports) because of safety oversights in\npractices and procedures in its electric, gas, and customer operations departments. Had\nExelon responded effectively to the second and third reports of the suspected natural\ngas leak, the accident would not have occurred. Exelon’s ineffective response to reports\nof the suspected natural gas leak at the accident home resulted in the suspected leak\nbecoming hazardous before Exelon repaired it.\n3 Probable Cause\nThe National Transportation Safety Board determines that the probable cause of\nthe August 11, 2024, home explosion in Bel Air, Maryland, was the Exelon Corporation\nsubsidiary Baltimore Gas and Electric Company’s ineffective response to reports of a\nsuspected natural gas leak, which allowed for a suspected leak, caused by electrical\narcing of electrical service lines, collocated in a common trench with a plastic gas service-\nline pipe and its tracer wire, to be left unrepaired for over 10 hours, resulting in gas\nleaking from the service-line pipe, migrating to the accident home, and igniting.\n4 Lessons Learned\nThe Bel Air accident demonstrates the importance of an effective and\ncoordinated response to reports of suspected natural gas leaks, particularly for\ncompanies whose operations include natural gas and electric utilities. Utilities collocated\nin a common trench, or otherwise located in close proximity, pose a hazard if operators\ndo not ensure that adequate separation is maintained. Operators with multiple\nsubsidiaries and utilities, like Exelon, must identify areas where two or more departments\nor utilities overlap and then prescribe specific procedures to govern how such\ndepartments need to work together to ensure public safety.\nThis accident showed that natural gas distribution pipeline operators must be\nable to receive all reports of suspected gas leaks. Operators must ensure that their\npublic-facing phone systems are set up to appropriately receive customer calls and that\nany call handlers on duty are adequately trained and fit to answer emergency calls.\nThrough our pipeline investigations, we have learned that pipeline safety management\n15\n\n<<<PAGE 16>>>\n\nPipeline Investigation Report\nPIR-26-04\nsystems can help pipeline distribution operators manage risks related to human errors\nand interdepartmental-safety concerns.22\nWe found here, and in many previous investigations, that, in the absence of\nadequate safety procedures and systems, natural gas alarms can be vital safeguards,\nalerting people to the presence of natural gas leaks. More information about natural gas\nalarms is available on the NTSB website.\n23\n22 (a) Pipeline safety management systems is a framework that assists pipeline operators in improving\ntheir safety performance. (b) See “Pipeline Safety Management Systems: Vital for the Safe Operation of\nPipelines” (NTSB Safety Alert, SA-095, January 7, 2024).\n23 http://www.ntsb.gov/Advocacy/SafetyIssues/Pages/Natural-Gas-Alarm-Safety-.aspx\n16\n\n<<<PAGE 17>>>\n\nPipeline Investigation Report\nPIR-26-04\nThe NTSB is an independent federal agency charged by Congress with\ninvestigating every civil aviation accident in the United States and significant events in the\nother modes of transportation—railroad, transit, highway, marine, pipeline, and\ncommercial space. We determine the probable causes of the accidents and events we\ninvestigate and issue safety recommendations aimed at preventing future occurrences. In\naddition, we conduct transportation safety research studies and offer information and\nother assistance to family members and survivors for each accident or event we\ninvestigate. We also serve as the appellate authority for enforcement actions involving\naviation and mariner certificates issued by the Federal Aviation Administration (FAA) and\nUS Coast Guard, and we adjudicate appeals of civil penalty actions taken by the FAA.\nThe NTSB does not assign fault or blame for an accident or incident; rather, as\nspecified by NTSB regulation, “accident/incident investigations are fact-finding\nproceedings with no formal issues and no adverse parties … and are not conducted for\nthe purpose of determining the rights or liabilities of any person” (Title 49 Code of\nFederal Regulations section 831.4). Assignment of fault or legal liability is not relevant to\nthe NTSB’s statutory mission to improve transportation safety by investigating accidents\nand incidents and issuing safety recommendation","truncated":true,"body_characters":40753}