That was the conclusion of a report released by the National Transportation Safety Board (NTSB) that determined the probable cause of the August 11, 2024, home explosion in Bel Air, Maryland.
On Sunday, August 11, 2024, at 6:48 a.m., a home explosion and fire occurred at 2300 Arthurs Woods Drive in Bel Air. The blast also damaged several residences and displaced families.
Exelon distributed natural gas to the accident home with a 1.25-inch plastic gas main and a 0.5-inch plastic gas service line. Around the time of the explosion, the gas main and gas service lines near the accident home were operating about 89 pounds per square inch, below the maximum allowable operating pressure of 99 pounds per square inch.
Power Outage
About 11 hours before the explosion, on Saturday, August 10, 2024, at 7:36 p.m., the accident homeowner’s real estate agent reported a power outage at the accident home through an Exelon app. At 7:51 p.m., an Exelon dispatcher for electric service sent an Exelon electric technician to investigate the power outage.
Meanwhile, about 0.2 miles south of the accident home, a passerby was walking in the neighborhood and smelled natural gas odorant.
At 8:27 p.m., the passerby reported the suspected natural gas leak to Exelon’s call center.
Because the passerby was not physically located at a building with an associated address, she provided the intersection closest to her, and then Exelon’s system identified the home at 2314 Arthurs Woods Drive, the home closest to the intersection.
The call-center agent added to the call an Exelon dispatcher for gas service, as Exelon’s procedures required, and, at 8:41 p.m., the gas dispatcher sent a gas technician to investigate the suspected natural gas leak at the nearby home. The NTSB did not find evidence the accident homeowner contacted Exelon to report a suspected natural gas leak or the accident home had a natural gas alarm installed.
A few minutes before at 8:34 p.m., an Exelon electric technician, dispatched to an area near the accident home to investigate the power outage, determined there had been an electrical fault in the area and referred the repair to an Exelon electric contractor.
Gas Smell in Air
At 8:39 p.m., the electric technician reported to an Exelon electric dispatcher the smell of natural gas odorant at the accident-home address. After diagnosing the electrical fault and reporting the suspected natural gas leak, the electric technician closed the job ticket and left. The electric technician said he was not aware the electrical service line to the accident home was in a common trench with a gas service line (electric technicians did not have access to this information).
Aerial view of the location of the fatal gas explosion in Bel Air, Maryland.Source: Harford County Sheriff’s Office
Then at 8:59 p.m., an electric dispatcher, relaying the electric technician’s message, reported to an Exelon gas dispatcher the smell of natural gas odorant at the accident-home address.
The gas dispatcher, the same one who had responded to the passerby’s earlier report, told the electric dispatcher a gas technician was on the way to the area, giving the address of the nearby home. Furthermore, the gas dispatcher did not send a gas technician to investigate the suspected natural gas leak at the accident home. The gas dispatcher said the electric dispatcher had provided the same intersection the passerby had provided about a half hour earlier (the intersection closest to the nearby home) as the location where the electric technician had smelled natural gas odorant.
However, the NTSB’s review of Exelon’s electric-dispatcher call logs showed the electric dispatcher had provided the accident home address, which was 0.2 miles away, as the location of the report; the gas dispatcher had not recorded the correct address of the electric dispatcher’s report of the suspected natural gas leak.
Gas Leak Investigation
At 9:08 p.m., an Exelon gas technician, dispatched to the nearby home to investigate the suspected natural gas leak, started checking the nearby home and several homes north of it for indications of natural gas.
Then at 9:45 p.m., the gas technician reported finding no indications of natural gas at the nearby home and left the accident neighborhood.When the NTSB asked the gas technician whether gas dispatch had told him about another report of a suspected natural gas leak in the area, he said that they had not. Consequently, the night before the explosion, while the gas technician looked for indications of natural gas at several homes in the accident neighborhood, he did not look for indications of natural gas at the accident home.
The next morning, on Sunday, August 11, 2024, at 6:08 a.m., a county water service technician who was marking utilities at the accident home smelled natural gas odorant and heard sounds of gas hissing. (He was marking utilities because an Exelon electric contractor was going to perform work at the accident home later that day and needed to know the location of the buried utilities.)
He phoned Exelon’s call center to report the suspected natural gas leak. The county worker said Exelon’s call system prompted him on the nature of his call but that after he had advanced through the prompts, the system went blank, as if the call had not reached a call-center agent.
As a result, the county worker dialed Exelon’s call center several more times, each time getting the same blank result.
No Answer at Call Center
After the explosion, the NTSB’s review of Exelon call-center logs and its interviews with Exelon employees showed Exelon’s call system had routed the county worker’s calls to one of five on-call agents, an agent who was on duty but not responsive.
The neighborhood where the explosion occurred. Map shows where the incident occurred and where the suspected natural gas leak initially ended up reported.Source: NTSB
At 6:16 a.m., as he was leaving the scene, the county worker notified his supervisor of the suspected leak at the accident home and of his inability to contact Exelon.
At the time of the accident, Exelon’s call system automatically answered incoming calls before randomly routing them to an available agent, not requiring the agent to initiate action to answer the call. The accident call-center agent said he had been drinking alcohol before his shift, which was an unscheduled-overtime shift, and had fallen asleep at his desk.
Exelon did not submit the accident call-center agent for postaccident drug and alcohol testing. Therefore, the NTSB could not quantify the extent of the call-center agent’s drug or alcohol impairment or determine whether it was a factor in the accident.
Meanwhile, at 6:22 a.m., the county worker’s supervisor reached an Exelon call-center agent and reported the suspected natural gas leak at the accident home.
Because the supervisor’s report cited sounds of gas hissing, criteria which Exelon called a “strong” report, in addition to dispatching a gas technician to the accident home, Exelon also contacted the Harford County Fire Department.
House Exploded
While the Harford County Fire Department was on the way to the scene, at 6:48 a.m., the explosion and fire occurred. An Exelon gas technician arrived on the scene at 7:12 a.m., after the explosion occurred.
The explosion killed the homeowner and one of Exelon’s electric contractors (two Exelon contractors had arrived on the scene to work on the power outage after the county worker had left). The explosion also injured three other people (including the second electric contractor).
Actions Taken
Exelon subsidiary BGE has taken the following actions in response to this accident:
- Transitioned to a call-center system that requires agents working over night and weekend shifts to manually answer incoming calls.
- Updated its procedures to require monitoring of natural gas leak calls every hour of the day and every day of the week (“24/7” monitoring). Additionally, supervisors and quality assurance team members review the calls in near-real time. Before the explosion, BGE did not regularly review natural gas leak calls in near-real time.
- Enhanced call-handler training. Increased dispatcher and call-agent training from a biannual requirement to a quarterly requirement.
- Developed a fitness-for-duty questionnaire for call handlers. Established questions supervisors must ask subordinate call handlers to determine whether the agents are ready to answer emergency calls.
- Updated its procedures for electric technicians responding to electrical faults. Upon arriving on the scene, the electric technician calls an electric dispatcher, who determines whether the electrical utility is in a common trench with a gas utility. If a gas utility is in the common trench, the electric technician must remain on the scene until a gas technician arrives. The gas technician will then evaluate whether a natural gas leak is present.
- Created a program to install a device, a resin conduit called a “split,” in all common trenches that are opportunistically exposed during construction activities. The split creates a thermal barrier between the gas and electrical service lines.
- Developed a pilot program to provide customers with natural gas alarms. The pilot should begin this year, pending jurisdictional approval.
Lessons Learned
In terms of lessons learned, the Bel Air incident showed 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 co-located in a common trench, or otherwise located in close proximity, pose a hazard if operators do not ensure adequate separation ends up 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.
Click here for more on the NTSB report.