Damage from the Silver Spring, Md., explosion and fire was so severe that investigators from the National Transportation Safety Board had to use the process of elimination to rule out potential causes. As a result, the investigation lasted for more than two and a half years. Source: National Transportation Safety Board |
Critical components of Washington Gas Light Co. infrastructure did not function as intended during the events leading up to an August 2016 explosion and fire that claimed seven lives, according to the National Transportation Safety Board.
As is the case in most major natural gas incidents, multiple failures interacted to make the Silver Spring, Md., accident as deadly and severe as it was. Seven residents of the Flower Branch apartment complex were killed, 65 other people were transported to the hospital for treatment, and three firefighters were injured, according to the National Transportation Safety Board, or NTSB.
A vent line designed to allow gas to escape if indoor gas equipment malfunctions was not properly connected, the NTSB said in its investigation findings. The vent line had originally been, and was supposed to be, connected to a component called a regulator, which brings gas pressure to the appropriate level for customer use. A malfunction in the regulator created overpressurization that required venting, and without the correct connection to the vent line, the gas stayed inside the meter room rather than escaping to the atmosphere, the NTSB concluded.
The damage from the explosion and fire made it difficult to figure out exactly how the equipment in the meter room had malfunctioned Aug. 10, 2016, but the type of regulator Washington Gas had used at the apartment complex has failed often enough in the past to suggest to the NTSB staff that a regulator failure was the likely cause.
The Flower Branch apartment complex where the explosion happened had gas regulators that used mercury as part of their process for establishing appropriate pressures. Mercury regulators were mostly installed during the 1940s and 1950s, so the ones in use now are more than half a century old.
NTSB investigators found that for only one of the regulators in the meter room, the threads where it would be screwed into the vent line were undamaged, showing that the connection had not blown out during the explosion. Rather, it had already been disconnected. Source: National Transportation Safety Board |
Washington Gas has been replacing its mercury regulators periodically. Over five years, Washington Gas replaced 992 regulators because of performance failures, according to the NTSB. But the board concluded that the utility relies on unvalidated information about both the location and condition of these regulators.
"As we all know, pipelines provide heating and cooking fuel to millions of homes and businesses throughout the nation," NTSB Chairman Robert Sumwalt said during an April 23 meeting. "But when pipelines fail, as we've seen today, the results can be tragic, as they were on the night of the explosion and fire in Silver Spring, Md."
The utility has disputed the NTSB's findings, arguing in a document filed with the safety board that the accident's cause is still unknown. Washington Gas pointed to a 2016 report from the Bureau of Alcohol, Tobacco, Firearms and Explosives, which said that in the weeks following the explosion, the bureau had not conclusively found an incident cause.
NTSB member Jennifer Homendy during an April 23 meeting argued against Washington Gas' assessment of the accident. Source: National Transportation Safety Board |
"Washington Gas concurs with the conclusion that the cause of this accident remains undetermined, even after the follow-on NTSB investigation," the utility wrote. "[T]he additional testing and data collection by the NTSB indicate that certain assumptions made in the early investigation stages regarding the source location of suspected fugitive gas in the basement level meter/storage room are now not supported by fact."
During the meeting, NTSB member Jennifer Homendy expressed outrage at the utility's response to the investigation.
"I strongly suggest that Washington Gas refocus its attention on actions they could have taken to prevent this accident from occurring rather than spend time telling us how to conduct our safety investigation," Homendy said.
The board made 13 recommendations based on its findings. The recommendations targeted not only Washington Gas, but federal and state pipeline safety regulators, the emergency response community, and research institutions that could advance methane detection technology.
The board said safety officials should require gas line regulators to be located outside rather than indoors, which would eliminate the need for a regulator vent line. It also said Washington Gas should take its mercury regulators out of service entirely, prioritizing multi-family homes such as apartment buildings.
Seven residents of the Flower Branch apartment complex were killed, 65 other people were transported to the hospital for treatment, and three firefighters were injured, the NTSB said. Source: Maryland Public Service Commission |
Many of the board's recommendations also related to improved methane detection. Residents had reported a gas smell six times in the weeks and months before the accident, although never to Washington Gas. On one occasion prior to the blast, the fire department came to investigate but was unable to access the meter room where the explosion ultimately originated.
"This agency's employees know that by the time they arrive at the accident's site, nothing that they can do can stop the worst from happening," Sumwalt said. "All that they, and we on the board, can ever do is to prevent the same thing from happening to others. Today's recommendations, if acted upon, will prevent such tragedies through systemwide improvements to equipment and procedures."