A gas company's faulty equipment is the most likely cause of an explosion at a suburban Maryland apartment complex that killed seven people in 2016, according to federal report issued Tuesday.
The explosion and fire at the Flower Branch apartments in Silver Spring caused a partial building collapse and sent 68 people, including three firefighters, to the hospital.
The National Transportation Safety Board has been investigating the cause of the explosion for nearly three years, and officials there called it one of their most difficult investigations because so much evidence was destroyed in the building collapse and fire.
At a meeting Tuesday, the board unanimously adopted the findings of its investigators, who determined that a faulty regulator left unconnected to a vent pipe inside a basement meter room most likely caused the explosion.
Washington Gas, the company responsible for maintaining the equipment the NTSB blames for the explosion, has disputed the board's findings.
Washington Gas President and CEO Adrian Chapman issued a statement Tuesday saying the utility remains saddened by the tragedy and committed to safety.
"However, we disagree with their findings as we don't believe the evidence indicates failure of our equipment that night. We also do not believe the NTSB sufficiently investigated the other potential causes of the explosion," Chapman said.
The board's findings do not just point a finger at Washington Gas. The board also found multiple communication gaps and missed opportunities to correct the leak that might have prevented the explosion.
NTSB Chairman Robert Sumwalt said people around the complex smelled natural gas six different times in the weeks and months before the explosion, but nobody ever called the gas company to report a possible leak.
Most glaringly, a complex resident called 911 to report the smell of natural gas July 25, about two weeks before the explosion. Firefighters responded to the scene and could not detect natural gas. But they were thwarted from conducting a thorough investigation because they couldn't gain access to the meter room from which the leak likely emanated. The locks had recently been changed and firefighters didn't have access to the correct key, even though county code requires that firefighters have such access.
Because no leak was detected, firefighters did not call Washington Gas. Neither did the 911 dispatcher.
The NTSB is recommending that 911 dispatchers automatically call the gas company any time a person calls to report the smell of natural gas, rather than relying on the public to make the call.
"We missed a very good opportunity to possibly have stopped this whole thing," said NTSB Vice Chairman Bruce Landsberg.
Among the other NTSB recommendations: installing regulators outside rather than inside so any venting occurs safely into the atmosphere, and an expedited phaseout of the mercury-based regulators of the kind that were in place at the apartment complex.
Most of those regulators date back to the 1940s and 1950s and have been targeted for phaseout because of environmental concerns over mercury. But NTSB staff said the age of the equipment increases the likelihood that they will fail and cause gas leaks.