The National Transportation Safety Board has been unable to determine the ignition source that sparked the explosion in a Silver Spring apartment complex meter room, where natural gas had been building up for at least three hours.
Seven people were killed and 65 were sent to the hospital after the explosion and fire at the Flower Branch Apartments on Aug. 10, 2016.
In announcing its findings during an NTSB board meeting, the agency announced its probable cause: “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,” according to the report approved Tuesday by the agency.