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Cause of Silver Spring apartment explosion still unknown

(Promesastudio /

(Promesastudio /

SILVER SPRING — Federal investigators found a disconnected vent pipe in an apartment building that exploded last year, killing seven people and injuring dozens.

But the Bureau of Alcohol, Tobacco, Firearms and Explosives says the cause of the August 2016 explosion and fire in a D.C. suburb in Maryland remains undetermined.

The Washington Post says the ATF released a report on the blast at the Flower Branch Apartments in Silver Spring on Tuesday. It said natural gas built up in the basement room where disconnected pipe was found.

The National Transportation Safety Board is also taking part in the investigation.