An explosion and three-alarm fire and an apartment building on Piney Branch in Silver Spring have left about 30 people injured and five to seven people still unaccounted for. Part of the building collapsed and debris has been strewn across the area. Montgomery County Fire Chief Scott Goldstein said the fire was reported just before midnight Wednesday. The fire damaged two four-level apartment buildings in the Flower Branch Apartments. About 90 people have been displaced. A search dog has found the scent of a possible victim under the debris pile. “We don’t know if that is a victim who is alive or a victim who is deceased,” Goldstein said. “Based on air currents, that could be an issue that the victim is over here, and it’s coming through the rubble pile, and coming out at a different point on the pile.” Fire investigators are not sure whether the explosion or the fire came first, and are interviewing residents to piece together the sequence of events.