A fire last night at a vacant building on the campus of the Rosewood Center in Owings Mills destroyed that building, and embers from the fire burned part of an adjacent vacant structure, a spokesman for the Baltimore County Fire Department said. Fire Director Kyrle Preis, the spokesman, said that because the two-story brick building was slated for demolition, the officer in charge at the scene ordered firefighters to let it burn rather than endanger the lives of firefighters. "It was declared a control burn," Preis said. The fire at the second building was extinguished. Rosewood, which opened in 1888, housed nearly 3,700 people at its peak. Its patient numbers have dwindled, and many long-vacant hospital buildings will soon be demolished.