A Washington DC Fire Sgt was critically injured, a toddler was killed and about 20 other people were also injured yesterday in a fire that forced hundreds of people out of an up-scale high-rise apartment building in far Southeast Washington. The cause of the fire at the Marbury Plaza apartments isn’t known, but a significant explosion was heard in the building on Good Hope Road before firefighters arrived, a D.C. fire department spokesman said. The DC Fire Sgt is still hospitalized.