Engine 2 and Rescue 1 responded to the report of a building fire at the Internal Revenue Service. Engine 2 arrived on scene with smoke showing. Engine 2 and Rescue 1 quickly found it to be a transformer fire in the B-1 level of the building. Units had to wait for Pepco to arrive to secure the power before the fire could be extinguished. Once Pepco arrived the fire was extinguished. Engine 2, Rescue 1 and the Deputy Fire Chief operated on the scene for about 2 hours before returning to service.