At 0934 hours, Box 15-06 sent Lebanon City companies to 750 Mifflin Street for a structure fire. Engine 19 arrived with smoke showing from the 3rd floor of a 3 story, brick, twin dwelling. A line was stretched from Engine 19 to the third floor for fire attack. Ladder 18 took the D side and ladder the roof. Commissioner 15 requested Rescue Engine 14 for RIT and put 2nd alarm on standby. The fire involved the walls and ceilings of the third floor and extending to the attached exposure. As conditions deteriorated, Commissioner 15 evacuated the building and set up for exterior operations. The second alarm was requested bringing county mutual aid companies to the scene (Engines 14, 39, Ladder 9, Rescue 42). Multiple hand lines placed in service and all of the visible fire was knocked down in about 30 minutes. A mayday was alerted for a firefighter who fell through the floor but was quickly removed with no serious injuries. The box was placed in service and units were out for 2.5 hours.