Companies were dispatched for the working bldg fire. Arriving units found heavy smoke & fire from the rear of a 2 story twin. Crews were hampered on their initial attack due to numerous fireworks in the dwelling going off. Fire extended to the "B" exposure and eventually through the roof. The evacuation alert was sounded and companies went to an exterior attack, placing 2 Tower Ladders, deck guns and several hand lines in svc.