At 09:39 Denver Firefighters were dispatched to a residential structure fire at 1208 South Mariposa Street. Tower 23 was returning from another call and reported heavy smoke in the air. Upon arrival Tower 23 found two single story, single family dwellings which were connected with a breezeway, well involved with fire on the interior and assumed command. Engine 23 laid in from Arizona & Mariposa and advanced a 1 3/4″ line for fire attack. The occupants reported everyone was safely out of the structure and after the completion of a 360, Tower 23 declared a defensive strategy. Truck 16 was assigned to open up the exterior and Engine 16 laid into the alley from Arizona & Lipan. Command reported power lines down on the charlie side. Engine 11 went to work on 23’s plug and The Rescue was assigned to the alpha side to pull another attack line. With all hands working command requested an extra Engine & Truck. Chief 7 assumed command and Chief 3 was assigned to the Charlie Side. After an initial knock down Engine & Tower 23 made a push inside when ammunition was heard firing off and command ordered a defensive attack again. After much of the fire was controlled and ammunition was consumed, crews began an offensive attack again. All searches proved negative, no extension to exposures was reported and no civilian injuries occurred. Two Firefighters were treated on scene by Denver Paramedics after their bunker gear was damaged by fire. They sustained minor burns to the ears and were released.