Fond du Lac firefighters are trying to determine what started a fire on the second-floor balcony of an apartment building. Fire/rescue responded to an eight-unit apartment building at 691 E. Scott St. The fire on the balcony was threatening the structure. The apartment building's fire alarm was working. Firefighters went inside the apartment and put out the fire quickly, but there was already smoke damage throughout the second floor and also heat damage to that unit. People who lived in that unit won't be able to move back in until damage is repaired.