Fire Commissioner Lloyd Ayers said on Monday that an electrical problem sparked the fire early Saturday morning at the Abbey House Apartments in the 400 block of Domino Lane.
Firefighters rescued a number of people, including one adult from a third floor window ledge.
Two female residents, both adults, were injured in the fire.
A firefighter also suffered serious head and internal injuries. Ayers said on Monday that the injured rescuer was in stable condition.
Despite the damage, about 90 percent of the building was saved from total destruction.
The apartment in which the fire started did have a working smoke alarm, Ayers said, which he credits with the fact that everyone escaped with their lives.
