Firefighters were called to a flat on the second floor of Berkeley Court in Don Road shortly before 7 pm, when a man returned home and found his lounge alight.
The fire was extinguished by firefighters wearing breathing apparatus and the flat was severely damaged by heat and smoke.
The occupier was taken to hospital for treatment for smoke inhalation after trying to tackle the blaze but was not detained.
It is believed the fire was caused by candles being left lit on top of an electric fire.
Watch commander Michael Baudains warned that householders should never try to tackle a fire but get out immediately and call the Fire Service.
