Firefighters from Heanor and Ilkeston had to force their way into a heavily smoke-logged ground floor flat in Langley Mill.
The incident happened at a property on Castle View just before midnight on Friday, January 7.
The alarm was raised when occupants from the upstairs flat were alerted when they heard the smoke alarm below going off.
Firefighters wearing breathing apparatus, used a thermal camera as they fought the flames.
The flat, which was unoccupied, was ventilated and searched and crews left the scene by 1am.
The fire caused minimal damage.
A fire investigation was launched the next day to determine what caused the blaze and police officers are still investigating what happened.