Four fire engines and around 25 firefighters were called to a flat fire on Tennyson Road in Hanwell.
Part of a four-roomed flat on the ground floor of a residential block was damaged by fire. One woman left the building before the Brigade arrived and was treated on scene by London Ambulance Service crews.
The Brigade was called at 0657 and the fire was under control by 0749. Fire crews from Ealing, Southall, Heston and Acton fire stations attended the scene.
The cause of the fire is under investigation.