Four fire engines and around 25 firefighters were called to a fire at a maisonette on Green Man Lane in West Ealing.
Most of a four-roomed maisonette split across the second and third floors of the building was damaged by fire. One woman and two men left the building before the Brigade arrived and were treated on scene by London Ambulance Service crews.
The fire is believed to have been caused by a candle.
A London Fire Brigade spokesperson said: "Candles are one of the most common causes of fire in the home. To avoid accidents, keep them out of the reach of children and pets.
"We recommend that you swap your candles for flameless, LED candles. They are much safer as you can leave them unattended and you don't have to worry about them being knocked over."
The Brigade was called at 1554 and the fire was under control by 1653. Fire crews from Ealing, Southall and Acton fire stations attended the scene.