Six fire engines and 35 firefighters and officers were called to a fire at a block of flats in Gloucester Terrace, Paddington on Saturday evening.
Part of a flat on the second floor and part of a flat on the third floor of the building were damaged by fire.
A man left the property before the arrival of the Brigade and was treated on scene by London Ambulance Service crews.
Neighbours were alerted to the fire after they heard smoke alarms sounding.
A London Fire Brigade spokesperson said: "Yet again smoke alarms help saving lives. Our advice is to have a working smoke alarm on every level of your home and the safest option is have the alarms linked together. This will give the earliest warning if there is a fire in your home."
The Brigade was called at 2359 and the fire was under control at 0133. Fire crews from Paddington, Kensington and North Kensington fire stations attended the scene.
The fire is believed to have been caused by an electrical fault within an extractor fan in a bathroom.