Six fire engines and around 40 firefighters were called to a fire and explosion at a house on North Road in Southall.
An end of terrace house converted into flats suffered significant structural damage and there was a fire which damaged part of the roof and first floor. Seven people left the building before the Brigade arrived and one man was treated at the scene by London Ambulance Service crews.
Station Commander Matt Williams, who was at the scene, said: "Crews tackled a fire on the first floor using an aerial ladder.
"Our Urban Search and Rescue crews carried out a systematic search of the building to check there were no other people inside.
"There were some local road closures in place so we advised motorists to avoid the area where possible.
"North Road at the junctions of High Street, Kinglsey Avenue and Shruberry Road were closed."
The Brigade was called at 0948 and the incident was over for firefighters by 1354. Fire crews from Southall, Ealing, Hillingdon, Hayes, Northolt and Heston fire stations were at the scene.
The cause is currently believed to be due to a leaking old propane powered heater which was found in the loft. It will be sampled for further examination.
A London Fire Brigade spokesperson said: "If you have any older propane powered heaters or equipment at home, it's worth checking that the rubber seals haven't perished.
"This can happen with older equipment and can cause a leak, which is what our fire investigators believe they have seen in this case."