Six fire engines and around 40 firefighters were called to a house fire on Percival Road in Feltham.
The first floor of a semi-detached house was destroyed by the fire and part of the ground floor and roof were damaged. Two teenage girls left the property before the Brigade arrived. They were treated on scene by London Ambulance Service crews and one of them was taken to hospital.
The fire is believed to have been accidental and involved a toaster.
A London Fire Brigade spokesperson said: "It's really important that you always check toasters and other appliances are turned off and unplugged when not in use, unless they’re designed to be left on, like your fridge or freezer.
"Keep clutter to a minimum on your kitchen work surfaces especially near toasters and hobs as they can accidentally switch them on or catch fire."
The Brigade's 999 Control Officers took 12 calls to the blaze.
The Brigade was called at 2032 and the fire was under control by 2159. Fire crews from Heathrow, Hayes, Heston and Feltham fire stations were at the scene as well as colleagues from Surrey Fire and Rescue Service.