Four fire engines and around 25 firefighters were called to a fire at a car garage on Wadsworth Road in Perivale.
A small part of the ground floor of the mid-terrace single storey garage was damaged by fire.
Two men and one woman left the building before the Brigade arrived. One man and woman were treated on scene by London Ambulance Service for smoke inhalation.
The Brigade was called at 1709 and the incident was over by 1859. Fire crews from Wembley, Northolt, Ealing and Acton fire stations were in attendance.
The cause of the fire is believed to be due to accidental ignition of spilt petrol from a battery operated diesel/oil pump.