Four fire engines and around 25 firefighters were called to a fire in a garage on Elmdon Road in Hounslow.
Half of a single storey garage was destroyed by fire.
Fire investigators believe the cause of the fire is accidental and due to the careless disposal of smoking materials.
A London Fire Brigade spokesperson said: "If you smoke it's vitally important you stub it right out, preferably in an ashtray.
"Always ensure your cigarette is completely out when you’ve finished smoking it. If you don’t, you risk causing a fire."
The Brigade was called at 0934 and the incident was over for firefighters at 1119. The Brigade's 999 Control officers deployed fire crews from Feltham and Heston fire stations.
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