Eight fire engines and around 60 firefighters were called to a fire at a hotel on Bath Road, Heathrow.
A ground floor sauna and plant room were destroyed by the blaze. Around 200 hotel guests and around 120 staff left the building before the Brigade arrived. There were no reports of any injuries.
The Brigade was called at 1612 the fire was under control by 1813. Fire crews from Hayes, Feltham, Hillingdon, and surrounding fire stations attended the incident.
The Brigade's fire investigators believe the fire was accidental and the cause was due to an electrical fault in the sauna unit.