Six fire engines and 35 firefighters and officers were called to a fire at a garage and associated outbuildings in Woodlands Drive in Stanmore.
The buildings were all destroyed by fire.
Two 63kg oxygen cylinders, two 15kg, one 10kg and one 5kg butane cylinders, one 63kg argon cylinder and one 86kg acetylene cylinder were in the affected buildings and were cooled to an ambient temperature by firefighters.
An exclusion zone was put in place during the incident and 30 residents were evacuated from neighbouring properties by the police as a precaution.
The Brigade was called at 1810 and the fire was under control at 2151. Fire crews from Stanmore, Harrow, Mill Hill, Wembley and Ruislip fire stations attended the scene.
The cause of the fire is under investigation.