Ten fire engines and around 70 firefighters were called to a fire at a car service workshop on an industrial estate on Lambs Lane North in Rainham.
Half of a single storey industrial unit was destroyed by fire.
One woman and one man left the building before the Brigade arrived. They were treated on scene by London Ambulance Service.
The Brigade was called at 1248 and the incident was over by 1426. Fire crews from Harold Hill, Dagenham, Barking, Wennington, Tottenham, East Ham and surrounding fire stations were in attendance.
The fire is believed to have been accidental and caused by the failure of the thermal cutout (an electrical safety device that interrupts electric current when heated to a specific temperature) in an oven.