Four fire engines and around 25 firefighters were called to a fire at an industrial unit on Hessel Street in Whitechapel.
Part of an office on the ground floor of the two-storey building was damaged by fire. One man was taken to hospital by London Ambulance Service crews.
The Brigade's Fire Investigators believe the fire was caused by an electric heater which was placed too close to combustible materials.
A London Fire Brigade spokesperson said: "The alarm was raised by a member of staff who heard crackling and noticed fire and smoke issuing from within the property. Thankfully, firefighters successfully prevented the fire from spreading to a number of neighbouring industrial properties.
"If you use an electric heater this winter, never leave it unattended. It’s really important to ensure heaters are placed well away from clothes, duvets and other items that can catch fire if they get too close and you should never placed anything on top of them.“
The Brigade was called at 1126 and the fire was under control by 1207. Fire crews from Bethnal Green, Shoreditch, Whitechapel and Poplar fire stations attended the scene.