Workers at a Manvers call centre were evacuated when an electrical fault caused smoke to spread through part of the building.
The early morning alarm call at Capita House on Meadow Road was due to smoke escaping from the communications room, where computers are housed.
Two fire engines from the nearby Dearne station attended the scene at 5am. They left at 6.30am after helping to ventilate the building.
The cause of the smoke was confirmed to be an electrical fault, and all workers had left the centre before the fire crews arrived.
A spokeswoman for Capita plc said: “There was an electrical fault which triggered the fire brigade call out but there was no fire and I understand that the fault has now been largely resolved.