The Fire Service was called to a fire in a farm shed at 1pm, with crews from Clinton, Waiwera, Clutha Valley and Balclutha attending.
Waiwera Chief Fire Officer Maurice Walter said the contractor had been welding a gate when sparks from his welding torch ignited bale-straw in a shed.
"The guy welding is injured. He has burns on his back and his arms," Mr Walter said.
Alena Lynch, St John Southern Regions communications, said the fire service called St John at 1.40pm.
"An ambulance from Balclutha attended. The patient had very minor injuries, and was taken to a general practitioner in Balclutha."
The shed, which Mr Walter estimates was 25m by 10m, was consumed by the fire and fire crews had to remove the bale straw to douse it with water.
"We had a digger driver in a breathing apparatus mask to get the stuff out of the shed - you can't get the fire out if you can't get water on it - we had to move it, otherwise it would have just kept burning."
