Hinds Volunteer Fire Brigade chief Dave Kingsbury said firefighters were at the scene on a farm in Hinds for about three hours last Thursday.
Engineering activity, such as grinding or welding, had been under way in a workshop in the shed prior to the blaze.
Kingsbury said a spark may have started the blaze afterwards when the shed was unoccupied.
"Make sure when heat is being created, there’s no stray sparks," Kingsbury said.
"Be vigilant of the activity that’s going on in the shed, go back a few minutes later and check."
Firefighters arriving at the scene worked to ensure the fire did not destroy a neighbouring shed, which also received some damage.
They also had to get hold of EA Networks to disconnect power at the site, as access to the shed was under power lines to a pole at the front of the shed.
Besides workshop equipment, the shed had two bays with firewood "which didn’t help matters".
The roof collapsed and machinery was used to drag out the firewood.
The brigade was supported by firefighters from Geraldine, Ashburton and Willowby brigades.
The fire followed one in a Hinds pump shed on a dairy farm two days prior.
Kingsbury said the pump shed fire may have been caused by rodents getting into its control panels.
