The fire was started accidentally by sparks from a grinder coming into contact with coal dust the previous day and igniting overnight.
Balclutha Primary School principal Vicki Neave said she was alerted to a fire on school property in Glasgow St about 3am yesterday.
"We were alerted by our security system and, by the time we arrived, the fire brigade was already on site and working to extinguish the fire.
"This is an old wooden building and, had the firefighters not acted so quickly and effectively to get the fire under control, we could have had a great big bonfire on our hands.
"It’s no exaggeration to say they’ve saved our school today."
Balclutha Senior Station Officer Jason Watt, in charge at the scene, said at first the fire was small but challenging due to its location.
"It wasn’t too bad when we pulled up about 2.45am, but eventually it got into the ceiling, and we had to work to remove several pieces of roofing iron to gain access to the fire.
"Luckily there was a firewall in place, otherwise we could have been looking at a new school. It’s been a good save today."
He said two Balclutha appliances and one from Kaitangata attended.
The blaze was under control by 4.30am, and firefighters remained on the scene after daybreak to tamp down any embers.
Fire and Emergency NZ specialist fire investigator Murray Milne-Maresca said the fire must initially have been seeded the previous day, after sparks from a grinder came into contact with coal dust from the boiler.
"It is important to take extra care when welding, grinding, working with hot tools, or undertaking any work with an open flame.
"Do welding and angle grinding in clear areas and make sure to remove any fire hazards or flammable materials before working with hot tools.
"Fire and Emergency recommends taking a quick walk around your worksite after completing work of this nature to check for any flames and to make sure any tools you are using are cool and away from potentially flammable items."
Mrs Neave said the school was having its boiler replaced.
"We’d like to reassure our school family that there’s no reason to be worried and that we’ll be open for the new school year on January 30 as planned.
"It just goes to show how grateful we should be for our local volunteer firefighters."
