A 40-year-old contractor was airlifted to hospital after a canister exploded at Fonterra construction site in Canterbury.
Emergency services were called to the Darfield milk processing plant site on West Coast Rd, about 50 minutes west of Christchurch, about 11am.
A St John ambulance spokeswoman said a building foam canister exploded and hit the construction worker's arm.
The man suffered a suspected fracture and was airlifted to Christchurch Hospital.
A Fonterra spokeswoman said the canister fired out of a caulking gun that suffered a mechanical failure.
