Rio Tinto is investigating the cause of the accident at the Saguenay-Lac-Saint-Jean facility and anode operations at the plant have been shutdown until further notice. Aluminium production will continue, according to a company spokesman.
The smelter produces 250,000 anodes per year.
Last year, the Alma smelter was engaged in a major dispute with its unionised workforce all of whom were locked out of the plant for just over six months. During that time, the plant relied upon non-unionised labour and was forced to cut two thirds of capacity.