The St. John's Regional Fire Department deployed its hazmat team early Saturday to deal with a chemical spill at a former dairy plant in the central area of the city.
At 1:44 a.m., crews arrived at the old Scotsburn building on Lemarchant Road.
SJRFD Platoon Chief Robert Fowler told CBC one of the large ammonia cylinders ruptured, causing the fumes to form an air cloud.
Fowler said the hazmat team then conducted a controlled release to remove the vapour cloud.
Once the procedure was complete, chemical levels were tested.
He said levels had returned to zero, and building personnel were permitted to return. Custodial staff have been dismantling the plant, readying equipment for transport.
Meanwhile, the Royal Newfoundland Constabulary blocked the road from oncoming traffic, as a precautionary measure.
Fowler said wind conditions were favourable and there was no need to evacuate area residents.
Crews had the scene cleaned up by 7 a.m.
It was announced in September that the Scotsburn plant would close later in the year.