File photo of Vale operations in Sudbury, Ont.GINO DONATO
A toxic gas leak at Vale SA's nickel smelter in Sudbury has been contained, after it spewed out yellowish noxious fumes early Thursday morning.
Brazilian-based Vale is investigating the cause of the leak of nitrogen dioxide, which can irritate the respiratory system and skin.
"There is no risk of additional substance travelling beyond company boundaries," Vale said in a statement. "There is no risk to the community."
At around 6 a.m. Thursday, Vale declared a Level 3 emergency and sounded its air horn. Residents in the nearby Copper Cliff community were told to stay inside, close their doors and windows, and turn off their air conditioners and other air-intake devices.
For about two hours, police surrounded the area and blocked roads to prevent drivers from entering the community.
By around 8:30 a.m., Vale had downgraded the emergency and said it was satisfied that the nitrogen dioxide mist had dissipated.
Police said the gas leak was a rare occurrence in Sudbury, home to some of the world's biggest nickel deposits, mines and smelter.
"I was surprised," said Staff Sergeant Craig Maki, of the Greater Sudbury Police. "I didn't hear the alarm, but saw Twitter blowing up on my way to work."
Vale said the leak occurred at the smelter's acid plant, which had been shut down for a routine maintenance checkup.
Rachelle Younglai