The Sudbury Star is the City of Greater Sudbury’s daily newspaper.
It was a tense Thursday morning for those who live and work in Copper Cliff and the surrounding area, but no injuries have been reported after two gases combined to form a toxic mist at the Vale acid plant.
While a joint investigation into the cause of the gas leak is still ongoing, company officials said there was a larger-than-expected reaction between water used to wash out a cooling tower and the acid remaining inside. That created a yellow plume of NOx, a combination of nitrogen oxide and nitrogen dioxide, in the air above the site.
Exposure to nitrogen dioxide can cause irritation of the nose, throat, eyes, skin and respiratory system. Large doses are potentially fatal. The gas is also a major pollutant that plays a role in causing smog.
Air horns began sounding at the smelter around 6 a.m. and a Level 3 emergency, denoting a release of hazardous material, was called. Police and emergency services personnel responded and roads around the area were closed to traffic, while residents were cautioned through local media to remain indoors.
After determining the plume had dissipated and there was no threat to the community, Vale issued an all-clear message just after 9 a.m. Area roads were opened shortly thereafter.
Jody Kuzenko, general manager of production services at Vale, said the gas plume formed as crews performed planned maintenance at the acid plant, which involved draining the towers and pipes of acid and then washing the inside with water.
“Earlier this morning, we had set up to complete a wash of our cooling tower, the vessel was opened and drain lines were installed at the bottom, which is part of the usual process,” Kuzenko said Thursday afternoon, during a media briefing at the Lionel E. Lalonde Centre in Azilda. “When we undertake this process, we do expect a reaction between the wash water and the acid in the vessel; however, not to the extent experienced this morning. The reaction created a mist on our property of NOx, which is a mix of nitrogen oxide and nitrogen dioxide. This mist is visible and creates a yellow-orange hue.”
That mist travelled over the tailings area, Kuzenko said, then the wind direction changed and it began to move over the slag dump.
“There was a concern about the mist entering the community and as a result, a Level 3 emergency was called at approximately 6 a.m., with the emergency horn sounding.”
The horn is tested each Monday at 1:30 p.m., she said, so residents who heard it Thursday morning would have known there was potential danger.
“This was a precaution, but an essential one,” Kuzenko said.
During a Level 3 emergency, residents are asked to remain indoors, close all doors and windows, turn off furnaces, air conditioners and any other air intakes and to remain inside until an all-clear message is delivered and the air horn has stopped.
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