The Inco Superstack in Sudbury, Ontario, with a height of , is the tallest chimney in Canada and the Western hemisphere, and the second tallest freestanding chimney in the world after the GRES-2 Power Station in Kazakhstan. It is also the second tallest freestanding structure of any type in Canada, behind the CN Tower but ahead of First Canadian Place. It is the 51st tallest freestanding structure in the world. The Superstack is located on top of the largest nickel smelting operation in the world at Vale's Copper Cliff processing facility in the city of Greater Sudbury. In 2018, Vale announced that the stack would be decommissioned and dismantled beginning in 2020. Two new, smaller stacks were constructed under the company's Clean Atmospheric Emissions Reduction Project. In July 2020, Vale announced that the Superstack had been officially taken out of service, but would remain operational in standby mode for two more months as a backup in the event of a malfunction in the new system, following which the dismantling of the Superstack would begin. As of August 2021, however, Vale has not yet announced the awarding of a demolition contract on the Superstack, and it remains unknown when demolition will actually begin. In addition to further reducing sulphur dioxide emissions by 85 per cent, the decommissioning of the stack is expected to cut the complex's natural gas consumption in half. History The Superstack was built by Inco Limited (and later purchased by Vale) at an estimated cost of 25 million dollars. Construction on the structure was underway during the Sudbury tornado of August 20, 1970; the structure swayed heavily in the wind, but remained standing and suffered only minor damage. Six workers were on top of the construction platform when the storm hit, and all survived. The same day was the final day of construction on the stack, with the construction fully completed by the evening of August 21. The stack entered into full operation in 1972. From the date of its completion until the Ekibastuz GRES-2 chimney was constructed in 1987, it was the world's tallest smokestack. Between the years 1972–75 it was the tallest freestanding structure in Canada. Prior to the construction of the Superstack, the waste gases contributed to severe local ecological damage. The Copper Cliff smelter was already home to some of the worlds tallest stacks, including two 500-foot chimneys constructed in 1928-29 and 1936. However