In February 1969, Sudbury’s skyline was poised for transformation. For decades, the three smelter stacks in Copper Cliff (two at 500 feet, one at 350) stood as silent witnesses to the industrial heartbeat of the area.
The International Nickel Company (INCO), the largest employer in the region at the time, processed nickel, copper and iron embedded in sulphide ores. Unfortunately, smelting these ores released immense quantities of sulphur dioxide, leaving a permanent signature on the surrounding forests and farms. And these stacks, while monumental for their time, could no longer contain the growing concerns over emissions and environmental damage.
With this in mind, INCO announced an ambitious plan: a single, colossal chimney, anchored to the solid rock of the Canadian Shield and soaring 1,250 feet above the ground, would replace the three smaller stacks.
This would signal a new era in industrial air pollution control.
"It will ensure that air in this area will be considerably cleaner on average than any other urban community in Ontario,” said Don Fraser, INCO's assistant general manager, when he made the announcement at a press conference at the President Hotel.
"It will eliminate any possibility that ground concentrations of sulphur dioxide from Copper Cliff will again reach the point where it can cause damage to vegetation."
But Fraser said the stack was not the ultimate answer.
"This is only an interim measure," he said. The intent of this $13,000,000 “Super-stack” project was to allow INCO time to develop new furnaces and processes that would further reduce sulphur emissions at the source.
The cost of the project was split in this way: $6,000,000 for the concrete stack, with a further $7,000,000 spent on two new electrostatic precipitators (which remove dust particles) and enlargement of existing precipitators in the smelter.
Mayor Joe Fabbro expressed jubilation on behalf of the city regarding the announcement, while also being somewhat prescient about the future regreening efforts.
“This is tremendously good news,” Fabbro said. “It indicates concern by the company for the community. Now we’ll be living in an atmosphere cleaner than ever in the past. It’ll be up to the city itself to look to recapturing the greenery by planting more trees.
“I can see a greener, more luxurious Sudbury in the future. We'll do our share, especially now that we won't have to worry about the sulfur dioxide element.”
Sudbury MPP Elmer Sopha, however, echoed a more pragmatic consensus.
“I’m delighted to see the company recognizing its public responsibilities… . It is a step in the way of progress,” Sopha said. “(Although) I, for one, adopt a wait-and-see attitude to see if the situation is abated.”
Sudbury East MPP Elie Martel (who passed away just last month) also expressed some concern with the idea of spreading pollution over a wider area.
“I'm glad to hear that something is being done at last,” Martel said. “But there are more questions concerning the removal of sulphur dioxide: Do people think we will smell it? Will it simply spread out the sulphur dioxide?”
Construction begins
These questions would remain unanswered as the first concrete for the Superstack’s foundation began to be poured in March 1970, marking the official beginning of construction.
Crew members recalled the sense of awe that greeted the first truckloads of concrete. The foundation alone was an unprecedented marvel, designed to support a structure weighing more than 64,000 tons. With its 1,250-foot-high walls tapering from 32 feet thick at the base to just ten inches at the top, the stack’s sheer scale demanded meticulous planning.
By June, work had shifted to the shaft itself. Crews operated 24 hours a day, Monday through Friday, using a precision high-speed slipforming system of German design, which at the time was a technological leap forward. Slipform construction is a method for continuously forming tall concrete structures by pouring concrete into a form that is steadily elevated by hydraulic jacks or other self-climbing mechanisms.
The slipforms consisted of two enormous steel collars, nested within each other, built from 52 overlapping plates, each four feet deep on the inside and five feet deep on the outside.
As the concrete was poured, the forms were adjusted inwards every ten inches to maintain the taper and wall thickness, guided by a computer in Germany using metric calculations. The computerized planning ensured that each vertical segment of the stack adhered precisely to specifications, but it also required constant vigilance from the engineers on site.
One of the unique problems that had to be overcome was the tendency of the slipform unit to rotate due to the spin of the earth. Continual checks had to be made with an optical vertical plumb. The process was delicate. Any deviation could have resulted in the world's largest corkscrew-shaped stack.
The sound of diesel hoists clattering across the site, and the rhythmic thump of concrete being dumped into the slipform became the soundtrack of Sudbury’s bold new endeavour. The result was the stack’s rise of just over one foot per hour toward its lofty goal.
Observers often compared the steady vertical growth to the unfolding of a gigantic mechanical flower, unfurling in measured increments against the blue Northern Ontario sky.
Construction delayed
Unfortunately, the construction schedule faced delays twice. Labour strikes and disputes in 1969 had already pushed the project back by a year. Then, INCO’s initial plan to have the Superstack operational by the spring of 1971 was postponed when a labour dispute resulted in a 48-hour work stoppage.
While the concrete stack sat at 593 feet (almost half its full height), workers walked off the job to back up demands for double time and a half pay, leaving scaffolding and steel beams idle against the skyline. Workers also felt that the present safety precautions and equipment would become less adequate as the stack neared its full height.
"We are meeting all the unions' requirements and working conditions," said Doug Summer, the project engineer for the contractor. "The strike is an illegal one and union officials have urged the men to return to their jobs. However, they are refusing to do so."
In the end, after meetings between the various unions and the contractor (Canadian Kellogg Co. Ltd.), the workers demands were not met, but they went back in full force anyway on all three shifts with an expectation that the stack would be up towards the end of August 1970 (the goal which was set before the walkout began).
Despite these setbacks, progress continued. From the ground, the stack’s growth was awe-inspiring.
By mid-summer, the structure had already surpassed 750 feet, eclipsing the nearby iron ore plant stack at 635 feet. Its presence became a daily fixture for Sudburians, who began to recognize the changing skyline as a symbol of progress and industrial ambition.
A ground-based hoist operated a four-man cage moving up the stack at a speed of 600 feet per minute.
Rest platforms were installed every 50 feet, with circular platforms every 150 feet to service aircraft warning lights, a crucial consideration for such an imposing structure.
As the height of the stack increased, it never appeared to be a bother to any of the workmen. "Most of the men started on the job at ground level and have worked up through the various levels as it rises,” Sumner, the project engineer, said. “I don't think they notice the height because it is a gradual thing which increases each day."
By mid-August 1970, all 1,245-feet of the concrete portion of the chimney was completed, a full week ahead of schedule. Wait, I can hear you say, isn’t the Superstack 1250-feet? The discrepancy between the 1,245-foot mark reached when they finished pouring concrete and the 1,250-foot total height is accounted for by a five-foot steel liner that tops off the concrete.
And so, five months and 19 days after the first concrete was poured, it was all finished. With no fanfare or ceremony, the last bit of concrete was poured at about 1.30 p.m. on a Friday. And, once fully cured, the workers dismantled the slipform unit atop the stack and shifted focus to the interior.
Inside the stack, another monumental task awaited. The steel liner, 45 feet in diameter and pre-fabricated in 100-foot sections, would be assembled from the top down by contractors with Dominion Bridge Company Ltd.
The top 60 feet, made of quarter-inch stainless steel, was designed to resist the corrosive effects of acidic gases. The liner, flues and electrostatic dust precipitators (to capture particulate matter) were essential to the stack’s environmental mission.
Then, on August 20, 1970, a violent storm tested the resilience of the structure and the crews. Everything was paused, cables were secured, and men huddled on platforms as the wind tore across the exposed surfaces. Yet, in spite of all of the damage to the stack’s surroundings (and the community at large) by the next day, work resumed, a testament to both courage and determination.
In 2017, Aarne Kovala, who worked on the construction crew for the Superstack, recalled what it was like to do the work and what it was like to be high up at work when the tornado blew through. You can read that story here.
The Superstack’s design was extraordinary not only for its height but for its engineering ingenuity. The structure incorporated more than 21,500 cubic yards of concrete reinforced with 1,050 tons of steel, tapering from 116 feet, five inches in diameter at its base to 51 feet, 9 inches at the top, encasing the 2,000 tonne, 45-foot steel liner that carried the actual smoke and gases. Access to the top of the stack was by a steel ladder, between the outside of the stack and the liner, with rest and maintenance platforms every 150 feet.
Concerns over Superstack’s effect
The environmental purpose of the stack remained a subject of scrutiny. Experts noted that while higher stacks do not eliminate pollution, they disperse it over a wider area, reducing concentrations at ground level.
A delegation from the French River Resorts Association feared that the proposed “super-stack,”would “spread toxic gases throughout an even greater range, possibly reaching the French River.” While a letter to the editor pointed out that based on their understanding of INCO’s announcement, “the superstack is being built to save money, not to reduce pollution.” They added that “it is to be hoped that the Ontario government will not be misled by this fact, and will insist on the installation of the most modern and efficient industrial or commercial systems available.”
Despite this, INCO representatives emphasized the Superstack would reduce ground-level sulphur dioxide concentrations by 90 per cent and spread emissions over a larger area to minimize vegetation damage.
Dr. Morris Katz, a professor at Syracuse State University, was among the Superstack’s designers. He actually designed a stack to meet pollution control standards at 1,000 feet in height, but INCO engineers deliberately increased the height by 25 per cent so as to be well over those standards.
At the time of the announcement of the Superstack’s construction, Louis Renzoni, INCO vice-president in process research, explained that the concept of chimney design had changed since the then-existing stacks had been built.
"Our (original) stacks were built so that gas was emitted at low velocity and just tumbled out the top,” he said. "The new stack will emit gas at high velocity so that it will plume out up to about 4,000 feet in the air."
This would place the gas in the path of radiant winds, which have a velocity three times greater than winds at ground level, so the resultant dispersion would be that much greater.
"A greater proportion will never reach the ground … and the natural cleansing action of the air, precipitation in rain and snow, and absorption by land, will be more efficient," Renzoni said.
Katz, the designer from Syracuse University, added that pollutants and chemicals being emitted into the air from the existing multi-stack system at the Copper Cliff operation would be reduced by nine-tenths due to three-dimensional distribution. The emissions would travel in a vertical direction and a horizontal direction as well as traveling towards the ground, he explained. And, “that which reaches the ground will be absorbed into the ground, lakes and rivers. There will be no chance of danger to humans or vegetation in the areas concerned.”
The stack comes to life
The day Aug. 21, 1972, dawned crisp and clear over Copper Cliff, signalling the end of the holidays for some 16,500 employees of INCO. As the first tendrils of smoke began to curl from the Superstack, the towering new addition to the skyline, propelled skyward by immense velocity and heat, Sudburians held their breath.
For decades, they had lived under a bitter pall of sulphur dioxide. Vegetation wilted, cars corroded and residents had grown accustomed to the acrid scent that clung to the air. This stack promised a cleaner future, not by removing sulphur dioxide, but by propelling it high enough to disperse before reaching their lungs, gardens and streets.
That first day of operation was met with quiet anticipation. Engineers monitored emissions, ensuring that gases traveled as designed, while maintenance crews inspected platforms, ladders and warning lights. Cameras documented the moment, capturing a new era of industrial achievement. The stack’s plume of smoke marked the culmination of a project that had demanded ingenuity, courage and patience.
Engineers, workers and everyday Sudburians marveled at the scale of the structure, which seemed to pierce the sky itself. To put it into perspective, the Superstack soared as high as the Empire State Building in New York City, a comparison that frequently made its way into conversations, newspaper articles, and even schoolyard chatter.
International attention came as well. When the Superstack reached its full height of 1,250 feet, it instantly claimed the title of the tallest smokestack in the world. It had surpassed the American Electric Power Corporation’s Mitchell, West Virginia, chimney, previously the world’s tallest at 1,206 feet (built only the previous year).
It was a monumental testament to both human ambition and industrial necessity. Its towering presence symbolized ambition, environmental caution and the human effort required to merge the two. Its construction stood as a monument to Sudbury’s industrial evolution.
While some considered it a marvel of modern engineering, others remained skeptical of its pollution mitigation claims. Yet all could agree that “the skyline had changed irrevocably” (at least, that’s what they thought anyways).
In the decades that followed, the Superstack would continue to inspire curiosity and debate, poetry and prose.
From foundation to apex, the Superstack’s story has been one of human endeavour meeting technological possibility. Anchored in the solid rock of the Sudbury Basin and rising 1,250 feet into the Northern Ontario sky, it remains a testament to what can be achieved when vision, skill and determination converge.
So, dear readers, we turn to you, it’s time to share with us your Superstack stories; your feelings and emotions as a small slice of Sudbury’s skyline is poised to change (and, this time) irrevocably.
Jason Marcon is a writer and history enthusiast in Greater Sudbury. He runs the Coniston Historical Group and the Sudbury Then and Now Facebook page. Memory Lane is made possible by our Community Leaders Program.