The explosions were visible from as far away as Niagara Falls. A massive orange fireball rising as high as 1,500 metres after one of the most potentially devastating events in Mississauga’s history.

A 106-car train transporting dangerous and highly flammable substances including butane, propane, toluene and chlorine was passing through the city 40 years ago on Nov. 10, on its way to Toronto from Windsor, Ont., when it derailed, causing a massive crash and several explosions, sending entire train cars and chunks of metal hurling through the air.

Nearly 250,000 people, including all of Mississauga and parts of Oakville, had to be evacuated for days, as one tanker carrying 90 tonnes of liquid chlorine began to leak, releasing the same deadly substance used on First World War soldiers in Ypres. It remained the largest peacetime evacuation in North America until Hurricane Katrina in 2005.

Today, many people are unaware of this dramatic chapter in local history, but at the time, several cities modelled their evacuation plans after Mississauga’s, and lessons learned from the derailment led to changes in the rules around transporting dangerous materials by rail.

Amazingly, no one died. The derailment happened to occur in a patch of sparsely populated land.

“A half-mile farther down on the track … we would have seen thousands of people wiped out,” Mayor Hazel McCallion, in her first term as mayor during the derailment, told the Star.

Instead, it became known as “the Mississauga Miracle.”

Canadian Pacific Train 54 originally started its journey in Windsor in the early afternoon of Nov. 10, 1979. It stopped in Chatham, picking up cars from Sarnia before heading to London to switch crews. These cars were carrying caustic soda, propane, chlorine, styrene and toluene, all highly flammable, combustible or otherwise dangerous substances that were expected to travel through highly populated parts of southern Ontario to reach their destination at the Toronto yard in Agincourt.

Trouble began in Milton when the friction started to build up in a wheel bearing on the 33rd car, carrying toluene. More modern freight cars at the time used roller bearings that don’t heat up the same way, but this car was equipped with an old-fashioned method that required lubrication by oil. This time, as detailed in the book “Derailment: The Mississauga Miracle,” that lubrication wasn’t adequate and the mechanism housing the wheel bearing became a “hot box.”

By the time the train was rolling through Mississauga at 80 km/h, shortly before midnight on a Saturday, residents reported seeing sparks and smoke coming out of the train. Others saw parts of the train on fire.

At 11:53 p.m., Lynn Riddel, who lived near the train tracks on Burnhamthorpe Road West, heard a loud bang and watched as two blazing wheels soared through the air and crashed through her fence and into her backyard.

The train, carrying a dangerous cocktail of chemicals, had lost an axle and two wheels on the car with the hot box, which then derailed along with 23 others at Mavis Road, north of Dundas Street West.

A deafening crash resounded through the area as the cars collided, and three cars exploded within a half-hour, sending a burst of flames shooting into the air, and chunks of metal flying every which way. One tanker ended up in a spot 675 metres away.

First-responders armed with every available piece of firefighting equipment in Mississauga battled the blaze but their efforts barely had any effect at first.

Eleven of the derailed tankers held propane, four had caustic soda, three styrene, three toluene and two box cars had fibreglass insulation.

But the biggest danger was one car carrying 90 tonnes of chlorine. It was the same lethal chemical Germans used on Canadian and English First World War soldiers in Ypres.

And this tanker was leaking noxious yellow-green clouds through a nearly three-foot-wide hole.

As the fire raged, the train’s crew leapt into action.

“Jesus Christ, Ted, one of them tank cars blew up,” Engineer Keith Pruss said to conductor Ted Nichol. He radioed dispatchers to report the explosion and stopped the train.

Then, in what author George Bibel referred to as an act “bordering on lunacy,” brakeman Larry Krupa jumped into the blaze to close a cock on one of the cars so his father-in-law, Pruss, could pull 27 cars carrying flammable goods away from the heat.

Krupa would be awarded an Order of Canada for his bravery and role in preventing even more, potentially deadly, explosions.

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Officials responding to the fire had no way to determine how much chlorine had leaked into the air.

It’s a heavy gas, so it drifts over varied terrain and settles low on the ground. Anyone who inhales it could die within minutes as the lungs fill with fluid, essentially leading to a painful suffocation.

The sleepy residents nearby the derailment had to be evacuated immediately. Twelve more evacuations would be conducted over a 20-hour period, as Dow Chemical Company experts used computers to produce weather forecasts, expanding the boundaries for evacuations.

Some people were moved to large public areas, like Daphne and Clive Pasley, with their 3-month-old baby, Darryl, at Streetsville Secondary School. Others were sent to Square One Shopping Centre. They would eventually be moved out of the city as evacuation boundaries continued to expand.

Ambulances were called from as far away as Kingston to transport patients from Mississauga General Hospital. In all, 139 ambulances and 300 ambulance workers showed up, as well as 27 other vehicles, including Mississauga, Oakville and Toronto transit buses, to help transport Mississauga residents to safety.

By the end of that first day, 218,000 people had been forced to flee their homes, six nursing homes and three hospitals. Older residents, like 100-year-old Hubert Would, were especially susceptible to the risk of chlorine poisoning, and had to be evacuated quickly.

Early Monday, Mississauga mayor Hazel McCallion, in her first term, ordered Mississauga “closed until further notice.” The Queen Elizabeth Way highway was shut down through Mississauga, with no one allowed in. Only police, firefighters and other officials walked the streets of the 284,000-resident city now turned into a ghost town.

The last of the fires finally went out amid the wreckage of the derailment early Tuesday. Firefighters had been allowing the flames to burn out on their own, only controlling and containing them.

But the chlorine tanker still had to be patched up. Experts believed about 75 per cent of the chlorine had escaped.

Ontario’s Environment and Labour Ministries did tests that mostly showed the air to be safe. But there were still pockets of chlorine in some low-lying areas.

Some residents were allowed back into the city but those closest to the derailment site would have to wait longer. CP Rail offered to cover hotel costs for about 1,000 people, which helped break up some of the frustrations brewing among residents.

Officials worked to patch up the hole on the chlorine tanker and pump the chemical into trucks so it could be shipped away. Finally, the danger was over.

On Friday, Nov. 16, 1979, Mississauga finally reopened. All residents were allowed back to their homes. The crisis had passed, and not a single person had perished or even suffered serious injuries.

McCallion, shown here at a news conference with then Ontario attorney-general Roy McMurtry, would credit much of that to the fact that Mississauga, unlike many other cities, actually had an emergency plan in place that it could follow, which was voluntary at the time. “After the train derailment, the province made it mandatory for all cities to have an emergency plan,” McCallion wrote in a chapter for the book “The Local Alternative: Decentralization and Economic Development.”

“In fact, many cities modelled their own emergency plans after Mississauga’s,” she wrote.

The derailment also sparked changes to some rules on transporting dangerous goods, including setting a minimum number of crew members on such trains and the standardization of hot box detectors and roller bearings, though critics still argue more change is needed.

After the Lac-Mégantic disaster in Quebec, which killed 47 people, Canada saw clearly how devastating the derailment of a train carrying dangerous materials can be.

And so as the city marks the 40th anniversary of the 1979 derailment, it’s with grateful if bewildered acknowledgment of just how tragic the disaster could have been.

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