At 11:53 PM on November 10, 1979, a wheel journal on the 33rd car of Canadian Pacific Freight Train 54 overheated and failed. The car left the tracks near the intersection of Mavis Road and Dundas Street in Mississauga, Ontario. The following 105 cars accordianed into a pile of ruptured tankers and boxcars. Several tank cars containing propane exploded, shooting fireballs into the night sky. One car, sliced open, released 90 tons of chlorine gas. Another leaked toluene. A third carried styrene. The resulting chemical fire was visible for miles.
The immediate response was defined by a single, staggering fact: over 200,000 people lived within three miles of the derailment. Police and officials, guided by a chemist from the Canadian Forces who identified the specific hazards, made a decisive call. They ordered a full evacuation. Using radio broadcasts and door-to-door alerts, they moved people out in a widening radius. Within 72 hours, approximately 218,000 residents—nearly the entire city—had left their homes. It was the largest peacetime evacuation in North American history until Hurricane Katrina.
The operation was methodical and, by all accounts, peaceful. Hospitals transferred patients. Shelters were set up. The police patrolled empty streets to prevent looting. The primary threat was the chlorine tank, which continued to leak. Firefighters could not approach the intense heat. They let the fire burn itself out, a process that took three days. The final evacuees returned home after five days. Remarkably, there were no serious injuries or fatalities directly from the derailment.
The event’s legacy is embedded in regulation. The Mississauga derailment led directly to mandatory installation of improved safety systems on rail tank cars in Canada, specifically the double-shelf coupler and thicker tank shells. It proved the viability of mass evacuation as a disaster response tool. The city’s calm during the crisis is still cited in emergency management textbooks. The accident vanished from the landscape; a municipal park and a few street names are the only markers of the night a suburb of Toronto simply walked away.