Freight train derailment north of Sept-Îles caused by rail stress and wheel defect

The Transportation Safety Board says it could not determine the exact cause of a freight train derailment near Sept-Îles in northern Quebec on December 28, but concluded the rail likely broke under stress from sharp temperature swings and the earlier passage of another train with a wheel defect.

Twenty-nine railcars and one locomotive derailed about 60 kilometres north of the city after an automatic emergency brake was triggered. No one was injured, and most of the spilled iron ore did not reach the frozen surface of the nearby Nipissis river.

The rail line recorded 47 broken-rail incidents in 2025, with more than half occurring in January and December—months of extreme temperature variation. The track, installed in 2022, had been inspected just three days before the derailment with no defects detected, the TSB said.

The report attributes the fracture to a combination of stressors: the rail's inability to withstand rapid temperature cycling and the cumulative effect of passage by the earlier train with a faulty wheel. The emergency braking system successfully prevented the derailment from spreading further down the line.