A report from the Transportation Safety Board of Canada says a derailment last year in southern Alberta was caused by an unstable track.
The derailment and chemical spill happened in the hamlet of Irvine on Aug. 2, 2019, forcing people from their homes and temporarily closing a stretch of the Trans-Canada Highway.
Officials had said that the flammable chemical involved in the spill was styrene, which is used to manufacture rubber, plastic and fibreglass.
No one was injured after the derailment and the spill was contained within a day.
The TSB report released Friday says despite repair work and inspections months before the derailment, the track subgrade remained unstable and was susceptible to “the effects of increased longitudinal forces produced by the high ambient temperatures.”
The report notes that temperatures in the area at the time were more than 30 C.
“The efficient management of longitudinal forces in (continuous welded rail) is an important maintenance function for railways,” the report notes.
Continuous welded rail can experience “large compressive and tensile longitudinal forces” from temperature changes or track maintenance, the report says.
“Compressive forces can induce track buckling while tensile forces can result in rail defect growth and rail pull-apart failures at joints.”
The board says the report concludes its investigation into the derailment.