An “undetected flaw” in the rail tracks is what caused a 27 car train derailment and potash spill near Silton, Sask. in 2021, the Transportation Safety Board of Canada (TSB) said.

The TSB released its findings in a report published on Tuesday.

On Oct. 15, 2021, a Canadian Pacific Railway Company (CP) freight train departed from Saskatoon’s Sutherland Yard. The train – consisting of one controlling and two remote locomotives – were tasked with transporting 200 hopper cars of potash to Regina.

At 5:02 a.m. on Oct. 16, the train deployed its emergency brake while travelling on the Lanigan subdivision near Silton, Sask.

The locomotive came to stop after travelling 2,100 feet.

The crew soon discovered that 27 cars had derailed on the west side of the track where many were breached – spilling a significant amount of potash in the area. No injuries came as a result of the derailment.

The scene of the derailment illustrated in the TSB report. (Courtesy: Transportation Safety Board of Canada)

Repair work of the destroyed section of track was completed the day after the accident. Total cleanup of the site was finished on Oct. 27, 2021.

The TSB investigation found that the west rail broke when pre-existing fatigue cracks (representing around 15 per cent of the rail head) spread down the base of the rail in a sudden overstress.

The head wear of the broken rail was within CP’s allowable service limits. However, the amount of wear increased the stresses on the rail from wheel loading which led to a reduced fatigue life and ultimately to the failure of the rail, the report outlined.

A diagram of the derailment scene. (Courtesy: Transportation Safety Board of Canada)

Additionally, the TSB outlined that CP’s regular flaw detection (RFD) testing exceeded regulatory requirements and highlighted the state of the testing technology as an issue.

“The accuracy limitations of current RFD testing equipment, combined with the transposed rail, rail head wear, and surface depression in the area of the rail fracture, most likely rendered the fatigue cracks difficult to detect,” the report read.

The board identified the limitations of rail flaw detection testing as an on-going risk.

“Given the limitations in accuracy of current rail flaw detection testing, rail with internal defects can sometimes be misclassified as free of defects, increasing the risk of failure and subsequent derailment,” the report read.

“Rail surface conditions may mask the presence of an emerging rail defect, increasing the risk that the defect will grow undetected.”

In July of 2022, CP installed its Rail Integrity Non-Vital Overlay Detectors (RINOD) system on the Lanigan Subdivision.

The system sends automatic notifications to the CP operations centre if a broken rail, rail gap, loose joint, or rail joint pull apart is detected.

“The notifications provide advance warnings that allow the Operations Centre to stop a train before it encounters any such track discontinuities in non-signalled territory.”