CN Gainford Derailment Caused by Transverse Defects

Here is the Transportation Safety Board of Canada press release and investigation report.

From the report:

Findings

Findings as to causes and contributing factors

1. The train derailed when 1 or more rail breaks occurred in the high rail as the train traversed the curve at the east end of Gainford siding.
2. The fragmentation of the rail was due to the presence of numerous transverse defects along the length of the high rail in the curve. The transverse defects initiated in areas of shelling that resulted from high traffic density and loading.
3. With a balance speed of 15.5 mph through the curve, which had a maximum speed of 25 mph, higher stresses were present at wheel/rail interface (i.e., the gauge face of the high rail). These higher stresses were conducive to the formation of shells and fatigue cracks along the gauge face of the high rail.
4. Critical size for 1 of the transverse defects was reached when the remaining rail head area, which was at or near its wear limits, could no longer support the load, resulting in the sudden and complete failure of the rail.
5. Although a rail flaw detection test had been performed less than 2 months before, the presence of head checking and shelling in the area of the rail running surface had adversely affected the ability of the system to detect the transverse defects.

Findings as to risk

1. If rail on only 1 side of a curve is replaced with rail of a different height, the curve's superelevation and balance speed will be altered, increasing the risk of higher stresses and damage to the other rail.
2. If surface defects on rails are not removed prior to ultrasonic rail flaw detection, there is a risk that internal rail defects will remain undetected, leading to broken rails and derailments.

Other findings

1. Despite increased rail testing at Gainford siding, the numerous transverse defects were not detected.
2. While double shelf couplers are designed to keep derailed tank cars coupled together, and tank car ends have been strengthened to withstand end impacts, tank car bodies are vulnerable to side impacts when derailed cars come apart.
3. Appropriate and effective measures were taken to protect the site and ensure public safety immediately following the derailment.
4. Given the longitudinal alignment of the 4 DOT 111 tank cars as they rolled over onto the main track, the absence of secondary impacts, and the absence of exposure to fire and explosion from subsequent derailing cars, the DOT 111 tank cars built to CPC-1232 standards were not heavily damaged in the derailment.