TORONTO (Reuters) - A fiery Canadian National Railway Co derailment in Alberta in 2013 was caused by rail defects that were not detected in tests just two months before the incident, Canada's Transportation Safety Board said on Tuesday.
The safety watchdog said the train derailed at a curve because the rail it was traveling on fractured. Investigators later found "numerous defects" along the curve.
Three tank cars released liquefied petroleum gas, which exploded and burned. There were no injuries, but 106 nearby homes were evacuated.
Transport Canada rules called for the track involved in the incident to be checked for flaws using ultrasonic detectors at least once a year, but CN Rail exceeded those guidelines, testing four times between January 2013 and the October 19 derailment.
"Ultrasonic testing has proven to be a reliable and economical testing method, but as with all non-destructive test methods, there can be limitations," said the board in its report.
After the accident CN did special rail inspections on foot, and launched a program to grind down similar sections of track. Grinding removes small defects, which can make ultrasonic detectors work better.
"As the TSB report indicates, CN implemented a number of additional safety measures following the incident, as the TSB investigation was taking place," CN said in an emailed statement.
Reporting by Allison Martell. Editing by Andre Grenon