SASKATOON, Nov. 16, 2016 /CNW/ - In its investigation report ( R14W0256) released today, the Transportation Safety Board of Canada (TSB) determined that a broken rail, due to an undetected defect, led to the October 2014 derailment of a Canadian National Railway (CN) freight train near Clair, Saskatchewan. There were no injuries, although a flash fire during the emergency response put CN emergency responders at risk. On 7 October 2014, a CN freight train proceeding westward from Winnipeg, Manitoba, destined to Edmonton, Alberta, derailed 26 cars, including six Class 111 tank cars loaded with dangerous goods, near Clair, Saskatchewan. Two of the tank cars, which were loaded with petroleum distillates, released product that subsequently caught fire. As a precaution, 50 residents within a five-mile (8 km) radius were evacuated and Provincial Highway 5 was closed. Approximately 650 feet of track was destroyed. This investigation identified risk factors related to the transportation of flammable liquids by rail, and safety management and oversight as outlined in the TSB Watchlist. Two of the Class 111 tank cars released product, and the damage to these cars was consistent with failures noted by the TSB in other investigations. The TSB made recommendations ( R14-01 and R14-02) to address these issues as part of the Lac-Mégantic investigation. The investigation determined that the train derailed when a sudden and catastrophic failure of one of the rails occurred under the train, due to the presence of an undetected defect. Poor rail surface conditions had masked the presence of this defect and reduced the effectiveness of visual inspections and ultrasonic inspections. Including this occurrence, the TSB has investigated seven occurrences in the past 10 years involving a rail break due to a pre-existing rail defect that was not detected by ultrasonic testing.