TSB describes ice jacking as ice building up at the base of the rail and lifting the rail from the tie plate rail seat. This condition occurs when roadway snow-clearing activities push road sand, salt and snow at a grade crossing onto rail tracks. The snow melts because of the salt, but the water can also pool by the track and refreeze. Ice can build up along the rail as the track experiences freeze and thawing cycles.
TSB said it observed ice jacking in at least one other investigation, a March 2011 derailment of a Canadian Pacific (NYSE: CP) coal train in British Columbia, according to a TSB report released on July 28 about the February 2020 incident.
“Although railways are aware of this condition and track supervisors are trained to recognize it, the condition can still be difficult to detect during a visual track inspection when snow is present,” the TSB report said.
The CN train was hauling 144 freight cars — 132 loaded and 12 empty — when it derailed on Feb. 18 near Emo, Ontario. The train consisted of two head-end locomotives, one distributed-power locomotive in the 103rd position and 73 cars carrying dangerous goods, of which 38 were carrying crude.
A train crew consisting of a locomotive engineer and conductor applied emergency air brakes while negotiating a 4-degree left-hand curve at 44 mph. The outside temperature at the time was around -27 degrees Celsius (-16.6 degrees Fahrenheit), and the area experienced several freeze and thaw cycles in the time leading up to the incident.
The train derailed, causing it to separate behind the 51st car. Six tank cars released a total of over 84,000 gallons of crude oil, TSB said. The report’s purpose was to determine the causes of the incident, and so it didn’t describe any penalties. However, TSB determined that the rolling stock had no defects while track maintenance met safety standards.
As a result of the incident, CN said it would clarify inspection expectations in its engineering track standards to require zone and production gangs that are doing work on one rail to inspect both rails to ensure they comply with track standards and that no hazards exist, according to the report.