Ice buildup underneath a rail led to the derailment of a train near Emo in February, the Transportation Safety Board TSB said in a report released Tuesday.

The derailment occurred on Feb. 18 as the CN train travelled from Winnipeg to Fort Frances.

The train was travelling at 44 mph when the derailment occurred at a bend in the tracks near Emo.

Thirty-three cars left the tracks, and crude oil was leaking from some of the derailed cars; six homes in the area were evacuated as a precaution.

There were no injuries, the TSB said.

The TSB said its investigation revealed snow and ice had built up adjacent to the high rail at the corner where the derailment occurred.

"Closer examination revealed that the snow and ice had built up between the underside of the rail base and the tie plate rail seats," the report states. "This caused the rail to become unseated from the tie plate and left the rail susceptible to gauge spreading under the load of the train, which led to the derailment. This is a phenomenon commonly referred to in the rail industry as 'ice jacking.'"

The investigation didn't find any problems with the train itself, the TSB said, and the tracks at the site the derailment "met or exceeded" minimum maintenance standards, the report states.

The tracks in the area had been inspected regularly, as well, the TSB said, with CN inspecting them several times over the course of January and February 2020, including two days before the derailment.

The TSB said railways are aware of ice jacking, but spotting it can be difficult during a visual track inspection when snow is present.

The TSB said CN has since clarified its inspection protocols, and now requires workers doing work on one rail to inspect both rails, to ensure no hazards exist.