PLASTER ROCK, N.B. -- The Transportation Safety Board says fatigue caused a wheel to fail on a freight train that derailed earlier this year in northern New Brunswick, sparking a fire that burned for days.

The CN (TSX:CNR) train was hauling crude oil and liquefied petroleum gas when 19 cars and a locomotive went off the tracks Jan. 7 near the village of Plaster Rock and caught fire.

No one was hurt, but 150 people were forced from their homes following the fiery derailment.

The board said early on that its investigation would focus on a cracked wheel on a car near the front of the 122-car train, which was en route to Moncton, N.B., from Toronto when it derailed.

In an update released today, the board says the wheel was manufactured in 1991 and had a crack under its surface that led to a shattered rim.

The board says damage on the track was caused by the derailed wheels battering the base of the rail.

It also says two older cars built in 1984 and 1996 were the primary source of the oil spill that led to the fire.