Details and the sequence of events began to take shape with the acknowledgment the locomotive suffered an engine fire just hours before the train derailed Saturday.
The blaze, which was quickly extinguished and thought to have been fed by the engine diesel, may have set in motion the subsequent disaster, experts and the company suggested.
Firefighters were forced to shut down the locomotive in order to combat the fire, depriving the train's brake system of its stable air compressors.
But that event by itself should not have cut the train loose, had a manual system also been activated.
"If you properly set your brakes, you can shut off the engine to the train," said Allan Zarembski, a professor in railroad engineering and safety program at the University of Delaware.
"There are several different ways to set brakes on a train. The most secure way is to set the air brakes and the hand brakes. If you set the air brakes and the hand brakes, you can shut off the train and walk away from the train and nothing should happen."
Specifically, if the devices at either end of the train which prevent air from being lost from the brake pipe — known as angle cocks — are left open, the train should remain stationary, experts said.
The chairman of Montreal, Maine & Atlantic Railway said Monday that shutting off the engine caused the brakes to fail.
"This accident may have been a very strange set of circumstances," said Chris Damas, a transportation expert at BCMI Research.
"Some of the procedures for locking down the train are going to be looked at," said Damas, who warned it may be too soon to begin debating the merits and drawbacks of moving crude oil by rail.
Most of the designated Class 1 railways, such as Canadian National (TSX:CNR) and Canadian Pacific (TSX:CP), have been hauling an increasing amount of oil, largely without incident, he said.
There are questions to be asked about what kind of expertise the regional carrier may have had with delicate cargo, he said.
"You have this train on a secondary rail which may have had less competence in chemicals and (hazardous materials) and crude," said Damas.
"It's a new business for them and so they weren't used to worrying about crude oil. They may not have had some procedures that would have been as automatic as a CN-CP, or Burlington."
Current federal legislation covers many of the safety procedures related to the accident, so it is not a matter of filling a regulatory hole, as some critics have suggested, Damas added.
Brake failure was cited by the country's transportation safety board in a runaway train incident in Edmundston, N.B., 18 years ago.
An eastbound CN freight train had halted at the town yards in December 1995 and the crew uncoupled while a second locomotive was hooked up.
Investigators found they had closed the angle cocks and not applied the hand brakes.
The 15 rail cars ended up rolling westward, uncontrolled, for about 1.4 kilometres through the main track switch, coming to a stop upright with no injuries.
With files by Murray Brewster in Ottawa and Sidhartha Banerjee in Montreal
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