The DOT-111 is a staple of the American freight rail fleet. But its flaws have been noted as far back as a 1991 safety study. Among other things, its steel shell is too thin to resist puncturing in accidents, which almost guarantees the car will tear open in an accident, potentially spilling cargo that could catch fire, explode or contaminate the environment.
“It’s too early to tell. There’s a lot of factors involved,” Ross said. “There’s a lot of energy here. The train came down on a fairly significant grade for 6.8 miles (11 kilometers) before it came into the town and did all the destruction it did.” He said the train was moving at 63 mph (101 kph) when it derailed.
Focus on Earlier Blaze in Quebec Train Derailment
http://www.rigzone.com/news/oil_gas/a/127622/Focus_on_Earlier_Blaze_in_Quebec_Train_Derailment/?all=HG2
Nantes Fire Chief Patrick Lambert said that when the same train caught fire hours prior to the accident, the engine was shut off per the standard operating procedure dictated by Montreal, Maine & Atlantic Railway.
The blaze was extinguished within about 45 minutes. And that’s where the fire department’s involvement ended, Lambert said.
“The people from MMA told us, ‘That’s great — the train is secure, there’s no more fire, there’s nothing anymore, there’s no more danger,’” Lambert told reporters. “We were given our leave, and we left.”
Edward Burkhardt, the president and CEO of the railway’s parent company Rail World, Inc., suggested that the decision to shut off the locomotive to put out the fire might have disabled the brakes. “An hour or so after the locomotive was shut down, the train rolled away,” Burkhardt told the Canadian Broadcast Corp.
Meanwhile, crews were working to contain 100,000 liters (27,000 gallons) of light crude that spilled from the tankers and made its way into nearby waterways. There were fears it could flow into the St. Lawrence River all the way to Quebec City.
I would expect trains to be like trucks. When the air is cut off, the breaks would lock.
Railway airbrake according to wiki.
http://en.wikipedia.org/wiki/Railway_air_brake
The lack of air pressure causes the brakes to lock.