Locomotive Fire Led To Quebec Disaster

Yahoo:

The problem was that the engine had been left on by the train's engineer to maintain pressure in the air brakes, Ed Burkhardt, chairman of Montreal, Maine & Atlantic Railway (MMA), said in an interview. As the pressure gradually "leaked off," the air brakes failed and the train began to slide downhill, he said.
The fire service said it contacted a local MMA dispatcher in Farnham, Quebec, after the blaze was out. "We told them what we did and how we did it," Lambert said.
Asked whether there had been any discussion about the brakes, he replied: "There was no discussion of the brakes at that time. We were there for the train fire. As for the inspection of the train after the fact, that was up to them."
It was not immediately clear what the MMA dispatcher did after speaking with the fire service. Burkhardt said the fire service should have also tried to contact the train's operator, who was staying at a nearby hotel.
"If the engine was shut off, someone should have made a report to the local railroad about that," he said.

Canadian crash investigators say they will look at the two sets of brakes on the train: the airbrakes and the handbrakes. Members of the team are due to speak to reporters at 10 a.m. (1400 GMT) on Tuesday.
Burkhardt said that after the pressure leaked out of the airbrakes, the handbrakes would not have been strong enough to keep the train in place.

I guess I didn't know too much about air brakes.  I thought if you lost air pressure, the brakes would engage, and that only when you built the pressure up would they disengage.  Anyway, the accident made a mess of that downtown.  Well the pipeline guys really think this scores one for them now.  That'll be an interesting discussion.