From this press release from MMA and CBC and National Post reports, the timeline appears to be:
- July 5, 23:15: Train stopped and tied down by engineer at Nantes. The train had 5 locomotives and 72 car loads of crude oil, destined for Irving Oil in Saint John, NB.
- July 5, 23:30: Nearby resident calls 911 and reports a fire in the parked train. Firefighters respond and put the fire out. A track maintenance employee of MMA was present.
- July 6, ?????: Train starts rolling downhill to Lac-Mégantic.
- July 6, 01:15: Train derailed at Rue Frontenac crossing in downtown Lac-Mégantic
- July 6 (later): Firefighters battle the intense blaze through the day. 13 intact carloads pulled from rear of train by MMA.
When equipment is left at any point a sufficient number of hand brakes must be applied to prevent it from moving. Special instructions will indicate the minimum hand brake requirements for all locations where equipment is left. If equipment is left on a siding, it must be coupled to other equipment if any on such track unless it is necessary to provide separation at a public crossing at grade or elsewhere.
(emphasis mine) The implication is that air brakes cannot be relied upon to hold a train in place. Again, I am strictly an amateur but this did catch my eye.
The National Transportation Safety Board is investigating and they have 14 people on the scene. I understand the locomotive event recorder has been recovered. That will help fill in the timeline as to when the train started moving, and most crucially, when the air brakes were released.
In addition to the tragic loss of life, the destruction of the town, there are concerns about water quality due to the quantity of spilled crude oil.
There are some railfan reports that the runaway train may have struck a set of propane cars that were in the town and those are what caused the initial explosions.
My heart is broken at the thoughts of the people killed and injured as a result of this terrible accident.
EDIT: More information here that confirms that the firefighters shut the engine down before battling the blaze.