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Village evacuated after Quebec train derailment

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Thanks for that explanation Ed.  I am familiar with most of those details, but I was not quite clear on the condition of the trainline with brakes applied, train standing, with engine coupled to it, with the angle cock of the engine and the one on the first car open, and engine running.  I suppose you could have some pressure in the trainline if brakes were applied in a service application.  But if you are leaving a train, I assume that you would have the brakes set just as if they had dynamited into full emergency.  So the trainline would be exhausted and maximum pressure would be in the cylinders.  And the trainline would be open to atmosphere at the brake valve in on the locomotive.  So under those conditions, what if that train stood like that for a month or more?  I know that if you set out cars, and dump the air, it will eventually leak off from the pressurized cylinders.  Some may leak off in only a matter of a few hours, and some may hold for several days or weeks.   When I refer to the brakes leaking off, I do not mean brakes releasing from reservoir leakage into a closed trainline.       Considering the standing train with engine running, and brakes full applied with trainline open to atmosphere, I assume there would be no way for the running engine to recharge or maintain a charge in the brake cylinders if air gradually leaked off of that pressurized portion of the circuit on each car.  If that is true, then it would have been completely irrelevant that the fire department shut off the MM&A engine that was running.  The running engine would have been completely disassociated from any role in maintaining pressure in the brake cylinders.  And even if that pressure leaked off over time, say three weeks, the running engine would still not be able to compensate for that loss of air pressure in the cylinders. But being that the brakes were released in only an hour or so, we could probably 100% rule out the possibility that the cylinders leaked off as I described above.  So I see your point that the only way the brakes could have been released is for somebody to have released them from the engineer’s brake valve or to have closed the lead angle cock of the first car if the engine was uncoupled, or closed that angle cock and/or the one on the engine if the engine remained coupled.  And then for the brakes to have released under any of those scenarios, there would need to be some leakage from one or more reservoirs into the closed trainline, which could release all of the brakes just like an intentional release would.      So why did they even leave the engine running in the first place?
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