[Paladin2]

If you look at the Lac Megantic rail yard pics you will see ~6 individual tank cars and one box car (some type of buffer car seems to be used by MMA to buffer the last locomotive from the first tank car in the string) strewn about more or less individually.

I'd suggest that these early cars overturned trying to get through the yard, tearing up the track(s) in the process until the following cars started to dig into the ground and block the following cars. The locomotives tend to have 3 axle trucks on each end and being as heavy as they are and having a lower center of gravity are tougher to derail.

Some are now suggesting that there may have been 4 propane cars sitting in the yard so now that may have to be factored in.

[Figment]

Waiting to see what investigation reveals. Rail car couplings aren’t small and tend to hold well although they are quite easy to disengage with a simple handle

[Smokin' Joe]

Some are now suggesting that there may have been 4 propane cars sitting in the yard so now that may have to be factored in.

That might explain the explosion better than a simple (although apparently energetic) derailment of crude tankers. Colliding with stationary propane cars might be enough to produce the sort of explosion and ensuing conflagration reported.

Sure crude will burn, and burn well--we had a multi-vehicle accident here where a crude hauler (semi) was involved and the vehicles burned when the tanker ruptured--but there was no explosion, just a big fire.