This wreck was created.
1. locomotives have a deadman switch which must be disengaged to let the engine move.
2. When train cars are unintentionally separated, all brakes on the train are automaticaly engaged.
3. It is surprising that tank cars filled with crude oil would explode is surprising as the stuff is not very volatile.
2. The tank cars only separated from the train at the derailment point.
3. Crude can have all sorts of hydrocarbons present. Where does straight run gasoline come from? Also look up BLEVE.
I believe you are talking about moving by the engine, not a gravity roll as happened here.
2. When train cars are unintentionally separated, all brakes on the train are automatically engaged.
Yes, each car has an air reservoir tank that provides pressure to engage the brakes on loss of main air supply. But those tanks don't last forever. They are intended to give the train operators time to set the hand brakes. They are not intended to hold the train indefinitely while unattended.
3. It is surprising that tank cars filled with crude oil would explode is surprising as the stuff is not very volatile.
The tank cars were DOT-111 design which US National Transportation Safety Board has advised these, when used to carry ethanol and crude oil, be reinforced to make them more resistant to punctures if trains derail.
The tanks didn't initially explode, but several did leak and a large pool fire started. Several tanks that did not rupture but sat in the burning pool eventually did explode after being heated and building up significant pressure.
You might want to look at the link in post #16 where the Chairman of the railroad operating this train talked about the engineer who left the train unattended did not appear to set sufficient hand brakes.