[JustPiper]

Many dead in Iran train blast Scores of people were killed in northeastern Iran when runaway train cars filled with fuel and chemicals derailed and exploded, destroying five nearby villages, Iranian officials say. Reports of the death toll range from 60 to 200

The train crashed through several villages
Train cars of petrol, fertilizer and sulfur products careered down the line, derailed, caught fire
It was not immediately clear what caused the 51 carriages to roll out of Abu Muslim station, outside Neishabour, but Iranian officials said there is no suggestion of any link to criminal or terrorist activity.
Iran's State news agency IRNA reported that "some vibrations" had set the cars in motion.

[Myrddin]

Railcars that heavy have a lot of inertia. They don't just get set in motion from "vibrations". SOP for the brakeman is to connect the brake hoses, open the angle cock valve, verify that the brake piston has pushed the shoes onto the wheel (and within the travel limit indicator), then release the handbrake. Before a car is allowed to break free from a train consist, the handbrakes must be set, angle cock valves closed and finally the coupler is released.

The consist on this train was purposely constructed of items that aren't normally permitted to be mixed AND the standard procedures were violated on a whole group of cars...not just a simple oversight on a car or two. It's hard to believe that it wasn't an deliberate act.