Union Pacific officials say they do not know what caused this derailment yet. Twenty-nine of the train's 116 railcars derailed, spilling piles and piles of petroleum coke. It's a black substance that looks like coal. Also spilled was ammonium nitrate, which is a white granular substance.
Union Pacific is looking at every factor from operator error to an obstruction on the tracks as a possible cause. Initially, Homeland Security agents were called to the scene, because ammonium nitrate is a type of fertilizer that has been used to make explosives. But in this form, fire investigators say it is harmless, and there was no danger to anyone.
HFD Assistant Fire Chief Adrian Trevino explained, "The fertilizer, the ammonium nitrate that is on the ground, it is in a stable form. It is a pellet form. There is no petroleum products close to it or any type of explosives close to it."
Police are urging drivers to avoid South Main if they can. As for the derailment, the Federal Railroad Administration will also investigate, but it has not released any information about a possible cause.