Hmm, heavy cars at the front of the train, empty lumber cars in the middle, and heavy cars (LPG and corn) near the rear while the train was pushed backwards by the engines into a curve. I'd like to see the evidence that it was a mechanical defect as opposed to a simple loading error. 

By the way, the responding fire department officer stated last night at a community forum that the cause was the nature of the way the cars were loaded and not loaded that caused the derailment, not a mechanical, and he doesn't have any financial motivation to be untruthful. 

He went on to say that if the propane tanker had exploded, the fireball would have been deadly for over 600 yards. What he didn't mention was that the 2nd Ave fire station that responded to this derailment within 4 minutes is within that 600 yard radius. Considering the number of such explosive cars being pushed around there, we should consider building a blast wall around the rail yard before we don't have anyone to respond.