Image credit: Original picture: Associated Press/Tony Gutierrez. Annotated by Cujo359.
The railroad car is a three-bay covered hopper. Here's some information from a Union Pacific site on this type of car:
|Cubic Capacity||Range from 4,600 to 5,200 cu. ft.|
|Gross Weight on Rail||Range from 263,000 to 286,000 lbs.|
|Load Limit||Range from 197,000 to 224,000 lbs.|
That car must have weighed at least thirty tons empty. Based on the pile next to it, it must have been at least partly full at the time. Yet the explosion knocked it off the rails and may have actually pushed it a little ways on its side.
It was one big explosion, particularly when you consider that this plant was operating on the edge of town, close to schools, apartments, and houses.