The blast in Texas is almost certainly unintentional, though the death toll was terribly high. It was a fertilizer plant, and the blast appears to have come after a fire had been burning for some time (several of the dead were first responders to that fire). When you get a fire around fertilizer....bad things happen. I seem to remember hearing that the deadliest explosion in US history was caused by a fertilizer laden ship blowing up. That happened down along the gulf somewhere, too, if I remember right.

On a lighter note, smoking was banned around the Capitol because people were afraid of all the fertilizer being produced by that particular factory. They later realized that manure is not the explosive kind of fertilizer.