Some speculation about an accident from "welding work happening nearby" has recently been put forth, but I don't know if that is a legitimate possibility or not.
...the welder in question was last seen departing the scene of the explosion at a high rate of speed. They do not expect to find him anytime soon.

Liberals are like a "Slinky". Totally useless, but somehow ya can't help but smile when you see one tumble down a flight of stairs!