I'm pretty sure it was not an accident. The plant blew up and was all over the news, the same day new gun laws (or something to do with banning guns) were being agreed upon. I think the government were just using it as a diversion to make the gun laws take a back seat in the media, so it didn't get found out.
There is also a video of what looks like a missile being fired at the fertilizer plant just before it blew up. You can barely see it's a missile, but when it's slowed down you can see something firing in from the left hand side, and then the plant explodes
I have alot more to say about it, but can't really be bothered to type.
Look it up on infowars.com - there's some crazy shit about the fertilizer plant, the boston bombings and even sandy hook.