From Fox News:

Two separate Islamist groups have claimed responsibility for that explosion at a Texas chemical plant that killed 15 and injured more than 100. In an Internet statement, the Army of the Levant said it was behind the blast. But another group calling itself the al-Qaeda Organisation for Holy War in the United States of America promised to issue a video of the attack to prove it was responsible. The FBI says neither one of them was responsible, they've ruled out terrorism as the cause of the blast."

I swear that the first thing I thought when I heard about this explosion was a terrorist cell. Think about it--this is the perfect target for a depeleted terrorist organization to hit--symbolic (oil) and under the federal radar for possible targets. I'm sure that Al Quaida pays far more attention to the FBI statements of credible threat than most Americans do--in fact, logic dictates that this was most likely a terrorist attack. But the FBI has ruled this out--of course, they offer no further explanation. Perhaps it was just a weather balloon...