They recently honored the first responders.
Apparently ALON USA and OHSA are investigating in private but the Chemical Safety and Hazard Investigation Board, a sort of NTSB agency that normally looks into such events, recently complained of being understaffed (and overwhelmed by a recent spate of industrial explosions) and decided not to investigate. With no deaths maybe not so unusual, but if nothing else it's a sad state of affairs from an occupational safety point of view.
As to causes other than accidental, even if early news reports said the FBI was called in there's nothing in open source world to suggest the explosion was terrorism other than its occurrence at an Israeli-owned oil facility several weeks after the death of one of the biggest terrorists in the world, presumably killed by Israel and occurring on President's Day.
Speaking of which, based on the pictures it's surprising the truther gang hasn't claimed Bushitler was testing a tactical nuke or trying to rig gas prices by taking out the 78 year old refinery in a country short on refineries. But hey, we're still waiting for word on how Bush cut those undersea cables. Oh well. Last we left that story the theory of a coordinated attack by "malicious mollusks" was still in play.