I would agree with you on the club fires, terrible tragedies but both born of stupidity and panci.
However, I wouldn't be putting terrorism too low on you list for the following reasons with the barge explosion:
1. The petroleum farm is a natural target and setting blowing up the barge would in the minds of bad guys result in secondary explosions crippling the US economy once again.
2. MO for terrorists is to blow up ships and tankers in port with suicide whack jobs. I'll be waiting for reports of who was on board that barge and were there any smaller vessels seen approaching it prior to explosion.
3. bin Laden's recent call for whackjobs to kill the infidel may have had more meaning than we thought.
4. It's a perfect target, maximum visibility, OIL, crippling to the US econonmy and panic in Central Park.
It may be an accident but terrorism would be high on my list.