You did not offend me, but you sure got me curious as to why you asked. As dumb as it sounds, one of the things done was to make there were ignition sources in all directions to try to make sure the cloud could not travel off site and did not have a chance to grow to its potential. And, no, I have not seen a refinery fire up close and personal, but in setting that place up, we saw many films of many such things.
I definitely agree with both of these statements. No offense to anyone here if you fit the age group, but people under the age of 20 or so don't have very good decision-making skill--or even decision-making capabilities. Their brains just haven't developed to that point yet. Since a good portion of the people involved in the "Occupy" movements are younger, they would seem to attract the attention of they younger crowd--who might be dumb enough to consider throwing a "chemical bomb" into a crowd to be "fun." I'm not saying that's the explanation, but I think if it were anything more serious, then the bomber would have thrown something more likely to be lethal to the people around it instead of counting on the off chance that the blast would come into contact with someone and do damage that way.