the heat of the explosion (left) is very intense and can "feed" already burning spots and flame them up without direct contact.
Originally posted by smurfy
reply to post by GoodOlDave
I'm not too sure about that. There had to be a lot of air compression coming off the collision at WTC2, some other videos shown a similar effect around WTC1. It is noticeable that smoke does come from windows that previously had none, that suggests that the windows were intact up to that point, the big question is, if there was enough air blast from the collision to blow out the windows from both the faces of the building we can see, and the face overlooking WTC2, or all faces for that matter.