There is an engineer on this thread right now. If you see this post would it be unusual for object to blow up when this bridge collapsed??
If you mean "explode," I'd say that's unusual (except for the fact that you have one or more fuel trucks involved here).
If you mean "lifted vertically in a sudden manner," I'd say it would not be all that unusual. It looks like one or more sections toppled instead of just collapsing, so the rotation of the slab (toppling motion) could easily lift cars, people, etc. up in the air.
I would expect that when the spans came down, the air under them had to be ‘blown out’ as the concrete spans fell...this might give the appearance of smoke etc. as the air rushed out from underneath the collapsing segments.
If I remember my physics correctly, an object will fall and accellerate at 9.8meters/sec2. So, if the bridge was 65 feet up it would take approx 2-2.5seconds to fall that distance so the speed at impact would be 100feet/second(?) so the air would have been blowing out pretty good, moving all sorts of dust and trash..
Just my really rough calcs...