"Um..plastic bottles...sounds like a baking soda device."
I agree. Chances are these "explosive devices" are nothing more than bored kids goofing off with vinegar and baking soda.
Not the smartest thing to do in today's climate, however.
These were not that type. My brother is a state policeman at Georgia Tech...These thngs were made to go off when handled. The person meant to kill/maim someone- this was no innocent prank.