It was a chemistry lab experiment designed to show reaction, but it really just produced a lot more fuss. A professor left a hand warmer on a burner which overheated and the plastic wrapper burned. That produced some fumes. It was any chemicals that vaporized, it was the packaging. Still, the university called in Fire and EMS and haz-mat trucks that ventilated the building and left after a couple of hours.
The building has been cleared and is reopened for normal activities.