It's now sounding more involved than first reported: "the incident began around 9:30 a.m. when firefighters were responding to reports of a chlorine leak at the chemical engineering building. Someone had run a vehicle into the building, and then someone started attacking people inside the building with a knife." Link: http://www.cbsnews.com/news/ohio-state-university-active-shooter-on-campus/
I am/was a certified HAZMAT initial response certified firefighter. If I would have ever seen a green cloud (chlorine gas), I'm using the rule of thumb method in my response. I'll close one eye & extend my arm with thumb raised in front of the open eye. If I can still see the scene around my thumb, I'm too close & will retreat more.