Der Jaeger
Generational EBUG
I had an experience with that without a mask when I was in high school. My mother nagged me until I agreed to go some banquet with her. About an hour into it, someone tossed a couple CS grenades into it. I managed to get my mother and a few others out before I couldn't take it anymore. It was some cop's kid that did it. Nothing ever came of it.
CS is an irritant designed for crowd dispersal, but we use it in training. The idea is for the new Soldiers to gain confidence that their mask will work. They go in with the mask on and sealed, and then do some movements with their heads so prove the seal. Then the break their mask seal with eyes closed, and reseal the mask, blowing the air in it out.
At the end, to show them what the mask was keeping out, they take of their masks for 5 seconds, and then leave the room into open air outside.