[Jason Abbadon]

Honestly...could they be making Meth? That uses some bad chemicals that could get through the vents.
But hey, for all we know, they could have painted their place, causing some reaction.
If they're photographers, the developers for old film process could do that...but how could they live there too?

Whatever it is, smoking cant be it- imagine the class action lawsuits if smke did that to plastics! Hell, my next door neighbor smokes outside my apartment door all the time (our doors are right next to each other) and my MU stuff in the living room, just insude the door, is fine.