[thspimpolds]

The "gas" is more like a fog of capsules. FM-200 is a common one. Basically it has a Fire suppression agent inside crystals which are blasted into the room by compressed air. These crystals melt when they get over a certain temperature and therefore won't kill you; however, breathing that in isn't really pleasant.

Source: I've been in an FM-200 discharge

[Scoundreller]

Does everyone carry an N95 or equivalent? I guess many of us have gotten good at donning them by now...