It can very nearly be. It's an oxygen displacer and non combustable in itself and non posionous but it's not oxygen! It can be lethal due to oxygen deprevation. What makes it fairly safe like you saw is that it's quite heavy compared to air and hungs the floor. Those that didn't leave were in my estimation quite foolish. Many years ago one of the halon similars (freon12) was spilled in a room I was working in, roughly 35 gallons of it due to a valve left open. I was quite blue when I was dragged out of the room as it had displaced all the air and only the fact that I'd been under the HEPA curtain doing work (also why I didn't initially notice it) there was outside make up fresh air added or I'd have been hospital fodder or worse. Freon and halon are related as florinated or halogenated hydrocarbons and both are low boiling point, heavy compared to air and non combustable. They are also both oxygen displacents makeing them dangerous in closed rooms and effective for fire control (both as a mild cooant and removing oxygen) while fairly inert. I'm sure there are varients of R134A in use or similar still used. Allison