Halon has been banned for years because 1) it's bad for the ozone layer and 2) it'll kill you. Newer systems (FM-200, Inergen, etc.) fight the fire by removing heat instead of removing oxygen.
Halon is still used. Unfortunately the same properties that makes it effective also makes it harm the ozone layer. It does not just remove heat or oxygen, it directly interferes with the reaction involved in combustion, making things stop burning.
Wasn't there also this technique of lowering oxygen levels so much that humans can still survive but fire won't spread as fast? Or did this turn out to be too expensive?
